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CA oil (cyclohexanone leh cyclohexanol inzawmkhawm) atanga adipic acid (nylon 66 hmahruaitu) electrosynthesis hi sustainable strategy a ni a, chu chuan traditional methods, condition khauh tak mamawhna chu a thlak thei a ni. Mahse, current density hniam leh oxygen evolution reaction inelna avangin a industrial application te chu nasa takin a tikhawtlai a ni. He hnathawhnaah hian nickel double hydroxide chu vanadium hmangin kan siam danglam a, chu chuan current density tihsan nan leh potential range zau takah (1.5–1.9 V vs. reversible hydrogen electrode) faradaic efficiency sang tak (>80%) kan vawng reng thei a ni. Experimental leh theoretical study-ah chuan V modification hian hna pawimawh pahnih a nei tih hmuhchhuah a ni a, chung zingah chuan accelerated catalyst reconstruction leh cyclohexanone adsorption tihchangtlun te pawh a tel. Concept finfiahna atan membrane-electrode assembly kan siam a, chu chuan adipic acid chu faradaic efficiency sang tak (82%) leh productivity (1536 μmol cm-2 h-1) neiin industrially relevant current density (300 mA cm-2)-ah a siam chhuak a, chutih rualin stability >50 h a nei thei bawk. He hnathawh hian adipic acid electrosynthesis atana catalyst tha tak, productivity sang tak leh industrial potential nei tak a lantir a ni.
Adipic acid (AA) hi aliphatic dicarboxylic acid pawimawh ber pawl a ni a, nylon 66 leh polyamide emaw polymer dang siamnaah hman a ni ber1. Industrial lamah chuan AA hi cyclohexanol leh cyclohexanone (ie, AA oil) inzawmkhawm chu oxidizing agent atan 50–60 vol% nitric acid hmanga oxidize-a siam a ni. Hetiang kalphung hian boruak lama harsatna a nei a, chu chu concentrated nitric acid leh nitrogen oxides (N2O leh NOx) te greenhouse gas anga emission nen a inzawm a ni2,3. H2O2 hi green oxidizing agent dang atan hman theih ni mah se, a man to lutuk leh a synthesis condition khauh tak avangin practically hman a harsa a, a man tlawm zawk leh sustainable zawk method a ngai a ni4,5,
Kum sawm kalta chhung khan electrocatalytic chemical leh fuel synthesis method te hian renewable energy hman leh boruak lum (eg, room temperature leh ambient pressure) hnuaia hnathawh a that avangin scientist te ngaihven a hlawh zual hle a ni7,8,9, Hemi chungchangah hian a chunga kan sawi tak hlawknate hmuh theihna tur bakah nitric acid leh nitrous oxide emission hman dan pangngaia thil siam chhuah hman thin hman lohna tur atan hian KA oil chu AA-a electrocatalytic conversion siam hi a pawimawh hle a ni (Figure 1a). Pioneering hna chu Petrosyan leh a thawhpuiten an thawk a, nickel oxyhydroxide (NiOOH)-a cyclohexanone (COR; cyclohexanone emaw cyclohexanol emaw) electrocatalytic oxidation reaction chu KA oil aiawh anga zirchian a ni tlangpui a, mahse current density hniam (6 mA cm-2) leh AA yield hniam (52%) a ni hmuh chhuah11,12. Chumi hnuah chuan COR activity tihpunna tur nickel-based catalyst siam chhuahna kawngah hmasawnna nasa tak a awm ta a ni. Entirnan, copper-doped nickel hydroxide (Cu-Ni(OH)2) catalyst chu cyclohexanol13-a Cα–Cβ cleavage tichak turin an siam a. Tun hnaiah Ni(OH)2 catalyst chu sodium dodecyl sulfonate (SDS) hmanga siam danglamin hydrophobic microenvironment siamin cyclohexanone14 tihausatu kan report a.
a KA oil electrooxidation hmanga AA siam chhuahna kawnga harsatna awmte. b Three-electrode system leh flow battery system-a Ni-based catalyst report tawh leh kan catalyst electrocatalytic COR tehkhin dan11,13,14,16,26. Reaction parameters leh reaction performance chungchang chipchiar takin Supplementary Table 1 leh 2-ah tarlan a ni.c H-cell reactor leh MEA-a COR atana kan NiV-LDH-NS catalyst-te catalytic performance, potential range zau takah hna thawk.
A chunga kan sawi takte hian COR activity tichangtlung mahse, Ni-based catalyst tarlan te hian potential hniam takah chauh AA Faraday efficiency (FE) (>80%) sang tak an lantir a, a tlangpuiin reversible hydrogen electrode (RHE, abbreviated VRHE) nena khaikhin chuan 1.6 V hnuai lam a ni. Chutiang chuan AA report-a partial current density (chu chu, current density zawng zawng FE-a puntir) chu 60 mA cm−2 hnuai lam a ni fo thin (Figure 1b leh Supplementary Table 1). Current density hniam tak hi industrial mamawh (>200 mA cm−2)15 aiin a hniam hle a, hei hian high-throughput AA synthesis atana electrocatalytic technology chu nasa takin a tikhawlo a ni (Figure 1a; chunglam). Current density tihpun nan hian positive potential tam zawk (electrode pathum system tan) emaw cell voltage sang zawk (electrode pahnih system tan) emaw hman theih a ni a, hei hi electrocatalytic transformation tam tak tan chuan a awlsam hle a, a bik takin oxygen evolution reaction (OER) tan chuan a awlsam hle. Mahse, anodic potential sang takah COR tan chuan OER hi AA FE tihtlem kawngah inelna lian tak a ni thei a, chu chuan energy efficiency a tihhniam thei a ni (Figure 1a; hnuai lam). Entirnan, hmasawnna hmasa (Figure 1b leh Supplementary Table 1) kan enfiah chuan SDS-modified Ni(OH)2-a AA FE chu applied potential 1.5 VRHE atanga 1.7 VRHE14-a tihpun a nih rualin 93% atanga 76%-ah a tlahniam tih kan hmu a, CuxNi1-x(OH)2/CF-a AA FE erawh a tlahniam tih kan hmuchhuak a, chu chu kan lungawi lo hle 93% atanga 69% ah a pung a, potential chu 1.52 VRHE atanga 1.62 VRHE16 ah a tisang a ni. Chutiang chuan AA-a reported partial current density chu potential sang zawkah chuan proportionally-in a pung lo a, hei hian AA performance tihchangtlunna chu nasa takin a tikhawtlai a, AA FE hniam vangin energy hman tamna pawh sawi loh. Nickel-based catalyst bakah hian cobalt-based catalyst hian COR17,18,19-ah catalytic activity a nei bawk. Mahse, potential sang zawkah chuan an efficiency a tlahniam a, Ni-based catalyst nena khaikhin chuan industrial application-ah potential limitation an nei tam zawk a, chu chu man inthlak danglamna nasa zawk leh inventory tenau zawk te hi a ni. Chuvangin, AA yield sang tak neih theihna tura hmantlak a nih theih nan COR-a current density sang tak leh FE nei Ni-based catalyst siam chhuah a duhthusam a ni.
He hnathawhnaah hian vanadium(V)-modified nickel layered double hydroxide nanosheets (NiV-LDH-NS) te chu COR kaltlangin AA siamna atana electrocatalyst tha tak angin kan report a, hei hian OER nasa taka tihtawp a nih avangin potential range zau takah hna a thawk a, H-cell leh membrane electrode assembly-ah te FE leh current density sang tak a nei thei a ni (MEAs; Figure 1 b). Kan hmuh hmasak ber chu Ni(OH)2 nanosheet catalyst (Ni(OH)2-NS) pangngai aia acetylene oxidation efficiency chu beisei angin, potential sang zawkah, 1.5 VRHE-a 80% atanga 1.9 VRHE-a 42%-ah a tlahniam tih kan lantir a ni. Chumi danglamna chu Ni(OH)2 chu V hmanga siam danglam hnuah NiV-LDH-NS chuan potential pek tawhah current density sang zawk a lantir a, a pawimawh zawk chu potential range zau takah FE sang zawk a vawng reng a ni. Entirnan, 1.9 VRHE-ah chuan current density 170 mA cm−2 leh FE 83% a lantir a, hei hi three-electrode system-a COR tan catalyst tha zawk a ni (Fig. 1c leh Supplementary Table 1). Experimental leh theoretical data atanga a lan dan chuan V modification hian Ni(OH)2 atanga high-valent Ni oxyhydroxides (Ni3+xOOH1-x) ah reduction kinetics a tipung a, hei hi COR tan active phase a ni. Chubakah, V modification hian catalyst surface-a cyclohexanone adsorption a tichak a, hei hian anodic potential sang takah OER tihtawp kawngah hmun pawimawh tak a chang a ni. NiV-LDH-NS thiltihtheihna lantir nan MEA flow reactor kan design a, industrially relevant current density (300 mA cm−2)-ah AA (82%) FE kan lantir a, hei hi membrane flow reactor-a kan result hmasa aiin a sang zawk hle (Fig. 1b leh Supplementary Table 2). AA (1536 μmol cm−2 h−1) yield inmil chu thermal catalytic process hmanga hmuh aiin a sang zawk (<30 mmol gcatalyst−1 h−1)4. Chubakah, MEA hman a nih chuan catalyst hian stability tha tak a nei a, FE >80% AA chu 200 mA cm−2-ah 60 h chhung a vawng reng a, FE >70% AA chu 58 h chhung 300 mA cm−2-ah a vawng reng bawk. A tawp berah chuan preliminary feasibility study (FEA) hmangin AA siamna atana electrocatalytic strategy hman man tlawmzia a tarlang a.
