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Kev siv hluav taws xob ntawm adipic acid (ib qho ua ntej ntawm nylon 66) los ntawm CA roj (kev sib xyaw ntawm cyclohexanone thiab cyclohexanol) yog ib qho tswv yim ruaj khov uas tuaj yeem hloov cov txheej txheem ib txwm muaj uas xav tau cov xwm txheej hnyav. Txawm li cas los xij, qhov ceev tam sim no qis thiab kev sib tw oxygen evolution reactions txwv nws cov ntawv thov kev lag luam. Hauv txoj haujlwm no, peb hloov kho nickel ob chav hydroxide nrog vanadium los txhim kho qhov ceev tam sim no thiab tswj hwm qhov ua tau zoo faradaic (> 80%) dhau ntawm ntau qhov muaj peev xwm (1.5–1.9 V vs. reversible hydrogen electrode). Kev tshawb fawb thiab kev tshawb fawb tau qhia ob lub luag haujlwm tseem ceeb ntawm V kev hloov kho, suav nrog kev tsim kho catalyst sai dua thiab kev txhim kho cyclohexanone adsorption. Ua pov thawj ntawm lub tswv yim, peb tau tsim ib lub rooj sib dhos membrane-electrode uas tsim cov adipic acid nrog kev ua tau zoo faradaic (82%) thiab kev tsim khoom (1536 μmol cm-2 h-1) ntawm qhov ceev tam sim no cuam tshuam rau kev lag luam (300 mA cm-2), thaum ua tiav kev ruaj khov > 50 h. Txoj haujlwm no qhia txog ib qho catalyst zoo rau electrosynthesis ntawm adipic acid nrog kev tsim khoom siab thiab kev lag luam muaj peev xwm.
Adipic acid (AA) yog ib qho tseem ceeb tshaj plaws ntawm aliphatic dicarboxylic acids thiab feem ntau yog siv rau hauv kev tsim cov nylon 66 thiab lwm yam polyamides lossis polymers1. Hauv kev lag luam, AA yog synthesized los ntawm oxidizing ib qho sib xyaw ntawm cyclohexanol thiab cyclohexanone (piv txwv li, AA roj) siv 50–60 vol% nitric acid ua tus neeg sawv cev oxidizing. Cov txheej txheem no muaj kev txhawj xeeb txog ib puag ncig ntsig txog kev tso tawm ntawm cov kua qaub nitric acid thiab nitrogen oxides (N2O thiab NOx) ua cov pa roj av2,3. Txawm hais tias H2O2 tuaj yeem siv ua lwm txoj hauv kev oxidizing ntsuab, nws cov nqi siab thiab cov xwm txheej synthesis hnyav ua rau nws nyuaj rau siv, thiab xav tau txoj hauv kev pheej yig dua thiab ruaj khov4,5,6.
Tau kaum xyoo dhau los no, cov tshuaj electrocatalytic thiab cov roj synthesis tau nyiam cov kws tshawb fawb ntau ntxiv vim lawv qhov zoo ntawm kev siv lub zog rov ua dua tshiab thiab ua haujlwm hauv qab qhov xwm txheej tsis hnyav (piv txwv li, chav sov thiab qhov siab ntawm huab cua) 7,8,9,10. Hauv qhov no, kev txhim kho kev hloov pauv electrocatalytic ntawm KA roj rau AA yog qhov tseem ceeb heev kom tau txais cov txiaj ntsig saum toj no nrog rau kev tshem tawm kev siv cov pa roj nitric acid thiab nitrous oxide uas ntsib hauv kev tsim khoom ib txwm muaj (Daim Duab 1a). Petrosyan et al., ua haujlwm ua thawj coj, uas tau tshaj tawm txog kev hloov pauv electrocatalytic ntawm cyclohexanone (COR; cyclohexanone lossis cyclohexanol tau kawm feem ntau ua sawv cev rau KA roj) ntawm nickel oxyhydroxide (NiOOH), tab sis qhov ceev tam sim no qis (6 mA cm-2) thiab qhov nruab nrab AA tawm (52%) tau txais 11,12. Txij thaum ntawd los, kev vam meej tseem ceeb tau ua tiav hauv kev txhim kho cov catalysts nickel-based los txhim kho COR kev ua ub no. Piv txwv li, ib qho catalyst uas muaj tooj liab doped nickel hydroxide (Cu-Ni(OH)2) tau synthesized los txhawb Cα-Cβ cleavage hauv cyclohexanol13. Tsis ntev los no peb tau tshaj tawm ib qho Ni(OH)2 catalyst hloov kho nrog sodium dodecyl sulfonate (SDS) los tsim ib qho hydrophobic microenvironment uas nplua nuj cyclohexanone14.
a Cov teeb meem ntawm AA tsim los ntawm electrooxidation ntawm KA roj. b Kev sib piv ntawm electrocatalytic COR ntawm Ni-raws li catalysts tau tshaj tawm yav dhau los thiab peb cov catalyst hauv peb-electrode system thiab flow battery system11,13,14,16,26. Cov ntaub ntawv ntxaws ntxaws ntawm cov txheej txheem tshuaj tiv thaiv thiab kev ua tau zoo ntawm cov tshuaj tiv thaiv tau muab rau hauv Cov Lus Qhia Ntxiv 1 thiab 2. c Catalytic kev ua tau zoo ntawm peb cov NiV-LDH-NS catalysts rau COR hauv H-cell reactor thiab MEA, uas ua haujlwm hla ntau yam peev xwm.
Txawm hais tias cov txheej txheem saum toj no tau txhim kho COR kev ua haujlwm, cov catalysts Ni-based tau piav qhia txog AA Faraday efficiency siab (FE) (> 80%) tsuas yog ntawm cov peev xwm qis qis, feem ntau qis dua 1.6 V piv rau cov electrode hydrogen rov qab (RHE, luv VRHE). Yog li, qhov ceev tam sim no ib nrab tau tshaj tawm (piv txwv li, tag nrho cov ceev tam sim no sib npaug los ntawm FE) ntawm AA yeej ib txwm qis dua 60 mA cm−2 (Daim Duab 1b thiab Cov Lus Qhia Ntxiv 1). Qhov ceev tam sim no qis dua qhov xav tau kev lag luam (> 200 mA cm−2)15, uas cuam tshuam loj heev rau cov thev naus laus zis electrocatalytic rau kev tsim AA siab (Daim Duab 1a; sab saum toj). Txhawm rau kom nce qhov ceev tam sim no, muaj peev xwm zoo dua (rau peb-electrode system) lossis lub zog hluav taws xob siab dua (rau ob-electrode system) tuaj yeem siv tau, uas yog ib txoj hauv kev yooj yim rau ntau qhov kev hloov pauv electrocatalytic, tshwj xeeb tshaj yog cov tshuaj tiv thaiv oxygen evolution (OER). Txawm li cas los xij, rau COR ntawm cov peev xwm anodic siab, OER tuaj yeem dhau los ua tus neeg sib tw tseem ceeb hauv kev txo FE ntawm AA, yog li txo qhov kev siv hluav taws xob (Daim Duab 1a; hauv qab). Piv txwv li, kev tshuaj xyuas qhov kev nce qib yav dhau los (Daim Duab 1b thiab Cov Lus Qhia Ntxiv 1), peb tau poob siab thaum pom tias FE ntawm AA ntawm SDS-modified Ni (OH) 2 txo qis los ntawm 93% mus rau 76% nrog kev nce qib ntawm 1.5 VRHE mus rau 1.7 VRHE14, thaum FE ntawm AA ntawm CuxNi1-x (OH) 2 / CF txo qis los ntawm 93% mus rau 69% nrog kev nce qib ntawm 1.52 VRHE mus rau 1.62 VRHE16. Yog li, qhov kev tshaj tawm ib nrab tam sim no ntawm AA tsis nce proportional ntawm cov peev xwm siab dua, uas feem ntau txwv tsis pub txhim kho ntawm AA kev ua tau zoo, tsis hais txog kev siv hluav taws xob siab vim yog FE qis ntawm AA. Ntxiv nrog rau cov catalysts raws li nickel, cov catalysts raws li cobalt kuj tau qhia txog kev ua haujlwm catalytic hauv COR17,18,19. Txawm li cas los xij, lawv qhov kev ua haujlwm txo qis ntawm cov peev xwm siab dua, thiab piv nrog Ni-based catalysts, lawv muaj ntau qhov kev txwv hauv kev siv hauv kev lag luam, xws li kev hloov pauv ntawm tus nqi ntau dua thiab cov khoom muag me dua. Yog li ntawd, nws yog qhov xav tau los tsim cov Ni-based catalysts nrog qhov ceev tam sim no siab thiab FE hauv COR kom ua rau nws siv tau los ua kom tau txais cov txiaj ntsig AA siab.
Hauv daim ntawv no, peb tshaj tawm vanadium (V)-modified nickel layered double hydroxide nanosheets (NiV-LDH-NS) ua cov electrocatalysts zoo rau AA ntau lawm los ntawm COR, uas ua haujlwm hla ntau qhov muaj peev xwm nrog OER txo qis, ua tiav FE siab thiab tam sim no ceev hauv ob qho tib si H-cells thiab membrane electrode assemblies (MEAs; Daim Duab 1 b). Peb thawj zaug qhia tias acetylene oxidation efficiency hla ib qho Ni (OH) 2 nanosheet catalyst (Ni (OH) 2-NS) txo qis, raws li xav tau, ntawm cov peev xwm siab dua, los ntawm 80% ntawm 1.5 VRHE rau 42% ntawm 1.9 VRHE. Hauv qhov sib piv ntse, tom qab hloov kho Ni (OH) 2 nrog V, NiV-LDH-NS tau pom qhov ceev tam sim no siab dua ntawm qhov muaj peev xwm thiab, qhov tseem ceeb dua, tswj hwm FE siab hla ntau qhov muaj peev xwm. Piv txwv li, ntawm 1.9 VRHE, nws tau qhia txog qhov ceev tam sim no ntawm 170 mA cm−2 thiab FE ntawm 83%, uas yog ib qho catalyst zoo dua rau COR hauv peb-electrode system (Daim Duab 1c thiab Supplementary Table 1). Cov ntaub ntawv sim thiab theoretical qhia tau hais tias V kev hloov kho txhawb nqa qhov kev txo qis kinetics los ntawm Ni (OH) 2 mus rau qhov muaj txiaj ntsig zoo Ni oxyhydroxides (Ni3 + xOOH1-x), uas ua haujlwm ua theem nquag rau COR. Ntxiv mus, V kev hloov kho tau txhim kho qhov adsorption ntawm cyclohexanone ntawm qhov chaw catalyst, uas ua lub luag haujlwm tseem ceeb hauv kev tswj hwm OER ntawm cov peev xwm anodic siab. Txhawm rau qhia txog lub peev xwm ntawm NiV-LDH-NS hauv qhov xwm txheej tseeb dua, peb tau tsim lub tshuab hluav taws xob MEA thiab qhia txog FE ntawm AA (82%) ntawm qhov ceev tam sim no cuam tshuam nrog kev lag luam (300 mA cm−2), uas yog siab dua li peb cov txiaj ntsig yav dhau los hauv lub tshuab hluav taws xob membrane (Daim Duab 1b thiab Supplementary Table 2). Qhov txiaj ntsig sib xws ntawm AA (1536 μmol cm−2 h−1) yog siab dua li qhov tau txais los ntawm kev siv cov txheej txheem thermal catalytic (<30 mmol gcatalyst−1 h−1)4. Ntxiv mus, cov catalyst tau qhia txog kev ruaj khov zoo thaum siv MEA, tswj FE >80% AA rau 60 teev ntawm 200 mA cm−2 thiab FE >70% AA rau 58 teev ntawm 300 mA cm−2. Thaum kawg, kev tshawb fawb ua ntej (FEA) tau qhia txog kev siv nyiaj ntawm txoj kev siv hluav taws xob rau kev tsim AA.
