AbstractDespite the fruitful achievements in the development of hydrogen production catalysts with record-breaking performances, there is still a lack of durable catalysts that could work under large current densities (>1000 mA cm⁻²). Here, we investigated the catalytic behaviors of Sr₂RuO₄ bulk single crystals. This crystal has demonstrated remarkable activities under the current density of 1000 mA cm⁻², which require overpotentials of 182 and 278 mV in 0.5 M H₂SO₄ and 1 M KOH electrolytes, respectively. These materials are stable for 56 days of continuous testing at a high current density of above 1000 mA cm⁻² and then under operating temperatures of 70 °C. The in-situ formation of ferromagnetic Ru clusters at the crystal surface is observed, endowing the single-crystal catalyst with low charge transfer resistance and high wettability for rapid gas bubble removal. These experiments exemplify the potential of designing HER catalysts that work under industrial-scale current density.