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 (T_p) 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 (E_1/2) 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 g_Zn^-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 g_Zn^-1), showing outstanding practical value. This study is expected to promote the commercialization of the electrocatalysts.