Literature hmasa lama kan sawi tawh ang khan Ni(OH)2 hi typical catalyst a ni a, COR tan activity tha tak a lantir a, chuvangin Ni(OH)2-NS13,14 hi a vawi khat nan coprecipitation method hmangin siam a ni. Sample-ah hian β-Ni(OH)2 structure a lang a, hei hi X-ray diffraction (XRD; Fig. 2a) hmangin a nemnghet a, ultra-thin nanosheets (thickness: 2–3 nm, lateral size: 20–50 nm) te chu high-resolution transmission electron microscopy (HRTEM; Supplementary Fig. 1) leh atomic force microscopy (AFM) tehna hmangin an enfiah bawk (Splementary Fig. 2) a ni. Nanosheets te hi ultra-thin an nih avangin aggregation an hmu bawk.
a Ni(OH)2-NS leh NiV-LDH-NS te X-ray diffraction pattern a ni. FE, throughput, leh AA current density chu b Ni(OH)2-NS leh c NiV-LDH-NS-ah potential hrang hrangah a awm. Error bar hian catalyst pakhat hmanga independent measurement pathum standard deviation a entir a ni. d NV-LDH-NS atanga HRTEM thlalak. Scale bar: 20 nm a ni. NiV-LDH-NS HAADF-STEM image leh a kaihhnawih elemental map Ni (green), V (yellow), leh O (blue) insem darh dan tarlanna. Scale bar: 100 nm a ni. f Ni(OH)2-NS (chunglam) leh NiV-LDH-NS (hnuailam) te Ni 2p3/2, g O 1 s, leh h V 2p3/2 XPS data te. i FE leh j hi cycle 7 chhunga catalyst pahnih chunga AA performance a ni. Error bar hian catalyst pakhat hmanga independent measurement pathum standard deviation a entir a, 10% chhungah a awm. a–c leh f–j te tana raw data chu raw data file-ah hian pek a ni.
Chumi hnuah Ni(OH)2-NS hian COR a nghawng dan kan zirchiang leh a. Constant potential electrolysis hmangin OER tel lovin potential hniam (1.5 VRHE)-ah AA 80% FE kan hmu a (Figure 2b), hei hian anodic potential hniam zawka OER aiin COR chu energetically-in a tha zawk tih a tilang a ni. By-product ber chu glutaric acid (GA) a ni tih hmuhchhuah a ni a, FE chu 3% a ni. Succinic acid (SA), malonic acid (MA), leh oxalic acid (OA) trace amounts awmna pawh HPLC hmangin an chhut bawk (product distribution atan Supplementary Figure 3 en rawh). He product-ah hian formic acid hmuh tur a awm lo a, hei hian carbonate hi C1 by-product angin a lo awm thei tih a tilang. He hypothesis hi test nan hian 0.4 M cyclohexanone electrolysis kimchang atanga electrolyte chu acidified a ni a, gaseous products te chu Ca(OH)2 solution hmangin an pass a ni. Chuvang chuan solution chu a turbid ta a, electrolysis hnua carbonate siam a nih thu a nemnghet ta a ni. Mahse, electrolysis process-a electric siam chhuah zawng zawng a tlem avangin (Figure 2b, c) carbonate concentration a hniam a, a zat chhiar a harsa hle. Hei bakah hian C2-C5 product dang pawh a lo piang thei a, mahse an zat erawh chu chhut theih a ni lo. Product zawng zawng zat hi chhiar harsa viau mah se, electrochemical equivalent zawng zawng atanga 90% chuan electrochemical process tam zawk chu hriatchhuah a nih thu a tarlang a, hei hian kan mechanistic hriatthiamna tur a siam a ni. Current density hniam (20 mA cm−2) avang hian AA yield chu 97 μmol cm−2 h−1 (Figure 2b) a ni a, hei hi catalyst mass loading (5 mg cm−2) atanga chhut chuan 19 mmol h−1 g−1 nen a inang a, hei hi thermal catalytic productivity (~30 mmol h−1 g−1) aiin a hniam zawk a ni Applied potential chu 1.5 atanga 1.9 VRHE-a a san chuan, overall current density chu a sang chho (20 atanga 114 mA cm−2) ni mahse, chutih rual chuan AA FE chu nasa takin a tlahniam a, 80% atanga 42% ah a tlahniam bawk. Positive potential tam zawka FE tlahniam chhan ber chu OER lama inelna vang a ni. A bik takin 1.7 VRHE-ah chuan OER inelna hian AA FE a tlahniam nasa hle a, chu chuan overall current density a san rualin AA performance a tihhniam deuh a ni. Chutiang chuan AA-a partial current density chu 16 atanga 48 mA cm−2-ah a pung a, AA productivity pawh a sang (97 atanga 298 μmol cm−2 h−1) ni mahse, energy dang tam tak hman a ni (2.5 W h gAA−1 more from 1.5 to 1.9 VRHE), chu chuan carbon emission 2.7 g CO2 a tipung a ni gAA−1 (chhut dan kimchang chu Supplementary Note 1-ah tarlan a ni). A hmaa kan sawi tawh OER chu anodic potential sang takah COR reaction nena inelna neitu anga report hmasa nen a inmil a, AA productivity tihchangtlunna atana harsatna tlangpui a ni14,17.
Ni(OH)2-NS-based COR catalyst tha zawk siam chhuah nan active phase kan zirchiang hmasa a. Kan in situ Raman spectroscopy result-ah (Supplementary Fig. 4) 473 cm-1 leh 553 cm-1-ah peak kan hmu a, hei hi NiOOH-a Ni3+-O bonds bending leh stretching nen a inmil a ni. NiOOH hi anodic potential-a Ni(OH)2 tihtlem leh Ni(OH)O pungkhawm avanga lo awm a ni tih documented a ni a, a bul berah chuan electrocatalytic oxidation-a active phase a ni20,21. Chuvangin, Ni(OH)2 atanga NiOOH-a phase reconstruction process ti chak chuan COR catalytic activity a tichak thei tih kan beisei.
Heteroatom modification hian transition metal oxides/hydroxides-ah phase reconstruction a tichak tih hmuhchhuah a nih avangin Ni(OH)2 chu metal hrang hrang hmanga siam danglam kan tum a ni22,23,24. Sample te hi Ni leh metal precursor pahnihna co-deposition hmanga siam a ni. Metal-modified sample hrang hrang zingah hian V-modified sample (V:Ni atomic ratio 1:8) (NiV-LDH-NS tia koh) hian COR-ah current density sang zawk a nei a (Supplementary Fig. 5) a pawimawh zawk chu potential window zau takah AA FE sang zawk a nei bawk. A bik takin, potential hniam (1.5 VRHE)-ah chuan NiV-LDH-NS current density chu Ni(OH)2-NS aiin a let 1.9-in a sang zawk (39 vs. 20 mA cm−2), AA FE chu catalyst pahnihah hian tehkhin theih a ni (83% vs. 80%). Current density sang zawk leh FE AA inang zawk avang hian NiV-LDH-NS productivity hi Ni(OH)2-NS aiin a let 2.1 in a sang zawk (204 vs. 97 μmol cm−2 h−1), hei hian V modification hian potential hniam takah current density a promoting effect a tilang chiang hle (Figure 2c).
Applied potential a san chuan (eg, 1.9 VRHE) NiV-LDH-NS-a current density chu Ni(OH)2-NS-a current density aiin a let 1.5-in a sang zawk (170 vs. 114 mA cm−2), a pung chu potential hniam zawk (a let 1.9-a sang) nen a inang a ni. Hriat tur pawimawh tak chu NiV-LDH-NS hian AA FE sang tak (83%) a vawng reng a, OER chu nasa takin a titawp (O2 FE 4%; Figure 2c), Ni(OH)2-NS leh a hmaa report tawh catalyst AA FE hniam zawk nei tam tak anodic potential sang takah a phak lo hle (Supplementary Table 1). Wide potential window (1.5–1.9 VRHE)-a AA FE sang tak avang hian 1.9 VRHE-ah AA generation rate 867 μmol cm−2 h−1 (174.3 mmol g−1 h−1 tlukpui) a awm a, hei hian electrocatalytic leh thermocatalytic system-ah pawh activity chu total mass loading hmanga normalized a nih chuan performance tha tak a lantir a ni NiV-LDH-NS sample te chu (Supplementary Fig. 6) a ni.
