Hydrogen will play a central role in the clean economy and in meeting ambitious climate targets. However, to realise its full potential, we must enable low cost, widespread production of zero-carbon H2 by water electrolysis, powered using renewable energy. Underlying this challenge is improved understanding of these complex systems from atoms to cells under real world operating conditions. AMPERE brings together experts from academia, national laboratories and industry to diagnose and understand degradation and performance-limiting processes in electrolysers. Crucially, this project will address the effects of system dynamics, a key but often overlooked aspect of operation when using intermittent energy sources such as solar and wind. We will leverage a unique toolbox of state-of-the-art measurement techniques, spanning length scales from ionic motion in the polymer membrane, to local electrochemical activity across electrode assemblies, water management and bubble formation. This will produce the definitive picture of multi-scale electrolyser dynamics and our focus on realistic production rates and in-situ/operando methods will ensure these insights will have practical relevance. Thus, the outputs of AMPERE will help usher in zero-carbon H2 at scale, as a chemical feedstock and energy vector for clean power generation, heating and transportation.