Turning the FeFe hydrogenase from <i>Clostridium beijerinckii</i> into an efficient H ₂ oxidation catalyst using a redox-active matrix

Hydrogenases are Nature's sustainable and efficient catalysts for the conversion between H⁺ and H₂. The obstacles that prevented their use as H₂ oxidation catalysts in fuel cells are being removed one by one, thanks to the continuous discovery of hydrogenases that have unexpected catalytic properties, the development of new methods for their scalable production and matrices that protect them. Obtaining an efficient biohybrid electrode that is scalable and robust under a large range of experimental conditions is still challenging. The FeFe hydrogenase of <i>Clostridium beijerinckii</i> is a very active catalyst of H₂ evolution and can be handled under O₂, and its production can potentially be scaled up. However, it was believed that it cannot be used for H₂ oxidation, as it is easily oxidized to an O₂-stable but inactive state. Here, we show that when the enzyme is embedded into a redox-active film whose reduction potential is finely tuned to the equilibrium potential of the H⁺/H₂ couple, the potential that the enzyme experiences can be buffered in a sharp window that is actually compatible with enzyme-catalyzed H₂ oxidation and prevents anaerobic inactivation. This leads us to provide the demonstration of an FeFe hydrogenase-based system that can be used for H₂ oxidation and that can be repeatedly exposed to O₂ during and between operational cycles.