The electrochemical reduction of carbon dioxide with renewable electrical energy sources, or by direct photoelectrocatalytic reduction, could provide a source of chemical feedstocks and high value chemicals of the future. Fundamental to photoelectrocatalytic reduction processes are electrochemical pathways. Past research on electrochemical reduction of CO2 showed low efficiency but demonstrated some success at forming hydrocarbons and C-C bonds. This research made clear that the electrochemical reduction mechanisms are complex and only sketchily understood.
Although the mechanism of CO2 reduction to high value products and fuels is uncertain, it is apparent that it requires a balance between CO adsorption, H availability, and intermediates that facilitate C-C bond coupling. Thus, catalyst selection and properties are factors, and the PI Robert Savinell of Case Western Reserve University proposes preliminary experiments on model surfaces of selected metals and composite metals that would provide evidence that tailoring electrocatalysts for CO2 reduction is a feasible approach.
The activity of an electrocatalyst towards electrochemical reduction of CO2 cannot be measured through comparative voltammetry alone. Consequently, the interpretation of electrochemical data by itself can be ambiguous and misleading. Therefore, electrochemical CO2 reduction must be combined with direct product analysis. PI Savinell proposes to use a new approach, Differential Electrochemical Mass Spectrometry, for the capture and analysis of the volatile products evolving from an electrode surface as a function of potential. The current is recorded simultaneously with m/e signals so product efficiencies and selectivity can be estimated, thus providing detailed information leading to mechanistic understanding of the reactions. These experiments and the preparation of the electrocatalysts are a challenge to develop and require a focused effort, which is the basis of this EAGER award. The proposed research is designed to show that the electrocatalytic approaches and methodologies proposed are feasible and can have a major impact in understanding of electrochemical reduction of carbon dioxide.
The preliminary data obtained from this research will provide the foundation of the experimental research program for the PhD dissertation studies of a chemical engineering/materials science graduate student. In addition, undergraduate students participating in this project will address experimental cell design and DEMS calibration. This EAGER project is likely to be helpful to attracting these undergraduate students to pursue graduate study because of their direct involvement in exciting experiments and socially relevant science.
This one year EAGER project was to develop preliminary data to support a comprehensive study of Electrochemical Reduction of Carbon Dioxide. The motivation for the research is the predicted doubling of energy consumption in the next 50 years. Since fossil fuels, including natural gas, are expected to satisfy much of this demand, the direct use of CO2 with renewable energy sources to produce high value chemicals such as alkanes, olefins, and other reduced hydrocarbon products becomes an attractive option. The primary purpose of this research is to address the fundamental electrocatalysis and reaction mechanisms for reducing carbon dioxide gas. The results of this one-year project are the following: (a.) Measurements of CO2 electrochemical reduction at interesting polycrystalline surfaces of Pt and Au were made and found to be similar to data as reported in the literature. There was an increase reduction reaction with CO2 relative to baseline hydrogen evolution at Au, and a lower reduction current with CO2 relative to baseline hydrogen evolution at Pt. The latter is due to the poisoning of Pt by CO intermediate. The reaction under CO2 with copper is not as straightforward, but seems to be consistent with the literature in that a peak in the reduction current is observed. These experiments clearly indicate the necessity of a DEMS (differential electrochemical mass spectroscopy) experiment in order to identify the activity and selectivity towards desired products, and distinguishing from side reactions on an electrocatalyst during CO2 reduction measurements. (b.) We demonstrated the ability of forming UPD layers of copper on macro-size substrates and on nano-particle substrates of Pt and Au, and confirmed their stability using stripping voltammetry and xps studies. This opens a way to tailor copper catalyst surfaces for detailed mechanistic studies of CO2 reduction. (c.) A laboratory DEMS system was made operational and tested with a Pt/C electrode and found to be responsive and reproducible. This instrumentation will allow simultaneous measurement of current and volatile products to determine potential dependent selectivity of electrocatalyst for CO2 reduction. (d.) Baseline performance of a hydrogen pump PEM fuel cell that operates under dry conditions and elevated temperature was measured. This cell and electrolyte will be important to exploring CO2 electrochemical reduction at elevated temperatures and under dry conditions. The grant supported a full-time chemical engineering/materials science graduate student, who completed her MS thesis on this project. The title of her thesis is " Study of copper underpotential deposition on Pt and Au disk electrode and electrocatalyst". A draft manuscript for publication on this work has been prepared. This project also provided the foundation for a PhD dissertation research of a full-time graduate student, who is supported by a scholarship from the Mexican government. The project also initiated collaboration with a colleague at the Massachusetts Institute of Technology.