First part of my research was to understand the facet-dependence, specifically (100) face of Cu nanomaterials in the selectivity of ethylene formation for CO2/CO reduction. Cu nanowires (NWs), embedded by five (100) facets on the side walls, were considered as a strong candidate to improve selectivity toward ethylene. Cu NWs with two different ratios were synthesized. I studied electrochemical reduction of both CO2 and CO in 0.1M KHCO3 solution on these Cu NWs. Both Cu NWs proved to be highly selective toward ethylene formation. However, Cu NWs exhibit a much higher activity in CO reduction other than CO2 reduction. In particular, 50nm NWs show the maximum Faradaic efficiency (FE) (up to 32.4% at −1.1 V vs reversible hydrogen electrode, RHE) and 4.25A/g mass activity of C2H4 in CO reduction. DFT calculations suggest that the strong selectivity of Cu NWs/NCs mainly stem from the (100) facets. Higher CO coverage and hydrogenated CO adsorbates effectively lower C-C coupling energy. In the second part, three ways were proposed in order to improve the activity of Cu NWs in CO2 reduction. This includes: 1) Introduction of Au NWs as an alternative CO source, 2) Introduction of Propylene Carbonate (PC) to increase CO2 solubility, 3) Acid treatment to roughen Cu NW surfaces. All three ways were found to be able to boost CO2 activity. However, product spectrum was altered and CO turned out to be the main product instead of C2H4. In the third part, de-alloying method was applied as an effective way to enhance activity in CO2 reduction. Cu48Pd52 nanoparticles (NPs) were synthesized as a precursor of de-alloying process. After nitric acid treatment, most of Cu was removed from the alloy NPs, creating etched CuPd NPs (E-CuPd-11). E-CuPd-11 NPs exhibit an onset potential of -0.05V, which is only 50mV higher than thermodynamic value. Within the range of -0.7V to -0.9V, faradic efficiency of formate and CO adds up to 100%, indicating a complete suppression over hydrogen evolution reaction. Maximum mass activity of 20.11mA/g was found on -1.1V. This finding sheds light on future design of highly active catalysts on CO2 reduction.
Zhang, Hongyi,
"Design of Selective and Active Nanocatalysts for CO2/CO Reduction"
(2017).
Chemistry Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.7301/Z0FX77X2
