Economic evaluation and catalyst design for hybrid water electrolysis systems

As a zero-carbon way to produce hydrogen, traditional water electrolysis is hindered by the sluggish kinetics of the oxygen evolution reaction (OER), which results in a high voltage input. Hybrid water electrolysis (HWE), which replaces the OER with economically viable electrooxidation reactions, could significantly lower the required voltage and, in turn, enhance energy conversion efficiency. Moreover, HWE could be integrated with certain existing industrial processes in principle; however, the feasibility and cost impact depend on substrate availability, product separation/purification, and long-term system durability. This review systematically categorizes three major types of alternative oxidation reactions based on their reaction mechanisms and products: conversion reactions (targeting the selective transformation of valuable substrates), degradation reactions (aimed at breaking down pollutants or hazardous compounds), and hydrogen carrier oxidation reactions (utilizing hydrogen-rich compounds such as ammonia to facilitate energy conversion). The economic feasibility, environmental benefits and relevant catalyst design strategies of these reactions are also explored. Finally, it summarizes the current research status of hybrid water electrolysis and discusses the challenges encountered, as well as prospects for development.