Nanoreactor of Nickel-Containing Carbon–Shells as Oxygen Reduction Catalyst

A nanoreactor of Ni@N-CNCs was fabricated and applied as a high-performance ORR catalyst. To fabricate Ni@N-CNCs, nickel particles were first prepared by reducing nickel chloride in aqueous solution. The template-directed carbon segregation method was used to synthesize carbon�shells on Ni particles. Ni particles were partially etched away to contain Ni nanoparticles within empty carbon nanocapsules (Ni@CNCs). The sample was further annealed at high temperature in ammonia gas, eventually to obtain Ni@N-CNCs with strong chemical bonds stabilized between Ni and N atoms. The content of Ni and annealing temperature were optimized. The electrocatalytic activity of Ni@N-CNCs was first evaluated by cyclic voltammetry (CV) in O2and N2-saturated 0.1 m KOH solution. Clear oxygen reduction peak at -0.14 V versus Ag/AgCl for Ni@N-CNCs is observed in O2-saturated KOH solution, whereas no evident peak is recorded in the same potential range in N2-saturated KOH solution, suggesting excellent ORR catalytic activity for our Pt-free Ni@N-CNCs, similar to commercial Pt/C. To further test electrochemical characteristics of Ni@N-CNCs, the rotating disk electrode (RDE) measurements were done at various rotation speeds. To further test electrochemical characteristics of Ni@N-CNCs, the rotating disk electrode (RDE) measurements were done at various rotation speeds. After adding methanol, the current density of Pt/C shows a sharp loss, while Ni@N-CNCs retain stable current response, indicating its better tolerance for possible methanol cross-over. The nanoreactor effect helps to increase the catalytic activity similar to that of commercial Pt/C catalysts.