Department of Chemistry, University of California, Irvine, CA 92697.
Department of Chemistry, University of California, Irvine, CA 92697
Proc Natl Acad Sci U S A. 2018 Dec 11;115(50):12686-12691. doi: 10.1073/pnas.1811396115. Epub 2018 Nov 21.
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.
电催化 CO 还原为可再生燃料的一个关键挑战是产物选择性。需要质子等价物的 CO 还原的理想产物，但关键的催化中间体也可以胜任直接质子还原为 H。了解如何在这些共享中间体处管理分歧的反应途径对于实现高选择性至关重要。质子还原为氢气和 CO 还原为甲酸盐通常都经过金属氢化物中间体。我们应用描述金属氢化物与 H 和 CO 反应性的热力学关系来生成热力学产物图，该图描绘了产物形成的自由能作为质子活度和氢性（∆G）或氢化物供体强度的函数。该图描绘了金属氢化物和质子活度的区域，其中 CO 还原是有利的，H 还原受到抑制。我们将我们的图应用于指导我们选择Pt(dmpe)作为潜在催化剂，因为相应的氢化物[HPt(dmpe)]具有正确的氢性来进入选择性 CO 还原可能发生的区域。我们通过实验验证了我们的选择；Pt(dmpe)在乙腈中是一种高度选择性的 CO 还原为甲酸盐的电催化剂（>90%的法拉第效率），在小于 100 mV 的过电势下，并且在电解后没有催化剂降解的证据。我们对选择性 CO 还原催化剂的报道说明了我们的热力学图如何指导选择性和高效催化剂的发现。