Ni(OH)2 chu V hmanga kan siam danglam hnua potential range zau takah current density sang leh FE sang tak hriatthiam nan NiV-LDH-NS structure kan characterize a. XRD result atanga a lan dan chuan V hmanga siam danglamna hian β-Ni(OH)2 atanga α-Ni(OH)2 ah phase transition a thlen a, V nena inzawm crystalline species hmuhchhuah a ni lo (Fig. 2a). HRTEM result atanga a lan dan chuan NiV-LDH-NS hian ultrathin Ni(OH)2-NS nanosheets te morphology a rochun a, lateral dimension pawh a inang vek a ni (Fig. 2d). AFM tehnaah chuan nanosheets te hi aggregation tendency chak tak a awm tih hmuhchhuah a ni a, chu chuan teh theih thickness 7 nm vel a siam a (Supplementary Fig. 7), hei hi Ni(OH)2-NS (thickness: 2–3 nm) aiin a lian zawk a ni. Energy-dispersive X-ray spectroscopy (EDS) mapping analysis (Figure 2e) hmangin nanosheet-ah hian V leh Ni element te chu a insem darh tha hle tih hmuhchhuah a ni. V electronic structure leh Ni chunga a nghawng dan chiang zawka hriat theih nan X-ray photoelectron spectroscopy (XPS) kan hmang a (Figure 2f–h). Ni(OH)2-NS hian Ni2+-a spin-orbit peaks characteristic tak tak a lantir a (hmeichhia peak chu 855.6 eV-ah, satellite peak chu 861.1 eV-ah, Figure 2f)25. Ni(OH)2-NS-a O 1 s XPS spectrum hi peak pathum-ah then theih a ni a, chung zingah chuan 529.9, 530.9 leh 532.8 eV-a peak awmte chu lattice oxygen (OL), hydroxyl group (Ni-OH) leh oxygen adsorbed on surface defects (OAds) te vang a ni (Figure 2g)26,27,28,29 a ni. V hmanga siam danglam hnuah V 2p3/2 peak a lo lang a, chu chu 517.1 eV (V5+), 516.6 eV (V4+) leh 515.8 eV (V3+)-a awm peak pathum-ah a inthen thei a, hei hian structure-a V chi hrang hrangte hi oxidation sang tak state-ah an awm ber tih a tilang a ni (Figure 2h)25,30,31. Tin, NiV-LDH-NS-a Ni 2p peak 855.4 eV-a awm chu Ni(OH)2-NS-a Ni(OH)2-NS-a Ni 2p peak nena khaikhin chuan negative-in (0.2 eV velin) a inthlak a, hei hian electron chu V atanga Ni-ah a transfer tih a tilang bawk. V modification hnua Ni valence state hniam tak hmuhchhuah chu Ni K-edge X-ray absorption near-edge spectroscopy (XANES) result nen a inmil hle (a chipchiar zawkna chu a hnuaia “V Modification Promotes Catalyst Reduction” section en rawh). 1 h chhung COR hmanga enkawl hnua NiV-LDH-NS chu NiV-LDH-POST tia vuah a ni a, transmission electron microscopy, EDS mapping, X-ray diffraction, Raman spectroscopy, leh XPS tehna hmangin a characterize kim vek a ni (Supplementary Figs. 8 leh 9). Catalyst te chu aggregate angin ultrathin nanosheet morphology neiin an awm reng a (Supplementary Fig. 8a–c). V leaching leh catalyst reconstruction avang hian sample te crystallinity a tlahniam a, V content a tlahniam bawk (Supplementary Fig. 8d–f). XPS spectra-ah chuan V peak intensity a tlahniam tih hmuhchhuah a ni (Supplementary Fig. 9), hei hi V leaching vang a ni. Chu bakah, O 1s spectrum analysis (Supplementary Fig. 9d) leh electron paramagnetic resonance (EPR) measurement (Supplementary Fig. 10) te chuan NiV-LDH-NS-a oxygen vacancy awm zat chu electrolysis 1 h hnuah a pung tih hmuhchhuah a ni a, hei hian Ni 2p binding energy-ah negative shift a thlen thei a ni (Supplementary Figs. 9 leh 10 en la chipchiar zawkin)26,27,32,33. Chutiang chuan NiV-LDH-NS hian COR 1 h hnuah structural change a nei tlem hle.
COR tihhmasawn nana V-in a chanvo pawimawh tak a neihzia nemnghet turin, coprecipitation method inang hmangin 1:8 tih loh chu V:Ni atomic ratio hrang hrang (1:32, 1:16, leh 1:4, NiV-32, NiV-16, leh NiV-4 tia ruat) nei NiV-LDH catalyst kan siam chhuak a. EDS mapping result atanga a lan dan chuan catalyst chhunga V:Ni atomic ratio chu precursor nen a inhnaih hle a ni (Supplementary Fig. 11a–e). V modification a san chuan V 2p spectrum intensity a sang chho zel a, Ni 2p region binding energy chu negative side-ah a inthlak chhunzawm zel a ni (Supplementary Fig. 12). Chutih rual chuan OL proportion pawh a pung zauh zauh bawk. Catalytic test result atanga a lan dan chuan V modification tlem ber (V:Ni atomic ratio 1:32) hnuah pawh OER hi a tha thei ang bera tihtawp theih a ni a, V modification hnuah O2 FE chu 1.8 VRHE-ah 27% atanga 11% ah a tlahniam a ni (Supplementary Fig. 11f). V:Ni ratio 1:32 atanga 1:8 a san chuan catalytic activity a sang chho ta a ni. Mahse, V modification a san belh zel (V:Ni ratio of 1:4) chuan current density a tlahniam a, hei hi Ni active sites (a bik takin NiOOH active phase; Supplementary Fig. 11f) density tlahniam vang niin kan ngai. V modification promoting effect leh Ni active sites humhalh avang hian V:Ni ratio screening test-ah hian V:Ni ratio 1:8 nei catalyst hian FE leh AA performance sang ber a nei a ni. Electrolysis hnuah pawh V:Ni ratio chu a awm reng em tih chiang zawka hriat theih nan catalyst hmante composition chu characterized a ni. Results atanga a lan dan chuan initial V:Ni ratio 1:16 atanga 1:4 nei catalyst te tan chuan V:Ni ratio chu reaction hnuah 1:22 vel ah a tlahniam a, hei hi catalyst reconstruction avanga V leaching vang pawh a ni thei (Supplementary Fig. 13). Hriat tur chu AA FEs tehkhin theih chu a tir lama V:Ni ratio chu 1:16 nen a inang emaw, a aia sang emaw a nih laiin hmuh a ni (Supplementary Fig. 11f), hei hi catalyst reconstruction avanga catalytic performance tehkhin theih catalyst-a V:Ni ratio inang lo a awm avanga sawifiah theih a ni.
COR performance tihchakna atana V-modified Ni(OH)2 pawimawhzia nemnghet lehzual turin Ni(OH)2-NS material-a V dah luh theihna tur synthetic method dang pahnih kan siam a. Pakhat chu mixing method a ni a, sample chu NiV-MIX tia sawi a ni a; a dang chu sequential sputtering method a ni a, sample chu NiV-SP tia sawi a ni. Synthesis chungchang chipchiar zawk chu Methods section-ah tarlan a ni. SEM-EDS mapping hmangin sample pahnih Ni(OH)2-NS surface-ah V chu hlawhtling takin siam danglam a ni tih hmuhchhuah a ni (Supplementary Fig. 14). Electrolysis result atanga a lan dan chuan 1.8 VRHE-ah chuan NiV-MIX leh NiV-SP electrode-a AA efficiency chu 78% leh 79% a ni a, an pahnih hian Ni(OH)2-NS (51%) aiin efficiency sang zawk an lantir a ni. Chubakah, NiV-MIX leh NiV-SP electrode-a OER chu Ni(OH)2-NS (FE O2: 27%) nena khaikhin chuan a tlahniam (FE O2: 7% leh 2%, a hnuaia mi ang hian) a ni. Heng results te hian Ni(OH)2-a V modification hian OER suppression a nghawng tha tih a nemnghet a ni (Supplementary Fig. 14). Mahse, catalyst-te stability a tlahniam a, hei hi COR cycle pasarih hnuah NiV-MIX-a FE AA chu 45%-ah a tlahniam a, NiV-SP-ah 35%-ah a tlahniam a, hei hian V species stabilize theihna tur kawng dik tak hman a ngai tih a tilang a, chu chu he thila catalyst pawimawh ber NiV-LDH-NS-a Ni(OH)2 lattice-a V modification ang chi hi a ni hnathawk.
