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

Abstract

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.

A simple in situ deposition of metal alloys on graphite surface based on Sb, Bi, Cu, and Sn as an electrocatalyst for V 3 + / V 2 + redox reaction

“…As seen in Figure 7, all Nyquist graphs consist of semicircular and linear parts in the high‐ and low‐frequency regions, respectively. This means that the V 3+ /V 2+ redox reaction is controlled by both the charge transfer and diffusion steps 5,48 . The semicircular part is responsible for the charge‐transfer process occurring at the electrode/electrolyte interface, while the linear part is associated with vanadium ion diffusion through the solution 10,49 .…”

“…Solar and wind power are the most widely used renewable energy resources; however, developing a large‐scale electrochemical energy storage system plays a vital role in supplying energy requirements 2 . Vanadium redox flow battery (VRFB) has become one of the most promising technologies for electrochemical energy storage devices due to its significant advantages over other energy storage systems such as long cycle life, high safety, and high efficiency 3‐5 . The main components of the VRFB are the proton exchange membrane, electrolyte, and electrodes.…”

“… 19 Additionally, it was reported that binary metal oxides have a better catalytic performance than single metal oxides 18 . However, most metal oxides have low conductivity, and they could not significantly increase battery performance at high current densities 5 . Kim et al explained that Mn 3 O 4 as a low‐cost catalyst has limited performance due to its low conductivity 9 …”

“…15,16 Generally, metal oxide (Mn 3 O 4 , PbO 2 , CeO 2 , WO 3 , TiO 2 , etc.) 2,5,10,17 and metal (Ni, Sb, Bi, Cu, Ir, Ni, etc.) are deposited on the carbon-based electrode to obtain more active sites for V 3+ /V 2+ redox pairs and enhance catalytic activity, cyclic stability, and energy efficiency of VRFB performance.…”

“…18 However, most metal oxides have low conductivity, and they could not significantly increase battery performance at high current densities. 5 Kim et al explained that Mn 3 O 4 as a low-cost catalyst has limited performance due to its low conductivity. 9 Metal catalysts have attracted considerable attention among various electrocatalysts for VRFB to accelerate redox reactions due to good electrical conductivity and high catalytic activity.…”