Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO₂ footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the ‘junctions’ between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Metal hydride (MH) thermal sorption compression is an efficient and reliable method allowing a conversion of energy from heat into a compressed hydrogen gas. The most important component of such a thermal engine – the metal hydride material itself – should possess several material features in order to achieve an efficient performance in the hydrogen compression. Apart from the hydrogen storage characteristics important for every solid H storage material (e.g. gravimetric and volumetric efficiency of H storage, hydrogen sorption kinetics and effective thermal conductivity), the thermodynamics of the metal–hydrogen systems is of primary importance resulting in a temperature dependence of the absorption/desorption pressures). Several specific features should be optimised to govern the performance of the MH-compressors including synchronisation of the pressure plateaus for multi-stage compressors, reduction of slope of the isotherms and hysteresis, increase of cycling stability and life time, together with challenges in system design associated with volume expansion of the metal matrix during the hydrogenation.The present review summarises numerous papers and patent literature dealing with MH hydrogen compression technology. The review considers (a) fundamental aspects of materials development with a focus on structure and phase equilibria in the metal–hydrogen systems suitable for the hydrogen compression; and (b) applied aspects, including their consideration from the applied thermodynamic viewpoint, system design features and performances of the metal hydride compressors and major applications

This paper presents the first part of a complete ex-situ characterisation of a wide range of commercial Gas Diffusion Layers (GDLs) used in low temperature and high temperature Proton Exchange Membrane (PEM) fuel cells. Physical and electrical characteristics of the GDLs are reported. The results show that the substrate structure has a significant effect on the mechanical and electrical properties of the GDL. Moreover, the Micro Porous Layer (MPL) structure determines the roughness of the surface, and affects the permeability and porosity of the GDL. It was found that the substrate treatment with PTFE affects the GDL characteristics; PTFE loading increases the GDLs hydrophobicity and permeability, however, decreases its overall porosity and resistivity. Adding a MPL to the substrate, results in a decrease in porosity and permeability and an increase in resistivity. The contact resistance of the GDL and the bipolar plate increases when the GDL thickness and PTFE loading are increased. This technical paper shows a close relationship between GDL materials and their physical characteristics and highlights the importance of optimising GDLs for fuel cell applications