Challenges to developing materials for the transport and storage of hydrogen.

Hydrogen has the highest gravimetric energy density of any energy carrier and produces water as the only oxidation product, making it extremely attractive for both transportation and stationary power applications. However, its low volumetric energy density causes considerable difficulties, inspiring intense efforts to develop chemical-based storage using metal hydrides, liquid organic hydrogen carriers and sorbents. The controlled uptake and release of hydrogen by these materials can be described as a series of challenges: optimal properties fall within a narrow range, can only be found in few materials and often involve important trade-offs. In addition, a greater understanding of the complex kinetics, mass transport and microstructural phenomena associated with hydrogen uptake and release is needed. The goal of this Perspective is to delineate potential use cases, define key challenges and show that solutions will involve a nexus of several subdisciplines of chemistry, including catalysis, data science, nanoscience, interfacial phenomena and dynamic or phase-change materials.