1. Design and development of cooperative single-atom catalysts.
(i) Cu–Sn single-atom surface alloys, where isolated Sn sites with high surface densities (up to 8%) are anchored on the Cu host, have been developed. (ii) A densely populated Ni single-atom on nanoparticle catalyst via direct solid-state pyrolysis has been synthesized. A series of powerful tools have been used to reveal the atomic structure of the single atom catalysts, including atom probe tomography, x-ray absorption spectroscopy, transmission electron microscopy, etc. Afterward, the synthesized samples were subjected to electrochemical testing such as linear sweep voltammetry (LSV) and constant voltage to determine the optimal elemental composition and single atom loading for the best CO2 electroredcution activity and selectivity.
2. Mechanistic investigations of the catalyst cathodes.
The mechanistic for electrochemical CO2 conversion has been investigated by the combination of in situ Raman, electrochemical analysis (e.g. ECSA, EIS, Tafel, etc.), and density functional theory simulations. In this way, the reaction pathways and adsorbed intermediates for CO2 conversion have been further understood. A general electronic tuning effect is observed for the cooperative single-atom catalysts, which can regulate the binding strength between active sites and intermediates, and breaks the performance limits set by the scaling relationship.
3. Development, characterisation, and optimisation of CO2-based full cells
To fabricate full cells based on electrochemical CO2 conversion. Three strategies have been explored for cell-level optimisation, including the use of gas diffusion electrode (GDE), the membrane electrode assembly (MEA) design, and the development of a strong acidic system. For Cu–Sn single-atom alloys, a CO Faradaic efficiency of 98% at a tiny overpotential of 30 mV in an alkaline flow cell has been achieved. For Ni single-atom catalysts, it delivers an industrial-relevant CO current of 310 mA cm−2 at a low cell voltage of -2.3 V, corresponding to an overall ultra-high energy efficiency of 57%. Besides, a high Faradaic efficiency for formic acid and CO production has been achieved in a strong acid system based on the cation effect, which can solve the carbonate issue in near-neutral and alkaline conditions.
These findings suggest that the development of cooperative SACs is effective for tuning the property of single-atom-sites through the atomic interactions, and subsequently modulating the CO2 reduction pathways. The well-defined active sites in SACs can provide an ideal model for mechanistic studies and enable the rational construction of catalysts through a three-pronged approach, comprising operando characterisations, theoretical modelling, and catalyst assessment under industrially relevant conditions.
We have published the research results of this project through world-leading peer-reviewed journals as either gold open access or green open access (with the deposition of publications in open access repositories) articles. I have attended two conferences, including 1. 2022 Renewable Energy: Solar Fuels Gordon Research Conference, Lucca (Barga), LU, Italy, May 8 - 13, 2022, (Poster presentation). 2. CUHK-Shenzhen 2022 Long Feng Science Forum, online Zoom meeting, August 19 - 21, 2022, (Oral presentation). In all the cases, a reference to EU funding was included.