Ni(OH)2-NS leh NiV-LDH-NS te stability te pawh COR chu cycle tam takah kan dah a. Reaction chu cycle khatah 1 h chhung an ti a, cycle tin hnuah electrolyte chu thlak leh a ni. 7th cycle hnuah Ni(OH)2-NS-a FE leh AA performance chu 50% leh 60% in a tlahniam a, OER erawh a pung tih hmuhchhuah a ni thung (Fig. 2i, j). Cycle tin hnuah catalyst-te cyclic voltammetry (CV) curve kan zirchiang a, Ni2+ oxidation peak chu a tlahniam zauh zauh tih kan hmu a, hei hian Ni redox ability a tlahniam tih a tilang (Supplementary Fig. 15a–c). Electrolysis laiin electrolyte-a Ni cation concentration a san rual hian (Supplementary Fig. 15d), performance degradation (FE leh AA productivity tlahniam) chu catalyst atanga Ni leaching vang kan ti a, chu chuan OER activity lantir thei Ni foamed substrate chu a exposure nasa zawk a ni. Chumi danglamna chu NiV-LDH-NS hian FE leh AA productivity tlahniam chu 10%-ah a ti hniam a (Fig. 2i, j), hei hian V modification hian Ni leaching chu nasa takin a titawp tih a tilang (Supplementary Fig. 15d). V modification-a stability tihpun dan hriatthiam nan theoretical calculation kan nei a. Literature hmasa34,35-a kan sawi tawh angin, catalyst active surface-a metal atom-te demetallization process-a enthalpy inthlak danglamna hi catalyst stability tehna atan descriptor dik tak atan hman theih a ni. Chuvangin, siam thar Ni(OH)2-NS leh NiV-LDH-NS (NiOOH leh NiVOOH, a hnuaia mi ang hian) chunglam (100) surface-a Ni atom-te demetallization process-a enthalpy inthlak danglamna chu chhut a ni (model siam dan chipchiar zawk chu Supplementary Note 2 leh Supplementary Fig. 16-ah tarlan a ni). NiOOH leh NiVOOH atanga Ni demetallization process chu entir a ni (Supplementary Fig. 17). NiVOOH (0.0325 eV)-a Ni demetallization-a energy cost chu NiOOH (0.0005 eV) aiin a sang zawk a, hei hian V modification hian NiOOH stability a tichak tih a tilang a ni.
NiV-LDH-NS-a OER inhibitory effect, a bik takin anodic potential sang takah, differential electrochemical mass spectrometry (DEMS) hmangin sample hrang hranga potential-dependent O2 formation zirchian a ni. Results atanga a lan dan chuan cyclohexanone awm lohnaah chuan NiV-LDH-NS-a O2 chu initial potential 1.53 VRHE-ah a lang a, hei hi Ni(OH)2-NS (1.62 VRHE)-a O2 aiin a hniam deuh hlek a ni (Supplementary Fig. 18). He result hian COR chhunga NiV-LDH-NS OER inhibition hi a intrinsic low OER activity vang a ni lo mai thei tih a tilang a, hei hi cyclohexanone tel lo Ni(OH)2-NS-a Ni(OH)2-NS-a current density aiin NiV-LDH-NS-a linear sweep voltammetry (LSV) curve-a current density sang deuh nen a inmil a ni (Supplementary Fig. 19). Cyclohexanone hman a nih hnuah O2 evolution tlai (COR thermodynamic advantage vang pawh a ni thei) hian low potential region-a AA FE sang tak chu a hrilhfiah a ni. Chu aia pawimawh zawk chu NiV-LDH-NS (1.73 VRHE)-a OER onset potential hi Ni(OH)2-NS (1.65 VRHE) aiin a tlai zawk a, hei hi positive potential tam zawka NiV-LDH-NS-a AA FE sang leh O2 FE hniam nen a inmil hle (Figure 2c).
V modification-in promoting effect a neih dan hriatthiam belh nan Ni(OH)2-NS leh NiV-LDH-NS-a OER leh COR reaction kinetics te chu an Tafel slope tehna hmangin kan zirchiang a. Hriat tur chu Tafel biala current density hi LSV test neih laiin Ni2+ chu Ni3+-ah potential hniam atanga potential sang takah a oxidation vang a ni. COR Tafel slope tehnaah Ni2+ oxidation-in nghawng a neih tihtlem nan catalyst chu 1.8 VRHE-ah min 10 chhung kan oxidize hmasa a, chutah chuan LSV test-te chu reverse scan mode-ah kan ti a, chu chu high potential atanga low potential-ah kan ti a ni (Supplementary Fig. 20). Tafel slope hmuh theih nan LSV curve hmasa chu 100% iR compensation hmangin siamthat a ni. Cyclohexanone awm lohnaah chuan NiV-LDH-NS (41.6 mV dec−1) Tafel slope chu Ni(OH)2-NS (65.5 mV dec−1) aiin a hniam zawk a, hei hian V modification hmangin OER kinetics a tichak thei tih a tilang (Supplementary Fig. 20c). Cyclohexanone dah a nih hnuah NiV-LDH-NS (37.3 mV dec−1) Tafel slope chu Ni(OH)2-NS (127.4 mV dec−1) aiin a hniam zawk a, hei hian V modification hian OER nena khaikhin chuan COR-ah kinetic effect a nei chiang zawk tih a tilang (Supplementary Fig. 20d). Heng results te hian V modification hian OER hi eng emaw chen a tichak a, mahse COR kinetics chu nasa takin a ti chak a, chu chuan AA FE a tipung tih a tilang.
A chunga V modification hian FE leh AA performance a tihhmasawn dan hriatthiam nan mechanism study kan ngaihtuah ber a ni. Report hmasa thenkhatah chuan heteroatom modification hian catalyst crystallinity a tihhniam thei a, electrochemically active surface area (EAS) a tisang thei a, chu chuan active site a tipung a, chu chuan catalytic activity a ti tha thei tih an lo tarlang tawh bawk Hetiang thil thleng thei hi chhui chian nan electrochemical activation hma leh hnuah ECSA measurement kan nei a, result atanga a lan dan chuan Ni(OH)2-NS leh NiV-LDH-NS te ECSA chu tehkhin theih a ni (Supplementary Fig. 21), V modification hnua active site density-in catalytic enhancement-a nghawng a neih dan chu a tel lo.
Mipui hriat dan chuan alcohol emaw nucleophilic substrate dang emaw Ni(OH)2-catalyzed electrooxidation-ah hian Ni(OH)2 hian electron leh proton a hloh hmasa a, chutah chuan electrochemical step hmangin anodic potential engemaw takah NiOOH-ah a tlahniam ta a ni Chumi hnuah NiOOH siam chu active COR species tak tak angin a thawk a, chemical step hmangin nucleophilic substrate atanga hydrogen leh electron te chu a la chhuak a, oxidized product a siam ta a ni20,41. Mahse, tun hnaiah chuan NiOOH-a tihhniam hi Ni(OH)2-a alcohol electrooxidation atana rate-determining step (RDS) hna thawk thei mah se, tun hnaia literature-a an sawi angin, Ni3+ alcohols oxidation hi Ni3+41, Literature ang chiaha report mechanistic study atanga infuih tharin, COR chhunga Ni3+ tihtlem avanga Ni2+ lo awm apiang in situ-a man turin probe molecule atan dimethylglyoxime disodium salt octahydrate (C4H6N2Na2O2 8H2O) kan hmang a (Supplementary Fig. 22 leh Supplementary Note 3). Results atanga a lan dan chuan Ni2+ a lo piang a, hei hian COR process chhung hian NiOOH chemical reduction leh Ni(OH)2 electrooxidation chu a rualin a thleng tih a nemnghet a ni. Chuvangin, catalytic activity hi Ni(OH)2 NiOOH-a tihtlem kinetics-ah nasa takin a innghat thei a ni. He principle hmang hian a dawtah chuan V siam danglamna hian Ni(OH)2 tihtlem a ti chak ang em tih leh chu chuan COR a ti \ha ang em tih kan zirchiang leh a.
Ni(OH)2-NS leh NiV-LDH-NS-a COR atana NiOOH active phase a nihzia lantir nan in situ Raman technique kan hmang hmasa ber a, positive potential-a NiOOH lo awm dan leh a hnu lama a hman dan enfiahin, a hmaa kan sawi tawh “electrochemical-chemical” process zawm a ni (Figure 3a). Chubakah, reconstructed NiV-LDH-NS reactivity chuan Ni(OH)2-NS reactivity a tluk pha a, hei hi Ni3+–O Raman signal bo chak lutuk hian a tilang chiang hle. Chumi hnuah NiV-LDH-NS hian cyclohexanone awm leh awm lohah Ni(OH)2-NS nena khaikhin chuan NiOOH siamna atana positive potential a nei tlem zawk tih kan hmuchhuak a (Figure 3b, c leh Supplementary Fig. 4c, d). Hriat tur pawimawh tak chu NiV-LDH-NS OER performance sang zawk hian Raman measurement objective hmalam lens-ah bubble tam zawk a stick a, chu chuan 1.55 VRHE-a Raman peak chu a bo tir a ni (Supplementary Fig. 4d). DEMS result (Supplementary Fig. 18) atanga a lan dan chuan potential hniam takah current density (Ni(OH)2-NS tan VRHE < 1.58 leh NiV-LDH-NS tan VRHE < 1.53) hi cyclohexanone awm lohna hmuna OER aiin Ni2+ ion siam thar leh vang a ni ber. Chutiang chuan LSV curve-a Ni2+ oxidation peak chu NiV-LDH-NS aiin a chak zawk a, hei hian V modification hian NiV-LDH-NS chu remodeling ability tihpunna a pe tih a tilang (a chipchiar zawka zirchianna atan Supplementary Fig. 19 en rawh).
a OCP condition hnuaia Ni(OH)2-NS (khawi lamah nge) leh NiV-LDH-NS (dinglam) te in situ Raman spectra chu 0.5 M KOH leh 0.4 M cyclohexanone-a 1.5 VRHE-a 60 s chhung preoxidation hnuah. b Potential hrang hranga 0.5 M KOH + 0.4 M cyclohexanone-a Ni(OH)2-NS leh c NiV-LDH-NS te in situ Raman spectra. d 0.5 M KOH leh e 0.5 M KOH leh 0.4 M cyclohexanone-a Ni K-edge-a Ni(OH)2-NS leh NiV-LDH-NS te in situ XANES spectra. Inset-ah hian 8342 leh 8446 eV inkar magnified spectral region a lang a. f Ni(OH)2-NS leh NiV-LDH-NS-a Ni awm zat chu potential hrang hrangah a awm. g Potential hrang hranga cyclohexanone dah hma leh dah hnua NiV-LDH-NS in situ Ni EXAFS spectra. h Ni(OH)2-NS leh NiV-LDH-NS te theoretical model te. Top: Ni(OH)2-NS-ah chuan Ni(OH)2-NS atanga NiOOH-a slow remodeling hian RDS angin hna a thawk a, cyclohexanone erawh chuan high-valent Ni species chu chemical step hmangin a tihtlem a, low-valent Ni state chu vawng rengin AA a siam chhuak thei a ni. Bottom: NiV-LDH-NS-ah chuan V modification hmangin remodeling step chu a awlsam phah a, chu chuan RDS chu remodeling step atanga chemical step-ah a transfer a ni. i Ni(OH)2-NS leh NiV-LDH-NS te siam thar leh a nih chuan Gibbs free energy hi a inthlak thin. aj leh i tana raw data chu raw data file ah a awm a.
