Co2NiO4/NF as bidirectional catalyst for quinoxaline hydrogenation/tetrahydroquinoxaline dehydrogenation in flow batteries

Abstract

This study addresses key challenges in conventional catalysis for the quinoxaline/tetrahydroquinoxaline liquid organic hydrogen carrier (LOHC) pair. These challenges include high energy consumption, reliance on precious metals, and catalyst irreversibility. We developed a novel strategy for fabricating an efficient bifunctional electrode. This strategy is based on electrodeposition from a deep eutectic ionic liquid. The Co−Ni bimetallic catalyst (Co2NiO4/NF) was constructed on a nickel foam (NF) substrate. This was achieved via electrodeposition in a choline chloride−propylene glycol ionic liquid. Physicochemical characterization confirmed the catalyst's unique structure. This structure is a composite of metallic cobalt and cobalt-nickel oxide. It also features uniformly distributed active sites. Electrochemical tests demonstrate high activity and selectivity for Co2NiO4/NF. It performs well in both the electrocatalytic hydrogenation of quinoxaline and the electrocatalytic dehydrogenation of tetrahydroquinoxaline. The catalyst also shows excellent cycling stability in both reactions. This enables efficient bidirectional catalysis for the reversible hydrogen storage and release processes of LOHCs on a single catalyst platform. Under optimal potentials, the Faradaic efficiency reached 99.84% (with 98.73% selectivity) for hydrogenation. For dehydrogenation, it reached 99.07% (with 98.96% selectivity). The performance enhancement is attributed to the electronic synergy between Co and Ni. This synergy optimizes the electrode's conductivity and reactant adsorption behavior. Furthermore, the reversible valence cycling of the cobalt/nickel redox couple provides a distinct kinetic advantage, and that continuously facilitates both the hydrogenation and dehydrogenation processes. This work provides a new material system and design approach. It aids in the development of low-cost, high-performance bifunctional catalysts for LOHCs. It also promotes progress toward the practical application of quinoxaline-based organic flow batteries.