Guest Editorial

In the 1980s and 1990s, progress in fuel cell and battery research evolved mainly around materials development, empirical approaches, and efforts focusing mostly separately on either the microscale (electrodes and electrolytes) or the macroscale (systems, thermodynamics, and balance-of-plant). Since the 2000s, with the advent of more powerful computing and modeling resources, and the general progress in the field, it has seen a shift to the merging of scales, the possibility of 3D probing and quantification with fuel cell stacks and battery packs becoming the focal point. In parallel, disciplines have merged, too: a holistic and a detailed understanding in the range of underlying phenomena of chemistry, physics, materials science, and mechanical engineering has been combined with the addition of the influence of an electrical field or current. This union is essential to achieve the progress needed for the commercial breakthrough expected from the technologies. It became established that both experimental and modeling aspects deserve simultaneous and an equally weighted consideration, and it is recognized that the correspondences between models and experiments deliver among the most valuable advances to the field, due to the level of confidence and insight they provide.