Atomically Adjustable Rhodium Catalyst Synthesis with Outstanding Mass Activity via Surface-Limited Cation Exchange

Rh has been widely studied as a catalyst for the promising hydrazine oxidation reaction that can replace oxygen evolution reactions for boosting hydrogen production from hydrazine-containing wastewater. Despite Rh being expensive, only a few studies have examined its electrocatalytic mass activity. Herein, surface-limited cation exchange and electrochemical activation processes are designed to remarkably enhance the mass activity of Rh. Rh atoms were readily replaced at the Ni sites on the surface of NiOOH electrodes by cation exchange, and the resulting RhOOH compounds were activated by the electrochemical reduction process. The cation exchange-derived Rh catalysts exhibited particle sizes not exceeding 2 nm without agglomeration, indicating a decrease in the number of inactive inner Rh atoms. Consequently, an improved mass activity of 30 A mg(Rh)(-1) was achieved at 0.4 V versus reversible hydrogen electrode. Furthermore, the two-electrode system employing the same CE-derived Rh electrodes achieved overall hydrazine splitting over 36 h at a stable low voltage. The proposed surface-limited CE process is an effective method for reducing inactive atoms of expensive noble metal catalysts.