Hydrogen storage materials: present scenarios and future directions

This review describes the present state of contemporary solid state hydrogen storage on the basis of research carried out during the last decade. The article focuses on the key aspects of materials based on the physical and chemical storage of hydrogen and emerging mechanisms for reversible storage. Among chemical storage materials, we consider metal hydrides (both light and complex), nitrides-imides-amides and other multi-component systems and discuss the emergence of coordination polymers (metal organic frameworks; MOFs) among solids exhibiting physical storage. Significant challenges remain if we are to meet the practical demands required of a solid state storage system, namely high storage density together with favourable sorption thermodynamics and kinetics and prolonged cycleability and lifetime. This review emphasises both how our understanding of the storage mechanism (as a process or phenomenon during hydrogen cycling) is evolving and how this understanding impacts on future materials design. The prospect of high capacity storage and fast kinetics in nanostructured materials is highlighted as is the role of complex, multi-component, composite systems in future hydrogen storage research.