Raws li cov ntaub ntawv dhau los, Ni(OH)2 yog ib qho catalyst ib txwm muaj uas qhia txog kev ua haujlwm zoo rau COR, yog li Ni(OH)2-NS13,14 tau tsim thawj zaug los ntawm txoj kev sib xyaw ua ke. Cov qauv qhia tau tias β-Ni(OH)2 cov qauv, uas tau lees paub los ntawm X-ray diffraction (XRD; Daim Duab 2a), thiab cov nanosheets ultra-thin (tuab: 2–3 nm, qhov loj ntawm sab: 20–50 nm) tau pom los ntawm kev ntsuas hluav taws xob kis tau zoo (HRTEM; Daim Duab Ntxiv 1) thiab atomic force microscopy (AFM) (Daim Duab Ntxiv 2). Kev sib sau ua ke ntawm cov nanosheets kuj tau pom vim lawv qhov xwm txheej ultra-thin.
a Cov qauv X-ray diffraction ntawm Ni(OH)2-NS thiab NiV-LDH-NS. FE, throughput, thiab AA tam sim no ceev ntawm b Ni(OH)2-NS thiab c NiV-LDH-NS ntawm ntau lub peev xwm sib txawv. Cov kab yuam kev sawv cev rau qhov sib txawv ntawm peb qhov kev ntsuas ywj pheej siv tib lub catalyst. d HRTEM duab ntawm NV-LDH-NS. Scale bar: 20 nm. HAADF-STEM duab ntawm NiV-LDH-NS thiab daim ntawv qhia elemental sib xws qhia kev faib tawm ntawm Ni (ntsuab), V (daj), thiab O (xiav). Scale bar: 100 nm. f Ni 2p3/2, g O 1 s, thiab h V 2p3/2 XPS cov ntaub ntawv ntawm Ni(OH)2-NS (sab saum toj) thiab NiV-LDH-NS (hauv qab). i FE thiab j yog AA kev ua tau zoo ntawm ob lub catalysts dhau 7 lub voj voog. Cov kab yuam kev sawv cev rau qhov sib txawv ntawm peb qhov kev ntsuas ywj pheej siv tib lub catalyst thiab nyob hauv 10%. Cov ntaub ntawv raw rau a-c thiab f-j tau muab tso rau hauv cov ntaub ntawv raw.
Tom qab ntawd peb tau soj ntsuam qhov cuam tshuam ntawm Ni(OH)2-NS rau COR. Siv cov electrolysis uas muaj peev xwm tas li, peb tau txais 80% FE ntawm AA ntawm qhov muaj peev xwm qis (1.5 VRHE) yam tsis muaj OER (Daim Duab 2b), qhia tias COR muaj zog dua li OER ntawm qhov muaj peev xwm anodic qis. Cov khoom tseem ceeb tau pom tias yog glutaric acid (GA) nrog FE ntawm 3%. Qhov muaj cov kua qaub succinic acid (SA), malonic acid (MA), thiab oxalic acid (OA) kuj tau ntsuas los ntawm HPLC (saib Daim Duab Ntxiv 3 rau kev faib khoom). Tsis muaj formic acid tau pom hauv cov khoom, qhia tias carbonate yuav raug tsim los ua C1 by-product. Txhawm rau sim qhov kev xav no, cov electrolyte los ntawm kev electrolysis tiav ntawm 0.4 M cyclohexanone tau acidified thiab cov khoom roj tau dhau los ntawm Ca(OH)2 kua. Yog li ntawd, cov kua tau dhau los ua turbid, lees paub qhov tsim ntawm carbonate tom qab electrolysis. Txawm li cas los xij, vim tias qhov hluav taws xob tsawg tag nrho tsim tawm thaum lub sijhawm electrolysis (Daim Duab 2b, c), qhov concentration ntawm carbonate yog qis thiab nyuaj rau ntsuas. Tsis tas li ntawd, lwm cov khoom C2-C5 kuj tseem yuav tsim tau, tab sis lawv cov nqi tsis tuaj yeem ntsuas tau. Txawm hais tias tag nrho cov khoom nyuaj rau ntsuas, 90% ntawm tag nrho cov electrochemical sib npaug qhia tias feem ntau ntawm cov txheej txheem electrochemical tau txheeb xyuas, uas muab lub hauv paus rau peb txoj kev nkag siab txog mechanistic. Vim tias qhov ceev tam sim no qis (20 mA cm−2), qhov txiaj ntsig ntawm AA yog 97 μmol cm−2 h−1 (Daim Duab 2b), sib npaug rau 19 mmol h−1 g−1 raws li qhov hnyav ntawm cov catalyst (5 mg cm−2), uas qis dua qhov thermal catalytic productivity (~ 30 mmol h−1 g−1)1. Thaum lub peev xwm siv tau nce ntxiv ntawm 1.5 mus rau 1.9 VRHE, txawm hais tias qhov ceev tam sim no tag nrho nce ntxiv (ntawm 20 mus rau 114 mA cm−2), tib lub sijhawm muaj kev txo qis tseem ceeb hauv AA FE, ntawm 80% mus rau 42%. Qhov txo qis hauv FE ntawm cov peev xwm zoo dua yog vim muaj kev sib tw rau OER. Tshwj xeeb tshaj yog ntawm 1.7 VRHE, kev sib tw OER ua rau muaj kev txo qis tseem ceeb hauv AA FE, yog li ntawd me ntsis txo qis AA kev ua tau zoo nrog kev nce ntxiv ntawm qhov ceev tam sim no. Yog li, txawm hais tias qhov ceev tam sim no ib nrab ntawm AA nce ntxiv ntawm 16 mus rau 48 mA cm−2 thiab AA tsim khoom nce ntxiv (ntawm 97 mus rau 298 μmol cm−2 h−1), ntau lub zog ntxiv tau siv (2.5 W h gAA−1 ntau dua ntawm 1.5 mus rau 1.9 VRHE), ua rau muaj kev nce ntxiv ntawm cov pa roj carbon ntawm 2.7 g CO2 gAA−1 (cov ntsiab lus xam tau muab rau hauv Cov Lus Qhia Ntxiv 1). OER uas tau sau tseg ua ntej ua tus neeg sib tw rau COR cov tshuaj tiv thaiv ntawm cov peev xwm anodic siab yog sib xws nrog cov ntawv ceeb toom yav dhau los thiab sawv cev rau qhov kev sib tw dav dav rau kev txhim kho AA kev tsim khoom14,17.
Txhawm rau tsim kom muaj cov tshuaj Ni(OH)2-NS-based COR catalyst zoo dua, peb xub tshuaj xyuas cov theem nquag. Peb pom cov ncov ntawm 473 cm-1 thiab 553 cm-1 hauv peb cov txiaj ntsig Raman spectroscopy hauv situ (Supplementary Fig. 4), uas sib raug rau qhov khoov thiab ncab ntawm Ni3+-O bonds hauv NiOOH, raws li. Nws tau sau tseg tias NiOOH yog qhov tshwm sim ntawm Ni(OH)2 txo qis thiab Ni(OH)O sib sau ua ke ntawm anodic potentials, thiab yog qhov tseem ceeb theem nquag hauv electrocatalytic oxidation20,21. Yog li ntawd, peb xav tias kev ua kom nrawm dua cov txheej txheem rov tsim kho theem ntawm Ni(OH)2 rau NiOOH tuaj yeem txhim kho cov haujlwm catalytic ntawm COR.
Peb tau sim hloov kho Ni (OH) 2 nrog cov hlau sib txawv vim nws tau pom tias kev hloov kho heteroatom txhawb nqa kev tsim kho dua tshiab hauv cov hlau hloov pauv oxides / hydroxides 22, 23, 24. Cov qauv tau tsim los ntawm kev sib koom ua ke ntawm Ni thiab tus thawj coj hlau thib ob. Ntawm cov qauv hlau hloov kho sib txawv, cov qauv V-hloov kho (V: Ni atomic ratio 1: 8) (hu ua NiV-LDH-NS) tau qhia txog qhov ceev tam sim no siab dua hauv COR (Supplementary Fig. 5) thiab qhov tseem ceeb dua, AA FE siab dua lub qhov rais dav dav. Tshwj xeeb, ntawm qhov muaj peev xwm qis (1.5 VRHE), qhov ceev tam sim no ntawm NiV-LDH-NS yog 1.9 npaug siab dua li ntawm Ni (OH) 2-NS (39 vs. 20 mA cm−2), thiab AA FE sib piv ntawm ob qho tib si catalysts (83% vs. 80%). Vim yog qhov ceev tam sim no siab dua thiab FE AA zoo sib xws, qhov tsim tau ntawm NiV-LDH-NS yog 2.1 npaug siab dua li ntawm Ni (OH) 2-NS (204 vs. 97 μmol cm−2 h−1), qhia txog qhov cuam tshuam ntawm V hloov kho rau qhov ceev tam sim no ntawm qhov qis potentials (Daim Duab 2c).
Nrog rau kev nce ntxiv ntawm cov peev xwm siv (piv txwv li, 1.9 VRHE), qhov ceev tam sim no ntawm NiV-LDH-NS yog 1.5 npaug siab dua li ntawm Ni (OH) 2-NS (170 vs. 114 mA cm−2), thiab qhov nce zoo ib yam li ntawm cov peev xwm qis dua (1.9 npaug siab dua). Qhov tseem ceeb, NiV-LDH-NS khaws cia AA FE siab (83%) thiab OER tau raug txo qis heev (O2 FE 4%; Daim Duab 2c), ua tau zoo dua Ni (OH) 2-NS thiab cov catalysts tau tshaj tawm yav dhau los nrog AA FE qis dua ntawm cov peev xwm anodic siab (Supplementary Table 1). Vim yog FE siab ntawm AA hauv lub qhov rais dav dav (1.5–1.9 VRHE), tus nqi tsim AA ntawm 867 μmol cm−2 h−1 (sib npaug rau 174.3 mmol g−1 h−1) tau ua tiav ntawm 1.9 VRHE, qhia txog kev ua tau zoo hauv electrocatalytic thiab txawm tias thermocatalytic systems thaum qhov kev ua haujlwm tau normalized los ntawm tag nrho cov pawg ntawm NiV-LDH-NS cov qauv (Supplementary Fig. 6).
