Grazing incidence X-Ray diffraction: identifying the dominant facet in copper foams that electrocatalyze the reduction of carbon dioxide to formate

Copper foams have been shown to electrocatalyze the carbon dioxide reduction reaction (CO2RR) to formate (HCOO-) with significant faradaic efficiency (FE) at low overpotentials. Unlike the CO2RR electrocatalyzed at copper foils, the CO2RR electrocatalyzed at porous copper foams selects for HCOO- essentially to the exclusion of hydrocarbon products. Formate is an environmentally friendly organic acid with many applications such as food preservation, textile processing, de-icing, and fuel in fuel cells. Thus, HCOO- is an attractive product from the CO2RR if it is produced at an overpotential lower than that at other electrocatalysts. In this study, grazing incidence X-ray diffraction (GIXRD) was used to identify the dominant surface facet of porous copper foams that accounts for its selectivity for HCOO- during the CO2RR. Included are data from the CO2RR at different temperatures using copper foams as the electrocatalyst. Under optimal reaction conditions at 2 degrees C, the FE for converting CO2 to HCOO- at Cu foams approaches 50% while the FE for hydrogen gas (H-2) falls below 40%, a significant departure from that obtained at polycrystalline Cu foils. Computational studies by others have proposed (200) and (111) facets of Cu foils thermodynamically favour methane and other hydrocarbons, CO, HCOO- from the CO2RR. Results from the GIXRD studies indicate Cu foams are dominated by the (111) facet, which accounts for the selectivity of Cu foams toward HCOO- regardless of temperature used for the CO2RR.