Anion Exchange Membrane Water Electrolysis (AEMWE) is a very promising technology for producing clean H2 at a target cost of 2 $/kg. Like Proton Exchange Membrane Water Electrolysis (PEMWE), this membrane-based technology has the advantages of an “all solid” system (coupling with intermittent energy sources, high energy efficiency, high purity of H2). In addition it allows the use of earth abundant transition metals as electrocatalysts for both the evolution of O2 at the anode (OER) and of H2 at the cathode (HER), as opposed to PEMWE, where these catalysts rely exclusively on rare and expensive Platinum-Group Metals (PGM). However several challenges remain for AEMWE to reach as high and stable performance as PEMWE and be spread on the market. To achieve the increase of performance in AEMWE, essential components of the MEA must be optimized, with a specific emphasis on HER catalysts. Indeed, while being very fast in acidic conditions, the HER kinetics in alkaline medium are slow because they imply the adsorption of a water molecule, generally considered as the rate-determining step. In order to improve the rate of this first step, the new concept of heterofunctional catalysts has recently emerged. It consists in the tight interfacing of two or more active components so as to create a synergy between them, thus favoring water dissociation. In particular, bifunctional catalysts combining (i) one material with good water dissociation properties and (ii) another one with appropriate hydrogen adsorption energies, have displayed a 7-fold increase in alkaline HER rate. In the HYKALIN project we propose to significantly improve the performances of AEMWE so they can compete favorably with PEMWE. To do so, we intend to cover some untouched aspects in this field, through an integrative approach dealing with both fundamental and more applied aspects. In particular, we aim at: 1) Developing a new class of transition-metal-based heterofunctional catalysts being highly active for the HER in alkaline medium. Ni, Co, Cu and Mo are selected because they are already known to be very active for this reaction. We target composite catalysts associating a metal with either an oxide or a sulfide. They will be obtained by a 2-step process to achieve a maximum number of interfaces and catalytic sites. In the first step, we will synthesize MM’ alloys where the two metals are distributed at the nanoscale, using either polyol or spray-drying processes. In a second step, these alloys will be converted in M@M’Ox and M@M’Sx by thermal treatment or solution route. We will focus on producing specific porous morphologies which are crucial to induce good gas and water transport inside the MEA in order to improve the performances. 2) Deeply characterizing their electrochemical properties as well as their structure by operando X-ray spectroscopy to understand and improve their activity. Chemical nature, stoichiometry and morphology of the catalysts will be investigated in order to understand the behavior of the materials in the catalytic layer under functioning conditions. Ab initio and DFT calculations will also be crucial in this section to complement the interpretation of the experimental results. This should allow us to propose a comprehensive mechanism for alkaline HER. 3) Finally the best catalysts will be processed into membrane electrode assemblies and tested in situ in AEMWE. We will optimize MEA preparation and investigate the best operation conditions for the 5 cm2 electrolysis cell in order to achieve performances better than Pt/C. In a second step, we will perform degradation studies and get information on the mechanism of performance decrease. This fundamental and applied approach will significantly improve knowledge in the still emerging field of alkaline electrolyzers and should allow, in the mid-term, major breakthroughs in the domain of advanced water electrolysis and carbon-free hydrogen production.