Yuav kom nkag siab txog qhov ceev tam sim no siab thiab FE siab dhau ntau qhov muaj peev xwm tom qab hloov kho Ni(OH)2 nrog V, peb tau piav qhia txog cov qauv ntawm NiV-LDH-NS. Cov txiaj ntsig XRD qhia tau hais tias kev hloov kho nrog V ua rau muaj kev hloov pauv theem ntawm β-Ni(OH)2 mus rau α-Ni(OH)2, thiab tsis muaj cov hom crystalline V-cuam tshuam tau pom (Daim Duab 2a). Cov txiaj ntsig HRTEM qhia tau hais tias NiV-LDH-NS tau txais cov morphology ntawm ultrathin Ni(OH)2-NS nanosheets thiab muaj cov qhov ntev zoo sib xws (Daim Duab 2d). Kev ntsuas AFM tau qhia txog kev sib sau ua ke ntawm cov nanosheets, ua rau muaj qhov tuab ntsuas tau kwv yees li 7 nm (Daim Duab Ntxiv 7), uas loj dua li Ni(OH)2-NS (tuab: 2–3 nm). Kev tshuaj xyuas X-ray spectroscopy (EDS) mapping analysis (Daim Duab 2e) qhia tau hais tias V thiab Ni cov ntsiab lus tau faib zoo hauv cov nanosheets. Txhawm rau piav qhia txog cov qauv hluav taws xob ntawm V thiab nws cov nyhuv rau Ni, peb siv X-ray photoelectron spectroscopy (XPS) (Daim Duab 2f-h). Ni (OH) 2-NS tau qhia txog cov yam ntxwv ntawm spin-orbit peaks ntawm Ni2 + (poj niam peak ntawm 855.6 eV, satellite peak ntawm 861.1 eV, Daim Duab 2f) 25. Lub O 1 s XPS spectrum ntawm Ni (OH) 2-NS tuaj yeem faib ua peb lub peaks, ntawm cov peaks ntawm 529.9, 530.9 thiab 532.8 eV yog muab rau lattice oxygen (OL), hydroxyl pawg (Ni-OH) thiab oxygen adsorbed ntawm qhov tsis zoo ntawm qhov chaw (OAds), feem (Daim Duab 2g) 26, 27, 28, 29. Tom qab kev hloov kho nrog V, lub ncov V 2p3/2 tau tshwm sim, uas tuaj yeem decomposed ua peb lub ncov nyob ntawm 517.1 eV (V5+), 516.6 eV (V4+) thiab 515.8 eV (V3+), feem, qhia tias cov hom V hauv cov qauv feem ntau muaj nyob rau hauv cov xeev oxidation siab (Daim Duab 2h) 25,30,31. Tsis tas li ntawd, lub ncov Ni 2p ntawm 855.4 eV hauv NiV-LDH-NS tau hloov pauv tsis zoo (los ntawm kwv yees li 0.2 eV) piv rau qhov ntawd hauv Ni (OH) 2-NS, qhia tias cov electrons tau hloov pauv los ntawm V mus rau Ni. Lub xeev valence qis ntawm Ni pom tom qab V hloov kho yog sib xws nrog Ni K-edge X-ray absorption near-edge spectroscopy (XANES) cov txiaj ntsig (saib ntu "V Modification Promotes Catalyst Reduction" hauv qab no kom paub meej ntxiv). Lub NiV-LDH-NS tom qab COR kho rau 1 teev tau raug xaiv los ua NiV-LDH-POST thiab tau piav qhia tag nrho siv kev siv lub tshuab hluav taws xob kis tau tus mob, EDS mapping, X-ray diffraction, Raman spectroscopy, thiab XPS ntsuas (Cov duab ntxiv 8 thiab 9). Cov catalysts tseem yog cov aggregates nrog ultrathin nanosheet morphology (Cov duab ntxiv 8a-c). Lub crystallinity ntawm cov qauv tau txo qis thiab cov ntsiab lus V txo qis vim yog V leaching thiab catalyst reconstruction (Cov duab ntxiv 8d-f). Cov XPS spectra tau qhia txog kev txo qis hauv V peak intensity (Cov duab ntxiv 9), uas tau muab rau V leaching. Ntxiv rau, kev tshuaj xyuas O1s spectrum (Daim duab ntxiv 9d) thiab kev ntsuas electron paramagnetic resonance (EPR) (Daim duab ntxiv 10) qhia tau hais tias qhov ntau ntawm cov pa oxygen vacancies ntawm NiV-LDH-NS nce tom qab 1 teev ntawm electrolysis, uas yuav ua rau muaj kev hloov pauv tsis zoo hauv Ni2p binding zog (saib Daim duab ntxiv 9 thiab 10 kom paub meej ntxiv)26,27,32,33. Yog li, NiV-LDH-NS tau qhia me ntsis kev hloov pauv ntawm cov qauv tom qab 1 teev ntawm COR.
Txhawm rau kom paub meej tias lub luag haujlwm tseem ceeb ntawm V hauv kev txhawb nqa COR, peb tau tsim cov tshuaj catalysts NiV-LDH nrog cov sib txawv V: Ni atomic ratios (1:32, 1:16, thiab 1:4, xaiv ua NiV-32, NiV-16, thiab NiV-4, feem) tshwj tsis yog 1:8 los ntawm tib txoj kev sib koom ua ke. Cov txiaj ntsig EDS mapping qhia tau tias V: Ni atomic ratio hauv catalyst ze rau qhov ntawm cov precursor (Supplementary Fig. 11a-e). Nrog rau kev nce ntawm V modification, qhov muaj zog ntawm V 2p spectrum nce ntxiv, thiab lub zog khi ntawm thaj tsam Ni 2p txuas ntxiv hloov mus rau sab tsis zoo (Supplementary Fig. 12). Tib lub sijhawm, qhov feem pua ​​ntawm OL maj mam nce ntxiv. Cov txiaj ntsig ntawm kev sim catalytic qhia tau tias OER tuaj yeem raug txo kom zoo txawm tias tom qab hloov kho V tsawg kawg nkaus (V:Ni atomic ratio ntawm 1:32), nrog rau O2 FE txo qis los ntawm 27% mus rau 11% ntawm 1.8 VRHE tom qab hloov kho V (Supplementary Fig. 11f). Nrog rau kev nce ntawm V:Ni piv los ntawm 1:32 mus rau 1:8, qhov kev ua haujlwm catalytic nce ntxiv. Txawm li cas los xij, nrog rau kev nce ntxiv ntawm V hloov kho (V:Ni piv ntawm 1:4), qhov ceev tam sim no txo ​​qis, uas peb xav tias yog vim qhov txo qis ntawm qhov ceev ntawm Ni cov chaw ua haujlwm (tshwj xeeb tshaj yog NiOOH theem ua haujlwm; Supplementary Fig. 11f). Vim yog qhov cuam tshuam ntawm V hloov kho thiab kev khaws cia ntawm Ni cov chaw ua haujlwm, catalyst nrog V:Ni piv ntawm 1:8 tau qhia txog qhov siab tshaj plaws FE thiab AA kev ua tau zoo hauv V:Ni kev xeem tshuaj ntsuam. Txhawm rau kom meej meej seb V:Ni piv puas tseem nyob ruaj khov tom qab electrolysis, cov khoom sib xyaw ntawm cov catalysts siv tau piav qhia. Cov txiaj ntsig qhia tau tias rau cov catalysts nrog thawj V: Ni piv ntawm 1:16 txog 1: 4, V: Ni piv txo qis mus txog li 1:22 tom qab qhov kev tshuaj tiv thaiv, uas tej zaum yuav yog vim qhov leaching ntawm V vim yog catalyst reconstruction (Supplementary Fig. 13). Nco ntsoov tias AA FEs sib piv tau pom thaum thawj V: Ni piv sib npaug lossis siab dua 1:16 (Supplementary Fig. 11f), uas tej zaum yuav piav qhia los ntawm catalyst reconstruction ua rau muaj V: Ni piv zoo sib xws hauv cov catalysts uas qhia txog kev ua tau zoo catalytic sib piv.
Txhawm rau kom paub meej ntxiv txog qhov tseem ceeb ntawm V-modified Ni(OH)2 hauv kev txhim kho kev ua tau zoo COR, peb tau tsim ob txoj kev tsim khoom siv los qhia V rau hauv cov ntaub ntawv Ni(OH)2-NS. Ib qho yog txoj kev sib tov, thiab cov qauv hu ua NiV-MIX; lwm qhov yog txoj kev sib txuas ua ke, thiab cov qauv hu ua NiV-SP. Cov ntsiab lus ntawm kev tsim khoom siv tau muab rau hauv ntu Txoj Kev. Daim ntawv qhia SEM-EDS qhia tau tias V tau hloov kho tiav ntawm qhov chaw Ni(OH)2-NS ntawm ob qho qauv (Daim Duab Ntxiv 14). Cov txiaj ntsig electrolysis qhia tau tias ntawm 1.8 VRHE, qhov ua tau zoo ntawm AA ntawm NiV-MIX thiab NiV-SP electrodes yog 78% thiab 79%, feem, ob qho tib si qhia tau tias muaj txiaj ntsig zoo dua li Ni(OH)2-NS (51%). Ntxiv mus, OER ntawm NiV-MIX thiab NiV-SP electrodes tau raug txo qis (FE O2: 7% thiab 2%, feem) piv rau Ni(OH)2-NS (FE O2: 27%). Cov txiaj ntsig no lees paub qhov cuam tshuam zoo ntawm V kev hloov pauv hauv Ni (OH) 2 ntawm OER kev tswj hwm (Daim duab ntxiv 14). Txawm li cas los xij, qhov ruaj khov ntawm cov catalysts tau raug cuam tshuam, uas tau pom los ntawm kev txo qis ntawm FE AA ntawm NiV-MIX mus rau 45% thiab ntawm NiV-SP mus rau 35% tom qab xya lub voj voog COR, uas txhais tau tias yuav tsum tau txais cov txheej txheem tsim nyog los tswj cov hom V, xws li V kev hloov pauv hauv Ni (OH) 2 lattice hauv NiV-LDH-NS, uas yog qhov tseem ceeb catalyst hauv txoj haujlwm no.
Peb kuj tau soj ntsuam qhov ruaj khov ntawm Ni(OH)2-NS thiab NiV-LDH-NS los ntawm kev muab COR rau ntau lub voj voog. Cov tshuaj tiv thaiv tau ua tiav rau 1 teev ib lub voj voog thiab cov electrolyte tau hloov tom qab txhua lub voj voog. Tom qab lub voj voog thib 7, qhov kev ua tau zoo ntawm FE thiab AA ntawm Ni(OH)2-NS tau txo qis 50% thiab 60%, raws li, thaum muaj kev nce hauv OER (Daim Duab 2i, j). Tom qab txhua lub voj voog, peb tau tshuaj xyuas cov kab cyclic voltammetry (CV) ntawm cov catalysts thiab pom tias qhov oxidation peak ntawm Ni2+ maj mam txo qis, qhia txog kev txo qis hauv lub peev xwm redox ntawm Ni (Daim Duab Ntxiv 15a-c). Nrog rau kev nce hauv Ni cation concentration hauv electrolyte thaum lub sijhawm electrolysis (Daim Duab Ntxiv 15d), peb tau muab qhov kev puas tsuaj ntawm kev ua tau zoo (txo qis FE thiab AA productivity) rau kev leaching ntawm Ni los ntawm cov catalyst, ua rau muaj kev cuam tshuam ntau dua ntawm Ni foamed substrate uas qhia txog OER kev ua haujlwm. Qhov sib piv, NiV-LDH-NS qeeb qeeb qhov kev poob qis hauv FE thiab AA tsim khoom mus rau 10% (Daim duab 2i, j), qhia tias V kev hloov kho tau zoo inhibit Ni leaching (Supplementary Fig. 15d). Txhawm rau kom nkag siab txog kev ruaj khov ntawm V kev hloov kho, peb tau ua cov kev suav theoretical. Raws li cov ntaub ntawv yav dhau los 34,35, qhov kev hloov pauv enthalpy ntawm cov txheej txheem demetallization ntawm cov hlau atoms ntawm qhov chaw nquag ntawm catalyst tuaj yeem siv ua tus piav qhia tsim nyog los ntsuas qhov kev ruaj khov catalyst. Yog li ntawd, qhov kev hloov pauv enthalpy ntawm cov txheej txheem demetallization ntawm Ni atoms ntawm (100) nto ntawm reconstructed Ni (OH) 2-NS thiab NiV-LDH-NS (NiOOH thiab NiVOOH, feem) tau kwv yees (cov ntsiab lus ntawm kev tsim qauv tau piav qhia hauv Supplementary Note 2 thiab Supplementary Fig. 16). Cov txheej txheem demetallization ntawm Ni los ntawm NiOOH thiab NiVOOH tau piav qhia (Supplementary Fig. 17). Tus nqi zog ntawm Ni demetallization ntawm NiVOOH (0.0325 eV) siab dua li ntawm NiOOH (0.0005 eV), qhia tias qhov kev hloov kho V ua rau muaj kev ruaj khov ntawm NiOOH.
