Chalcogenide electrocatalysts for oxygen-depolarized aqueous hydrochloric acid electrolysis

Several Rh- and Ru-based carbon-supported chalcogenide electrocatalysts were evaluated as oxygen-depolarized cathodes for HCl electrolysis applications. The roles of both crystallinity and morphology of the electrocatalysts were explored by investigating several synthetic processes for materials, specifically patented E-TEK methods and the non-aqueous method. The activity of the electrocatalysts for ORR was evaluated via RDE studies in 0.5 M HCl, and compared to state of the art Pt/C and Rh/C systems. Rh_xS_y/C, Co_xRu_yS_z/C, and Ru_xS_y/C materials synthesized from the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The amorphous non-aqueous moieties, while exhibiting little depolarization due to the presence of high concentrations of Cl⁻ in the RDE studies, were unsuitable for operation in a true ODC HCl electrolyzer cell because of irreversible dissolution resulting from the high concentration (∼5 M) of HCl. In contrast, the Ru-based materials from the E-TEK methods were unaffected by the depolarizing conditions of an uncontrolled shutdown. These Ru-based electrocatalysts, being on the order of seven times less expensive than the state of the art Rh_xS_y material, may prove to be of economic benefit to the HCl electrolysis industry.