Synthesis and Evaluation of RhxSy Catalyst with Functionalized Carbon for HOR/HER in H2-Br2 Reversible Fuel Cell

Abstract

Synthesis and characterization of a RhxSy catalyst with high mass specific electrochemical active surface area (ECSA/mass) for the H2-Br2 fuel cell are discussed in this paper. Supporting carbon materials were functionalized to create more suitable nucleation sites for the precipitation of rhodium sulfide nano-particles resulting in a catalyst with a smaller particle size, better particle distribution, and higher hydrogen oxidation and evolution reaction performance. XPS and FT-IR were used to analyze the amounts and the types of surface functional groups on the carbon substrate. The results confirm that the dominant functional group on the carbon is the ketone group. TEM and cyclic voltammetry results confirm that the catalysts with treated carbon have smaller average particle size (7.2 nm vs. 13.2 nm) and higher mass specific ECSA (21.8 m2/g-Rh vs. 9.1 m2/g-Rh) than those with the untreated carbon. The H2-Br2 fuel cell test results show that the catalysts with functionalized carbon have better performance in the kinetic region but poorer performance in the mass transfer dominant region. The issue was identified to be due to the poor affinity of the ketone group on the carbon surface with the Nafion ionomer in the catalyst ink and is currently being addressed.