Recent Advances in Anodic Electrocatalysts for High-Current-Density Hybrid Water Splitting

Abstract

Electrochemical water splitting for hydrogen (H₂) production represents a promising technology to achieve carbon neutrality. However, its widespread application is severely limited by the sluggish kinetics and high theoretical potential (1.23 V) of the anodic oxygen evolution reaction (OER), which dominates the overall energy consumption. Hybrid water splitting (HWS) systems, which integrate thermodynamically more favorable anodic oxidation reactions of small molecules with the cathodic hydrogen evolution reaction (HER), provide an innovative approach for efficient and energy-saving H₂ production. Crucially, achieving operation at industrially relevant high current densities (> 200 mA·cm⁻²) is paramount for the practical implementation of these HWS systems. This review systematically summarizes recent advances in the development of high-performance anodic electrocatalysts for high-current-density applications. Key design strategies of anodic electrocatalysts are elaborated, including (i) surface chemistry engineering (e.g., elemental doping, defect/strain/phase engineering, heterostructure construction) to optimize electronic structure and intermediates adsorption energetics; (ii) micro-/nano-structure design (e.g., nanowires, nanosheets, microspheres, aligned- channel electrodes) to enhance mass transport and expose active sites; and (iii) catalyst-electrolyte interface tuning (e.g., leveraging local electric fields, pH effects, introducing adsorbed anions) to regulate reactant concentrations and reaction pathways. We then comprehensively discuss the coupling of various small molecules (e.g., urea, hydrazine, methanol, ethanol, glycerol, aldehyde, glucose, amine and sulfion) oxidation reactions with the HER for efficient and energy-saving H₂ production under high current density conditions, with a particular focus on mitigating the competition from the OER. Finally, we present perspectives on the remaining challenges and future research directions, including the rational design of catalysts with high intrinsic activity and selectivity, in-depth mechanistic investigations using advanced in situ/operando techniques, the development of efficient flow reactors and membrane electrode assemblies for industrial operation, and strategies to enhance long-term stability. This review aims to provide valuable insights for the advancement of hybrid water splitting systems toward large-scale, cost-efficient and energy-saving H₂ production.

Keywords

Anodic electrocatalysts / Hybrid water splitting / Energy-saving hydrogen production / High current density / Small molecules electrooxidation / Hydrogen evolution reaction / Urea oxidation reaction / Alcohol oxidation reaction / Aldehyde oxidation reaction

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