Electrocatalytic characteristics of quinoxaline hydrogenation/tetrahydroquinoxaline dehydrogenation of CoMoO4/NF as a bifunctional catalyst in flow batteries

Abstract

Quinoxaline (QXL) is highly promising as a negative electrode material of flow batteries due to its high theoretical capacity and low redox potential. However, its practical application is hindered by sluggish hydrogenation/dehydrogenation kinetics and susceptibility to side reactions such as the hydrogen evolution reaction. To address this issue, a bimetallic CoMoO4 catalyst was constructed on nickel foam (NF) via an electrodeposition method (CoMoO4/NF). The synergistic effect between Co and Mo enables efficient and reversible conversion of the QXL/tetrahydroquinoxaline (THQXL) redox. CoMoO4/NF possesses a porous structure with uniformly dispersed active sites, resulting in a significantly enhanced electrochemically active surface area. CoMoO4/NF at –0.30 V (vs. RHE) in half-cell tests achieves a hydrogenation conversion of 99.4% and a selectivity of 97.7%, and which at 1.5 V (vs. RHE) attains a dehydrogenation conversion of 99.9% and a selectivity of 99.3%. CoMoO4/NF in QXL∥K4[Fe(CN)6] flow batteries also deliver a discharge capacity of 19.5 mAh and a Coulombic efficiency of 24.38% at 2 mA cm⁻2 of discharge current density, and which exhibits good stability with over 10 cycles. The synergistic catalytic mechanism is explained, Co sites primarily drive hydrogenation and dehydrogenation, while Mo sites promote the generation and transfer of hydrogen species. This study provides an effective strategy and experimental basis for the design of highly active and stable electrode materials for nitrogen-containing heteroaromatic flow batteries.