Doped rhodium sulfide and thiospinels hydrogen evolution and oxidation electrocatalysts in strong acid electrolytes

Abstract

Hydrogen evolution and oxidation activity of several carbon-supported rhodium thiospinels (CuRh2S4, CoRh2S4, FeRh2S4, and NiRh2S4) are evaluated in sulfuric acid and compared with Ir, Ru, and Pd-doped and undoped Rh17S15 on carbon. The metal sulfides are synthesized on carbon by reacting metal chlorides with hydrogen sulfide at 350 °C. Mixtures of Cu, Co, Fe, and Ni salts with RhCl3 formed thiospinels. The minority metals, Pd, Ru, or Ir, incorporate into the Rh17S15 structure at low concentrations (1 %). The hydrogen evolution and oxidation activities of the thiospinels in sulfuric acid are lower than pure Rh17S15/C, with NiRh2S4/C showing the highest activity of the thiospinels, and CuRh2S4/C seen to be unstable in sulfuric acid, even for short times (1 min). The hydrogen evolution and oxidation activities normalized to an estimate of the electrocatalyst area for the 1 % Pd, Ru, and Ir in Rh17S15/C are slightly lower than pure Rh17S15/C and all metal sulfides have a lower hydrogen evolution activity than platinum, even when normalizing to surface area.