Identifying Activity and Selectivity Trends for the Electrosynthesis of Hydrogen Peroxide via Oxygen Reduction on Nickel-Nitrogen-Carbon Catalysts

The electrocatalytic production of hydrogen peroxide (H2O2) through the two-electron oxygen reduction reaction (ORR) requires cost-effective catalysts with high selectivity, activity, and stability. Herein we report the synthesis and electrocatalytic assessment of nickel-nitrogen-carbon (Ni-N-C) electrocatalysts to gain insight into ORR activity and selectivity toward the production of H2O2. The activity and selectivity of the catalysts depended on the amount of nickel added during synthesis as well as the pH of the electrolyte. The materials were found to be heterogeneous in nature, consisting of nitrogen-doped carbon structures containing Ni species, including Ni3S2 and covered metallic Ni particles. The presence of Ni during synthesis was imperative for the ORR performance in acidic electrolytes but had minimal impact on the performance in alkaline electrolytes. By experimentally demonstrating that Ni3S2, metallic Ni, and N-doped carbon species were not the source of activity, we postulate that atomically dispersed Ni-Nx/C sites are responsible for the ORR performance in acidic electrolytes, with an activity of -0.3 mA cm-2 and a H2O2 selectivity of 43% measured for the best Ni-N-C catalyst at 0.5 V vs RHE. This work highlights the potential and generates scientific insight into Ni-N-C catalysts to guide the design of improved performance metal-nitrogen-carbon catalysts based on inexpensive precursors and simplistic syntheses.