Ag/Sn Dual-Atoms with Synergistic Electrocatalysis for High-Power Density Vanadium Flow Batteries.

Electrocatalyst with high activity is crucial to improve the power density of a vanadium flow battery (VFB), which is one of the most promising technologies in long duration large-scale energy storage. However, the accelerated redox reaction of vanadium ions normally accompanies hydrogen evolution as well. Herein, the Ag/Sn dual atoms electrocatalysts (Ag/Sn-DAs) are reported, exhibiting both high electrocatalytic activity and hydrogen evolution overpotential. Electrochemical in situ characterization indicates that the Ag/Sn-DAs can significantly promote the dehydration of [V(H2O)6]3+/[V(H2O)6]2+ and effectively inhibit hydrogen evolution reaction (HER). Theoretical calculations reveal that the optimized electronic structure and d-band center of Ag by the adjacent Sn change the *H adsorption sites and reduce the dehydration energy barrier of [V(H2O)6]3+/[V(H2O)6]2+. As a result, a VFB single cell assembled with Ag/Sn-DAs decorated graphite felt (GF) electrode delivers a high energy efficiency (EE) of 81.2% at a current density of 200 mA cm-2 and a peak power density of 925 mW cm-2, which is much higher than pristine GF (66.7% and 700 mW cm-2). This work presents a paradigm for synergistic catalysis in VFBs.