Crystalline Ni ₅ P ₄ evolves hydrogen with electrical-efficiency comparable to platinum—while being corrosion-resistant in both acid and base for >16 hours.

The design of active and durable catalysts for the H₂O/O₂ interconversion is one of the major challenges of electrocatalysis for renewable energy. The oxygen evolution reaction (OER) is catalyzed by SrRuO₃ with low potentials (ca. 1.35 V_RHE), but the catalyst’s durability is insufficient. Here we show that Na doping enhances both activity and durability in acid media. DFT reveals that whereas SrRuO₃ binds reaction intermediates too strongly, Na doping of ~0.125 leads to nearly optimal OER activity. Na doping increases the oxidation state of Ru, thereby displacing positively O p-band and Ru d-band centers, weakening Ru-adsorbate bonds. The enhanced durability of Na-doped perovskites is concomitant with the stabilization of Ru centers with slightly higher oxidation states, higher dissolution potentials, lower surface energy and less distorted RuO₆ octahedra. These results illustrate how high OER activity and durability can be simultaneously engineered by chemical doping of perovskites.

Proton exchange membrane water electrolysis is a promising technology to produce green hydrogen from renewables, as it can efficiently achieve high current densities. Lowering iridium amount in oxygen evolution reaction electrocatalysts is critical for achieving cost-effective production of green hydrogen. In this work, we develop catalysts from Ir double perovskites. Sr₂CaIrO₆ achieves 10 mA cm⁻² at only 1.48 V. The surface of the perovskite reconstructs when immersed in an acidic electrolyte and during the first catalytic cycles, resulting in a stable surface conformed by short-range order edge-sharing IrO₆ octahedra arranged in an open structure responsible for the high performance. A proton exchange membrane water electrolysis cell is developed with Sr₂CaIrO₆ as anode and low Ir loading (0.4 mg_Ir cm⁻²). The cell achieves 2.40 V at 6 A cm⁻² (overload) and no loss in performance at a constant 2 A cm⁻² (nominal load). Thus, reducing Ir use without compromising efficiency and lifetime.

The production of green hydrogen in water electrolyzers is limited by the oxygen evolution reaction (OER). State-of-the-art electrocatalysts are based on Ir. Ru electrocatalysts are a suitable alternative provided their performance is improved. Here we show that low-Ru-content pyrochlores (R₂MnRuO₇, R = Y, Tb and Dy) display high activity and durability for the OER in acidic media. Y₂MnRuO₇ is the most stable catalyst, displaying 1.5 V at 10 mA cm⁻² for 40 h, or 5000 cycles up to 1.7 V. Computational and experimental results show that the high performance is owed to Ru sites embedded in RuMnO_x surface layers. A water electrolyser with Y₂MnRuO₇ (with only 0.2 mg_Ru cm⁻²) reaches 1 A cm⁻² at 1.75 V, remaining stable at 200 mA cm⁻² for more than 24 h. These results encourage further investigation on Ru catalysts in which a partial replacement of Ru by inexpensive cations can enhance the OER performance.