Txhawm rau kom paub meej tias OER inhibitory effect ntawm NiV-LDH-NS, tshwj xeeb tshaj yog ntawm cov anodic potentials siab, differential electrochemical mass spectrometry (DEMS) tau ua los tshawb xyuas qhov potential-dependent O2 tsim ntawm ntau yam qauv. Cov txiaj ntsig tau qhia tias thaum tsis muaj cyclohexanone, O2 ntawm NiV-LDH-NS tshwm sim ntawm qhov pib potential ntawm 1.53 VRHE, uas qis dua me ntsis ntawm O2 ntawm Ni(OH)2-NS (1.62 VRHE) (Supplementary Fig. 18). Qhov tshwm sim no qhia tau hais tias OER inhibition ntawm NiV-LDH-NS thaum lub sijhawm COR tej zaum yuav tsis yog vim nws qhov intrinsic qis OER kev ua ub no, uas yog sib xws nrog qhov siab dua me ntsis tam sim no density hauv linear sweep voltammetry (LSV) curves ntawm NiV-LDH-NS dua li ntawm Ni(OH)2-NS tsis muaj cyclohexanone (Supplementary Fig. 19). Tom qab kev qhia txog cyclohexanone, qhov kev hloov pauv O2 qeeb (tej zaum vim yog qhov zoo ntawm thermodynamic ntawm COR) piav qhia txog FE siab ntawm AA hauv thaj chaw qis qis. Qhov tseem ceeb tshaj, qhov OER pib muaj peev xwm ntawm NiV-LDH-NS (1.73 VRHE) qeeb dua li ntawm Ni(OH)2-NS (1.65 VRHE), uas yog sib xws nrog FE siab ntawm AA thiab FE qis ntawm O2 ntawm NiV-LDH-NS ntawm cov peev xwm zoo dua (Daim Duab 2c).
Yuav kom nkag siab ntxiv txog qhov cuam tshuam ntawm V kev hloov kho, peb tau tshuaj xyuas OER thiab COR cov tshuaj tiv thaiv kinetics ntawm Ni (OH) 2-NS thiab NiV-LDH-NS los ntawm kev ntsuas lawv cov Tafel slopes. Nws tsim nyog sau tseg tias qhov ceev tam sim no hauv thaj chaw Tafel yog vim qhov oxidation ntawm Ni2 + rau Ni3 + thaum lub sijhawm xeem LSV los ntawm qhov muaj peev xwm qis mus rau qhov muaj peev xwm siab. Txhawm rau txo qhov cuam tshuam ntawm Ni2 + oxidation ntawm COR Tafel slope ntsuas, peb thawj zaug oxidized cov catalyst ntawm 1.8 VRHE rau 10 feeb thiab tom qab ntawd ua qhov kev xeem LSV hauv hom scan rov qab, piv txwv li, los ntawm qhov muaj peev xwm siab mus rau qhov muaj peev xwm qis (Supplementary Fig. 20). Tus thawj LSV nkhaus tau kho nrog 100% iR compensation kom tau txais Tafel slope. Yog tsis muaj cyclohexanone, qhov Tafel slope ntawm NiV-LDH-NS (41.6 mV dec−1) qis dua li ntawm Ni(OH)2-NS (65.5 mV dec−1), qhia tias OER kinetics tuaj yeem txhim kho los ntawm V modification (Supplementary Fig. 20c). Tom qab kev qhia txog cyclohexanone, qhov Tafel slope ntawm NiV-LDH-NS (37.3 mV dec−1) qis dua li ntawm Ni(OH)2-NS (127.4 mV dec−1), qhia tias V modification muaj qhov cuam tshuam kinetic ntau dua rau COR piv rau OER (Supplementary Fig. 20d). Cov txiaj ntsig no qhia tias txawm hais tias V modification txhawb nqa OER rau qee qhov, nws ua rau COR kinetics nrawm dua, ua rau FE ntawm AA nce ntxiv.
Yuav kom nkag siab txog qhov cuam tshuam ntawm kev hloov kho V saum toj no rau kev ua haujlwm ntawm FE thiab AA, peb tau tsom mus rau kev kawm txog lub tshuab. Qee cov ntawv tshaj tawm yav dhau los tau qhia tias kev hloov kho heteroatom tuaj yeem txo qhov crystallinity ntawm cov catalysts thiab ua rau thaj chaw electrochemically active (EAS), yog li ua rau muaj ntau qhov chaw nquag thiab yog li txhim kho cov haujlwm catalytic36,37. Txhawm rau tshawb nrhiav qhov ua tau no, peb tau ua qhov kev ntsuas ECSA ua ntej thiab tom qab electrochemical activation, thiab cov txiaj ntsig tau qhia tias ECSA ntawm Ni (OH) 2-NS thiab NiV-LDH-NS zoo sib xws (Daim duab ntxiv 21), tsis suav nrog qhov cuam tshuam ntawm qhov ceev ntawm qhov chaw nquag tom qab V hloov kho ntawm kev txhim kho catalytic.
Raws li kev paub dav dav, hauv Ni (OH) 2-catalyzed electrooxidation ntawm cov cawv lossis lwm cov nucleophilic substrates, Ni (OH) 2 thawj zaug poob cov electrons thiab protons thiab tom qab ntawd raug txo kom NiOOH los ntawm cov kauj ruam electrochemical ntawm qee qhov anodic potential38,39,40,41. Lub NiOOH tsim tom qab ntawd ua haujlwm ua hom COR tiag tiag kom tshem tawm hydrogen thiab electrons los ntawm nucleophilic substrate los ntawm cov kauj ruam tshuaj lom neeg los tsim cov khoom oxidized20,41. Txawm li cas los xij, nws tau tshaj tawm tsis ntev los no tias txawm hais tias kev txo qis rau NiOOH yuav ua haujlwm ua tus nqi txiav txim siab kauj ruam (RDS) rau electrooxidation ntawm cawv ntawm Ni (OH) 2, raws li tau hais hauv cov ntaub ntawv tsis ntev los no, qhov oxidation ntawm Ni3 + cawv yuav yog ib qho txheej txheem los ntawm kev hloov pauv tsis-redox electron los ntawm cov orbitals tsis muaj neeg nyob ntawm Ni3 + 41,42. Tau txais kev tshoov siab los ntawm kev tshawb fawb txog kev siv tshuab uas tau tshaj tawm hauv cov ntaub ntawv tib yam, peb tau siv dimethylglyoxime disodium ntsev octahydrate (C4H6N2Na2O2 8H2O) ua ib qho tshuaj ntsuam kom ntes tau txhua yam Ni2+ tsim los ntawm Ni3+ txo thaum lub sijhawm COR (Daim Duab Ntxiv 22 thiab Daim Ntawv Qhia Ntxiv 3). Cov txiaj ntsig tau qhia txog kev tsim ntawm Ni2+, lees paub tias kev txo qis tshuaj ntawm NiOOH thiab electrooxidation ntawm Ni(OH)2 tshwm sim tib lub sijhawm thaum lub sijhawm COR. Yog li ntawd, kev ua haujlwm catalytic yuav nyob ntawm qhov kinetics ntawm Ni(OH)2 txo rau NiOOH. Raws li lub hauv paus ntsiab lus no, peb tom ntej no tshawb xyuas seb qhov kev hloov kho ntawm V puas yuav ua kom nrawm dua qhov kev txo qis ntawm Ni(OH)2 thiab yog li txhim kho COR.
Peb thawj zaug siv cov txheej txheem Raman hauv situ los qhia tias NiOOH yog theem nquag rau COR ntawm Ni(OH)2-NS thiab NiV-LDH-NS los ntawm kev soj ntsuam kev tsim ntawm NiOOH ntawm cov peev xwm zoo thiab nws cov kev siv tom qab tom qab kev qhia txog cyclohexanone, ua raws li cov txheej txheem "electrochemical-chemical" uas tau hais los saum toj no (Daim Duab 3a). Ntxiv mus, qhov kev ua haujlwm ntawm NiV-LDH-NS rov tsim dua ntau dua li Ni(OH)2-NS, raws li pov thawj los ntawm kev ploj ntawm Ni3+–O Raman teeb liab. Tom qab ntawd peb tau qhia tias NiV-LDH-NS tau pom tias muaj peev xwm tsawg dua rau kev tsim NiOOH piv rau Ni(OH)2-NS thaum muaj lossis tsis muaj cyclohexanone (Daim Duab 3b, c thiab Daim Duab Ntxiv 4c, d). Qhov tseem ceeb, qhov kev ua tau zoo dua ntawm NiV-LDH-NS ua rau muaj ntau lub npuas lo rau ntawm lub lens pem hauv ntej ntawm lub hom phiaj ntsuas Raman, uas ua rau Raman ncov ntawm 1.55 VRHE ploj mus (Daim Duab Ntxiv 4d). Raws li cov txiaj ntsig DEMS (Daim Duab Ntxiv 18), qhov ceev tam sim no ntawm qhov muaj peev xwm qis (VRHE < 1.58 rau Ni (OH) 2-NS thiab VRHE < 1.53 rau NiV-LDH-NS) feem ntau yog vim kev tsim kho dua tshiab ntawm Ni2 + ions es tsis yog OER thaum tsis muaj cyclohexanone. Yog li, qhov oxidation peak ntawm Ni2 + hauv LSV nkhaus muaj zog dua li ntawm NiV-LDH-NS, qhia tias V kev hloov kho muab rau NiV-LDH-NS nrog kev txhim kho kev txhim kho (saib Daim Duab Ntxiv 19 rau kev tshuaj xyuas ntxaws ntxaws).
a Cov duab Raman hauv situ ntawm Ni(OH)2-NS (sab laug) thiab NiV-LDH-NS (sab xis) nyob rau hauv OCP tej yam kev mob tom qab preoxidation ntawm 1.5 VRHE hauv 0.5 M KOH thiab 0.4 M cyclohexanone rau 60 s. b Cov duab Raman hauv situ ntawm Ni(OH)2-NS thiab c NiV-LDH-NS hauv 0.5 M KOH + 0.4 M cyclohexanone ntawm ntau yam potentials. d Cov duab XANES hauv situ ntawm Ni(OH)2-NS thiab NiV-LDH-NS ntawm Ni K-edge hauv 0.5 M KOH thiab e 0.5 M KOH thiab 0.4 M cyclohexanone. Daim duab qhia txog thaj chaw spectral loj hlob ntawm 8342 thiab 8446 eV. f Cov xeev Valence ntawm Ni hauv Ni(OH)2-NS thiab NiV-LDH-NS ntawm ntau yam potentials. g Hauv qhov chaw Ni EXAFS spectra ntawm NiV-LDH-NS ua ntej thiab tom qab cyclohexanone ntxig rau ntawm ntau lub peev xwm sib txawv. h Cov qauv theoretical ntawm Ni (OH) 2-NS thiab NiV-LDH-NS. Sab saum toj: Ntawm Ni (OH) 2-NS, qhov kev hloov pauv qeeb los ntawm Ni (OH) 2-NS mus rau NiOOH ua haujlwm ua RDS, thaum cyclohexanone txo cov hom Ni siab-valent los ntawm cov kauj ruam tshuaj lom neeg kom tswj tau lub xeev Ni qis-valent los tsim AA. Hauv qab: Ntawm NiV-LDH-NS, cov kauj ruam hloov pauv yog pab txhawb los ntawm V kev hloov pauv, ua rau kev hloov pauv ntawm RDS los ntawm cov kauj ruam hloov pauv mus rau cov kauj ruam tshuaj lom neeg. i Lub zog Gibbs dawb hloov pauv thaum rov tsim kho Ni (OH) 2-NS thiab NiV-LDH-NS. Cov ntaub ntawv raw rau aj thiab i tau muab rau hauv cov ntaub ntawv raw.
