Directing the reactivity of metal hydrides for selective CO reduction.

A critical challenge in electrocatalytic CO reduction to renewable fuels is product selectivity. Desirable products of CO reduction require proton equivalents, but key catalytic intermediates can also be competent for direct proton reduction to H Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H and CO to generate a thermodynamic product diagram, which outlines the free energy of product formation as a function of proton activity and hydricity (∆G), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO reduction is favorable and H reduction is suppressed. We apply our diagram to inform our selection of Pt(dmpe) as a potential catalyst, because the corresponding hydride [HPt(dmpe)] has the correct hydricity to access the region where selective CO reduction is possible. We validate our choice experimentally; Pt(dmpe) is a highly selective electrocatalyst for CO reduction to formate (>90% Faradaic efficiency) at an overpotential of less than 100 mV in acetonitrile with no evidence of catalyst degradation after electrolysis. Our report of a selective catalyst for CO reduction illustrates how our thermodynamic diagrams can guide selective and efficient catalyst discovery.