Iridium nanorods as a robust and stable bifunctional electrocatalyst for pH-universal water splitting

Abstract Bifunctional electrocatalyst for efficiently catalyzing hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in pH-universal electrolyte is desirable for the industrial overall water splitting technology. In this work, we have synthesized Iridium nanorods (Ir-NR/C) by annealing Ir nanoparticles at 300 °C requiring comparatively low overpotentials of 290 mV, 296 mV and 305 mV to achieve current density of 10 mA cm−2 for OER catalysis in 0.5 M H2SO4, 1 M KOH and 1 M PBS with a low Ir loading of 14 μg cm−2, respectively, resulting in ∼30 times higher mass activity compared to commercial IrO2. Moreover, stable OER performance is recorded due to the formed thin amorphous Iridium oxides (IrOx) layer protecting the underneath metallic Ir from direct electrochemical dissolution and coalescences. Besides, IrOx layer negligibly affects the HER performance in acidic medium; but promotes the HER catalytic activities in alkaline and neutral electrolytes since the Volmer step (water dissociation) is efficiently catalyzed by IrOx layer enabling a 6-fold better mass activity than benchmarked Pt/C. Ir-NR/C performs superior stability during HER catalysis in a wide pH range ascribed the prevention of Ir migration and aggregation. Finally, the assembled water splitting device by Ir-NR/C shows robust activity and exceptional stability than benchmarked Pt/C-IrO2 in pH-universal electrolytes.