Synthesis of the H-cluster framework of iron-only hydrogenase

Fuel cells: iron is the new platinum In conventional hydrogen fuel cells the rapid interconversion of protons and electrons to hydrogen requires catalysis by expensive metals, usually platinum. In the living world enzymes catalyse this same reaction at extraordinary rates using abundant metals. Tard et al . now report the chemical synthesis of the iron–sulphur structure at the heart of the hydrogenase protein. The resulting iron–sulphur framework functions as an electrocatalyst for proton reduction, a potentially important step towards new materials to replace platinum in the anodes of fuel cells. The metal-sulphur active sites of hydrogenases catalyse hydrogen evolution or uptake at rapid rates. Understanding the structure and function of these active sites—through mechanistic studies of hydrogenases 1 , 2 , 3 , 4 , synthetic assemblies 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 and in silico models 13 , 14 , 15 —will help guide the design of new materials for hydrogen production or uptake 16 . Here we report the assembly of the iron-sulphur framework of the active site of iron-only hydrogenase (the H-cluster), and show that it functions as an electrocatalyst for proton reduction. Through linking of a di-iron subsite to a {4Fe4S} cluster, we achieve the first synthesis of a metallosulphur cluster core involved in small-molecule catalysis. In addition to advancing our understanding of the natural biological system, the availability of an active, free-standing analogue of the H-cluster may enable us to develop useful electrocatalytic materials for application in, for example, reversible hydrogen fuel cells. (Platinum is currently the preferred electrocatalyst for such applications, but is expensive, limited in availability and, in the long term, unsustainable 17 .)