Electrons from hydrogen.

The growing need for hydrogen-based fuel cells has driven research into hydrogenase (H(2)ase)-a natural enzyme that catalyses the extraction of electrons from H(2) in water under ambient conditions. Unfortunately, the exact mechanism by which H(2)ase achieves this feat has remained a matter of some controversy until now, with many mechanisms being inconsistent with experimental data. Recently, however, we have been able to produce a successful catalytic mimic of H(2)ase that replicates key aspects of it. This paper begins with an overview of the research from many groups that preceded this discovery, followed by a detailed analysis of the key points that set our unique functional model apart-that is to say a proton-like "hydride" species, a surprisingly low-valent Ni(I)Ru(I) complex and the key insight that two molecules of H(2) are required for electron extraction.