Catalyst tihtlem laiin atomic leh electronic structures evolution zirchian nan in situ X-ray absorption spectroscopy (XAS) experiment kan nei a, hei hian Ni chi hrang hrangte dynamics chu step thum a zawna chhui theihna hmanraw chak tak a pe a: OER, cyclohexanone injection, leh COR at open circuit potential (OCP). Figure-ah hian cyclohexanone injection hma leh injection hnua Ni-a potential sang chho zel K-edge XANES spectra tarlan a ni (Figure 3d, e). Chutiang bawka potential-ah chuan NiV-LDH-NS absorption edge energy chu Ni(OH)2-NS aiin a positive zawk tih a chiang hle (Figure 3d, e, inset). Condition tin hnuaia Ni valence average chu XANES spectra linear combined fit leh Ni K-edge absorption energy shift regression hmanga chhut a ni (Figure 3f), reference spectrum chu literature chhuah tawh atanga lak a ni (Supplementary Fig. 23)
Step hmasa berah (cyclohexanone, OER process nena inmil; Figure 3f, veilam), unreconstructed catalyst (<1.3 VRHE) potential-ah chuan NiV-LDH-NS (+1.83)-a Ni valence state chu Ni(OH)2-NS (+1.97) aiin a hniam deuh a, hei hi V atanga electron transfer vang a ni thei Ni, a chunga kan sawi tak XPS result nen a inmil hle (Figure 2f). Potential-in reduction point (1.5 VRHE) a pelh chuan NiV-LDH-NS (+3.28)-a Ni valence state chu Ni(OH)2-NS (+2.49) nena khaikhin chuan a pung tih a lang chiang zawk. Potential sang zawk (1.8 VRHE)-ah chuan NiV-LDH-NS (+3.64)-a Ni particle hmuh chhuah valence state chu Ni(OH)2-NS (+3.47) aiin a sang zawk a ni. Tun hnaia report-a a lan dan chuan he kalphung hi Ni3+xOOH1-x (Ni3+x hi Ni3+ leh Ni4+ chi hrang hrang inzawmkhawm a ni) structure-a high-valent Ni4+ species siam nen a inmil a, hei hian a hmain alcohol dehydrogenation-ah catalytic activity tihpun a lo lantir tawh a ni38,39, Chuvangin, COR-a NiV-LDH-NS performance sang zawk hi catalytically active high-valent Ni species siam theihna tura reducibility tihpun vang a ni thei.
Step hnihnaah (ring hawn hnua cyclohexanone dah luh, Figure 3f)-ah chuan catalyst pahnih a Ni valence state chu nasa takin a tlahniam a, hei hi cyclohexanone hmanga Ni3+xOOH1-x tihtlem dan nen a inmil a, hei hi in situ Raman spectroscopy result nen a inmil a ni (Figure 3a), Ni valence state chu a bul tanna state-ah a lo kir leh tawh mai (step hmasa ber at low potential), hei hian Ni redox process chu Ni3+xOOH1-x-ah a reversibility a tilang a ni.
Step thumna (COR process)-ah chuan COR potential (1.5 leh 1.8 VRHE; Figure 3f, dinglam)-ah Ni(OH)2-NS-a Ni valence state chu tlem chauh (+2.16 leh +2.40) a pung a, hei hi step hmasa lama potential inang (+2.49 leh +3.47) aiin a hniam zawk hle. Heng results te hian cyclohexanone injection hnuah COR chu Ni(OH)2-NS-a NiOOH leh cyclohexanone inkara chemical step aiin Ni2+ chu Ni3+x-a slow oxidation (ie, Ni reconstruction) vangin kinetically limited a ni tih a tilang a, chu chuan Ni chu low-valence state-ah a dah a ni. Chutiang chuan Ni(OH)2-NS-a COR process-ah Ni reconstruction hian RDS hna a thawk thei tih kan thutlukna siam a ni. Chumi danglamna chu NiV-LDH-NS hian COR process chhung hian Ni species valence sang tak (>3) a vawng reng a, potential inang (1.65 leh 1.8 VRHE)-a step hmasa ber nen khaikhin chuan valence chu a tlahniam tlem zawk (0.2 aia tlem) a ni a, hei hian V modification hian kinetically-in Ni2+ chu Ni3+x-a oxidation a tichak tih a tilang a, hei hian Ni reduction process chu a ti chak zawk tih a tilang a ni cyclohexanone tihtlem nana chemical step aiin. Extended X-ray absorption fine structure (EXAFS) result-ah pawh cyclohexanone awmnaah Ni–O (1.6 atanga 1.4 Å) leh Ni–Ni(V) (2.8 atanga 2.4 Å) bonds te chu a inthlak danglam kim vek tih hmuhchhuah a ni bawk. Hei hi Ni(OH)2 phase chu NiOOH phase-a siam thar lehna leh cyclohexanone hmanga NiOOH phase chemical reduction nen a inmil hle (Fig. 3g). Mahse, cyclohexanone hian Ni(OH)2-NS reduction kinetics chu nasa takin a tikhawlo a (a chipchiar zawkna chu Supplementary Note 4 leh Supplementary Fig. 24 en rawh).
A pum puiin Ni(OH)2-NS (Fig. 3h, chunglam)-ah chuan NiOOH chemical reduction laiin cyclohexanone atanga AA siam chhuahna chemical step aiin Ni(OH)2 phase atanga NiOOH phase-a slow reduction step chu COR process pumpui RDS atan a thawk thei a ni. NiV-LDH-NS (Fig. 3h, hnuai lam)-ah chuan V modification hian Ni2+ atanga Ni3+x-a oxidation kinetics a tichak a, chu chuan NiVOOH siamna a ti chak zawk (chemical reduction hmanga ei ai chuan), chu chuan RDS chu chemical step lam pan turin a sawn a ni. V modification avanga Ni reconstruction awm dan hriatthiam nan theoretical calculation kan nei leh a. Fig. 3h a kan hmuh angin Ni(OH)2-NS leh NiV-LDH-NS te reconstruction process kan simulate a. Ni(OH)2-NS leh NiV-LDH-NS-a lattice hydroxyl group awmte chu electrolyte-a OH- lakchhuah hmangin deprotonated an ni a, electron tlachham lattice oxygen an siam a ni. Chemical reaction inmilte chu hetiang hi a ni:
Reconstruction-a Gibbs free energy change chu chhut a ni (Figure 3i), NiV-LDH-NS (0.81 eV) chuan Ni(OH)2-NS (1.66 eV) aiin Gibbs free energy change a tlem zawk tih a tarlang a, hei hian V modification hian Ni reconstruction atana voltage mamawh a tihhniam thu a tarlang. Reconstruction tihhmasawn hian COR pumpui energy barrier a tihhniam thei niin kan ring (a chipchiar zawkna chu a hnuaia reaction mechanism study en rawh), chu chuan current density sang zawkah reaction a ti chak thei a ni.
A chunga kan zirchianna hian V modification hian Ni(OH)2 phase rearrangement rang tak a thlen a, chu chuan reaction rate a tisang a, chu chuan COR current density a tisang bawk. Mahse, Ni3+x sites hian OER activity a tichak thei bawk. Cyclohexanone tel lo LSV curve atang chuan NiV-LDH-NS current density chu Ni(OH)2-NS aiin a sang zawk tih a chiang hle (Supplementary Fig. 19), hei hian COR leh OER reaction te hian competitive reaction a siam a ni. Chuvangin, NiV-LDH-NS aiin AA FE a sang zawk tih hi phase rearrangement tichaktu V modification hian a sawifiah kim thei lo.
