Selenium-doped mixed metal oxide nanoparticles decorated on g-C3N4 and MXene sheets as promising bifunctional oxygen electrocatalysts for rechargeable Zn–air batteries

Abstract

The design of bifunctional electrocatalysts to conduct an appropriate oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for high-performance zinc–air batteries is one of the most important challenges for sustainable energy storage devices. Herein, a novel composition of a bifunctional electrocatalyst including a selenium-doped cobalt iron mixed metal oxide decorated on sulfur-doped g-C₃N₄ and Ti₃C₂T_x, SeCF-MMO/SgCN:MX, is prepared. The mixed metal oxide including cobalt and iron, doped with selenium, presents good OER capability while the synergetic effect between sulfur-doped g-C₃N₄ and Ti₃C₂T_x (x = OH, F, O) leads to an enhanced ORR capability of the mentioned bifunctional electrocatalyst. The presence of MXene and the 3D morphology of the SeCF-MMO particles during the calcination process led to enhanced active surface area and electrical conductivity of the final composite. The polarization between OER and ORR, ΔE, for the SeCF-MMO/SgCN:MX sample is lower (0.70 V) than those of electrocatalysts previously reported. Furthermore, the fabricated zinc–air battery presents a good power density of 140 mW cm⁻² with a small gap between charge and discharge, 0.85 V, and good stability. Moreover, the solid-state zinc–air battery presents appropriate performances at different states of bending. The superior performance of the SeCF-MMO/SgCN:MX sample is mainly attributed to the high conductivity of the optimized Ti₃C₂T_x-g-C₃N₄ composite and the synergistic interplay facilitated by the selenium-doped cobalt iron mixed metal oxide. This approach heralds a novel class of bifunctional nanostructures with promising prospects for applications in electrocatalysis and zinc–air battery technologies.