Understanding the activity transport nexus in water and CO$_{2}$ electrolysis: State of the art, challenges and perspectives

This article reviews the challenge of expanding the current research focus on water and CO2 electrolysis from catalyst-related insights towards achieving complete understanding of the activity transport nexus within full electrolysis cells. The challenge arises from the complex interaction of a multitude of phenomena taking place at different scales that span several orders of magnitude. An overview of current research on materials and components, experiments and simulations are provided. As well as obvious differences, there are similar principles and phenomena within water and CO$_{2}$ electrolysis technologies, which are extracted. Against this background, a perspective on required future research within the individual fields, and the need for a multidisciplinary research approach across natural, materials and engineering sciences to tackle the activity transport nexus is presented.