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1 Supporting Informtion Nnostructured Nickel Coltite Antispinel s Bifunctionl Electroctlyst for Overll Wter Splitting Leiming To, Yiing Li, Mn Li, Guoying Go, Xin Xio, Mingkui Wng,*, Xingxing Jing, Xiowei Lv, Qingwei Li, Shsh Zhng, Zhixin Zho, Chun Zho, nd Yn Shen Wuhn Ntionl Lortory for Optoelectronics nd Deprtment of Physics, Huzhong University of Science nd Technology, Luoyu Rod 1037, Wuhn, P. R. Chin School of Chemistry, University of New South Wles, Sydney, New South Wles 2052, Austrli Density Functionl Theory (DFT) Clcultion. Model Development. Adsorption Model. Supplementry Figures (Figure S1-S15) Supplementry Tles (Tle S1-S3) Supplementry References S1

2 Supplementry Methods Density Functionl Theory (DFT) Clcultion. The CASTEP pckge ws employed in the first-principles clcultions. 1,2 The clcultion ws sed on density functionl theory using plne-wve pseudopotentil formlism, ided y the Accelrys Mterils Studio (Accelrys Inc.) grphicl front-end interfce. The exchnge correltion functionl ws treted using the generlized grdient pproximtion (GGA) with the Perdew Burke Ernzerhof (PBE) functionl. 3 The geometries of ll the systems were optimized, in which conjugted grdient technique ws used in direct minimiztion of the Kohn-Shm energy functionl nd pseudopotentils were employed to represent core electrons. Plne-wve functions were used s sis sets. 4 The nd structure, the totl nd prtil density of sttes (DOS), nd the electron density were clculted. Model Development.The NiCo 2 O 4 crystllogrphic informtion file (CIF) cme from Co(NiO 2 ) 2 (ID: mp ), in which Co nd Ni were switched. 5 The fine qulity ws used in the NiCo 2 O 4 unit cell prmeter optimiztion. The Monkhorst-Pck grid k-points (5 5 5) were used to provide cell prmeters. NiCo 2 O 4 unit cell optimiztion ws performed with the conditions tht the tomic forces, mximum displcement, nd totl energy vrition were less thn ev Å 1, Å, nd ev tom 1, respectively. It hs cuic symmetry nd elongs to the FD-3m spce group with cell prmeters = Å, = 5.844Å, c = Å, nd α = β = γ = This structure of NiCo 2 O 4 hs (311) min crystllogrphic plne. The NiCo 2 O 4 (311) surfce, typicl high-index surfce, ws constructed y cleving the optimized unit cell. The NiCo 2 O 4 (311) surfce included six of the twelve kinds of M-terminted surfces, s shown in Figure S8. The NiCo 2 O 4 (311) surfce ws modelled y periodiclly repeted p (1 1) sl with 4 frctionl thickness (contining 56 toms tomic) nd seprted y 12.5 Å-thick vcuum region to void S2

3 the interctions etween two periodic sls. The ottom 3 lyers were fixed t its originl ulk position nd the top 10 lyers were fully relxed for structure optimiztion. The fine qulity ws used in the NiCo 2 O 4 (311) surfce prmeter optimiztion. The Monkhorst-Pck grid k-points (2 4 1) were used to provide cell prmeters. The NiCo 2 O 4 (311) surfce optimiztion ws performed with the stop conditions tht the tomic forces, mximum displcement, nd totl energy vrition re less thn ev tom 1, Å, nd ev tom 2, respectively. The lowest one of clculted totl energy ws chosen from 12 kinds of M-terminted surfces. The optimized NCO-NSs-(311) surfce, s shown in Figure S9, consists of Co, Ni t position A nd Ni t position B. The NiCo 2 O 4 (311) nnowires chose the optimized NCO-NSs-(311) surfce ut the vcuum region were seprted y 0 Å thick. The sl contined 56 toms nd the optimiztion condition used medi qulity (Figure S10). The sl cell prmeters were = Å, = Å, c = Å, nd α = β = 90, γ = The sl cell prmeters ws then reuild with = Å, = Å, c = Å, nd α = β = γ = 90. NiCo 2 O 4 (3 1 1) nnowire optimiztion used medi qulity (Figure S11). The Pt (111) surfce ws modeled y periodiclly repeted p (2 2) sl with 13 frctionl thickness (contins 52 toms tomic) nd seprted y 12.5 Å-thick vcuum. The ottom 4 lyers were fixed t their originl ulk positions nd the top 9 lyers were fully relxed for structure optimiztion. Surfce prmeters optimiztion used medi qulity (Figure S 12). The RuO 2 (110) surfce included Ru-terminted, 1 lyer O-terminted nd 2 lyer O-terminted surfces, s shown in Figure S12 S12d. RuO 2 (110) surfce ws modeled y periodiclly repeted p (1 1) sl with 12 frctionl thickness (contins 72 toms tomic) nd seprted y 12.5 Å-thick vcuum. The ottom 3 lyers were fixed t their originl ulk positions nd the top 10 lyers were fully S3

