Metal and Metal Oxide Electrocatalysts for Redox Flow Batteries

Abstract

Redox flow batteries (RFBs) are one of the promising technologies for large‐scale energy storage applications. For practical implementation of RFBs, it is of great interest to improve their efficiency and reduce their cost. One of the key components of RFBs that can greatly influence the efficiency and final cost is the electrode. The chemical and structural nature of electrodes can modify the kinetics of redox reactions and the accessibility of the electroactive species to available active sites. The ideal electrocatalyst for RFBs must have good activity for the desirable redox reaction, provide a high surface area, and exhibit sufficient conductivity and durability over repeated use. One strategy is to coat the electrode with metal and metal oxide electrocatalysts. Metal electrocatalysts have the advantage of high conductivity, while metal oxide catalysts are usually less expensive and so more economically attractive. In order to gain a better understanding of the performance of the electrocatalysts in RFBs, a comprehensive review of the progress in the development of metal and metal oxide electrocatalysts for RFBs is provided and a critical comparison of the latest developments is presented. Finally, practical recommendations for advancement of electrocatalysts and effective transfer of knowledge in this field are provided.

Electrocatalysts for Using Renewably-Sourced, Organic Electrolytes for Redox Flow Batteries

“…Cathode catalysts are usually chosen from platinum group metals, as these elements are all active as hydrogenation catalysts [6,[13][14][15]21,[40][41][42][43][44][45][46][47]. Their utility is limited when the supporting electrolyte is aqueous because they are also active for reducing water (to make H 2 ).…”

“…Anode catalysts are also usually chosen from carbon-supported platinum group metals or metal oxides [44,49,50] because such materials do not readily oxidize. Boron-doped diamond offers a high overpotential for the oxygen evolution reaction [51][52][53][54][55], and is therefore useful for oxidizing organics at voltages above the decomposition voltage of water.…”

Molybdenum-assisted reduction of VO2+ for low cost electrolytes of vanadium redox flow batteries

“…Therefore, it can be expected that all electrolytes exhibit similar performance in terms of CE. VE is a factor that reflects the resistance of the electrode 56 . As the current density increased, a decrease in VE due to an increase in overpotential was observed for all electrolytes.…”

Origin of the catalytic activity at graphite electrodes in vanadium flow batteries

“…It is thus more remarkable that the original proposed reaction mechanism via oxygen functional groups (OFGs, Figure 1a) is still regularly cited and reproduced in literature up to this year. [9][10][11][12] A lot of scientific and industrial activities regarding VFBs focus on improving graphite-based felt electrodes by the application of OFGs through oxidative treatments such as thermal, chemical, electrochemical, alkaline or acid activation, to facilitate the negative (V III + e − ⇌ V II , E 0 = −0.26 V vs. SHE) and positive (V V O2 + + 2 H + + e − ⇌ V IV O 2+ + H2O, E 0 = 1.0 V vs. SHE) half-cell reactions. [13][14][15][16][17][18][19][20][21] The later observed performance enhancement is then ascribed to an elevated quantity of surface oxygen.…”