Alkaline media-ah chuan nucleophilic substrate-te electrooxidation reaction hian Langmuir–Hinshelwood (LH) model a zawm tlangpui tih hi pawm tlangpui a ni. A bik takin, substrate leh OH− anion te chu catalyst chung lamah inelna neiin an coadsorb a, adsorbed OH− chu active hydroxyl group (OH*) ah oxidized a ni a, chu chu nucleophiles oxidation atan electrophile angin a thawk a, hei hi a hmain experimental data leh/ emaw theoretical calculation hmanga hmuhchhuah tawh mechanism a ni45,46, Chutiang chuan reactants concentration leh an ratio (organic substrate leh OH−) chuan catalyst surface-a reactant coverage chu a control thei a, chu chuan FE leh target product yield a nghawng thei a ni14,48,49,50. Kan dinhmunah chuan NiV-LDH-NS-a cyclohexanone surface coverage sang chuan COR process a duh zawk tih kan hypothesis a, a lehlamah chuan Ni(OH)2-NS-a cyclohexanone surface coverage hniam chuan OER process a duh zawk tih kan hypothesis a ni.
A chunga kan sawi tak hypothesis hi test nan hian reactants (C, cyclohexanone, leh COH−) concentration nena inzawm experiment series pahnih kan nei hmasa a. Experiment hmasa ber chu cyclohexanone C content hrang hrang (0.05 ~ 0.45 M) leh fixed COH− content (0.5 M) nei Ni(OH)2-NS leh NiV-LDH-NS catalyst-ah constant potential (1.8 VRHE)-a electrolysis hmanga tih a ni. Tichuan, FE leh AA productivity chu chhut a ni ta a ni. NiV-LDH-NS catalyst tan chuan AA yield leh cyclohexanone C inzawmna hian LH mode-ah “volcanic type” curve pangngai a lantir a (Fig. 4a), hei hian cyclohexanone coverage sang tak chu OH− adsorption nen a inel tih a tilang a ni. Ni(OH)2-NS tan chuan AA yield chu cyclohexanone C 0.05 atanga 0.45 M-a a san chuan monotonically-in a pung a, hei hian cyclohexanone bulk concentration chu sang tak (0.45 M) ni mahse a surface coverage chu a la hniam hle tih a tilang. Chu bakah, COH− 1.5 M-a a san chuan cyclohexanone C a zirin Ni(OH)2-NS-ah “volcanic type” curve hmuh a ni a, NiV-LDH-NS nena khaikhin chuan performance inflection point chu a tlai a, hei hian Ni(OH)2-NS-a cyclohexanone adsorption chak lo a nihzia a tilang lehzual a ni (Supplementary Fig. 25a leh Note 5). Tin, NiV-LDH-NS-a AA FE chu C-cyclohexanone lakah a sensitive hle a, C-cyclohexanone chu 0.05 M atanga 0.3 M-a tihpun a nih chuan 80% aia tam thlengin a pung chak hle a, hei hian NiV-LDH-NS-ah cyclohexanone chu awlsam takin a enrich tih a tilang a ni (Figure 4b). Chumi danglamna chu C-cyclohexanone concentration tihpun hian Ni(OH)2-NS-a OER chu nasa takin a titawp lo a, hei hi cyclohexanone adsorption tling lo vang pawh a ni thei. Chumi kalh zawng chuan, COH−-in catalytic efficiency-a a innghahna chhui chian belh a nih chuan NiV-LDH-NS nena khaikhin chuan cyclohexanone adsorption a ṭha zawk tih a nemnghet bawk a, hei hian COR process-ah COH− sang zawk a tuar thei a, AA-a FE tihhniam lohvin a tuar thei a ni (Supplementary Fig. 25b, c leh Note 5).
0.5 M KOH-a C hrang hrang nei cyclohexanone-a b Ni(OH)2-NS leh NiV-LDH-NS-a AA leh EF productivity. c NiOOH leh NiVOOH-a cyclohexanone adsorption energies. d AA FE chu Ni(OH)2-NS leh NiV-LDH-NS-ah 0.5 M KOH-ah leh 0.4 M cyclohexanone-ah 1.80 VRHE-ah discontinuous leh constant potential strategy hmangin. Error bar hian sample pakhat hmanga independent measurement pathum standard deviation a entir a, 10% chhungah a awm. e Top: Ni(OH)2-NS-ah chuan cyclohexanone, surface area C hniam tak chu cyclohexanone hian a adsorb chak lo hle a, hei hian OER tan inelna nasa tak a siam a ni. Bottom: NiV-LDH-NS-ah chuan cyclohexanone C surface area concentration sang tak hmuh a ni a, cyclohexanone adsorption tihpun a ni a, chu chuan OER a titawp a ni. a–d atana raw data chu raw data file-ah a awm a.
NiV-LDH-NS-a cyclohexanone adsorption tihchak test nan electrochemical coupled quartz crystal microbalance (E-QCM) hmangin adsorbed species-te mass change chu real time-ah kan enfiah a. Results atanga a lan dan chuan NiV-LDH-NS-a cyclohexanone adsorption capacity hmasa ber chu OCP state-a Ni(OH)2-NS-a adsorption capacity aiin a let 1.6-in a lian zawk a, he adsorption capacity danglamna hi potential 1.5 VRHE-a a san chuan a pung lehzual a ni (Supplementary Fig. 26). NiOOH leh NiVOOH-a cyclohexanone adsorption behavior zirchian nan spin-polarized DFT calculation an ti a (Figure 4c). Cyclohexanone hian NiOOH-ah Ni-center-ah adsorption energy (Eads) -0.57 eV-in a adsorb a, cyclohexanone erawh NiVOOH-ah Ni-center emaw V-center emaw-ah a adsorb thei a, hetah hian V-center hian Eads (-0.69 eV) hniam zawk a pe a, hei hi adsorption chak zawk hmuhchhuah tawh nen a inmil a ni cyclohexanone chu NiVOOH ah a awm.
Cyclohexanone adsorption tihpun hian AA siam a tichak thei a, OER a titawp thei tih finfiah belh turin discontinuous potential strategy hmangin catalyst surface-ah cyclohexanone enrich turin kan hmang a (Ni(OH)2-NS leh NiV-LDH-NS tan), hei hi report hmasa atanga infuih a ni. 51, 52 A bik takin COR-ah potential 1.8 VRHE kan hmang a, chutah chuan OCP state-ah kan thlak a, chutah chuan 1.8 VRHE-ah kan thlak leh a ni. Chutiang a nih chuan electrolyse inkara OCP state-ah cyclohexanone chu catalyst chung lamah a pung khawm thei a ni (a kalphung chipchiar zawk chu Methods section en rawh). Results atanga a lan dan chuan Ni(OH)2-NS leh NiV-LDH-NS tan chuan discontinuous potential electrolysis hman hian constant potential electrolysis nena khaikhin chuan catalytic performance a ti tha zawk tih a tarlang (Figure 4d). Hriat tur pawimawh tak chu Ni(OH)2-NS hian NiV-LDH-NS aiin COR (AA FE: 51% atanga 82%) leh OER tihtawp (O2 FE: 27% atanga 4%) ah hmasawnna nasa zawk a lantir a, hei hi adsorption capacity chak lo zawk (chu chu, Ni(OH)2-NS) chu a hun laia potential electrolysis hmanga tih a ni.
A pum puiin NiV-LDH-NS-a OER tihkhawtlai chhan hi cyclohexanone adsorption tihchak vang a ni thei (Figure 4e). Ni(OH)2-NS (Figure 4e, chunglam)-ah chuan cyclohexanone adsorption chak lo tak chuan cyclohexanone coverage a ti tlem hle a, catalyst surface-ah OH* coverage a sang hle bawk. Chuvangin OH* chi tam lutuk hian OER tan inelna nasa tak a thlen ang a, AA FE pawh a tlahniam ang. Chumi danglamna chu NiV-LDH-NS (Figure 4e, hnuai lam)-ah chuan V modification hian cyclohexanone adsorption capacity a tipung a, chu chuan cyclohexanone surface C a tipung a, adsorbed OH* species chu COR atan a hmang tangkai hle a, AA siamna a tichak a, OER a titawp bawk.
V modification hian Ni species siam thar lehna leh cyclohexanone adsorption a nghawng dan kan zirchian bakah hian V hian COR atanga AA formation pathway a thlak danglam em tih pawh kan zirchiang bawk. Literature-ah hian COR pathway hrang hrang engemaw zat rawt a ni a, kan reaction system-ah hian an awm theih dante kan zirchiang a (chipchiar zawkin Supplementary Fig. 27 leh Supplementary Note 6 en rawh)13,14,26. Pakhatnaah chuan COR pathway step hmasa ber chu cyclohexanone initial oxidation hmanga key intermediate 2-hydroxycyclohexanone siam a ni thei tih report a ni (2)13,14. A kalphung dik tak finfiah nan 5,5-dimethyl-1-pyrrolidine N-oxide (DMPO) hmangin catalyst chunglama active intermediate adsorbed te chu kan trap a, EPR kan zirchiang a. EPR result-ah chuan COR process chhung hian catalyst pahnihah hian C-centered radicals (R ) leh hydroxyl radicals (OH ) a awm tih hmuhchhuah a ni a, hei hian cyclohexanone-a Cα − H dehydrogenation hian intermediate enolate radical (1) a siam tih a tilang a, chu chu OH*-in a oxidize leh a, 2 a siam leh a ni (Fig. 5a leh Supplementary Fig. 28). Catalyst pahnihah hian intermediate inang chiah chiah hmuh ni mah se, NiV-LDH-NS-a R signal area fraction chu Ni(OH)2-NS aiin a sang zawk a, hei hi cyclohexanone adsorption capacity tihpun vang pawh a ni thei (Supplementary Table 3 leh Note 7). V hian a hnu lama oxidation step a siam danglam dawn em tih test nan electrolysis atana starting reactants atan 2 leh 1,2-cyclohexanedione (3) kan hmang leh a. Ni(OH)2-NS leh NiV-LDH-NS-a potential intermediate (2 leh 3) te electrolysis result-ah chuan product selectivities inang tlang a awm a, hei hian Ni(OH)2-NS emaw NiV-LDH-NS-a COR reaction chu kawng inang hmanga kal a nih thu a tarlang (Figure 5b). Chubakah, AA hi 2 chu reactant atana hman a nih chauhvin product lian ber a ni a, hei hian AA hi catalyst pahniha 3-a a hnu lama oxidation ai chuan Cα − Cβ bond of 2 cleavage hmanga direct oxidation process hmanga hmuh a nih thu a tilang a, a chhan chu 3 chu starting reactant atana hman a nih khan GA-ah a inthlak ber a ni (Supplementary Figures 29, 30).
