Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2017 Supporting Information NiSe 2 Pyramids Deposited on N-doped Graphene Encapsulated Ni Foam for High-Performance Water Oxidation Jing Yu, a, b Qianqian Li, a Cheng-Yan Xu, b, * Na Chen, b Yuan Li, a Heguang Liu, a Liang Zhen, b Vinayak P. Dravid, a Jinsong Wu a, * a Department of Materials Science and Engineering, NUANCE Center, Northwestern University, Evanston, IL 60208, USA. b School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, China. S1
Fig. S1 SEM images of initial graphite (a) and exfoliated graphene (b). Fig. S2 SEM images of N-doped graphene encapsulated Ni foam. S2
(a) N-Graphene Graphene Graphite C 1s N 1s O 1s (b) C 1s Raw 284.6 ev 286.4 ev 288.2 ev 0 200 400 600 800 (c) (d) C 1s Raw 284.6 ev 285.8 ev 286.6 ev 288.4 ev 280 282 284 286 288 290 292 294 N 1s N-Graphene Graphene Raw 400.8 ev 400.2 ev 399.6 ev 398.7 ev Graphite 280 282 284 286 288 290 292 294 394 396 398 400 402 404 406 Fig. S3 (a) XPS survey spectra of natural graphite, exfoliated graphene and N doped graphene. (b) C 1s of exfoliated graphene, (c) C 1s of N doped graphene, (d) N 1s of N doped graphene. The high-resolution C 1s spectra of graphene N doped graphene are compared in Fig. S3b and c. The three peaks at 284.6, 286.4 and 288.2 ev can be ascribed to sp 2 hybridized C atoms, C O and C=O configurations, respectively. The emerging peak at 285.8 in N doped graphene reveals the appearance of new C N bond. The survey spectra in Fig. S3a clearly prove the presence of N 1s in N-graphene. Furthermore, the N 1s spectrum can be fitted to four peaks, including pyridinic N (398.7 ev), C-N-C (399.6 ev), pyrrolic N (400.2 ev), and graphitic N (400.8 ev). The results suggest the successful introducation of N element into graphene. S3
Fig. S4 TEM image (a), STEM image (b) and EDX mappings of N doped graphene (c, d). S4
Fig. S5 Optical photograph of the deposited NG/NiSe 2 /NF electrode on the surface of N- doped graphene encapsulated Ni foam. JCPDS no 88-1711 20 30 40 50 60 70 80 2 (degree) Fig. S6 XRD pattern of NiSe 2 powder scraped from NG/NiSe 2 /NF electrode. S5
Fig. S7 Low-magnification SEM images of NG/NiSe 2 /NF. Fig. S8 SEM images of NiSe 2 /NF (a) and G/NiSe 2 /NF (b). S6
Fig. S9 (a) Cross-section SEM image, (b) SEM image, (c) EDS and (d,e) EDS elemental mappings of NG/NiSe 2 /NF. S7
100 80 Ni(OH)2/NiSe2/NF NiSe2/NF j (ma cm -2 ) 60 40 20 0 1.2 1.3 1.4 1.5 1.6 Potential (V vs. RHE) 1.7 Fig. S10 LSV curves of NiSe 2 grown on cleaned Ni foam and hydrothermal treatment Ni foam. The latter presented enhanced OER activity, indicating the synergistic effect between NiSe 2 and oxidized Ni substrate. j (ma cm -2 ) 350 300 250 200 150 100 0.5 h 1 h 2 h 50 0 1.2 1.3 1.4 1.5 1.6 Potential (V vs. RHE) 1.7 Fig. S11 LSV curves of deposited NG/NiSe 2 /NF films with different deposition time. Increasing catalyst loading with longer deposition time will lead to the increase of active sites to accelerate the electrocatalytic process. Meanwhile, excess deposition (longer than 1 hour deposition) will lead to overgrowth and even multilayers which will block surface active sites and the electron transfer. S8
