Facet effect of MnCo2O4 nanocrystals for enhanced oxygen reduction reaction in alkaline medium

Understanding the mechanism of the four-electron transfer oxygen reduction reaction (ORR) and the structure-activity relationship of spinel oxide remains a challenge. Two bimetallic manganese-cobalt spinel oxide supported on carbon nanotube (MnCo2O4/CNT) composite materials with different crystal planes exposed are synthesized in this paper by adding unequal amounts of ammonia during the hydrothermal process. Physical characterization results indicate that the exposed surfaces of the two materials (MnCo2O4/CNT-100, MnCo2O4/CNT-800) are (001) and (112), respectively. Electrochemical tests demonstrate that the MnCo2O4/CNT-800 composite material exposed to the (112) crystal plane exhibit higher ORR catalytic activity in alkaline electrolyte, with a half-wave potential of 0.79 V and a limiting current density of 5.15 mA cm(-2). The outstanding activity is attributed to the greater specific surface area, the exposure of high-index crystal plane and the high-valence metal sites on the surface. Density functional theory (DFT) calculations reveal that the active sites on the (112) crystal plane have improved adsorption and ORR thermodynamics. This work provides a strategy for developing the advanced bimetallic spinel electrocatalysts by adjusting the exposed plane.

Automated summary

In this paper, two bimetallic manganese-cobalt spinel oxide supported on carbon nanotube (MnCo2O4/CNT) composite materials with different crystal planes exposed were synthesized by adjusting the amount of ammonia during the hydrothermal process. It was found that the MnCo2O4/CNT-800 composite material exposed to the (112) crystal plane exhibited higher oxygen reduction reaction (ORR) catalytic activity in alkaline electrolyte. This was attributed to the greater specific surface area, exposure of high-index crystal plane, and high-valence metal sites on the surface. Density functional theory (DFT) calculations confirmed the improved adsorption and ORR thermodynamics on the (112) crystal plane. This work provides a strategy for the development of advanced bimetallic spinel electrocatalysts.