Directing the Reactivity of Metal Hydrides for Selective CO2 Reduction

A critical challenge in electrocatalytic CO 2 reduction to renewable fuels is product selectivity. Desirable CO 2 reduction products require proton equivalents, but key catalytic intermediates in CO 2 reduction can also be competent for direct proton reduction to H 2 . Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO 2 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 2 to generate a modified Pourbaix diagram which outlines product favorability as a function of pro-ton activity and hydricity (ΔG H- ), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO2 reduction is favorable and H+ reduction is suppressed. We apply our diagram to inform our selection of [Pt(dmpe) 2 ](PF 6 ) 2 as a potential catalyst because the corresponding hydride [HPt(dmpe) 2 ]+ has the correct hydricity to access the region where selective CO2 reduction is possible. We validate our choice experimentally; [Pt(dmpe) 2 ](PF6) 2 is a highly selective electrocatalyst for CO 2 reduction to formate (>90 % Faradaic efficiency) at an overpotential of less than 100 mV with no evidence of catalyst degradation after electrolysis. Our report of a new selective catalyst for CO 2 reduction illustrates how our modified Pourbaix diagrams can guide selective and efficient catalyst discovery.