The excessive dependence on fossil fuels contributes to the majority of CO2 emissions, influencing on the climate change. One promising alternative to fossil fuels is green hydrogen, which can be produced through water electrolysis from renewable electricity. However, the variety and complexity of hydrogen evolution electrocatalysts currently studied increases the difficulty in the integration of catalytic theory, catalyst design and preparation, and characterization methods. Herein, this review first highlights design principles for hydrogen evolution reaction (HER) electrocatalysts, presenting the thermodynamics, kinetics, and related electronic and structural descriptors for HER. Second, the reasonable design, preparation, mechanistic understanding, and performance enhancement of electrocatalysts are deeply discussed based on intrinsic and extrinsic effects. Third, recent advancements in the electrocatalytic water splitting technology are further discussed briefly. Finally, the challenges and perspectives of the development of highly efficient hydrogen evolution electrocatalysts for water splitting are proposed.

Figure 2. Schematic acidic OER mechanisms, in which both single-and dual-site pathways are presented. a) The adsorbate evolution mechanism (AEM). b) The lattice oxygen evolution mechanism (LOM).

Developing effective, stable, and economical catalysts toward overall water splitting under industrial conditions is crucial for the large-scale production of green hydrogen. Herein, we report a general method to fabricate bimetallic phosphide heterojunctions on nickel foam (NF) for water electrolysis. Benefiting from the unique self-supported integrated structure and optimized electronic structure, the Co2P–Ni12P5/NF and Fe2P–Ni12P5/NF heterojunction exhibits ultralow overpotentials of 219 mV for hydrogen evolution and 342 mV for oxygen evolution at 1000 mA cm–2 in 1 M KOH, respectively. Notably, the assembled two-electrode system attains a high current density of 1000 mA cm–2 with a low cell voltage of 1.678 V under simulated industrial electrolysis conditions. Furthermore, when applied in an anion-exchange membrane water electrolysis (AEMWE) cell, Co2P–Ni12P5/NF||Fe2P–Ni12P5/NF exhibits superior performance over commercial Pt/C/NF||IrO2/NF. Our study provides a general method for developing economical and practical water-splitting electrocatalysts for large-scale renewable hydrogen production.

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Water electrolysis, a process for producing green hydrogen from renewable energy, plays a crucial role in the transition toward a sustainable energy landscape and the realization of the hydrogen economy. Oxygen evolution reaction (OER) is a critical step in water electrolysis and is often limited by its slow kinetics. Two main mechanisms, namely the adsorbate evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM), are commonly considered in the context of OER. However, designing efficient catalysts based on either the AEM or the LOM remains a topic of debate, and there is no consensus on whether activity and stability are directly related to a certain mechanism. Considering the above, we discuss the characteristics, advantages, and disadvantages of AEM and LOM. Additionally, we provide insights on leveraging the LOM to develop highly active and stable OER catalysts in future. For instance, it is essential to accurately differentiate between reversible and irreversible lattice oxygen redox reactions to elucidate the LOM. Furthermore, we discuss strategies for effectively activating lattice oxygen to achieve controllable steady-state exchange between lattice oxygen and an electrolyte (OH− or H2O). Additionally, we discuss the use of in situ characterization techniques and theoretical calculations as promising avenues for further elucidating the LOM.

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The development of efficient and economical electrocatalysts for oxygen evolution reaction (OER) is of paramount importance for the sustainable production of renewable fuels and energy storage systems; however, the sluggish OER kinetics involving multistep four proton‐coupled electron transfer hampers progress in these systems. Fortunately, surface reconstruction offers promising potential to improve OER catalyst design. Anion modulation plays a crucial role in controlling the extent of surface reconstruction and positively persuading the reconstructed species' performances. This review starts by providing a general explanation of how various types of anions can trigger dynamic surface reconstruction and create different combinations with pre‐catalysts. Next, the influences of anion modulation on manipulating the surface dynamic reconstruction process are discussed based on the in situ advanced characterization techniques. Furthermore, various effects of survived anionic groups in reconstructed species on water oxidation activity are further discussed. Finally, the challenges and prospects for the future development directions of anion modulation for redirecting dynamic surface reconstruction to construct highly efficient and practical catalysts for water oxidation are proposed.