Bimetallic Thin Film NiCo-NiCoO as Superior Bifunctional Electro- catalyst for Overall Water Splitting in Alkaline Media

Transcription

1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2017 Supportting Information for Bimetallic Thin Film NiCo-NiCoO as Superior Bifunctional Electro- catalyst for Overall Water Splitting in Alkaline Media Yun Xiao, Pengfang Zhang, Xin Zhang, * Xiaoping Dai, Yangde Ma, Yao Wang, Yan Jiang, Mengzhao Liu, Yue Wang. State Key Laboratory of Heavy Oil Processing College of Chemical Engineering, China University of Petroleum Beijing (China) National Institute of Metrology, Beijing , China *Corresponding author. zhangxin@cup.edu.cn

2 Calculation method The TOF value (s -1 ) was calculated from equation (1): TOF = J A 4 F n (1) J is obtained at overpotential = 300 mv, normalized by geometric area of GCE ( cm 2 ), A is the geometric area of GCE ( cm 2 ), F is the Faraday constant, n is the mole number of active sites on the electrode, n(metallic Ni and Co) is the mole number of active sites for HER, n(total Ni and Co elements) is the mole number of active sites for OER, via equation below: n (metallic Ni and Co) = m loading A r metallic NiCo/NiCo NiCoO2@NC NA M w (2) n (total Ni and Co ) = m loading A r total NiCo/NiCo NiCoO2@NC NA M w (3) where mloading is the loading mass via drop-casting, A is the geometric area of GCE ( cm 2 ), r metallic NiCo/NiCo NiCoO2@NC is the weight ratio of Ni-Co alloy in NiCo-NiCoO r total NiCo/NiCo NiCoO2@NC is the weight ratio of total Ni and Co elements in NiCo-NiCoO NA is Avogadro's constant, Mw is the molecular weight of active sites. Mass activity (A g -1 ) values were calculated from the electrocatalyst loading mloading(0.14 mg cm -2 ) and the measured current densityj (ma cm -2 ) at η = 300 mv: Mass activity = J m loading (4)

3 Table S1. Compositions of thin film NiCo-NiCoO NiCoO 2, Ni-NiO@NC, Co-CoO@NC determined by ICP-MS and XPS Sample bulk content(wt%) by ICP-MS Surface content(wt%) by XPS Co Ni Co : Ni (atom) C N O Co Ni Co : Ni (atom) Ni-NiO@NC Co-CoO@NC NiCoO NiCo-NiCoO NiCo@NC NiCoO

4 Table S2. The surface area and pore volume of NiCo-NiCoO NiCoO 2, Ni-NiO@NC, Co-CoO@NC Material Surface area Pore volume Average pore m 2 g- 1 cm 3 g -1 diameter(nm) NiCo-NiCoO Ni-NiO@NC Co-CoO@NC NiCoO

5 Table S3. The quantitative results of H 2 -TPR characterization Catalyst Weight Reduction Peak area H 2 consumption Ni/Co in Metallic Oxides Ni/Co content content (mg) Temperature ( C ) mmol (wt%) (wt%) NiCo-NiCoO / Ni-NiO@NC Co-CoO@NC

6 Table S4. Comparison of the electrocatalytic activity of NiCo-NiCoO to some representatively reported OER catalysts in basic solutions. Material Loading Electrolyte η (V) Tafel slope mg cm ma cm -2 mv/decade Reference NiCo-NiCoO M KOH This work Commercial IrO 2 /C M KOH This work Co 3 O 4 /N-rmGO M KOH Nat. Mater. 2011, 10, Co 3 O 4 /NiCo 2 O M KOH J. Am. Chem. Soc. 2015, 137, 16, NixCo 3 -xo M NaOH Adv. Mater. 2010, 22, Co-P film M KOH Angew. Chem., Int. Ed. 2015, 54, α-ni(oh) 2 /GC M KOH Chem. Mater. 2014, 26, NiCo-NS M KOH Nat. Commun. 2014, 5, NiCoLDHs M KOH Nano Lett. 2015, 15, CoP/C M KOH J. Mater. Chem. A. 2016, 4, 23, PNG-NiCo 2 O M KOH ACS Nano 2013, 7,

7 Table S5. Comparison of the electrocatalytic activity of NiCo-NiCoO to some representatively reported HER catalysts for basic solutions. Material Loading Electrolyte η (mv) Tafel slope mg cm ma cm -2 mv/decade NiCo-NiCoO M KOH This work Commercial Pt/C M KOH This work Reference Co@N-C M KOH J. Mater. Chem. A 2014, 2, Co-NCNT/CC M KOH ChemSusChem 2015, 8, CoOx@CN M KOH J. Am. Chem. Soc. 2015, 137, CoSe 2 nanosheet M KOH ACS Nano 2014, 4, Ni 0.33 Co 0.67 S 2 nanowire M KOH Adv. Mater. 2010, 22, Co-NRCNTs M KOH Angew. Chem., Int. Ed. 2014, NiCo 2 S M KOH Nanoscale 2015, 7, NiCo 2 O M NaOH Angew. Chem., Int. Ed. 2016, 55, Co-P film M KOH Angew. Chem., Int. Ed. 2015, 54,