4 relxed for structure optimiztion. Surfce prmeters optimiztion used medi qulity. One lyer O-terminted RuO 2 (110) surfce ws the most stle one. Adsorption Model. In n lkline electrolyte the rection could e written s 6 : Cthode: 2H 2 O + * + 2e OH + H * + H 2 O + e (1) 2OH + H 2 + * (2) Anode: 4OH + * HO * + 3OH + e (3) O * + H 2 O+ 2OH + 2e (4) HOO * + H 2 O + OH + 3e (5) O 2 + 2H 2 O + * + 4e (6) We clculted the inding energies of the intermedites H 2 O *, H 2 *, H *, HO *, O *, HOO *, nd O 2 * on spinel surfces: E H2 O = E H 2O E E(H 2 O) (7) E H2 = E H 2 E E(H 2 ) (8) E H = E H E E(H) (9) E HO = E HO E E(OH) (10) E O = E O E E(O) (11) E HOO = E HOO E E(HOO) (12) E O2 = E O 2 E E(O 2 ) (13) where ΔE(H 2 O * ), ΔE(H 2 * ), ΔE(H * ), ΔE(HO * ), ΔE(O * ), ΔE(HOO * ), nd ΔE(O 2 * ) represent the clculted DFT energies of the sustrte surfce nd S4

5 respectively with dsortes. E H2O, E H2, E O2 clculted DFT energies of H 2 O,H 2 nd O 2 molecules in the gs phse. The vlues of the inding energy re shown in Tle S2. Molecule H 2 O *, H 2 *, H *, HO *, O *, HOO *, nd O 2 * were put on top of surfce ctive site, nd initil distnces were set t 1.0 Å etween molecule nd ctive site ll dsortes. Prmeters optimiztion used medi qulity. The NCO-NSs-(311) nd NCO-NWs-(311) surfce ctive sites re the coordintely unsturted site (CUS) on top of metlion fivefold coordinted. For molecule H 2 O, HO, HOO, DFT showed tht O ws down while H ws up (in Figure S13 nd S14). The Pt(111) surfce ctive site is the fcc hollow, where molecule H 2 O *, H 2 *, H *, HO *, O *, HOO *, nd O 2 * were put on. 7 For molecule H 2 O, HO, HOO, DFT showed tht O ws down while H ws up. The RuO 2 (110) surfce ctive site is the coordintely unsturted site (CUS) on top of metlion fivefold coordinted. 8, 9 For molecule H 2 O, HO, HOO, DFT showed tht O ws up while H ws down. S5

6 j cp (ma cm 2 ) Supplementry Figures NCO-NSs NCO-NWs mf cm mf cm v (mv s 1 ) Figure S1 Electrochemicl cpcitnce mesurements chrging current density differences j plotted ginst scn rtes curve v of NCO-NSs nd NCO-NWs; Liner j cp vs. scn rtes plots in the potentil region V in 1 M KOH t 25 o C. S6

7 θ ( deg.) log ( Z (ohm)) θ (deg.) log ( Z (ohm)) Hz; Z = 143 ohm cm 2 ; C dl = 6.9 mf cm 2 Slope = log (f (Hz)) Hz; Z = 58 ohm cm 2 ; C dl = 17 mf cm 2 Slope = log (f (Hz)) Figure S2 Typicl Bode plot of ) NCO-NSs, ) NCO-NWs electrodes vs HgO/Hg, in 1M KOH t 25 o C (geometricl re: cm 2 ) S7

8 Current density (ma cm 2 ) Current density (ma cm 2 ) V V r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m Potentil (V vs RHE) r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m V 1.475V Potentil (V vs RHE) Figure S3 ) ECSA-corrected HER nd ) ECSA-corrected OER LSV curve of NCO-NSs without ir correction t sweep rte of 5 mv s 1 nd RRDE with rottion speeds of 400, 625, 900, 1225, 1600, 2025, 2500 r.p.m., respectively. S8