Txhawm rau tshawb nrhiav qhov kev hloov pauv ntawm cov qauv atomic thiab hluav taws xob thaum lub sijhawm txo cov catalyst, peb tau ua qhov kev sim X-ray absorption spectroscopy (XAS) hauv situ, uas tau muab cov cuab yeej muaj zog los tshawb nrhiav qhov dynamics ntawm Ni hom hauv peb kauj ruam sib law liag: OER, cyclohexanone txhaj tshuaj, thiab COR ntawm qhov qhib circuit potential (OCP). Daim duab qhia txog K-edge XANES spectra ntawm Ni nrog kev nce ntxiv potential ua ntej thiab tom qab cyclohexanone txhaj tshuaj (Daim Duab 3d, e). Ntawm tib lub peev xwm, lub zog ntug nqus ntawm NiV-LDH-NS yog qhov zoo dua li ntawm Ni (OH) 2-NS (Daim Duab 3d, e, inset). Qhov nruab nrab valence ntawm Ni nyob rau hauv txhua qhov xwm txheej tau kwv yees los ntawm kev sib xyaw ua ke ntawm XANES spectra thiab regression ntawm Ni K-edge absorption zog hloov pauv (Daim Duab 3f), nrog rau cov spectrum siv los ntawm cov ntaub ntawv luam tawm (Supplementary Fig. 23) 43.
Hauv thawj kauj ruam (ua ntej kev qhia txog cyclohexanone, sib raug rau OER txheej txheem; Daim duab 3f, sab laug), ntawm lub peev xwm ntawm cov catalyst tsis tau tsim kho (<1.3 VRHE), lub xeev valence ntawm Ni hauv NiV-LDH-NS (+1.83) qis dua me ntsis ntawm Ni (OH) 2-NS (+1.97), uas tuaj yeem yog vim qhov hloov pauv hluav taws xob los ntawm V mus rau Ni, sib xws nrog cov txiaj ntsig XPS saum toj no (Daim duab 2f). Thaum lub peev xwm tshaj qhov txo qis (1.5 VRHE), lub xeev valence ntawm Ni hauv NiV-LDH-NS (+3.28) qhia txog kev nce ntxiv pom tseeb dua piv rau Ni (OH) 2-NS (+2.49). Ntawm lub peev xwm siab dua (1.8 VRHE), lub xeev valence ntawm Ni cov khoom me me tau txais ntawm NiV-LDH-NS (+3.64) siab dua li Ni (OH) 2-NS (+3.47). Raws li cov ntawv ceeb toom tsis ntev los no, cov txheej txheem no sib raug rau kev tsim cov hom Ni4+ uas muaj txiaj ntsig zoo hauv cov qauv ntawm Ni3+xOOH1-x (Ni3+x yog cov hom sib xyaw ntawm Ni3+ thiab Ni4+), uas tau qhia txog kev ua haujlwm catalytic zoo dua hauv cawv dehydrogenation38,39,44. Yog li ntawd, kev ua tau zoo dua ntawm NiV-LDH-NS hauv COR tej zaum yuav yog vim muaj kev txo qis kom tsim cov hom Ni uas muaj txiaj ntsig zoo.
Hauv kauj ruam thib ob (kev qhia txog cyclohexanone tom qab qhib lub nplhaib, Daim Duab 3f), lub xeev valence ntawm Ni ntawm ob qho catalysts txo qis ntau, uas sib raug rau cov txheej txheem txo qis ntawm Ni3 + xOOH1-x los ntawm cyclohexanone, uas yog sib xws nrog cov txiaj ntsig ntawm in situ Raman spectroscopy (Daim Duab 3a), thiab lub xeev valence ntawm Ni yuav luag rov qab mus rau lub xeev pib (thawj kauj ruam ntawm qhov muaj peev xwm qis), qhia txog kev thim rov qab ntawm cov txheej txheem redox ntawm Ni rau Ni3 + xOOH1-x.
Hauv kauj ruam thib peb (txheej txheem COR) ntawm COR potentials (1.5 thiab 1.8 VRHE; Daim Duab 3f, sab xis), lub xeev valence ntawm Ni hauv Ni(OH)2-NS tsuas yog nce me ntsis xwb (+2.16 thiab +2.40), uas qis dua li ntawm tib lub peev xwm hauv thawj kauj ruam (+2.49 thiab +3.47). Cov txiaj ntsig no qhia tau tias tom qab txhaj tshuaj cyclohexanone, COR raug txwv los ntawm kev oxidation qeeb ntawm Ni2+ rau Ni3+x (piv txwv li, Ni reconstruction) es tsis yog los ntawm cov kauj ruam tshuaj lom neeg ntawm NiOOH thiab cyclohexanone ntawm Ni(OH)2-NS, uas tawm hauv Ni hauv lub xeev qis-valence. Yog li, peb xaus lus tias Ni reconstruction tuaj yeem ua haujlwm ua RDS hauv txheej txheem COR ntawm Ni(OH)2-NS. Qhov sib txawv, NiV-LDH-NS tswj tau qhov muaj nqis siab ntawm Ni hom (> 3) thaum lub sijhawm COR, thiab qhov muaj nqis txo qis dua (tsawg dua 0.2) piv rau thawj kauj ruam ntawm tib lub peev xwm (1.65 thiab 1.8 VRHE), qhia tias V kev hloov kho kinetically txhawb nqa qhov oxidation ntawm Ni2 + rau Ni3 + x, ua rau Ni txo cov txheej txheem sai dua li cov kauj ruam tshuaj lom neeg ntawm cyclohexanone txo qis. Cov txiaj ntsig ntawm X-ray absorption fine structure (EXAFS) kuj tau qhia txog kev hloov pauv tag nrho ntawm Ni-O (los ntawm 1.6 txog 1.4 Å) thiab Ni-Ni (V) (los ntawm 2.8 txog 2.4 Å) bonds nyob rau hauv qhov muaj cyclohexanone. Qhov no yog sib xws nrog kev tsim kho dua tshiab ntawm Ni (OH) 2 theem mus rau NiOOH theem thiab kev txo qis tshuaj lom neeg ntawm NiOOH theem los ntawm cyclohexanone (Daim duab 3g). Txawm li cas los xij, cyclohexanone ua rau muaj kev cuam tshuam loj heev rau kev txo qis kinetics ntawm Ni (OH) 2-NS (saib Cov Lus Qhia Ntxiv 4 thiab Cov Lus Qhia Ntxiv 24 kom paub meej ntxiv).
Zuag qhia tag nrho, ntawm Ni(OH)2-NS (Daim Duab 3h, sab saum toj), cov kauj ruam txo qis qeeb los ntawm Ni(OH)2 theem mus rau NiOOH theem yuav ua haujlwm ua RDS ntawm tag nrho COR txheej txheem es tsis yog cov kauj ruam tshuaj lom neeg ntawm AA tsim los ntawm cyclohexanone thaum lub sijhawm txo qis tshuaj lom neeg ntawm NiOOH. Ntawm NiV-LDH-NS (Daim Duab 3h, hauv qab), V hloov kho txhim kho oxidation kinetics ntawm Ni2+ rau Ni3+x, yog li ua kom nrawm dua qhov tsim ntawm NiVOOH (es tsis yog kev siv los ntawm kev txo qis tshuaj lom neeg), uas hloov RDS mus rau kauj ruam tshuaj lom neeg. Txhawm rau nkag siab txog Ni reconstruction los ntawm V hloov kho, peb tau ua cov kev suav theoretical ntxiv. Raws li pom hauv Daim Duab 3h, peb tau simulated cov txheej txheem rov tsim kho ntawm Ni(OH)2-NS thiab NiV-LDH-NS. Cov pab pawg lattice hydroxyl ntawm Ni(OH)2-NS thiab NiV-LDH-NS raug deprotonated los ntawm kev rho tawm OH- hauv electrolyte los tsim cov electron-deficient lattice oxygen. Cov tshuaj tiv thaiv sib xws yog raws li nram no:
Qhov kev hloov pauv zog Gibbs dawb ntawm kev tsim kho dua tshiab tau suav (Daim Duab 3i), thiab NiV-LDH-NS (0.81 eV) tau qhia txog kev hloov pauv zog Gibbs dawb me dua li Ni (OH) 2-NS (1.66 eV), qhia tias qhov kev hloov pauv V txo qhov hluav taws xob uas xav tau rau kev tsim kho dua tshiab Ni. Peb ntseeg tias kev txhawb nqa kev tsim kho dua tshiab yuav txo qhov teeb meem zog ntawm tag nrho COR (saib kev kawm txog cov txheej txheem tshuaj tiv thaiv hauv qab no kom paub meej ntxiv), yog li ua kom cov tshuaj tiv thaiv sai dua ntawm cov qhov ceev tam sim no siab dua.
Qhov kev tshuaj xyuas saum toj no qhia tau hais tias qhov kev hloov pauv V ua rau muaj kev hloov pauv sai ntawm Ni (OH) 2, yog li ua rau muaj kev cuam tshuam ntau ntxiv thiab, ua rau, qhov ceev tam sim no COR. Txawm li cas los xij, Ni3 + x qhov chaw kuj tseem tuaj yeem txhawb nqa OER kev ua ub no. Los ntawm LSV nkhaus tsis muaj cyclohexanone, nws pom tseeb tias qhov ceev tam sim no ntawm NiV-LDH-NS siab dua li ntawm Ni (OH) 2-NS (Daim Duab Ntxiv 19), uas ua rau COR thiab OER cov tshuaj tiv thaiv los tsim cov tshuaj tiv thaiv sib tw. Yog li ntawd, FE siab dua ntawm AA dua li ntawm NiV-LDH-NS tsis tuaj yeem piav qhia tag nrho los ntawm V kev hloov pauv txhawb nqa qhov kev hloov pauv theem.
Feem ntau lees txais tias hauv alkaline media, cov tshuaj electrooxidation ntawm nucleophilic substrates feem ntau ua raws li Langmuir-Hinshelwood (LH) qauv. Tshwj xeeb, cov substrate thiab OH− anions yog sib tw coadsorbed ntawm qhov chaw catalyst, thiab cov adsorbed OH− yog oxidized rau cov pab pawg hydroxyl nquag (OH*), uas ua haujlwm ua electrophiles rau oxidation ntawm nucleophiles, ib qho mechanism uas tau ua pov thawj los ntawm cov ntaub ntawv sim thiab / lossis kev suav theoretical45,46,47. Yog li, qhov concentration ntawm reactants thiab lawv qhov piv (organic substrate thiab OH−) tuaj yeem tswj hwm qhov kev npog reactant ntawm qhov chaw catalyst, yog li cuam tshuam rau FE thiab cov txiaj ntsig ntawm cov khoom lag luam 14,48,49,50. Hauv peb qhov teeb meem, peb xav tias qhov kev npog cyclohexanone siab hauv NiV-LDH-NS nyiam cov txheej txheem COR, thiab rov qab, qhov kev npog cyclohexanone qis hauv Ni (OH) 2-NS nyiam cov txheej txheem OER.
