Carbon-Supported Rh17S15-Rh Electrocatalysts Applied in the Oxygen Reduction Reaction.

Rh₁₇S₁₅-Rh catalysts supported on acid-treated carbon black were prepared from RhCl₃ by a facile method using sulfur source ((NH₄)₂S₂O₃) and reducing agent (NaBH₄), followed by an additional thermal treatment at 650 °C in argon. The prepared catalyst comprised an Rh₁₇S₁₅ single crystalline phase and a zero-valent metal (Rh) phase supported on a conductive carbon. By XRD characterization, the constituent ratio of Rh₁₇S₁₅ to Rh in the electrocatalysts, ranging from 51-95 %, varied with the increase of amount of (NH₄)₂S₂O₃ or NaBH₄. Morphologies of the resulting catalysts were characterized by transmission electron microscopy (TEM) technique. Most of particles were found to have a distribution of agglomerates ranging in size from 10 to 50 nm. In studying the effect of the constituent phases of chalcogenide electrocatalysts on oxygen reduction reaction activity, it is paramount to understand and optimize the structure sensitivity of the reaction, which will aid in determining the optimal ratio of Rh₁₇S₁₅ to Rh of the electrocatalyst. Activity and stability of the prepared catalysts were addressed using a series of cyclic voltammetry (CV) experiments in 1 M HCl electrolyte, in which the electrocatalyst of 95 % of Rh₁₇S₁₅ was found to be the most stable. The rotating disk electrode (RDE) experiment indicated the sulfide catalyst with 82 % of Rh₁₇S₁₅ showed the better performance for the ORR, which was discussed based on the compromise between the stability for the constituent phase of Rh₁₇S₁₅ in 1 M HCl and enhanced activity found for Rh phase. [ABSTRACT FROM AUTHOR]