A Comparison of Aqueous CO2 Reduction on Ni-Ga Thin Films and Nanoparticles

Wednesday, 4 October 2017: 11:40
National Harbor 8 (Gaylord National Resort and Convention Center)
S. A. Francis, A. T. Chu (Princeton University), D. A. Torelli, J. C. Crompton (California Institute of Technology, Joint Center for Artificial Photosynthesis), N. S. Lewis (California Institute of Technology), and A. B. Bocarsly (Princeton University)
It was recently reported that thin films of nickel-gallium, prepared simply by drop-casting aqueous salt solutions onto graphite plates, were active for carbon dioxide reduction in aqueous carbonate electrolytes acidified to pH 6.8 with 1 atm CO2. The Ni-Ga thin films produce mixtures of methane, ethylene and ethane at potentials as anodic as -0.48V vs RHE, representing some of the lowest onset potentials for C2-product formation reported to date. While polycrystalline Cu also produces CH4 and C2H4, the onset potential for these products on Ni-Ga films is several hundred millivolts more positive. However, the current densities on Ni-Ga are ~ 3 orders of magnitude lower than Cu. One strategy to improve the current densities is the use of nanostructured Ni-Ga catalysts. Thus, we present a novel synthesis of Ni-Ga nanoparticles for the purpose of probing their carbon dioxide reduction behavior. Micrometer sized clusters of Ni3Ga nanoparticles (~8-13 nm in diameter) were synthesized from the reflux of Ni(COD)2 and Ga(acac)3 salts in 1-octadecene solvent at 310°C (COD = cyclooctadiene, acac = acetylacetonate). The nanoparticles were supported on carbon black (Vulcan XC-72) and fabricated onto a glassy carbon electrode with ionomer solution. Interestingly, in aqueous K2SO4 electrolyte saturated with 1 atm CO2 (pH 4.38), the Ni-Ga nanoparticles reduced CO2 to formic acid with Faradaic efficiencies as high as 36% at -0.92 V vs RHE. This contrasting activity to Ni-Ga thin films is discussed with an emphasis on the effect of composition, surface structure, and support of the catalyst.