Diffusion-Restricted Cation Exchange Derived Rhodium Nanoparticles for Hydrazine Assisted Hydrogen Production

Abstract

Water splitting using renewable energy is a promising hydrogen production method without carbon emission. However, oxygen evolution reaction still suffers from its large overpotential and sluggish kinetics. Thus, alternative oxidation reactions rather than oxygen evolution reaction, such as ammonia, alcohols and hydrazine oxidation reaction are developed for hydrogen production. Rh is one of the most promising catalysts for electrochemical hydrazine splitting that can promote hydrogen evolution reaction on the cathode, which is a much more energy-saving way to generate hydrogen gas than water splitting. Unfortunately, Rh is also one of the most expensive novel metals on the market. Nevertheless, only a few studies have considered the amount of used Rh. In this study, the diffusion-restricted cation exchange (CE) process is suggested as an effective method to reduce the mass of inactive Rh for enhanced mass activity. By immersing the NiOOH substrate in the Rh3+ aqueous solution, Rh3+ atoms are easily exchanged with Ni3+ atoms in the NiOOH lattice on the surface, and the RhOOH forms on the outermost layer. Then, the RhOOH compounds are reduced into metallic rhodium by an electrochemical reduction process, resulting in fine Rh nanoparticles smaller than 2 nm. Due to the suppression of Rh aggregation, a doubled mass activity for electrocatalytic hydrazine oxidation reaction is attained compared to that of conventional electrodeposited Rh catalysts. As a result, the proposed CE-derived Rh catalyst shows stability over 36 hours under the two-electrode hydrazine splitting system.