All-vanadium redox flow batteries (VRFBs) are considered promising candidates for large-scale energy storage systems due to their flexible power scale design, high efficiency, deep discharge, long cycle life and environmental friendliness. The performance and efficiency of a VRFB is affected by many factors, including component materials, battery design, electrolyte composition and operating conditions. Among the key components, porous electrodes play a key role, as the electrochemical reaction occurs on the fiber surface of the electrode. As such, many studies have focused on improving reaction kinetics by modifying the surface of the electrode. In this work, the effect of varying the compression ratio (CR) of graphite felts on the performance and efficiency of a VRFB are investigated. The impedance of a single VRFB under varying CRs of graphite felts at various operating conditions were also measured. The results suggest that performance of a VRFB increases with increasing CR due to the decrease of area resistance and concentration overpotential. The porous electrode compressed from 6.5 to 4 mm demonstrates the optimal energy efficiency of 73% at the operating current density 80 mA cm−2 and electrolyte flow rate 100 mL min−1.

Abstract:A direct borohydride/peroxide fuel cell (DBPFC) generates electrical power by recirculating liquid anolyte and catholyte between the stack and reservoirs, which is similar to the operation of flow batteries. To enhance the accessibility of the catalyst layer to the liquid anolyte/catholyte, graphite felts are employed as the porous diffusion layer of a single-cell DBPFC instead of carbon paper/cloth. The effects of the type of anode alkaline solution and operating conditions, including flow rate and temperature of the anolyte/catholyte, on DBPFC performance are investigated and discussed. The durability of the DBPFC is also evaluated by galvanostatic discharge at 0.1 A·cm −2 for over 50 h. The results of this preliminary study show that a DBPFC with porous graphite electrodes can provide a maximum power density of 0.24 W·cm −2 at 0.8 V. The performance of the DBPFC drops slightly after 50 h of operation; however, the discharge capacity shows no significant decrease.