Performance improvement of the liquid-fed SO2-depolarized electrolyzers for anolyte with high H2SO4 concentration

As the hydrogen producing step of the hybrid sulfur process, SO2-depolarized electrolysis (SDE) needs to be operated with anolyte of high H2SO4 concentration, aiming at the high hydrogen production efficiency. However, the SDE cell is facing the challenge of rising impedance when anolyte H2SO4 concentration is increased. In this study, the performance of liquid-fed SDE cells is improved by using a thinner PEM and three-dimensional anode, especially for the anolyte with high H2SO4 concentration. The underlying mechanism of the SDE performance improvement is also discussed. The results show that effectively reducing the concentration polarization impedance is the key to improving the SDE performance. Significantly different from what is expected, PEM thickness reduction could not sharply decrease ohmic impedance. Instead, the application of thin PEMs can significantly reduce the concentration polarization impedance of the cathode reaction. As for the application of three-dimensional anode, it decreases anode concentration polarization dramatically. Finally, the combination of PEM thickness reduction and three-dimensional anode greatly improves the SDE performance of the electrolyzer. The influence of operating conditions on performance is studied for the optimized cell GF-212. When the anolyte H2SO4 concentration set at 50 wt%, the current density could reach 560 mA/cm2 at 1.0 V cell voltage, 360 mL/min anolyte flow rate and 80 degrees C. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.