Txhawm rau sim cov lus qhia saum toj no, peb tau ua ob qho kev sim uas cuam tshuam nrog qhov concentration ntawm cov reactants (C, cyclohexanone, thiab COH−). Qhov kev sim thawj zaug tau ua tiav nrog electrolysis ntawm qhov muaj peev xwm tas li (1.8 VRHE) ntawm Ni(OH)2-NS thiab NiV-LDH-NS catalysts nrog cov ntsiab lus cyclohexanone C sib txawv (0.05 ~ 0.45 M) thiab cov ntsiab lus COH− tas li (0.5 M). Tom qab ntawd, FE thiab AA productivity tau suav. Rau NiV-LDH-NS catalyst, kev sib raug zoo ntawm AA yield thiab cyclohexanone C tau qhia txog cov kab "volcanic type" hauv hom LH (Daim duab 4a), qhia tias qhov kev pab them nqi cyclohexanone siab sib tw nrog OH− adsorption. Thaum rau Ni (OH) 2-NS, AA cov txiaj ntsig tau nce monotonically nrog kev nce ntawm C20 ntawm cyclohexanone los ntawm 0.05 txog 0.45 M, qhia tias txawm hais tias qhov concentration ntawm cyclohexanone siab (0.45 M), nws qhov kev npog saum npoo tseem qis heev. Tsis tas li ntawd, nrog kev nce ntawm COH− txog 1.5 M, ib qho nkhaus "volcanic type" tau pom ntawm Ni (OH) 2-NS nyob ntawm C20 ntawm cyclohexanone, thiab qhov inflection point ntawm kev ua tau zoo tau qeeb piv nrog NiV-LDH-NS, ntxiv pov thawj qhov tsis muaj zog adsorption ntawm cyclohexanone ntawm Ni (OH) 2-NS (Supplementary Fig. 25a thiab Note 5). Ntxiv mus, FE ntawm AA ntawm NiV-LDH-NS yog rhiab heev rau C-cyclohexanone thiab nce sai sai mus rau ntau dua 80% thaum C-cyclohexanone tau nce los ntawm 0.05 M mus rau 0.3 M, qhia tias cyclohexanone tau yooj yim nplua nuj ntawm NiV-LDH-NS (Daim Duab 4b). Hauv kev sib piv, kev nce qhov concentration ntawm C-cyclohexanone tsis tau cuam tshuam qhov OER ntawm Ni (OH) 2-NS, uas tej zaum yog vim tsis txaus adsorption ntawm cyclohexanone. Ntawm qhov tod tes, kev tshawb nrhiav ntxiv ntawm kev vam khom ntawm COH− ntawm catalytic efficiency kuj tau lees paub tias adsorption ntawm cyclohexanone tau zoo dua piv rau NiV-LDH-NS, uas tuaj yeem ua siab dua COH− thaum lub sijhawm COR txheej txheem yam tsis txo qis FE ntawm AA (Supplementary Fig. 25b, c thiab Note 5).
Kev tsim khoom ntawm AA thiab EF ntawm b Ni(OH)2-NS thiab NiV-LDH-NS ntawm cyclohexanone nrog C sib txawv hauv 0.5 M KOH. c Lub zog adsorption ntawm cyclohexanone ntawm NiOOH thiab NiVOOH. d FE ntawm AA ntawm Ni(OH)2-NS thiab NiV-LDH-NS hauv 0.5 M KOH thiab 0.4 M cyclohexanone ntawm 1.80 VRHE siv cov tswv yim tsis sib xws thiab tas li. Cov kab yuam kev sawv cev rau qhov kev hloov pauv tus qauv ntawm peb qhov kev ntsuas ywj pheej siv tib tus qauv thiab nyob hauv 10%. e Sab saum toj: Ntawm Ni(OH)2-NS, cyclohexanone nrog thaj chaw qis C yog adsorbed tsis muaj zog los ntawm cyclohexanone, ua rau muaj kev sib tw muaj zog rau OER. Hauv qab: Ntawm NiV-LDH-NS, qhov concentration siab ntawm cyclohexanone C tau pom nrog kev nce ntxiv ntawm adsorption ntawm cyclohexanone, ua rau muaj kev txwv ntawm OER. Cov ntaub ntawv raw rau a-d tau muab tso rau hauv cov ntaub ntawv raw.
Txhawm rau sim qhov kev nqus ntawm cyclohexanone ntawm NiV-LDH-NS, peb siv electrochemical coupled quartz crystal microbalance (E-QCM) los saib xyuas qhov kev hloov pauv ntawm cov hom adsorbed hauv lub sijhawm tiag tiag. Cov txiaj ntsig tau qhia tias lub peev xwm nqus thawj zaug ntawm cyclohexanone ntawm NiV-LDH-NS yog 1.6 npaug loj dua li ntawm Ni (OH) 2-NS hauv lub xeev OCP, thiab qhov sib txawv no hauv lub peev xwm nqus ntxiv nce ntxiv thaum lub peev xwm nce mus txog 1.5 VRHE (Supplementary Fig. 26). Spin-polarized DFT kev suav tau ua los tshawb xyuas tus cwj pwm nqus ntawm cyclohexanone ntawm NiOOH thiab NiVOOH (Daim Duab 4c). Cyclohexanone nqus mus rau ntawm Ni-center ntawm NiOOH nrog lub zog adsorption (Eads) ntawm -0.57 eV, thaum cyclohexanone tuaj yeem nqus mus rau ntawm Ni-center lossis V-center ntawm NiVOOH, qhov twg V-center muab Eads qis dua (-0.69 eV), sib xws nrog qhov pom muaj zog adsorption ntawm cyclohexanone ntawm NiVOOH.
Yuav kom paub tseeb ntxiv tias qhov kev nqus ntawm cyclohexanone tuaj yeem txhawb nqa AA tsim thiab tiv thaiv OER, peb siv txoj kev tsis sib xws los ua kom cyclohexanone nplua nuj ntawm qhov chaw catalyst (rau Ni (OH) 2-NS thiab NiV-LDH-NS), uas tau tshoov siab los ntawm cov ntawv ceeb toom yav dhau los. 51, 52 Tshwj xeeb, peb tau siv lub peev xwm ntawm 1.8 VRHE rau COR, tom qab ntawd hloov nws mus rau lub xeev OCP, thiab tom qab ntawd hloov nws rov qab mus rau 1.8 VRHE. Hauv qhov no, cyclohexanone tuaj yeem sib sau ua ke ntawm qhov chaw catalyst hauv lub xeev OCP ntawm electrolyses (saib ntu Txoj Kev rau cov txheej txheem ntxaws ntxaws). Cov txiaj ntsig tau qhia tias rau Ni (OH) 2-NS thiab NiV-LDH-NS, siv cov peev xwm tsis sib xws electrolysis tau txhim kho kev ua haujlwm catalytic piv nrog cov peev xwm electrolysis tas mus li (Daim Duab 4d). Qhov tseem ceeb, Ni(OH)2-NS tau qhia txog kev txhim kho zoo dua hauv COR (AA FE: ntawm 51% txog 82%) thiab kev txo qis ntawm OER (O2 FE: ntawm 27% txog 4%) dua li NiV-LDH-NS, uas yog vim qhov tseeb tias cyclohexanone accumulation tuaj yeem txhim kho ntau dua ntawm cov catalyst nrog lub peev xwm adsorption qis dua (piv txwv li, Ni(OH)2-NS) los ntawm kev siv hluav taws xob tsis tu ncua.
Zuag qhia tag nrho, qhov kev txwv ntawm OER ntawm NiV-LDH-NS tuaj yeem yog vim muaj kev nce ntxiv ntawm cyclohexanone (Daim Duab 4e). Ntawm Ni(OH)2-NS (Daim Duab 4e, sab saum toj), qhov kev nqus tsis muaj zog ntawm cyclohexanone ua rau muaj kev npog cyclohexanone tsawg thiab muaj kev npog OH* siab ntawm qhov chaw catalyst. Yog li ntawd, cov hom OH* ntau dhau yuav ua rau muaj kev sib tw hnyav rau OER thiab txo FE ntawm AA. Qhov sib piv, ntawm NiV-LDH-NS (Daim Duab 4e, hauv qab), qhov kev hloov kho V ua rau muaj peev xwm nqus ntawm cyclohexanone ntau dua, yog li ua rau qhov chaw C ntawm cyclohexanone ntau dua thiab siv cov hom OH* uas tau nqus rau COR zoo, txhawb nqa AA tsim thiab tiv thaiv OER.
Ntxiv rau kev tshawb nrhiav qhov cuam tshuam ntawm V kev hloov kho rau kev tsim kho dua tshiab ntawm Ni hom thiab cyclohexanone adsorption, peb kuj tau tshawb nrhiav seb V puas hloov pauv txoj hauv kev tsim AA los ntawm COR. Ntau txoj hauv kev COR sib txawv tau raug tshaj tawm hauv cov ntaub ntawv, thiab peb tau tshuaj xyuas lawv cov peev xwm hauv peb lub kaw lus tshuaj tiv thaiv (saib Daim Duab Ntxiv 27 thiab Daim Ntawv Qhia Ntxiv 6 kom paub meej ntxiv) 13,14,26. Ua ntej, nws tau tshaj tawm tias thawj kauj ruam ntawm txoj hauv kev COR yuav cuam tshuam nrog kev pib oxidation ntawm cyclohexanone los tsim cov khoom siv nruab nrab tseem ceeb 2-hydroxycyclohexanone (2) 13,14. Txhawm rau txheeb xyuas cov txheej txheem, peb tau siv 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) los ntes cov khoom siv nruab nrab uas tau adsorbed rau ntawm qhov chaw catalyst thiab kawm txog EPR. Cov txiaj ntsig EPR tau qhia txog qhov muaj cov C-centered radicals (R) thiab hydroxyl radicals (OH) ntawm ob qho catalysts thaum lub sijhawm COR, qhia tias Cα - H dehydrogenation ntawm cyclohexanone tsim cov intermediate enolate radical (1), uas tom qab ntawd oxidized los ntawm OH * los tsim 2 (Daim duab 5a thiab Daim duab ntxiv 28). Txawm hais tias cov intermediates zoo ib yam tau txheeb xyuas ntawm ob qho catalysts, qhov feem pua ​​ntawm thaj tsam ntawm R teeb liab ntawm NiV-LDH-NS yog siab dua li ntawm Ni (OH) 2-NS, uas tej zaum yog vim muaj peev xwm adsorption ntawm cyclohexanone (Daim Ntawv Ntxiv 3 thiab Lus Cim 7). Peb ntxiv siv 2 thiab 1,2-cyclohexanedione (3) ua cov tshuaj reactants pib rau electrolysis los sim seb V puas yuav hloov kho cov kauj ruam oxidation tom ntej. Cov txiaj ntsig electrolysis ntawm cov peev xwm intermediates (2 thiab 3) ntawm Ni (OH) 2-NS thiab NiV-LDH-NS qhia tau tias cov khoom xaiv zoo sib xws, qhia tias COR tshuaj tiv thaiv ntawm Ni (OH) 2-NS lossis NiV-LDH-NS tau mus los ntawm cov kev zoo sib xws (Daim Duab 5b). Ntxiv mus, AA yog cov khoom tseem ceeb tsuas yog thaum 2 tau siv ua reactant, qhia tias AA tau txais los ntawm cov txheej txheem oxidation ncaj qha los ntawm kev txiav ntawm Cα - Cβ daim ntawv cog lus ntawm 2 es tsis yog oxidation tom qab rau 3 ntawm ob qho tib si catalysts, txij li nws tau hloov pauv mus rau GA thaum 3 tau siv ua reactant pib (Cov Duab Ntxiv 29, 30).
