An investigation on Cu-based amorphous binary alloy for efficient reduction of CO2 into useful fuels

Abstract

Electrocatalytic conversion of CO2 to useful fuels has potential advantages as a method to use CO2 as a chemical feedstock in terms of using water as a proton source at ambient condition and being easily combined with renewable energy. Thus far, electrochemical conversion of CO2 into useful fuels (formate, carbon monoxide, methanol and so on) has been successfully demonstrated, however, the production of C4 or longer hydrocarbons as a major product has never been achieved. Thus, our group focused on developing a new platform of catalysts which could lead to efficient production of long chain hydrocarbons beyond currently available C1, C2 and C3 chemicals. In this research, we adopted amorphous Cu-Ti as new CO2 reduction electrode to enhance activity for the synthesis of long chain hydrocarbons. At first, to understand the effect of atomic concentration, CO2 reduction reaction (CO2RR) properties of amorphous Cu-Ti alloys with different compositions (Cu40Ti60, Cu50Ti50, Cu60Ti40) were evaluated using cyclic voltammetry (CV). Amorphous Cu40Ti60 exhibited the best catalytic performance and required the least overpotential to reach partial current density of 1 mA cm-2 for CO2 reduction. The outstanding property was explained by stronger binding affinity of the electrode to carbon oxygenates, as shown by CO2-TPD. These observations indicate that Ti is responsible for increasing the bond strength between electrode surface and reaction intermediates. Next, we found that amorphous Cu40Ti60 electrode has superior catalytic activity for butanol formation. Product analysis after bulk electrolysis by gas chromatography (GC) and nuclear magnetic resonance (NMR) confirmed the production of n-butanol, acetaldehyde, methyl formate, CO, H2 and so on. This was the first to report C4 product (n-butanol) with high Faradaic efficiency (25%) from the reduction of CO2. This result implies that amorphous nature of alloy induced strong interaction with carbon oxygenates and facilitated C-C bond formation of adsorbate. Moreover, potential dependent product analysis was conducted in order to construct the reaction mechanism from CO2 to n-butanol. As a result, it was suggested that butanol was produced by condensation of two C2 intermediates, excluding possibility of chain addition to create C3 intermediate. In this study, we successfully produced C4 products from CO2RR by using amorphous Cu40Ti60 alloy as a working electrode. From this result, we could provide valuable insights for developing efficient CO2 conversion pathway for long chain hydrocarbons using C2 building blocks. It was achieved by introducing amorphous binary alloys which were capable of controlling atomic composition and its arrangement.