Cathode/Anode Interface and Performance of a Membrane-Free Thermally Regenerative Flow Battery via Density-Induced Self-Stratified Electrolytes

Thermally regenerative batteries have promising applications in low-temperature waste-heat recovery, but ammonia crossover severely reduces battery power generation and its stability. To address this issue, a membrane-less self-stratified thermally regenerative flow battery was constructed to alleviate ammonia crossover. The interface visualization, power generation feasibility, and the effects of flow rate were investigated. The results reveal that the density difference of the anolyte/catholyte leads to self-stratification. The interface moves continually due to ammonia diffusion in the static catholyte, resulting in a significant decrease in the battery performance. By regulating the catholyte flow rate, a steady anode–cathode interface can be achieved, thereby solving the key problem of ammonia crossover and achieving stable power generation. Increasing the catholyte flow rate can produce a stable interface and prevent the interface from moving to the cathode. However, a high catholyte flow rate will allow the interface to surpass the anode electrode, causing battery performance to increase and then decrease with flow rate. Increasing the ammonia flow rate can effectively improve the anode mass transfer and battery performance. The interface is affected by temperature change, so the interface is investigated at different temperatures. Within a specific range, there is no significant change in the position of the interface, and the battery’s maximum power density improves linearly with temperature.