The production of hydrogen (H2) from electrochemical reduction of a proton source, ideally water, represents an attractive approach for storing the electrical energy transiently produced by renewable energy sources such as sun and wind. It is well-known that the hydrogen evolution reaction (HER) is efficiently catalyzed in aqueous acid solutions by platinum group metals (PGMs) [1]. However, there is also a general consensus that high cost and limited natural abundance of PGMs are obstacles to their utilization in sustainable technologies. On the other hand, enzymes are a continuous source of inspiration for the design of catalysts. Several microorganisms efficiently produce and uptake H2 using hydrogenases (H2ases). The active sites of these enzymes contain nickel and/or iron, which are both earth-abundant first row transition metals [2]. Unfortunately, H2ases are often sensitive to oxygen and expensive to isolate hampering large-scale applications. Yet, the crystallographic characterization of NiFe and FeFe H2ases, as well as a better understanding of their biological functions provided by spectroscopy, electrochemistry, and theoretical calculations, has opened new routes for developing efficient molecular HER catalysts based on first row transition metals such as iron [3], nickel [4] and even cobalt [5]. This presentation will bring a particular focus on the reactivity of several representative biomimetic models for the H2ases. Reactivities of interest include protonation, H2 and CO binding, and redox. [1] J.K. Nørskov, T. Bligaard, A. Logadottir, J.R. Kitchin, J.G. Chen, S. Pandelov, U. Stimming, Trends in the Exchange Current for Hydrogen Evolution, J. Electrochem. Soc. 152 (2005) J23. [2] W. Lubitz, H. Ogata, O. Rudiger, E. Reijerse, Hydrogenases, Chem. Rev. 114 (2014) 4081–4148. [3] F. Gloaguen, T.B. Rauchfuss, Small molecule mimics of hydrogenases: hydrides and redox, Chem. Soc. Rev. 38 (2009) 100–108. [4] W.J. Shaw, M.L. Helm, D.L. DuBois, A modular, energy-based approach to the development of nickel containing molecular electrocatalysts for hydrogen production and oxidation, Biochim. Biophys. Acta. 1827 (2013) 1123–1139. [5] N. Queyriaux, R.T. Jane, J. Massin, V. Artero, M. Chavarot-Kerlidou, Recent developments in hydrogen evolving molecular cobalt(II)-polypyridyl catalysts, Coord. Chem. Rev. 304–305 (2015) 3–19.