Fig. 1. CV curves of NC-GC WE in (a) 2 mM H2PtCl6 + 0.05 M LiClO4 + DMF; (b) (red line) 2 mM K2PtCl4 + 0.05 M LiClO4 + DMF, (black line) 0.05 M LiClO4 + DMF; (c) (red line) 0.67 mM Ni(NO3)2 + 0.05 M LiClO4 + DMF, (black line) 0.05 M LiClO4 + DMF; (d) 2 mM H2PtCl6 + 0.67 mM Ni(NO3)2 + 0.05 M LiClO4 + DMF at a scan rate of 50 mV s-1.

Fig. 2. Typical TEM images and the corresponding histogram of particle size distribution of Pt-Ni/C electrocatalysts. (a) Pt-Ni-1.60/C; (b) Pt-Ni-1.70/C; (c) Pt-Ni-1.73/C; (d) Pt-Ni-1.80/C.

Fig. 3. Electrochemical evaluation for Pt-Ni-1.60/C, Pt-Ni-1.70/C, Pt-Ni-1.73/C and Pt-Ni-1.80/C. (a) CV curves in N2-saturated 0.1 M HClO4 at a scan rate of 20 mV s-1; (b) Tafel plots with their slops at low overpotential region derived from polarization curves of the four samples and the commercial Pt/C catalysts; (c) Tafel plots comparisons of the series of electrocatalysts in the area specific activity; (d) area specific activity for the four samples and the commercial Pt/C catalysts.

Fig. 4. (a-c) Typical STEM-EDS element mapping images of Pt, Ni for Pt-Ni-1.73/C electrocatalyst; (e) corresponding line-scanning images which directions follow the red arrows in (d); (f) HRTEM image and the inset Fig. is its fast Fourier transformation (FFT) pattern.

Fig. 5. (a) CV curve in the electrolyte of 2 mM H2PtCl6 + 0.67 mM Ni(NO3)2 + 0.05 M LiClO4 + H2O (the inset is the TEM image of electrocatalyst prepared at potential of 0.1 V vs. RHE); (b) CV curves of in the electrolyte of 2 mM H2PtCl6 + 0.05 M LiClO4 + DMF (red line) and 0.05 M LiClO4 + DMF (black line) (the inset is the TEM image of as-synthesized Pt/C electrocatalyst at -1.80 V vs. Ag+/Ag). Scan rate: 50 mV s-1.

Fig. 6. (a) Structures of Pt-Graphene and Ni-graphene before (State 1) and after (State 2) the electrodeposition of Pt atoms. The gray, navy, orange and yellow represent carbon, Pt, Ni and newly-deposited Pt atom respectively; (b) Energy evolutions of Pt electrodeposition on Pt site and Ni site at U = 0.315 V vs. SHE; (c) Energy evolutions of Pt electrodeposition on Pt site and Ni site at U = 0 V vs. SHE.

Fig. 7. (a) The schematic structure diagrams of two states for the four slabs with adsorbed Pt*(the yellow color). The blue color represents deposited Pt layer, and the orange color represents located Ni; (b) The reduction potential profiles of Pt deposition on the four slabs at the electrode potential of U = 0.862 V vs. SHE; (c) The reduction energy profiles of Pt deposition on the four slabs at the electrode potential of U = 0 V vs. SHE.

Fig. 8. Schematic illustration for the growth mechanism of Pt/C and Pt-Ni/C. It is noted that the differences on radius of precursor ions and metal atoms are neglected for better presentation on the main growth process.