Highly Active Porous-Carbon-Supported CuO Nanoparticles as Electrocatalysts for the Phenazine/Hihydrophenazine Redox Reaction in Aqueous Organic Flow Batteries

Phenazine derivatives hold significant promise as redox-active species for aqueous flow batteries (AFBs); however, their practical application is often hindered by sluggish reaction kinetics, resulting in diminished accessible capacity, poor rate capability, and suboptimal efficiency. To address this issue, we developed a cost-effective, highly active porous-carbon-supported copper oxide (CuO/PC) nanoparticle catalyst by ultrasonically dispersing commercial CuO nanoparticles on the surface of porous carbon materials. This nanocatalyst significantly enhances the redox kinetics of the phenazine/dihydrophenazine reaction, leading to improved energy efficiency and capacity utilization in phenazine-based AFBs. The CuO/PC electrode demonstrates remarkable electrocatalytic activity, evidenced by an approximate 114% increase in redox current compared with the pristine carbon fiber electrode. In practical AFB applications, this translates to substantially increased energy efficiency and capacity utilization, particularly under high current density conditions. This enhanced battery performance is partly attributed to the oxygen vacancies within CuO, which facilitate electronic and ionic transport while simultaneously augmenting the catalytic sites for the phenazine/dihydrophenazine redox reactions. Density functional theory calculations further elucidate that the substantial improvement in electrocatalytic performance stems from two key factors: the strong adsorption capacity of carbon-supported oxygen-vacancy-enriched CuO (CuOv/C) for phenazine-based species and the in situ formation of a built-in electric field at the heterogeneous interface between CuOv and the carbon support.