PNNL

Abstract

This tutorial review explores the different roles played by the first and second coordination spheres of transition metal catalysts for electrochemical oxidation and production of H2. Studies of the relationships between ligand structures and the thermodynamic properties of transition metal hydrides are used to develop guiding principles for understanding and controlling such features as the hydride acceptor ability of metal complexes. This approach can be generalized to understand the relative energies of all intermediates that result from M-H bond cleavage reactions. A second important tool in catalyst design is the use of pendant bases, or proton relays, incorporated into the second coordination sphere of the catalyst to control the binding and heterolytic cleavage of H2, the coupling of electron- and proton-transfer events, and the movement of protons between the metal center and solution. The combination of these two tools, thermodynamic models to control M-H bond energetics and proton relays to control proton movement, has been useful in the development of highly active catalysts for the electrochemical oxidation and production of H2. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.