Ultrafine-Grained Porous Ir-Based Catalysts for High-Performance Overall Water Splitting in Acidic Media

Iridium (Ir)-based materials are known to be state-of-the-art electrocatalysts for catalyzing the oxygen evolution reaction (OER) in proton-exchange membrane (PEM) water electrolysis. However, it remains challenging for Ir-based catalysts to simultaneously achieve high catalytic activity and good stability in a strongly acidic environment. Herein, we report the fabrication of self-supported nanoporous ultrafine-grained IrO₂ electrodes (np-IrO₂) through the electrochemical activation of melt-spun Ir₁₂Al₈₈ ribbons under the OER conditions in 0.5 M H₂SO₄. The as-obtained np-IrO₂ needs only 240 mV to deliver 10 mA cm^–2 and can sustain continuous OER electrolysis in strong acid at an unusually high current density of 100 mA cm^–2 for 30 h without substantial degradation. Moreover, we find that the electrochemical activation of Ir₁₂Al₈₈ ribbons under the hydrogen evolution reaction (HER) conditions results in the formation of nanoporous IrAl alloy electrodes (np-IrAl), which show outstanding catalytic performance for HER in 0.5 M H₂SO₄. We further demonstrate that by using np-IrO₂ as an anode and np-IrAl as a cathode, we can accomplish overall acidic water splitting at 10 mA cm^–2 with a low voltage of 1.52 V. Remarkably, the np-IrO₂∥np-IrAl electrode pair is able to split water stably in 0.5 M H₂SO₄ at a high current density of 100 mA cm^–2 for up to 40 h, showing substantial promise for use in PEM water electrolysis.