(509h) Bridging Understanding between Electrochemical and Thermal Processes for CO2 conversion

Conventional thermal CO₂ conversion requires high temperature (400- 750^oF) and high pressure (10- 40 bar) whereas electrochemical processes face large overpotentials. Slow electron transfer kinetics that yield unsatisfactory selectivity and catalyst deactivation are both in common. To overcome these challenges, novel catalyst discovery has been a primary research focus for both thermal and electro-catalysis. However, similar catalysts result in different product distributions under the same reaction as temperature, pressure and applied potential. Although the catalysts share similar chemical properties, preparation method, material form (powder vs electrode), the differences in the reaction environment make direct comparison in reaction mechanism and energetics very difficult. This study investigates the CO₂ reduction reaction in thermal and electrochemical media utilizing the same catalyst, i.e. Cu-based bimetallic catalysts on modified supports. The catalyst is tested in a fixed-bed reactor and in a membrane-electrode-assembly (MEA)-type electrolyzer by utilizing powder and gas diffusion electrodes (GDE), respectively. This direct comparison allows for unprecedented insights to be gained as the CO₂ conversion product distribution are investigated under two different approaches (i.e., temperature and pressure for thermal, the cell voltage for electrochemical) using the exact same catalyst. As a reference, commercial CuZn on Al₂O₃ was tested first and resulted high selectivity towards CO (50%) in the electrochemical CO₂ reduction while yielded in 85% methanol selectivity at 200^oC in a fixed-bed reactor. Comparison extended to in-house synthesized Cu-based bimetallic catalysts including Cu-In (Figure 1), and Cu-Ag catalysts. Complete understanding of the effect of temperature versus voltage on the product formation rates and on the catalyst dynamics in two media have been investigated by in situ studies (including in-situ DRIFTS, environmental-TEM, and XPS) and as well as by spent catalyst characterization.