9 Current density (ma cm 2 ) Current density (ma cm 2 ) V V r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m r.p.m V V Potentil (V vs RHE) Potentil (V vs RHE) Figure S4 ) ECSA-corrected HER nd ) ECSA-corrected OER LSV curve of NCO-NWs without ir correction t sweep rte of 5 mv s 1 nd RRDE with rottion speeds of 400, 625, 900, 1225, 1600, 2025, 2500 r.p.m., respectively. S9

10 J 1 (cm 2 ma 1 ) V 0.25 V 0.23 V 0.21 V 0.19 V V J 1 (cm 2 ma 1 ) V 1.43 V 1.45 V 1.47 V 1.48 V 1.50 V J 1 (cm 2 ma 1 ) c 1 ((r.p.m.) 1/2 ) 0.35 V 0.33 V 0.31 V 0.29 V 0.27 V J 1 (cm 2 ma 1 ) d 1 ((r.p.m.) 1/2 ) 1.39 V 1.41 V 1.43 V 1.45V 1.47 V 1.49 V 0.25 V ((r.p.m.) 1/2 ) ((r.p.m.) 1/2 ) Figure S5 Koutecky-Levich plots of electroctelyzed HER (, c), nd OER (, d) for NCO-NSs nd NCO-NWs, respectively. S10

11 TOF (s -1 ) TOF (s -1 ) NCO-NSs NCO-NWs NCO-NSs NCO-NWs Potentil (V vs RHE) Potentil (V vs RHE) Figure S6 The turnover frequency (TOF) of NCO-NSs nd NCO-NWs for ) HER nd ) OER in N 2 1M KOH solution t rottion speed of 1,600 r.p.m. The corresponding TOF t overpotentil of 0.3 V. re listed for comprison. S11

12 c Ni O Co d e f g Figure S7 Sl model of NCO-NSs-(311). There re 13 lyers nd 12 kinds of terminted surfce models from () side view of NCO-NSs-(311): ) nd ) re respective side view nd top view of 1 lyer (Ni nd Co)-terminted surfce model of NCO-NSs-(311). c) g) re top view of 2, 3, 4, 8 nd 11 lyer-terminted surfce models of NCO-NSs-(311), respectively. Blue ll, red ll nd green ll represent Ni, O nd Co, respectively. S12

13 Ni-B Side view Co Ni-B Ni-A Co Ni-A Top view Ni O Co Figure S8 The optimized model for NCO-NSs-(311): ) side view nd ) top view; The terminted surfce model consists of Co, Ni t position A nd Ni t position B. S13

14 Side view Ni O Co Top view Figure S9 Model of the slp for NCO-NWs-(311): ) side view nd ) top view. S14

15 Side view Ni O Co Top view Figure S10 Sl model of p(2 1) NCO-NWs-(311): ) side view nd ) top view. The yellow rrow line indictes the direction of NCO-NWs-(311) s seen from ). One end of NCO-NWS-(311) is shown in ). S15

16 Pt c d e f Ru O g h Figure S11 Model of Pt(111) nd RuO 2 (110) slp: ) side view nd e) top view of Pt; ) side view nd f) top views of 1 lyer O-terminted RuO 2 (110); c) side view nd g) top views of Ru-terminted RuO 2 (110); d) side view nd h) top views of 2 lyer O-terminted RuO 2 (110). S16

17 c d e f g h Figure S12 Adsorption model of ) clen, ) H 2 *, c) H *, d) H 2 O *, e) HO *, f) O *, g) HOO *, nd h) O 2 * on top of surfce ctive site Ni for NCO-NSs-(311) surfce,the verticl height of species from the surfce re 1.0 nm. S17

18 Ni O Co H c e d f g h Figure S13 Adsorption model of ) clen, () H 2 *, (c) H *, d) H 2 O * (e) HO *, (f) O *, (g) HOO *, nd (h) O 2 * on top of surfce ctive site Ni for NCO-NWs-(311) surfce, the verticl height of species from the surfce re 1.0 nm. S18

19 c d e f Ni O Co H Figure S14 The optimized dsorption model of H * nd O * on top of surfce ctive site of Co, Ni-A nd Ni-B. ), ), c) d), e), nd f) re H * nd O * reltive positions of Ni-A, Ni-B, Co position for NCO-NSs-(311) surfce fter optimized, respectively. S19

