Preparation of Copper Based Tandem Catalysts for Electrochemical Carbon Dioxide Reduction Reaction

Abstract

Electrochemical carbon dioxide reduction reaction (CO₂RR), which can use renewable electricity as the power source, is able to convert the over-accumulated CO2 in the Earth’s atmosphere into value-added chemicals and fuels and thus holds great promise to achieve carbon neutrality. Particularly, the multi-carbon (C₂₊) products of CO₂RR attract more attention as they have much higher energy content and larger economic value than the single-carbon (C₁) ones. To date, copper (Cu) is the most distinctive catalyst that can facilitate the reduction of CO₂ to various C₂₊ products with a considerable Faradaic efficiency (FE). However, the FE of C₂₊ products on current Cu-based catalysts still is too low to meet the practical applications. In this thesis, we focus on a very unique approach, designing advanced Cu-based tandem catalysts with specific facets or unconventional phases, to improve the CO₂RR performance towards C₂₊ products.

In the first part, we delicately synthesize three kinds of Ag-Cu Janus nanostructures with ¹ facets (JNS-100) for highly selective tandem electrocatalytic reduction of CO₂ to multi-carbon products. Through controlling the surfactant and reduction kinetics of Cu precursor, we realize the confined growth of Cu with {100} facets on one of the six equal faces of Ag nanocubes. Compared with Cu nanocubes, Ag₆₅-Cu₃₅ JNS-100 demonstrate much superior selectivity for both ethylene and multi-carbon products in CO₂RR at less negative potentials. Density functional theory calculations reveal that the compensating electronic structure and carbon monoxide spillover in Ag₆₅-Cu₃₅ JNS-100 contribute to the enhanced CO₂RR performance.

In the second part, via good dispersion of the fcc-2H-fcc Au nanorods (NRs) and controlling the concentration of Cu precursors, we synthesize the fcc-2H-fcc Au-Cu co-axial heteronanostructures (CAHs), with the Cu domain mainly growing on the side direction of Au NRs. Importantly, the Cu domain of the Au-Cu CAHs has the unconventional 2H phase. The fcc-2H-fcc Au-Cu CAHs show a great CO₂RR performance, achieving the selectivity towards C₂H₄ and C₂₊ products of 50.5% and 75.7% at -1.1 V (vs reversible hydrogen electrode (RHE)) in H-type cell, respectively. This value is much higher than that (43.6%, 65.7%) of the commercially fcc Cu nanoparticles, respectively. We believe the exposed Au domain and the unconventional 2H phase in the Cu domain both contribute to this great CO₂RR performance.

In the third part, we report the site-selective growth of Cu on fcc-2H-fcc Au NRs, obtaining the fcc-2H-fcc Au-Cu Janus nanostructures (JNSs), which break the symmetric growth mode of Cu on Au. In terms of CO₂RR performance, the fcc-2H-fcc Au-Cu JNSs exhibit excellent performance in both H-type and flow cells, with FE of 55.5% and 84.3% for ethylene and multi-carbon products, respectively. In-situ experimental results and theoretical calculations reveal the co-exposure of 2H-Au and 2H-Cu domains in Au-Cu JNSs diversifies the CO* adsorption configurations and promotes the CO* spillover and subsequent C-C coupling towards ethylene generation with reduced energy barriers.

Date of Award	7 Aug 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Zhanxi FAN (Supervisor)