Carbon-supported low-loading rhodium sulfide electrocatalysts for oxygen depolarized cathode applications

Abstract

Noble metal chalcogens are the preferred choice of electrocatalyst materials over pure metals and metal alloys in many industrial processes involving operation in highly corrosive environment. The depolarised electrolysis of hydrochloric acid represents one of such processes; in this case, rhodium sulfide is incorporated into gas diffusion electrode structure for use as oxygen-consuming cathode. An increased dispersion of the rhodium/ sulfurcompoundisanevidentgoaltoobtainhighlyactivecatalystsystemswhilemaintainingsimilaractivity.InstudyingtheeffectofRhxSyloadingon carbononoxygenreductionreactionactivity,itisparamounttounderstandandoptimizethestructuresensitivityofthereaction.Doingsowillnotonly aidindeterminingtheoptimalmetalloadingbutmoreimportantlywillcontrolthecommercialviabilityoftheelectrocatalyst.Inthepresentwork,the RhxSyloadingonVulcanXC72-RwasstudiedintermsofmorphologicalcharacteristicsandORRactivity.Physicochemicalcharacterizationsuggests that the preparation methodology of such chalcogens plays a fundamental role in terms of chemical structure. ORR kinetics was addressed using a seriesofrotatingdiskelectrodeexperimentsin1 MHClelectrolyte,inwhichtheoptimalRhxSyloadingwasfoundtobeat15 wt.%,avaluetwotimes lower with respect to the commercially available 30 wt.% material. Any higher dispersion results in no significant increase in the overall electrocatalytic performance. Based on the increased Rh utilization and enhanced activity found for the low-loading RhxSy/C samples, we report a significant development in terms of materials and material employment for the oxygen depolarized electrolysis of HCl. # 2007 Elsevier B.V. All rights reserved.