NiV-LDH-NS chu 0.5 M KOH + 0.4 M cyclohexanone-ah EPR signal a ni. b 2-hydroxycyclohexanone (2) leh 1,2-cyclohexanedione (3) te electrocatalytic analysis result. Electrolysis chu 0.5 M KOH leh 0.1 M 2 emaw 3 emaw ah 1.8 VRE ah darkar khat chhung an ti a. Error bar hian catalyst pakhat hmanga independent measurement pahnih standard deviation a entir a. c Catalyst pahnih chunga COR reaction pathways ruahman. d Ni(OH)2-NS (khawi lamah nge) leh d NiV-LDH-NS (dinglamah)-a COR kawng awm dan schematic illustration. Arrow sen hian V modification hian COR process-a a tihhmasawn step hrang hrangte a tarlang a ni. a leh b te tana raw data chu raw data file ah hian pek a ni.
A pum puiin Ni(OH)2-NS leh NiV-LDH-NS te hian kawng inang hmangin COR an catalyze tih kan hmuchhuak a: cyclohexanone chu catalyst chung lamah adsorb a ni a, dehydrogenated a ni a, electron a hloh a, 1 a siam a, chu chu OH* hmangin oxidized a ni a, 2 a siam a, chu chu multistep transformation hmangin AA siam a ni (Figure 5c). Mahse, cyclohexanone chu reactant atana hman a nih chuan OER competition chu Ni(OH)2-NS-ah chauh hmuh a ni a, oxygen tlem ber chu 2 leh 3 chu reactant atana hman a nih chuan a la khawm thung. Chutiang chuan catalytic performance-a danglamna hmuhchhuah chu reaction pathway inthlak danglamna aiin V modification avanga RDS energy barrier leh cyclohexanone adsorption capacity inthlak danglamna vang a ni thei. Chuvangin catalyst pahnih a reaction pathways RDS kan zirchiang a. A chunga kan sawi tak in situ X-ray acoustic spectroscopy result hian V modification hian COR reaction-a RDS chu reconstruction stage atanga chemical stage-ah a sawn a, NiOH phase leh high-valent Ni species te chu NiV-LDH-NS-ah a awm reng tih a tarlang (Fig. 3f, Supplementary Fig. 24, leh Note 4). CV tehnaah hian potential region hrang hrangte hmun tina current density-in a entîr reaction process-te chu kan zirchiang leh a (a chipchiar zawkna chu Supplementary Fig. 31 leh Note 8 en rawh) H/D kinetic isotope exchange experiment kan nei a, chungte chuan a pum puiin NiV-LDH-NS-a COR-a RDS-ah chuan reduction aiin chemical stage-a Cα − H bond cleavage a tel tih kan hmu chhuak a ni stage (a chipchiar zawkna chu Supplementary Fig. 32 leh Note 8 en rawh).
A chunga kan sawi tawh ang hian V modification-in nghawng a neih zawng zawng chu Figure 5d-ah hian kan hmu a. Ni(OH)2-NS leh NiV-LDH-NS catalyst te hian anodic potential sang takah surface reconstruction an nei a, COR chu kawng inang hmangin an catalyze thin. Ni(OH)2-NS (Figure 5d, veilam)-ah chuan COR process chhungin reconstruction step chu RDS a ni a; NiV-LDH-NS-ah erawh chuan (Figure 5d, dinglam) V modification hian reconstruction process nasa takin a ti chak a, RDS chu cyclohexanone Cα−H dehydrogenation-ah a chantir a, 1 a siam a, chu bakah chuan cyclohexanone adsorption chu V site-ah a thleng a, NiV-LDH-NS-ah a tichak a, hei hian OER tihtawp a tipung a ni.
Potential range zau takah FE sang tak nei NiV-LDH-NS electrocatalytic performance tha tak ngaihtuah chungin AA siam chhuah chhunzawm zel theihna turin MEA kan design a. MEA hi anode atan NiV-LDH-NS hmangin, cathode atan commercial PtRu/C hmangin53 leh anion exchange membrane (type: FAA-3-50) hmangin an inzawm khawm a (Figure 6a leh Supplementary Fig. 33)54. A chunga kan zirchiannaah hian cell voltage a tlahniam a, AA FE chu 0.5 M KOH nen tehkhin theih a nih avangin anolyte concentration chu 1 M KOH-ah optimized a ni (Supplementary Fig. 25c). LSV curve record te chu Supplementary Fig. 34-ah hian tarlan a ni a, hei hian NiV-LDH-NS COR efficiency chu Ni(OH)2-NS aiin a sang zawk tih a tilang a ni. NiV-LDH-NS thatna lantir nan constant current electrolysis chu step current density 50 atanga 500 mA cm−2 inkar hmangin an ti a, a inmil cell voltage chu record a ni. Results atanga a lan dan chuan NiV-LDH-NS hian current density 300 mA cm−2-ah cell voltage 1.76 V a nei a, hei hi Ni(OH)2-NS (2.09 V) aiin 16% velin a hniam zawk a, hei hian AA siamchhuahnaah energy efficiency a sang zawk tih a tilang a ni (Fig. 6b).
Flow battery chu a schematic diagram a ni. b Current density hrang hranga 1 M KOH leh 0.4 M cyclohexanone-a Ni(OH)2-NS leh NiV-LDH-NS-a iR compensation nei lo cell voltage. c Current density hrang hrangah Ni(OH)2-NS leh NiV-LDH-NS-ah AA leh FE yield a awm. Error bar hian catalyst pakhat hmanga independent measurement pahnih standard deviation a entir a. d Kan hnathawhna catalytic performance leh reported flow battery system dangte nena khaikhin14,17,19. Reaction parameter leh reaction characteristics te chu Supplementary Table 2-ah chipchiar takin tarlan a ni.e Hun rei tak test-naah NiV-LDH-NS-a AA cell voltage leh FE chu 200 leh 300 mA cm−2-ah a ni. Be atana raw data chu raw data file angin pek a ni.
