Oxygen-tolerant proton reduction catalysis: much O-2 about nothing?

Proton reduction catalysts are an integral component of artificial photosynthetic systems for the production of H-2. This perspective covers such catalysts with respect to their tolerance towards the potential catalyst inhibitor O-2. O-2 is abundant in our atmosphere and generated as a by-product during the water splitting process, therefore maintaining proton reduction activity in the presence of O-2 is important for the widespread production of H-2. This perspective article summarises viable strategies for avoiding the adverse effects of aerobic environments to encourage their adoption and improvement in future research. H-2-evolving enzymatic systems, molecular synthetic catalysts and catalytic surfaces are discussed with respect to their interaction with O-2 and analytical techniques through which O-2-tolerant catalysts can be studied are described.