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

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 Ti3C2Tx, 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 Ti3C2Tx (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, Delta E, 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 Ti3C2Tx-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. 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.