(a) Ni 2p (b) Ni 2p Se 3d C 1s N 1s O 1s 0 200 400 600 800 1000 1200 (c) (d) Se 3d 850 860 870 880 O 1s Ni-O O-H 50 52 54 56 58 60 62 526 528 530 532 534 536 Fig. S12 XPS analysis of NG/NiSe 2 /NF after OER test. (a) survey, (b-d) High-resolution XPS of Ni 2p, Se 3d and O 1s, respectively. Fig. S13 SEM images of NG/NiSe 2 /NF after OER in 0.1 M KOH. S9
Graphene Ni Foam JCPDS no 88-1711 10 20 30 40 50 60 70 80 2 (degree) Fig. S14 XRD pattern of NG/NiSe 2 /NF after OER in 0.1 M KOH -Z'' (ohm) 500 400 300 200 0.3 V 0.4 V 0.5 V 0.6 V 0.7 V 100 0 0 100 200 300 400 500 600 700 Z' (ohm) Fig. S15 Nyquist plots of NG/NiSe 2 /NF at different potentials (vs. RHE). The tremendously reduced R ct values upon increasing overpotentials suggest the accelerated charge transfer kinetics. S10
j (ma cm -2 ) (a) 0.3 0.2 0.1 0.0-0.1-0.2-0.3 (b)1.5 0.76 0.78 0.80 0.82 0.84 0.86 Potential (V vs. RHE) j (ma cm -2 ) 1.0 0.5 0.0-0.5-1.0-1.5 (c) 2.4 0.62 0.64 0.66 0.68 0.70 0.72 Potential (V vs. RHE) j (ma cm -2 ) 1.6 0.8 0.0-0.8-1.6-2.4 0.74 0.76 0.78 0.80 0.82 0.84 0.86 Potential (V vs. RHE) Fig. S16 Electrochemical CV curves of different electrodes at different scanning rates from 20 mv/s to 200 mv/s with an interval point of 20 mv/s in 0.1 M KOH. (a) NiSe 2 /NF, (b) G/NiSe 2 /NF, (c) NG/NiSe 2 /NF. S11
Supplementary Tables Table S1. Comparison of OER activity of some non-noble catalysts. Catalyst electrolyte J η (mv) Ref. (ma cm -2 ) NG/NiSe 2 /NF 0.1 M KOH 20 307 This work NG/NiSe 2 /NF 1 M KOH 100 330 This work NF-Ni 3 Se 2 /Ni 1 M KOH 100 353 Nano Energy, 2016, 24, 103. Co 0.13 Ni 0.87 Se 2 /Ti 1 M KOH 100 320 Nanoscale, 2016, 8, 3911. Ni 3 Se 2 /CF 1 M KOH 50 340 Catal. Sci. Technol., 2015, 5, 4954 NiSe nanowire/ni 1 M KOH 35 400 Angew. Chem., Int. Ed., 2016, 55, 1710. NiSe/NF 1 M KOH 20 270 Angew.Chem., 2015, 127, 9483. CoO x -CoSe 1 M KOH 100 300 J. Mater. Chem. A, 2016, 4, 10933. NiCo 2 O 4 1 M KOH 100 ~470 Adv. Energy Mater., 2015, 5, 1402031. (Ni, Co) 0.85 Se 1 M KOH 122 360 Adv. Mater., 2016, 28, 77. NiCo LDH 1 M KOH 10 367 Nano Lett., 2015, 15, 1421. NiSe 2 0.1 M KOH 10 410 ACS Appl. Mater. Interfaces, 2016, 8, 5327. CoSe 2 /N-Graphene 0.1 M KOH 10 366 ACS Nano, 2014, 8, 3970. Ni 3 Se 2 0.3 M KOH 10 310 Energy Environ. Sci., 2016, 9, 1771. N-Co 9 S 8 /G 0.1 M KOH 10 409 Energy Environ. Sci., 2016, 9, 1320. CoSe 2 0.1 M KOH 10 320 J. Am. Chem. Soc., 2014, 136, 15670. S12