Highly Active Ag Nanoparticle Electrocatalysts toward V2+/V3+ Redox Reaction

A high power density vanadium flow battery (VFB) is essential for reducing the cost of a VFB system. The power density of a VFB is currently limited by the negative half-cell since the negative V2+/V3+ reaction has sluggish reaction kinetics and high activation overpotential. In this work, a silver (Ag) nanoparticle-decorated graphite felt (GF) was designed and prepared by the electrodeposit method for VFB applications. By regulating the deposition current density and loading amount of metallic Ag, the Ag nanoparticles with a size of 30–80 nm are evenly deposited on the carbon fibers. Combining high electrical conductivity and high electrocatalytic activity of Ag nanoparticles, the activation energy for the V2+/V3+ redox reaction is reduced dramatically. Thus, the reaction kinetics of the V2+/V3+ redox couple is accelerated, and a very low charge-transfer resistance of only 1.743 Ω is obtained for GF-Ag-3, which is much lower than that of pristine GF (525 Ω). Accordingly, the voltage efficiency and energy efficiency with GF-Ag-3 can reach 85 and 82% in a VFB single cell, respectively, at a current density of 200 mA cm–2. This paper shows an effective and simple way to prepare a highly effective electrocatalyst toward the V2+/V3+ redox reaction.