20 Intensity (.u.) Intensity (.u.) Intensity (.u.) Co Co 2p 1/2 Co Co 2p 3/2 S Ni 2p 1/2 Ni 2p 3/2 Ni3+ Ni S () () Binding Energy (ev) () () Binding Energy (ev) c O 1s () () Binding Energy (ev) Figure S15 XPS spectr of ) Co2p, ) Ni2p, c) O1s for () NCO-NWs, () NCO-NSs, where S represents stellite pek nd circle represents the pek position. The peks of Co nd O t the surfce remin lmost unchnged for the three smples, ut the iggest chnge re Ni 3+ /Ni 2+ concentrtion increment t Ni 2p 3/2. S20

21 Supplementry Tles Tle S1. Results of roughness fctor (R F ) mesurements on NCO-NSs nd NCO-NWs in 1M KOH t 25 o C C dl (mf cm -2 ) θ mx ( o ) Slop R F Imp CV Imp CV NCO-NSs NCO-NWs RuO Pt20%C Note: The impednce method is revited to Imp. The cyclic voltmmetry (CV) cures method is revited to CV. S21

22 Tle S2. The clculted inding energy H 2 * H * H 2 O * HO * O * HOO * O 2 * NCO-NSs-(311) NCO-NWs-(311) Pt(111) RuO 2 (110) ΔE(eV) Δd (Ǻ) ΔE(eV) Δd (Ǻ) ΔE(eV) Δd (Ǻ) ΔE(eV) Δd (Ǻ) Note: ΔE represents the clculted DFT energies of the sustrte surfce nd respectively with dsortes. Δd is the clculted DFT distnce of the sustrte surfce nd respectively with dsorte. E H2O, E H2, E O2 clculted DFT energies of H 2 O, H 2 nd O 2 molecules in the gs phse. S22

23 Tle S3 The vlues of the free energy nd the inding energy Surfce E sustrte (ev) Surfce with dsorte E totl (ev) E (ev) Δd (Ǻ) NCO-NSs NCO-NSs-1-Co-O NCO-NSs NCO-NSs-1-Ni-A-O NCO-NSs NCO-NSs-1-Ni-B-O NCO-NSs NCO-NSs-1-Co-H NCO-NSs NCO-NSs-1-Ni-A-H NCO-NSs NCO-NSs-1-Ni-B-H Note: NCO-NSs-1, 2, 3, 4, 8 nd11 lyer-terminted surfce models of NCO-NSs-(311), respectively (s shown in Figure S1). The smllest inding energy ws mrked in red. H * nd O * were put on top of Co, Ni-A, Ni-B position for NCO-NSs-1 surfce (s shown in Figure S19). E sustrte nd E represent the clculted DFT energies of the sustrte nd sustrte with dsortes, respectively. Δd is the clculted DFT distnce of the sustrte surfce nd respectively with dsorte. E H2O, E H2, E O2 clculted DFT energies of H 2 O, H 2 nd O 2 molecules in the gs phse. S23

24 Supplementry References 1. Clrk Stewrt J., S. M. D., Pickrd Chris J., Hsnip Phil J., Proert Mtt I.J., Refson Keith, Pyne Mike C., First Principles Methods Using Cstep. Z. Krist. Cryst. Mter. 2005, 220, Segll M. D., L. P. J. D., Proert M.J., Pickrd C.J., Hsnip P.J., Clrk S.J., Pyne M.C., First-Principles Simultion: Ides, Illustrtions nd the Cstep Code. J. Phys. Condens. Mt. 2002, 14, Perdew John P., B. K., Wng Yue, Generlized Grdient Approximtion for the Exchnge-Correltion Hole of Mny-Electron System., Phys. Rev. B 1996, 54, Monkhorst Hendrik J., P. J. D., Specil Points for Brillouin-Zone Integrtions. Phys. Rev. B 1976, 13, Mterils projects, 6. Rossmeisl, J.; Logdottir, A.; Norskov, J. K., Electrolysis of Wter on (Oxidized) Metl Surfces. Chem. Phys. 2005, 319, Xu, Y.; Run, A. V.; Mvrikkis, M., Adsorption nd Dissocition of O 2 on Pt Co nd Pt Fe Alloys. J. Am. Chem. Soc. 2004, 126, Mn, I. C.; Su, H. Y.; Clle-Vllejo, F.; Hnsen, H. A.; Mrtinez, J. I.; Inoglu, N. G.; Kitchin, J.; Jrmillo, T. F.; Norskov, J. K.; Rossmeisl, J., Universlity in Oxygen Evolution Electroctlysis on Oxide Surfces. Chemctchem 2011, 3, Rossmeisl J., Q. Z. W., Zhu H., Kroes G. J., Nørskov, J. K., Electrolysis of Wter on Oxide Surfces. J. Electronl. Chem 2007, 607, S24