Nanostructured Copper@Carbon Fiber Composite as an Advanced Anode Catalyst in High-Performance Aqueous Viologen Flow Batteries

Redox flow batteries (RFBs) are a promising technology for large-scale energy storage due to their decoupled power and energy architecture, high scalability, and safety. Redox-active organic materials (ROMs) have emerged as promising candidates for RFB applications due to their molecular diversity, structural flexibility, cost effectiveness, and environmental compatibility. However, the sluggish kinetics of promising ROMs like methyl viologen (MV) on conventional carbon felt (CF) electrodes remain a critical bottleneck, necessitating the development of highly active electrocatalysts. Herein, we report the development of a novel nanostructured copper-on-carbon-felt composite (Cu@CF) electrode fabricated via a facile electrodeposition method incorporating organic additives. The Cu@CF electrode significantly enhances the intrinsic kinetic rate constant (k0) of the MV redox reaction by approximately 3-fold compared to that of pristine CF, demonstrating its superior intrinsic catalytic capability. An MV//N,N,N-2,2,6,6-heptamethylpiperidinyl-oxy-4-ammonium (TEMPTMA) aqueous organic redox flow battery (AORFB) full cell assembled using Cu@CF as the anode catalyst demonstrates substantially enhanced performance metrics, including remarkably low area-specific resistance (ASR), higher discharge capacity (85.1% utilization at 30 mA cm–2), a maximum power density of 235.4 mW cm–2 (46% higher than the CF cell), and excellent energy efficiency (EE) of 79.7% at 80 mA cm–2. Furthermore, this Cu@CF cell exhibits superior long-term stability over 500 cycles, maintaining an average EE of 78.52% and effectively suppressing undesirable side reactions like dimerization and disproportionation of MV+• (the reduced state of MV2+). This work establishes Cu@CF as a high-performance, durable, and low-cost electrocatalyst, offering a practical strategy to advance viologen-based AORFB technology.