8 Table S6. TOF for HER of and Pt/C Catalyst Current density (ma cm -2 ) at η=300 mv Current density (ma cm -2 ) at η=500 mv TOF H (S -1 ) TOF H (S -1 ) at η=300 mv at η=500 mv Mass activity (A g -1 ) at η=300 mv Mass activity (A g -1 ) at η=500 mv NiCo-NiCoO Ni-NiO@NC Co-CoO@NC Pt/C NiCo@NC

9 Table S7. TOF for OER of NiCo-NiCoO Ni-NiO@NC, Co-CoO@NC, NiCo@NC, NiCoO and IrO 2 Catalyst Current density (ma cm -2 ) Current density (ma cm -2 ) TOF O (S -1 ) TOF O (S -1 ) Mass activity (A g -1 ) Mass activity (A g -1 ) at η=300 mv at η=500 mv at η=300 mv at η=500 mv at η=300 mv at η=500 mv NiCo-NiCoO Ni-NiO@NC Co-CoO@NC IrO NiCo@NC NiCoO

10 Table S8. theoretical TOF numbers of NiCo-NiCoO TOF TOF cal-h (S -1 ) TOF cal-o (S -1 ) TOF calm-h (S -1 ) TOF calm-o (S -1 ) η(mv) η=300 η=500 η=300 η=500 η=300 η=500 η=300 η=500 NiCo-NiCoO

11 Table S9. Comparison of the electrocatalytic activity of NiCo-NiCoO to some representatively reported bifunctional electrocatalysts for overall water splitting in 1.0 M KOH solution. Catalyst Catalyst Substrate Overall Voltage (V) Reference Cathode (H 2 ) Athode (O 2 ) at j=10 ma cm -2 NiCo-NiCoO NiCo-NiCoO Ni foam 1.44 This work NiFeLDH NiFeLDH Ni foam ~1.70 Science 2014, 345, CoOx@CN CoOx@CN Ni foam 1.62 J. Am. Chem. Soc. 2015, 137, NiSe NWs NiSe NWs Ni foam 1.63 Angew. Chen. Int. Ed. 2015, 54, Ni-Fe-O Ni-Fe-O Ni foam 1.51 Nat. Commun. 2015, 6, Ni 0.33 Co 0.67 S 2 NiCo 2 O 4 Ti foam ~1.73 Adv. Energy Mater. 2015, 5, Ni 2 P nanoparticle Ni 2 P nanoparticle Ni foam 1.63 Energy Environ. Sci. 2015, 8, Ni 4 P 5 film Ni 4 P 5 film Ni foam 1.7 Angew. Chem. Int. Ed. 2015, 54, Co-P film Co-P film Ni foam 1.63 Angew. Chen. Int. Ed. 2015, 54, EG/Co 0.85 Se/NiFe-LDH EG/Co 0.85 Se/NiFe-LDH EG foam 1.67 Energy Environ. Sci. 2016, 9, CoP nanorod CoP nanorod Ni foam 1.62 Adv. Funct. Mater. 2016, 25,

12 a b 1 μm 200 nm Figure S1. (a) SEM image and (b) TEM image of NiCo-NiCoO obtained by directly calcination under 600 o C

13 Figure S2. XRD pattern of NiCoDH precursor [Ni(OH) 2 (JCPDS no ); Co(OH) 2 (JCPDS no )]

14 a b c d Figure S3. (a) XRD patterns of NiCo@NC, NiCoO and NiCo-NiCoO (b-d) XPS patterns of NiCo@NC and NiCoO (b) Ni 2p; (c) Co 2p; (d) O 1s.

15 Figure S4. SEM images of (a) (b) and c) NiCoO2.

16 Frequency(%) Frequency(%) a b c 100 nm ±3.6 nm Diameter(nm) Diameter(nm) Figure S5. TEM images of (a) Ni-NiO@NC with the inset showing the corresponding particle-size distribution histogram; (b) Co-CoO@NC with the inset showing the corresponding particle-size distribution histogram; c) NiCoO ±3.2 nm

17 a b c Figure S6. (a) XPS patterns of N 1s of NiCo-NiCoO (b) HER linear sweep voltammetry (LSV) curves of NiCo-NiCoO and NiCo-NiCoO (c) OER LSV curves of NiCo-NiCoO and NiCo-NiCoO

18 a b c d e f Figure S7. (a) XPS patterns of N 1s of Ni-NiO@NC; (b-f) CV measurements in a non-faradic current region ( V vs. RHE, no ir-corrected) at scan rates of 5, 10, 25, 50 and 100 mv s -1 of b) NiCo-NiCoO c) Ni-NiO@NC, d) Co-CoO@NC, e) NiCoO 2 and f) NC in 1 M KOH.

19 a b Figure S8. TEM images of (a) NiCo@NC and (b) NiCoO

20 a b c d Figure S9. (a) Cyclic voltammetry (CV) curves of NiCo@NC recorded at a scan rate of 50 mv s -1 in 1.0 M KOH solution; (b-d) XPS spectrum of CV conditioned species: (b) Ni 2p; (c) Co 2p; (d) O 1s.

21 a b c Figure S10. XPS spectrum of OER conditioned NiCo- NiCoO (a) Ni 2p; (b) Co 2p; (c) O 1s.

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