SusChEM: A Mechanistic Approach to Understanding and Lowering the Overpotential for CO2 Reduction to C1 Organic Products

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The NSF Chemical Catalysis Program supports the efforts of Professor Andrew B. Bocarsly of Princeton University to investigate the mechanisms of carbon dioxide (CO2) reduction to one carbon (C1) organic products: formic acid, formaldedhyde or methanol. In the case of methanol, a 6-electron, 6-proton reaction is required which can be undertaken using either a one-electron redox mediator or in some cases can be observed to occur via a direct CO2-surface interaction. In all cases, a complex reaction mechanism is implicated. The research group examines the rate limiting step(s) associated with the formation of formate, one of the major reaction products. Heterogeneous CO2 reduction at post-transition metal oxide interfaces, interface-free CO2 reduction using transition metal based molecular systems, and cyanogel systems for CO2 electroreduction are under study. The first two topics explore the critical question of the role of a reactive surface in the reaction pathway. To consider this question under kinetically limiting conditions leading to formate formation, the team examines anodized post transition metal electrodes. These materials are catalytic in the absence of an additional dissolved catalyst, allowing the research group to look specifically at the range of heterogeneous processes occurring directly at the electrode interface during CO2 reduction. The study is organized using periodic trends, with zinc, cadmium, indium, bismuth and lead selected as key systems. The second study attacks the problem from the opposite direction. In this study, aromatic amine catalysts are used to carry-out the reduction of CO2 in the absence of a surface. Here, advantage is taken of the photoexcited ruthenium(bipyridyl) systems, charge transfer quenched by an aromatic amine to generate CO2 reduction absent an electrode interface. The team also explores manganese complexes containing bisphosphinine (L2) ligands, in this regard. The final study uses cyanogel chemistry to both generate alloy materials that will facilitate the electrode-based studies, and to produce novel electrolytes that are known to have a high CO2 capacity. Understanding CO2 activation is a critical chemical challenge as it contributes to the development of new fuel resources and as well as potentially lowering greenhouse gases in the environment. In addition to its pivotal role in the education of next generation electrochemical researchers, who are key to an alternate energy future, this program impacts K-12 education by providing an excellent tool for teaching both students and teachers fundamental chemical concepts using the currently topical problem of greenhouse gas control as a motivating principle. Another important aspect of the proposed program is its close affiliation with an aggressive startup company that is focused on taking this research out of the laboratory and into the real world. Demonstration scale systems that will convert CO2 into commercial chemicals are planned.