Stability of template based porous Ag catalysts for electrochemical CO2 reduction

Abstract

As CO2 concentrations continue to rise, effectively converting CO2 is essential. Electrochemical CO2 reduction can use renewable energy sources and close the carbon cycle. Transition metals can electrochemically reduce CO2 to several products. Ag is able to convert CO2 to CO, a great starting product for many industrial processes, including fuels, drugs, and other products. High current densities (>200 mA/cm2) are needed to make this technique viable in industry. In this project, porous catalysts have been used to increase current densities because of their high surface area. Furthermore, research has shown that using the flow cell could increase the current density further, while also being scalable and tackling diffusion limitation problems. Porous Ag was deposited on carbon cloth by lectrodeposition of AgNO3 on PMMA spheres. These spheres were later removed leaving the inverse porous Ag system. The porous system using PMMA was adjusted and a gas diffusion electrode was created. This GDE was tested in both types of cells for comparison. SEM shows that an inverse porous system was created, while XRD showed the presence of crystalline Ag. The flow cell increased the JCO by a factor of 5 for a 0.5 mg/cm2 loading and a factor of 7.6 for a 2.2 mg/cm2 loading (at around -1V vs RHE). Furthermore, the faradaic efficiencies increase in H2 selectivity over time while CO selectivity decreases due to Pt deposition on the cathode. This was solved by replacing the Pt anode with IrO2 which majorly increased faradaic efficiencies that remained stable for over 10 hours of catalysis. The porous system does indicate change after performing catalysis for short periods while the double layer capacitance shows insignificant change during these short periods, further research is needed to elaborate on this. The system is stable for over 10 hours of catalysis and adjusting the PMMA template Ag system on a GDE was a great step in achieving increased current densities.