Advanced high-entropy materials for fuel cells and water electrolysis

High-entropy materials (HEMs) represent a paradigm shift in developing efficient components of proton exchange membrane fuel cells/water electrolysis and solid oxide fuel cells/water electrolysis for hydrogen energy conversion and storage. This comprehensive review summarizes foundational breakthroughs and emerging applications of HEMs across those electrochemical energy devices, examines the roles of high configurational entropy and lattice distortion in HEMs, focusing on their fundamental enhancement of the thermodynamic stability and kinetic durability of device components under extreme operational conditions. Modern design paradigms - spanning AI-driven high-throughput screening to multi-scale computational modeling - are critically analyzed alongside advanced synthesis techniques, including solvent-free mechanochemical processing and ultrafast thermal shock methods. The multifunctional roles of HEMs are systematically examined through numerical examples in the literature. The analysis shows that the electrodes leveraging entropy-stabilized active sites demonstrate unprecedented activity for hydrogen oxidation (HOR), oxygen reduction (ORR), and water-splitting reactions (HER/OER) in both solid oxide and proton-exchange membrane systems; the electrolytes with HEMs exhibit tunable O^2-/proton conductivities with exceptional interfacial compatibility; and interconnects and coatings with HEMs can mitigate chromium poisoning and degradation through entropy-mediated diffusion barriers. Several technical challenges in the development and application of HEMs are analyzed, and the corresponding research directions for overcoming the challenges are proposed toward the practical application of HEMs. A multidisciplinary roadmap integrating in situ characterization, machine learning optimization, and circular economy principles to accelerate HEM deployment in fuel cells and water electrolysis is also emphasized for energy conversion and storage infrastructure.