Hetihlai hian Fig. 6c-a kan hmuh angin NiV-LDH-NS hian a bul berah chuan current density sang zawk (200 atanga 500 mA cm-2)-ah FE tha (83% atanga 61%) a vawng reng a, chu chuan AA productivity (1031 atanga 1900 μmol cm-2 h-1) a ti tha zawk a ni. Hetihlai hian electrolysis hnuah cathode compartment-ah adipic acid anion 0.8% chauh hmuh a ni a, hei hian kan dinhmunah chuan cyclohexanone transition hi a pawimawh lo tih a tilang (Supplementary Fig. 35). Chumi danglamna chu current density tihpun rate inang chiah a nih chuan Ni(OH)2-NS-a AA FE chu 61% atanga 34%-ah a tlahniam a, hei hian AA productivity tihchangtlun a ti harsa hle (762 to 1050 μmol cm-2 h-1). A bik takin, OER atanga inelna nasa tak avang hian AA performance chu tlem pawh a tlahniam a, chuvangin AA FE chu current density a san chuan nasa takin a tlahniam a (200 atanga 250 mA cm−2, Supplementary Fig. 5). Kan hriat dan chuan NiV-LDH-NS catalyst hmanga MEA hmanga catalytic result hian a hmaa report tawh, Ni-based catalyst hmanga flow reactor-te performance aiin a sang zawk hle a ni (Supplementary Table 2). Chubakah, Fig. 6d-a kan hmuh angin, NiV-LDH-NS hian Co-based catalyst, chu chu graphene-supported Co3O4 (Co3O4/GDY) Chu bakah, AA siamchhuahna atana energy hman dan kan zirchiang a, AA hman zat chu a hniam hle tih kan hmuchhuak a, current density 300 mA cm-2 leh cell voltage 1.76 V-ah 2.4 W h gAA-1 chauh a ni (a chhut dan kimchang chu Supplementary Note 1-ah tarlan a ni). Tun hmaa kan report tawh Co3O4/GDY atana 4.1 W h gAA-1 result tha ber nen khaikhin chuan kan hnathawhnaah hian AA siamna atana energy hman zat chu 42% in a tlahniam a, productivity pawh a let 4 in a pung bawk (1536 vs. 319 μmol cm-2 h-1)
MEA-a hun rei tak chhunga AA siam chhuahna atana NiV-LDH-NS catalyst stability chu current density 200 leh 300 mA cm-2-ah an zirchiang a (Figure 6e). OH− hi current density sang zawkah a hman chak zawk avangin 300 mA cm-2-a electrolyte renewal rate chu 200 mA cm-2-a electrolyte renewal rate aiin a sang zawk a ni (a chipchiar zawkna chu subsection “Electrochemical measurements” en rawh). Current density 200 mA cm-2-ah chuan COR efficiency average chu 6 h hmasa berah 93% a ni a, chutah chuan 60 h hnuah 81%-ah tlem a tlahniam a, chutih laiin cell voltage chu 7% (1.62 V atanga 1.73 V)-in tlem a pung a, hei hian stability tha tak a tilang a ni. Current density chu 300 mA cm−2-a a san chuan AA efficiency chu a danglam lo tluk a ni (85% atanga 72% ah a tlahniam a, mahse 46-h test chhungin cell voltage chu nasa takin a pung (1.71 atanga 2.09 V, 22% nena inmil) a ni (Figure 6e). Performance tihchhiatna chhan ber chu cyclohexanone-in anion exchange membrane (AEM) a tihchhiat vang niin kan ngai a, chu chuan electrolyzer cell-a cell resistance leh voltage a tisang a ni (Supplementary Fig. 36), chu chu anode atanga cathode-a electrolyte leakage tlem nen a inzawm a, chu chuan anolyte volume a tlahniam a, chu chu tihtawp a ngai a ni electrolysis hmanga tih a ni. Chu bakah, AA FE tlahniam chhan pawh hi catalyst leaching vang pawh a ni thei a, hei hian OER tan Ni foam hawn a ti tha hle. 300 mA cm−2-a stability tihchhiatnaah corroded AEM-in nghawng a neih dan entir nan 46 h electrolysis hnuah AEM thar hmangin kan thlak a. Beisei ang ngeiin catalytic efficiency chu chiang takin a lo awm leh a, cell voltage chu a tir lama a value (2.09 atanga 1.71 V) thlengin nasa takin a tlahniam a, chutah chuan electrolysis 12 h hnuah a sang chho deuh a (1.71 atanga 1.79 V, 5% a pung; Figure 6e).
A pum puiin, current density 200 mA cm−2-ah 60 h continuous AA production stability kan nei thei a, hei hian AA-a FE leh cell voltage chu a enkawl tha hle tih a tilang a ni. Current density sang zawk 300 mA cm−2 kan enchhin bawk a, overall stability 58 h kan hmu a, 46 h hnuah AEM chu a tharin kan thlak leh a ni. A chunga zirchiannate hian catalyst stability a lantir a, industrially ideal current densities-a AA siam chhunzawm zelna tur MEA-in hun rei tak chhunga a stability tihchangtlun nan nakin lawkah higher-power AEM siam a tulzia chiang takin a tarlang bawk.
Kan MEA hnathawh dan a zirin AA siam chhuah dan kimchang tak kan rawt a, chutah chuan substrate feeding, electrolysis, neutralization, leh separation unit te pawh a tel a ni (Supplementary Fig. 37). Alkaline electrolyte electrocatalytic carboxylate production model hmanga system economic feasibility tehna atan performance analysis hmasa ber neih a ni Chutiang a nih chuan, sensoah hian capital, operations, leh materials (Fig. 7a leh Supplementary Fig. 38) te a tel a, sum hmuh chu AA leh H2 production atanga lo chhuak a ni. TEA result atanga a lan dan chuan kan hnathawh dan (current density 300 mA cm-2, cell voltage 1.76 V, FE 82%) hnuaiah chuan a senso leh sum lakluh zawng zawng chu US$2429 leh US$2564 a ni a, hei hi AA siam chhuah ton khatah US$135 net profit-ah a letling a ni (a chipchiar zawkna chu Supplementary Note 9 en rawh).
a Base case scenario hnuaia AA electrochemical process senso zawng zawng FE chu 82%, current density 300 mA cm−2, leh cell voltage 1.76 V. b FE leh c current density-a senso pathumte sensitivity analysis. Sensitivity analysis-ah chuan zirchian tawh parameter chauh chu tihdanglam a ni a, parameter dangte chu TEA model hmangin a awm reng a ni. d FE leh current density hrang hrangin AA electrosynthesis hlawkna leh Ni(OH)2-NS leh NiV-LDH-NS hmanga hlawkna a nghawng dan, cell voltage chu 1.76 V-ah a awm reng anga ngaih a ni a, a–d tana input data chu raw data file-ah pek a ni.
He premise atang hian FE leh current density in AA electrosynthesis hlawkna a nghawng dan kan zirchiang lehzual a. AA FE-ah hian hlawkna hi a sensitive hle tih kan hmu a, a chhan chu FE tlahniam hian operating cost nasa takin a tipung a, chu chuan overall cost nasa takin a tipung a ni (Figure 7b). Current density chungchangah chuan current density sang zawk (>200 mA cm-2) hian capital cost leh plant sakna senso tihtlem nan a pui a, a bik takin electrolytic cell area tihtlem a ni a, chu chuan hlawkna a tipung a ni (Figure 7c). Tuna density awm mek nen khaikhin chuan FE hian hlawkna a nghawng nasa zawk a ni. FE leh current density-in hlawkna a nghawng dan characterize-in, hlawkna a awm theih nan industrially relevant current density (>200 mA cm-2)-a FE sang (>60%) neih a pawimawhzia chiang takin kan hmu a ni. AA FE value sang tak avang hian NiV-LDH-NS chu catalyst atan hmangin reaction system chu 100–500 mA cm−2 inkar ah a tha reng a (pentagram dots; Figure 7d). Mahse, Ni(OH)2-NS tan chuan current density sang takah (>200 mA cm−2) FE tihhniam chuan result tha lo tak a thlen a (circles; Figure 7d), hei hian current density sang takah FE sang tak nei catalyst pawimawhzia a tilang chiang hle.
Capital leh operating cost tihtlem nana catalyst pawimawhna bakah hian kan TEA assessment hian profitability hi kawng hnih in tihchangtlun belh theih a nih thu a tarlang bawk. A hmasa ber chu neutralization unit by-product anga potassium sulfate (K2SO4) chu market-a hralh chhuah dun a ni a, mahse sum lakluhna tur US$828/t AA-1 (Supplementary Note 9) a ni. A pahnihna chu processing technology tihchangtlun a ni a, chutah chuan material recycling emaw, AA separation technology man tlawm zawk (neutralization leh separation unit aia danglam zawk) siam chhuah te pawh a tel a ni. Tuna hman mek acid-base neutralization process hian material cost sang tak a thlen thei a (chu chuan share lian ber a nei a, 85.3%) a ni a, chung zinga 94% chu cyclohexanone leh KOH ($2069/t AA-1; Figure 7a) vang a ni a, mahse a chunga kan sawi tawh ang khan he process hian a pumpuiah hlawkna a la nei tho a ni. KOH leh unreacted cyclohexanone lakchhuahna atana hmanraw changkang zawk, KOH14 lakchhuah kim theihna tur electrodialysis (electrodialysis hmanga US$1073/t AA-1 senso tur ruahman; Supplementary Note 9) hmangin material man hi tihhniam belh theih a ni tih kan rawt a ni.
A tawi zawngin, Ni(OH)2 nanosheet-ah V kan dah lut a, current density sang takah aluminium atom electrolysis efficiency sang tak kan nei thei a ni. Wide potential range 1.5–1.9 VRHE leh high current density 170 mA cm−2 hnuaiah NiV-LDH-NS-a AA FE chu 83–88% a tling a, OER erawh chu effective takin 3%-ah a tlahniam thung. V modification hian Ni2+ chu Ni3+x-ah a tlahniam a, cyclohexanone adsorption a tichak bawk. Experimental leh theoretical data atanga a lan dan chuan stimulated reconstruction hian cyclohexanone oxidation atana current density a tisang a, COR RDS chu reconstruction atanga Cα − H scission hmanga dehydrogenation ah a sawn a, cyclohexanone adsorption tihpun chuan OER a titawp thung. MEA siam chhuah hian industrial current density 300 mA cm−2-ah AA siam chhunzawm zel a ti thei a, record AA efficiency 82% a nei a, productivity 1536 μmol cm−2 h−1 a nei bawk. Darkar 50 chhung test-naah NiV-LDH-NS hian MEA-ah AA FE sang tak a neih theih avangin stability tha tak a nei tih hmuhchhuah a ni (200 mA cm−2-ah darkar 60 chhung > 80%; 300 mA cm−2-ah darkar 58 chhung > 70%). Hriat tur chu industrially ideal current densities-a hun rei tak chhunga stability neih theihna turin AEM chak zawk siam a ngai a ni. Hei bakah hian TEA hian AA siamna atana reaction strategy hmanga economic lama hlawkna awmte leh senso tihtlem belh zelna tura high-performance catalyst leh advanced separation technology hman a pawimawhzia a tarlang bawk.