Electrochemical reduction of carbon dioxide to produce fuels and feedstocks may represent one possible strategy for utilizing carbon dioxide that would otherwise contribute towards global warming. The use of electrical potential for making and breaking chemical bonds can allow for reductions in the temperature and pressure needed to drive reactions, enabling modular conversion of point sources of carbon dioxide. We are interested in organometallic macrocycles which can catalyze the conversion of carbon dioxide to syngas, a key chemical intermediate than can be converted into diverse hydrocarbons, alcohols, acids, and esters.

In our work, we have developed metal phthalocyanine catalysts anchored on modified carbon supports, which exhibit high turnover frequencies for reducing carbon dioxide to carbon monoxide. Our supported catalyst alleviates transport limitations that have complicated prior studies, enabling mechanistic studies that provide a molecular-level picture of how metal phthalocyanines drive the desired proton/electron transfers needed to reduce carbon dioxide. Our results indicate how the reaction can be tuned from an electron transfer mechanism to a proton-coupled electron transfer mechanism, with increased rates for the latter. We have also identified regimes in which the catalyst can operate at high ionic strength, minimizing losses due to ionic resistance.

Our results highlight the interplay of kinetics and transport in the widely observed behavior of metal phthalocyanines, as well as potential strategies for mitigating transport limitations. This may inspire concerted molecular level design of metal phthalocyanine catalysts with engineering of transport in reactors. These studies may enable design of catalysts with current densities needed for scalable electrolyzers.