Acidified water electrolysis with fast kinetics is widely regarded as a promising option for producing H 2 . The main challenge of this technique is the difficulty in realizing sustainable H 2 production (SHP) because of the poor stability of most electrode catalysts, especially on the anode side, under strongly acidic and highly polarized electrochemical environments, which leads to surface corrosion and performance degradation. Research efforts focused on tuning the atomic/nano structures of catalysts have been made to address this stability issue, with only limited effectiveness because of inevitable catalyst degradation. A systems approach considering reaction types and system configurations/operations may provide innovative viewpoints and strategies for SHP, although these aspects have been overlooked thus far. This review provides an overview of acidified water electrolysis for systematic investigations of these aspects to achieve SHP. First, the fundamental principles of SHP are discussed. Then, recent advances on design of stable electrode materials are examined, and several new strategies for SHP are proposed, including fabrication of symmetrical heterogeneous electrolysis system and fluid homogeneous electrolysis system, as well as decoupling/hybrid-governed sustainability. Finally, remaining challenges and corresponding opportunities are outlined to stimulate endeavors toward the development of advanced acidified water electrolysis techniques for SHP.

Inorganic compounds with different crystalline and amorphous states may show distinct properties in catalytic applications. In this work, we control the crystallization level by fine thermal treatment and synthesize a semicrystalline IrO x material with the formation of abundant boundaries. Theoretical calculation reveals that the interfacial iridium with a high degree of unsaturation is highly active for the hydrogen evolution reaction compared to individual counterparts based on the optimal binding energy with hydrogen (H*). At the heat treatment temperature of 500 °C, the obtained IrO x -500 catalyst has dramatically promoted hydrogen evolution kinetics, endowing the iridium catalyst with a bifunctional activity for acidic overall water splitting with a total voltage of only 1.554 V at a current density of 10 mA cm–2. In light of the remarkable boundary-enhanced catalysis effects, the semicrystalline material should be further developed for other applications.

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