CoNi-N/P-Doped Carbon Nanotubes as Catalysts for Efficient Oxygen Reduction Reaction.

Transition metals (TMs) supported by heteroatom-doped carbon materials are considered to be the potential alternatives to the Pt/C catalyst owing to their low cost, outstanding electrocatalytic efficiency, and excellent electrochemical durability. In this paper, N/P-doped carbon nanotube (CNT) (N/P-CNT)-supported monometallic (Co, Ni) and bimetallic (CoNi) catalysts were synthesized by one-step pyrolysis using diammonium hydrogen phosphate, 2-methylimidazole and organometallic salts as precursors, and the CNT as the catalyst carrier; the effects of transition TM types and pyrolysis temperature (Tp) on the microstructure and electrochemical properties were explored. The analysis exhibited that the CoNi bimetallic catalyst was superior to both Co and Ni monometallic catalysts, and the catalysts pyrolyzed at 900 °C exhibited a better graphitization degree. The optimal CoNi-N/P-CNT-900 displayed remarkable oxygen reduction reaction electrocatalytic performance with a half-wave potential (E1/2) of 0.86 V and excellent methanol tolerance and stability. Moreover, the Zn-air battery coated with CoNi-N/P-CNT-900 demonstrated a larger open circuit voltage of 1.577 V, a larger peak power density of 212.89 mW cm-2 at 357.8 mA cm-2, as well as a higher specific capacity of 799 mA h gZn-1, superior to that of the Pt/C catalyst (1.492 V, 96.04 mW cm-2 at 216.8 mA cm-2, 735 mA h gZn-1), showing outstanding practical value. This study is expected to promote the commercialization of the electrocatalysts.