SO2-depolarized electrolysis using porous graphite felt as diffusion layer in proton exchange membrane electrolyzer

The hybrid sulfur (HyS) process, which is composed of SO2-depolarized electrolysis (SDE) reaction and sulfuric decomposition reaction, is one of the simplest thermochemical cycles for producing hydrogen by water splitting. SDE is currently conducted in a proton exchange membrane (PEM) electrolyzer. In this work, a novel PEM electrolyzer structure is proposed. Graphite felt with large void content is used as the diffusion layer. In the electrolyzer, porous graphite felt plays the role of evenly distributing fluid and conducting electricity. The gap between the polar plate and the catalytic layer is occupied by the electrolyte solution and graphite felt, which effectively reduces the ohmic impedance of the electrolyzer. The effects of the main parameters including graphite felt compression ratio, anodic fluid flow rate, and sulfuric acid concentration, as well as temperature are investigated. Under optimized operating conditions, the current density reaches 800 mA/cm2 at cell voltage of 1.094 V, which is remarkably better than reported SDE performance using conventional PEM electrolyzers.