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

Abstract

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 °C, the FE for converting CO₂ to HCOO⁻ at Cu foams approaches 50% while the FE for hydrogen gas (H₂) 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.