Searching General Sufficient-and-Necessary Conditions for Ultrafast Hydrogen-Evolving Electrocatalysis

The development of cost-effective and high-performance electrocatalysts for the hydrogen evolution reaction (HER) is one critical step toward successful transition into a sustainable green energy era. Different from previous design strategies based on single parameter, here the necessary and sufficient conditions are proposed to develop bulk non-noble metal oxides which are generally considered inactive toward HER in alkaline solutions: i) multiple active sites for different reaction intermediates and ii) a short reaction path created by ordered distribution and appropriate numbers of these active sites. Computational studies predict that a synergistic interplay between the ordered oxygen vacancies (at pyramidal high-spin Co ³⁺ sites) and the O 2p ligand holes (OLH; at metallic octahedral intermediate-spin Co ⁴⁺ sites) in RBaCo ₂ O _{5.5+ δ} (δ = 1/4; R = lanthanides) can produce a near-ideal HER reaction path to adsorb H ₂ O and release H ₂ , respectively. Experimentally, the as-synthesized (Gd _0.5 La _0.5 )BaCo ₂ O _5.75 outperforms the state-of-the-art Pt/C catalyst in many aspects. The proof-of-concept results reveal that the simultaneous possession of ordered oxygen vacancies and an appropriate number of OLH can realize a near-optimal synergistic catalytic effect, which is pivotal for rational design of oxygen-containing materials.