Tribological challenges in hydrogen: Solutions for the future energy transition

Hydrogen-powered internal combustion engines (H 2 ICEs) are increasingly recognised as a key solution in the global transition from fossil fuels to sustainable energy sources. While hydrogen offers significant potential as a clean energy carrier, its integration into ICE technology, and related hydrogen-based applications, presents distinct tribological challenges that must be resolved to achieve optimal engine performance, longevity, and efficiency. This review synthesises the current body of knowledge on key tribological issues facing metal-metal tribosystems, including lubricant behaviour, hydrogen embrittlement, tribofilm formation, and coatings, within hydrogen environments. It also considers the implications for broader hydrogen tribosystems, such as polymer–metal and ceramic contacts, highlighting both recent technical advancements and existing gaps. By offering a comprehensive pathway for future research and cross-industry collaboration aimed at overcoming these tribological barriers, the review concludes with practical recommendations that ultimately pave the way for the reliable and widespread adoption of hydrogen-fuelled combustion systems and beyond. • Overview of tribological challenges in hydrogen systems, from internal combustion engines to broader applications. • Focus on hydrogen embrittlement and lubricant degradation, highlighting impacts of water contamination. • Outlines mechanisms of hydrogen-induced wear and evaluates countermeasures such as tribofilms and advanced lubricants. • Compares metallic, polymeric, and ceramic tribosystems under hydrogen and how additives or coatings enhance durability. • Proposes future research directions, from hydrogen-environment test methods to next-generation materials and coatings.