Iridium Improves BOR Selectivity of Ru-Based Catalysts for Direct Borohydride Fuel Cells

Direct borohydride fuel cells (DBFCs) are considered as a promising energy storage method because of their high theoretical cell voltage and high energy density. However, the sluggish kinetics and low fuel utilization have limited its practical application. According to density functional theory calculations, we found that the high-valency ruthenium (Ru) site not only promotes electrochemical borohydride oxidation reaction (eBOR) kinetics but also tends to catalyze hydrolysis. Doping iridium (Ir) species into a Ru-based catalyst effectively inhibits hydrolysis and improves eBOR selectivity. Herein, a catalyst of Ru-Ir supported on carbon powder (RuIrOx-C) was prepared by a sol–gel method. The RuIrOx-C catalyst achieves a remarkable power density of 236 mW cm–2, which is 47% higher than that of the control RuOx-C catalyst. Additionally, DBFCs show excellent stability and can work continuously for 210 h at a current density of 100 mA cm–2. In situ attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIRS) indicated that the high-valence Ru site accelerates the eBOR kinetics, while reducing the adsorption of water molecules on the catalyst surface. This reduction inhibits the hydrolysis reaction and improves the reaction selectivity. This work opens a way for the design and development of eBOR catalysts with excellent activity, stability, and selectivity.