Toward the Ideal Alkaline Hydrogen Evolution Electrocatalyst: a Noble Metal‐Free Antiperovskite Optimized with A‐Site Tuning

To achieve the ideal non-noble-metal HER electrocatalyst in alkaline media, developing conductive systems with multiple active sites targeting every elementary step in the alkaline HER, is highly desirable but remains a great challenge. Herein, a conductive noble metal-free antiperovskite CdNNi₃ is reported with intrinsic metallic characteristics as a highly efficient alkaline HER electrocatalyst, which is designed by the facile A-site tuning strategy with the modulation the electronic structures and interfacial water configurations of antiperovskites. Impressively, the HER performance of CdNNi₃ antiperovskite is superior to various state-of-the-art non-noble metal catalysts ever reported, and also outperforms the commercial Raney Ni catalyst when assemble as the cathode in the practical anion exchange membrane water electrolyzer (AEMWE) device. With insights from comprehensive experiments and theoretical calculations, the CdNNi₃ can create synergistic dual active sites for catalyzing different elementary steps of the alkaline HER; namely, the Ni site can effectively facilitate the H₂O dissociation and OH^- desorption, while the unusual Cd-Ni bridge site is active for the optimal H^* adsorption and H₂ evolution. Such multifunction-site synergy, together with inherent high electrical conductivity, enables the CdNNi₃ antiperovskite to fulfill the essential criteria for an ideal non-noble-metal alkaline HER electrocatalyst with excellent performance.