(617fc) Trace Levels of Copper in Carbon Materials Show Significant Electrochemical CO2 Reduction Activity

Authors: 
Lum, Y., Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Lab
Ager, J. W. III, Joint Center for Artificial Photosynthesis
Bell, A. T., University of California, Berkeley
Kwon, Y., Joint Center for Artificial Photosynthesis
Clark, E. L., Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Lab
Lobaccaro, P., Joint Center for Artificial Photosynthesis
Carbon materials are frequently used as supports for electrocatalysts because they are conductive and have high surface area. However, recent studies have shown that these materials can contain significant levels of metallic impurities that can dramatically alter their electrochemical properties. Here, the electrocatalytic activity of pure graphite (PG), graphene oxide (GO), and carbon nanotubes (CNT) dispersed on glassy carbon (GC) are investigated for the electrochemical CO2 reduction reaction (CO2RR) in aqueous solution. It was observed that PG, GO, and CNT dispersed on GC all exhibit significant electrochemical activity that can be ascribed to impurities of Ni, Fe, Mn, and Cu. The level of Cu in GO can be particularly high and is the cause for the appearance of methane in the products produced over this material when it is used for the CO2RR. Washing these supports in ultrapure nitric acid is effective in removing the metal impurities and results in a reduction in the electrochemical activity of these forms of carbon. In particular, for GO, nearly all of the catalytically relevant metals can be removed. Electrochemical deposition of Cu on GO and PG supported on GC, and on GC itself, increased both the electrochemical activity of these materials and the production of methane via CO2RR. Particularly high rates of methane formation per unit of Cu mass were obtained for Cu electrodeposited on GO and PG supported on GC. We suggest that this high activity may be due to the preferential deposition of Cu onto defects present in the graphene sheets comprising these materials.