Cov teeb liab EPR ntawm NiV-LDH-NS hauv 0.5 M KOH + 0.4 M cyclohexanone. b Cov txiaj ntsig ntawm kev tshuaj xyuas electrocatalytic ntawm 2-hydroxycyclohexanone (2) thiab 1,2-cyclohexanedione (3). Electrolysis tau ua tiav hauv 0.5 M KOH thiab 0.1 M 2 lossis 3 ntawm 1.8 VRE rau ib teev. Cov kab yuam kev sawv cev rau qhov kev hloov pauv tus qauv ntawm ob qhov kev ntsuas ywj pheej siv tib lub catalyst. c Cov kev tshuaj xyuas tau npaj tseg ntawm COR ntawm ob lub catalysts. d Daim duab kos ntawm txoj kev COR ntawm Ni (OH) 2-NS (sab laug) thiab d NiV-LDH-NS (sab xis). Cov xub liab qhia txog cov kauj ruam uas V hloov kho txhawb nqa hauv cov txheej txheem COR. Cov ntaub ntawv raw rau a thiab b tau muab rau hauv cov ntaub ntawv raw.
Zuag qhia tag nrho, peb tau ua pov thawj tias Ni(OH)2-NS thiab NiV-LDH-NS catalyze COR los ntawm txoj kev zoo sib xws: cyclohexanone yog adsorbed rau ntawm qhov chaw catalyst, dehydrogenated thiab poob electrons rau daim ntawv 1, uas tom qab ntawd oxidized los ntawm OH* rau daim ntawv 2, ua raws li kev hloov pauv ntau kauj ruam los tsim AA (Daim Duab 5c). Txawm li cas los xij, thaum cyclohexanone siv ua reactant, OER kev sib tw tau pom tsuas yog ntawm Ni(OH)2-NS, thaum qhov tsawg tshaj plaws ntawm cov pa oxygen tau sau thaum 2 thiab 3 siv ua reactants. Yog li, qhov sib txawv pom hauv kev ua tau zoo catalytic yuav yog vim muaj kev hloov pauv hauv RDS lub zog thaiv thiab cyclohexanone adsorption peev xwm tshwm sim los ntawm V hloov pauv es tsis yog kev hloov pauv hauv txoj kev tshuaj tiv thaiv. Yog li ntawd peb tau tshuaj xyuas RDS ntawm cov kev tshuaj tiv thaiv ntawm ob qho tib si catalysts. Cov txiaj ntsig ntawm X-ray acoustic spectroscopy hauv qhov chaw saum toj no qhia tau hais tias V hloov pauv RDS hauv COR cov tshuaj tiv thaiv los ntawm theem rov tsim kho mus rau theem tshuaj, khaws cov theem NiOOH thiab cov hom Ni siab tseem nyob rau ntawm NiV-LDH-NS (Daim Duab 3f, Daim Duab Ntxiv 24, thiab Lus Cim 4). Peb tau tshuaj xyuas ntxiv txog cov txheej txheem tshuaj tiv thaiv uas sawv cev los ntawm qhov ceev tam sim no hauv txhua qhov ntawm thaj chaw sib txawv thaum lub sijhawm ntsuas CV (saib Daim Duab Ntxiv 31 thiab Lus Cim 8 kom paub meej ntxiv) thiab ua cov kev sim pauv isotope kinetic H/D, uas tau ua pov thawj ua ke tias RDS ntawm COR ntawm NiV-LDH-NS cuam tshuam nrog kev sib cais ntawm Cα - H daim ntawv cog lus hauv theem tshuaj es tsis yog theem txo qis (saib Daim Duab Ntxiv 32 thiab Lus Cim 8 kom paub meej ntxiv).
Raws li qhov kev tshuaj xyuas saum toj no, qhov cuam tshuam tag nrho ntawm V kev hloov kho tau pom hauv Daim Duab 5d. Ni(OH)2-NS thiab NiV-LDH-NS catalysts dhau los ntawm kev tsim kho dua tshiab ntawm qhov muaj peev xwm anodic siab thiab catalyze COR ntawm txoj kev zoo sib xws. Ntawm Ni(OH)2-NS (Daim Duab 5d, sab laug), kauj ruam tsim kho dua tshiab yog RDS thaum lub sijhawm COR; thaum ntawm NiV-LDH-NS (Daim Duab 5d, sab xis), V kev hloov kho tau ua kom nrawm dua cov txheej txheem tsim kho dua tshiab thiab hloov RDS mus rau hauv Cα−H dehydrogenation ntawm cyclohexanone los ua 1. Tsis tas li ntawd, cyclohexanone adsorption tau tshwm sim ntawm qhov chaw V thiab tau txhim kho ntawm NiV-LDH-NS, uas tau pab txhawb rau kev txwv ntawm OER.
Xav txog qhov kev ua tau zoo electrocatalytic zoo heev ntawm NiV-LDH-NS nrog FE siab dhau ntau qhov muaj peev xwm, peb tau tsim MEA kom ua tiav kev tsim khoom tas mus li ntawm AA. MEA tau sib sau ua ke siv NiV-LDH-NS ua anode, kev lag luam PtRu / C ua cathode53 thiab anion pauv membrane (hom: FAA-3-50) (Daim Duab 6a thiab Daim Duab Ntxiv 33)54. Txij li thaum lub cell voltage txo qis thiab FE ntawm AA yog sib piv nrog 0.5 M KOH hauv kev tshawb fawb saum toj no, qhov anolyte concentration tau ua kom zoo rau 1 M KOH (Daim Duab Ntxiv 25c). Cov kab LSV kaw tau pom hauv Daim Duab Ntxiv 34, qhia tias COR efficiency ntawm NiV-LDH-NS yog siab dua li ntawm Ni (OH) 2-NS. Txhawm rau qhia txog qhov zoo tshaj plaws ntawm NiV-LDH-NS, qhov hluav taws xob tas mus li tau ua tiav nrog qhov ceev tam sim no ntawm 50 txog 500 mA cm−2 thiab qhov hluav taws xob sib xws tau sau tseg. Cov txiaj ntsig tau qhia tias NiV-LDH-NS tau pom tias muaj lub zog hluav taws xob ntawm 1.76 V ntawm qhov ceev tam sim no ntawm 300 mA cm−2, uas yog kwv yees li 16% qis dua li ntawm Ni (OH) 2-NS (2.09 V), qhia txog nws cov txiaj ntsig zoo dua hauv kev tsim AA (Daim duab 6b).
Daim duab kos ntawm lub roj teeb ntws. b Lub zog hluav taws xob ntawm tes tsis muaj iR them nyiaj rau Ni (OH) 2-NS thiab NiV-LDH-NS hauv 1 M KOH thiab 0.4 M cyclohexanone ntawm qhov sib txawv tam sim no. c AA thiab FE tso zis rau Ni (OH) 2-NS thiab NiV-LDH-NS ntawm qhov sib txawv tam sim no. Cov kab yuam kev sawv cev rau qhov kev hloov pauv tus qauv ntawm ob qhov kev ntsuas ywj pheej siv tib lub catalyst. d Kev sib piv ntawm kev ua haujlwm catalytic ntawm peb txoj haujlwm nrog lwm cov roj teeb ntws tau tshaj tawm 14,17,19. Cov kev ntsuas tshuaj tiv thaiv thiab cov yam ntxwv tshuaj tiv thaiv tau teev tseg hauv cov ntsiab lus ntxiv hauv Rooj Ntxiv 2. e Lub zog hluav taws xob ntawm tes thiab FE ntawm AA ntawm NiV-LDH-NS ntawm 200 thiab 300 mA cm−2 hauv kev sim ntev, raws li. Cov ntaub ntawv raw rau be yog muab ua cov ntaub ntawv raw.
Lub caij no, raws li tau pom hauv daim duab 6c, NiV-LDH-NS yeej tswj tau FE zoo (83% txog 61%) ntawm qhov ceev tam sim no siab dua (200 txog 500 mA cm-2), yog li txhim kho AA tsim khoom (1031 txog 1900 μmol cm-2 h-1). Lub caij no, tsuas yog 0.8% ntawm adipic acid anions tau pom hauv cathode compartment tom qab electrolysis, qhia tias cyclohexanone hloov pauv tsis tseem ceeb hauv peb qhov xwm txheej (Supplementary Fig. 35). Hauv kev sib piv, nrog rau tib qho kev nce ntawm qhov ceev tam sim no, FE ntawm AA ntawm Ni (OH) 2-NS txo qis los ntawm 61% txog 34%, uas ua rau nws nyuaj rau txhim kho AA tsim khoom (762 txog 1050 μmol cm-2 h-1). Tshwj xeeb, qhov kev ua tau zoo ntawm AA txawm tias me ntsis txo qis vim yog kev sib tw muaj zog los ntawm OER, thiab yog li FE ntawm AA txo qis nrog qhov nce ntawm qhov ceev tam sim no (los ntawm 200 txog 250 mA cm−2, Daim Duab Ntxiv 5). Raws li peb paub, cov txiaj ntsig catalytic siv MEA nrog NiV-LDH-NS catalysts ntau dua li qhov kev ua tau zoo ntawm cov reactors ntws uas tau tshaj tawm yav dhau los nrog Ni-based catalysts (Daim Ntawv Ntxiv 2). Ntxiv mus, raws li tau pom hauv Daim Duab 6d, NiV-LDH-NS tau qhia txog qhov zoo tseem ceeb hauv qhov ceev tam sim no, lub zog hluav taws xob ntawm tes, thiab FE ntawm AA piv nrog qhov ua tau zoo tshaj plaws Co-based catalyst, piv txwv li, graphene-txhawb nqa Co3O4 (Co3O4 / GDY)17. Ntxiv rau, peb tau soj ntsuam qhov kev siv zog ntawm AA ntau lawm thiab qhia tau tias qhov kev siv AA tsawg heev, tsuas yog 2.4 W h gAA-1 ntawm qhov ceev tam sim no ntawm 300 mA cm-2 thiab lub zog ntawm tes ntawm 1.76 V (cov kev xam kom ntxaws tau muab rau hauv Cov Lus Qhia Ntxiv 1). Piv nrog rau qhov tshwm sim zoo tshaj plaws ntawm 4.1 W h gAA-1 rau Co3O4 / GDY tau tshaj tawm yav dhau los, kev siv zog rau AA ntau lawm hauv peb txoj haujlwm tau txo qis los ntawm 42% thiab kev tsim khoom tau nce ntxiv los ntawm 4 zaug (1536 vs. 319 μmol cm-2 h-1)17.
