Wednesday, 4 October 2017: 11:40
National Harbor 8 (Gaylord National Resort and Convention Center)
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.