Novel electrode design having gradually increasing porosity in a vanadium redox flow battery

Vanadium redox flow battery systems safely and efficiently store energy obtained from conventional energy sources (e.g. natural gas, petroleum and coal, and so on.) and renewable energy sources (e.g. solar, and, so on.). These battery systems need to be analyzed in depth since they are one of the most attractive energy storage technology. This study numerically investigates the effects of gradually increasing electrode porosity on potential performance, overpotentials, current densities, species concentrations, and pressure distributions in the VRFB during discharge process. In order to reveal these effects, two-dimensional and steady-state numerical models composed of four different cases are solved. Electrode porosity is constant at 94% for both electrodes in Case 1. While the negative electrode porosity is gradually increased from 64% to 94% (step by 10%) along the electrode thickness towards the membrane in Case 2, the positive electrode porosity is gradually changed from 64% to 94% along the same direction in Case 3. The other electrode porosity is kept constant at 94% in Case 2 and Case 3. Case 4 has electrodes having gradually increasing porosity in both half-cells. The numerical results show that Case 4 has higher potential performance, lower overpotential, and more uniform current distributions than the other cases. Furthermore, there are slight changes in the concentration distributions of consumed and produced species in all cases. Moreover, pressure drop in the region having 64% porosity is too much in cases applied gradually increasing porosity.