Qhov ruaj khov ntawm NiV-LDH-NS catalyst rau kev tsim AA ntev hauv MEA tau soj ntsuam ntawm qhov ceev tam sim no ntawm 200 thiab 300 mA cm-2, feem (Daim Duab 6e). Txij li thaum OH− siv sai dua ntawm qhov ceev tam sim no siab dua, tus nqi rov ua dua electrolyte ntawm 300 mA cm-2 siab dua li ntawm 200 mA cm-2 (saib subsection "Electrochemical measurements" rau cov ntsiab lus). Ntawm qhov ceev tam sim no ntawm 200 mA cm-2, qhov nruab nrab COR efficiency yog 93% hauv thawj 6 teev, tom qab ntawd me ntsis txo qis mus rau 81% tom qab 60 teev, thaum lub zog hluav taws xob ntawm tes me ntsis nce 7% (los ntawm 1.62 V txog 1.73 V), qhia txog kev ruaj khov zoo. Nrog rau qhov ceev tam sim no nce mus txog 300 mA cm−2, qhov ua tau zoo ntawm AA tseem yuav luag tsis hloov pauv (txo qis los ntawm 85% mus rau 72%), tab sis qhov hluav taws xob ntawm lub cell tau nce ntxiv ntau (los ntawm 1.71 mus rau 2.09 V, sib raug rau 22%) thaum lub sijhawm sim 46-teev (Daim Duab 6e). Peb xav tias qhov laj thawj tseem ceeb rau qhov kev ua haujlwm poob qis yog qhov xeb ntawm daim nyias nyias pauv anion (AEM) los ntawm cyclohexanone, uas ua rau muaj kev nce ntxiv ntawm qhov tsis kam ntawm lub cell thiab qhov hluav taws xob ntawm lub electrolyzer cell (Daim Duab Ntxiv 36), nrog rau qhov xau me ntsis ntawm electrolyte los ntawm anode mus rau cathode, ua rau muaj kev txo qis hauv qhov ntim anolyte thiab qhov xav tau kom nres qhov electrolysis. Tsis tas li ntawd, qhov txo qis hauv FE ntawm AA kuj tseem tuaj yeem yog vim qhov leaching ntawm cov catalysts, uas nyiam qhov qhib ntawm Ni ua npuas ncauj rau OER. Yuav kom qhia tau qhov cuam tshuam ntawm AEM uas lwj ntawm qhov kev puas tsuaj ntawm kev ruaj khov ntawm 300 mA cm−2, peb tau hloov nws nrog AEM tshiab tom qab 46 teev ntawm electrolysis. Raws li qhov xav tau, qhov ua tau zoo ntawm catalytic tau rov qab los, nrog rau lub zog hluav taws xob ntawm lub cell txo qis mus rau tus nqi pib (los ntawm 2.09 txog 1.71 V) thiab tom qab ntawd nce me ntsis thaum 12 teev tom ntej ntawm electrolysis (los ntawm 1.71 txog 1.79 V, nce 5%; Daim Duab 6e).
Zuag qhia tag nrho, peb tau ua tiav 60 teev ntawm kev ruaj khov ntawm AA ntawm qhov ceev tam sim no ntawm 200 mA cm−2, qhia tias FE thiab lub zog ntawm AA tau tswj hwm zoo. Peb kuj tau sim qhov ceev tam sim no siab dua ntawm 300 mA cm−2 thiab ua tiav qhov ruaj khov tag nrho ntawm 58 teev, hloov AEM nrog ib qho tshiab tom qab 46 teev. Cov kev tshawb fawb saum toj no qhia txog kev ruaj khov ntawm cov catalyst thiab qhia meej meej txog qhov xav tau kev txhim kho yav tom ntej ntawm cov AEMs muaj zog dua los txhim kho kev ruaj khov mus sij hawm ntev ntawm MEA rau kev tsim AA txuas ntxiv ntawm qhov ceev tam sim no zoo tagnrho hauv kev lag luam.
Raws li kev ua tau zoo ntawm peb lub MEA, peb tau thov kom muaj cov txheej txheem tsim khoom AA tiav suav nrog kev pub cov khoom siv, electrolysis, neutralization, thiab cov chav sib cais (Daim Duab Ntxiv 37). Kev tshuaj xyuas kev ua tau zoo ua ntej tau ua los ntsuas qhov ua tau zoo ntawm lub kaw lus siv cov qauv tsim khoom alkaline electrolyte electrocatalytic carboxylate 55. Hauv qhov no, cov nqi suav nrog peev, kev ua haujlwm, thiab cov ntaub ntawv (Daim Duab 7a thiab Daim Duab Ntxiv 38), thiab cov nyiaj tau los ntawm AA thiab H2 tsim tawm. Cov txiaj ntsig TEA qhia tau tias nyob rau hauv peb cov xwm txheej ua haujlwm (tam sim no ceev 300 mA cm-2, cell voltage 1.76 V, FE 82%), tag nrho cov nqi thiab cov nyiaj tau los yog US $ 2429 thiab US $ 2564, feem, txhais ua qhov txiaj ntsig ntawm US $ 135 ib tuj ntawm AA tsim tawm (saib Daim Ntawv Qhia Ntxiv 9 kom paub meej).
a Tag nrho tus nqi ntawm AA electrochemical txheej txheem nyob rau hauv qhov xwm txheej pib nrog FE ntawm 82%, tam sim no ceev ntawm 300 mA cm−2, thiab cell voltage ntawm 1.76 V. Kev tshuaj xyuas rhiab heev ntawm peb tus nqi rau b FE thiab c tam sim no ceev. Hauv kev tshuaj xyuas rhiab heev, tsuas yog cov kev ntsuas kawm tau hloov pauv thiab lwm cov kev ntsuas tau khaws cia tas li raws li TEA qauv. d Cov teebmeem ntawm FE sib txawv thiab tam sim no ceev ntawm qhov txiaj ntsig ntawm AA electrosynthesis thiab qhov txiaj ntsig siv Ni (OH) 2-NS thiab NiV-LDH-NS, xav tias lub cell voltage khaws cia tas li ntawm 1.76 V. Cov ntaub ntawv nkag rau a-d tau muab rau hauv cov ntaub ntawv raw.
Raws li qhov kev xav no, peb tau tshawb nrhiav ntxiv txog qhov cuam tshuam ntawm FE thiab qhov ceev tam sim no rau qhov txiaj ntsig ntawm AA electrosynthesis. Peb pom tias qhov txiaj ntsig yog qhov rhiab heev rau FE ntawm AA, txij li qhov txo qis hauv FE ua rau muaj kev nce ntxiv ntawm tus nqi ua haujlwm, yog li ua rau tus nqi tag nrho nce ntxiv (Daim Duab 7b). Hais txog qhov ceev tam sim no, qhov ceev tam sim no siab dua (> 200 mA cm-2) pab txo cov nqi peev thiab tus nqi tsim kho cog, feem ntau los ntawm kev txo qis thaj chaw electrolytic cell, yog li ua rau muaj kev nce ntxiv ntawm cov txiaj ntsig (Daim Duab 7c). Piv nrog qhov ceev tam sim no, FE muaj qhov cuam tshuam loj dua rau cov txiaj ntsig. Los ntawm kev piav qhia txog qhov cuam tshuam ntawm FE thiab qhov ceev tam sim no rau cov txiaj ntsig, peb pom tseeb tias qhov tseem ceeb ntawm kev ua tiav FE siab (> 60%) ntawm cov ceev tam sim no cuam tshuam nrog kev lag luam (> 200 mA cm-2) kom ntseeg tau tias muaj txiaj ntsig. Vim yog tus nqi FE siab ntawm AA, lub kaw lus tshuaj tiv thaiv nrog NiV-LDH-NS ua catalyst tseem zoo nyob rau hauv qhov ntau ntawm 100–500 mA cm−2 (pentagram dots; Daim Duab 7d). Txawm li cas los xij, rau Ni (OH) 2-NS, txo qis FE ntawm qhov ceev tam sim no siab (> 200 mA cm−2) ua rau muaj cov txiaj ntsig tsis zoo (lub voj voog; Daim Duab 7d), qhia txog qhov tseem ceeb ntawm cov catalysts nrog FE siab ntawm qhov ceev tam sim no siab.
Ntxiv rau qhov tseem ceeb ntawm cov tshuaj catalysts hauv kev txo cov peev thiab cov nqi khiav lag luam, peb qhov kev ntsuam xyuas TEA qhia tias kev ua lag luam tuaj yeem txhim kho ntxiv rau ob txoj kev. Thawj qhov yog los sib koom muag potassium sulfate (K2SO4) ntawm kev ua lag luam ua cov khoom lag luam ntawm chav tsev neutralization, tab sis nrog cov nyiaj tau los ntawm US $ 828 / t AA-1 (Supplementary Note 9). Qhov thib ob yog los ua kom zoo dua cov txheej txheem ua tiav, suav nrog kev siv cov khoom siv rov ua dua lossis kev tsim cov thev naus laus zis sib cais AA uas pheej yig dua (lwm txoj hauv kev rau cov chav tsev neutralization thiab kev sib cais). Cov txheej txheem acid-base neutralization uas siv tam sim no tuaj yeem ua rau cov nqi khoom siv siab (uas suav rau qhov feem ntau ntawm 85.3%), uas 94% yog vim cyclohexanone thiab KOH ($ 2069 / t AA-1; Daim Duab 7a), tab sis raws li tau hais los saum toj no, cov txheej txheem tseem muaj txiaj ntsig zoo. Peb xav tias cov nqi khoom siv yuav raug txo kom tsawg dua los ntawm cov txheej txheem siab dua rau kev rov qab tau KOH thiab cyclohexanone tsis muaj zog, xws li electrodialysis rau kev rov qab tau tag nrho ntawm KOH14 (kwv yees tus nqi ntawm US $ 1073 / t AA-1 ntawm electrodialysis; Cov Lus Qhia Ntxiv 9).
Hauv kev xaus lus, peb tau ua tiav qhov ua tau zoo ntawm kev siv hluav taws xob ntawm cov txhuas atom ntawm qhov ceev tam sim no los ntawm kev qhia V rau hauv Ni (OH) 2 nanosheets. Nyob rau hauv ntau qhov muaj peev xwm ntawm 1.5–1.9 VRHE thiab qhov ceev tam sim no ntawm 170 mA cm−2, AA FE ntawm NiV-LDH-NS tau mus txog 83–88%, thaum OER tau raug txo kom zoo rau 3%. Kev hloov kho V txhawb nqa kev txo qis ntawm Ni2 + rau Ni3 + x thiab txhim kho kev nqus ntawm cyclohexanone. Cov ntaub ntawv sim thiab kev xav qhia tias kev tsim kho dua tshiab ua rau muaj qhov ceev tam sim no rau cyclohexanone oxidation thiab hloov RDS ntawm COR los ntawm kev tsim kho dua tshiab mus rau dehydrogenation uas muaj Cα - H scission, thaum kev nqus ntawm cyclohexanone txhawb nqa OER. Kev txhim kho ntawm MEA tau ua tiav kev tsim khoom AA tas mus li ntawm qhov ceev tam sim no ntawm 300 mA cm−2, cov ntaub ntawv AA ua haujlwm ntawm 82%, thiab kev tsim khoom ntawm 1536 μmol cm−2 h−1. Kev sim 50-teev qhia tau hais tias NiV-LDH-NS muaj kev ruaj khov zoo vim nws tuaj yeem tswj tau AA FE siab hauv MEA (> 80% rau 60 teev ntawm 200 mA cm−2; > 70% rau 58 teev ntawm 300 mA cm−2). Yuav tsum nco ntsoov tias muaj qhov xav tau los tsim cov AEM muaj zog dua kom ua tiav kev ruaj khov mus sij hawm ntev ntawm cov khoom siv tam sim no zoo tagnrho hauv kev lag luam. Tsis tas li ntawd, TEA qhia txog cov txiaj ntsig kev lag luam ntawm cov tswv yim tshuaj tiv thaiv rau AA tsim khoom thiab qhov tseem ceeb ntawm cov catalysts ua tau zoo thiab cov thev naus laus zis sib cais siab heev kom txo cov nqi ntxiv.