Dynamic restructuring of coordinatively unsaturated copper paddle wheel clusters drives CO2 reduction efficiently

Abstract

Coordinatively unsaturated metal sites in metal–organic frameworks (MOFs) hold promises for improving activity and selectivity of catalyst. As the building unit of many MOFs, copper paddle-wheel (CPW) is of great interest to function as activity sites for CO2 reduction due to the ability of copper cations to attract and activate CO2 molecules. However, little is known about the real structure of these active sites for their dynamic structural changes under realistic operating conditions. Here, we apply to design defect metal−organic framework HKUST-1 with coordinatively unsaturated copper paddle wheel through a facile “atomized trimesic acid” strategy, reveal its dynamic behaviour during electrochemical reconstruction and prove its superior CO2 reduction activity. Through comprehensive analysis of various in situ spectroscopy characterizations, it is demonstrated that unsaturated copper paddle wheel clusters [CU-CPWC, Cu2(HCOO)3] are finally formed during electrochemical reconstruction and act as the real active sites. Mechanistic studies based on density functional theory calculations reveal that the higher d band center in CU-CPWC compared with that in CPW accelerates the electron transport from copper atoms to CO2 molecules, which can be exploited to improve the CO2 reduction performance.

Iodide-mediated Cu catalyst restructuring during CO2electroreduction

“…11,19,20,23 The key role of Cu + in improving the selectivity towards C 2+ products has also been postulated in other high-performance Cu catalysts for CO 2 RR. 11,15,[18][19][20][31][32][33][34][35] We also mention here that while we had previously reported similar re-structuring and fragmentation in Cu 2 O cubes during reaction, 3 the re-precipitation of Cu 2 O particles when the potential was returned to OCP was not seen in those experiments (see ESI Fig. 10 † for a comparison with oxidized Cu islands).…”

Reconstruction-induced NiCu-based catalysts towards paired electrochemical refining

“…2e shows the Cu K-edge XANES spectra with electron transitions from 1s to 4p states, including the 1s → 4p z transition and the 1s→ 4p xy transition. 37,38 The higher 1s → 4p z transition intensity indicates the gradual reduction of copper species in NiCu–OH. Furthermore, the Fourier-transform extended X-ray absorption fine structure (FT-EXAFS) spectra shown in Fig.…”

Dynamic Evolution of Active Sites in Electrocatalytic CO2 Reduction Reaction: Fundamental Understanding and Recent Progress

“…Interestingly by using a doping strategy, Cu δ+ species can be stabilized on Cu catalysts in situ electrochemically reduced from sulfur‐doped Cu MOFs, which contributed to *CO intermediate coupling step and efficient production of C 2 H 4 with selectivity up to 60% in H‐type cell. [ 140 ]…”

“…Interestingly by using a doping strategy, Cu δ+ species can be stabilized on Cu catalysts in situ electrochemically reduced from sulfur-doped Cu MOFs, which contributed to *CO intermediate coupling step and efficient production of C 2 H 4 with selectivity up to 60% in H-type cell. [140] Indeed, for Cu surface with mixed Cu + and Cu 0 site, CO 2 RR selectivity can be regulated, that mixed states favor C 2 product (C 2 H 4 and ethanol), while C 1 products (CO, formate, and methane) are preferably generated on Cu + -or Cu 0 -dominated surface. [33] It was demonstrated by Chou et al that the atop-adsorbed CO (CO atop ) intermediates were obtained on Cu 1 -dominated surface, which can be further hydrogenated to methane.…”