Single-atom tailored atomically-precise nanoclusters for enhanced electrochemical reduction of CO2-to-CO activity

The development of facile tailoring approach to adjust the intrinsic activity and stability of atomically-precise metal nanoclusters catalysts is of great interest but remians challenging. Herein, the well-defined Au8 nanoclusters modified by single-atom sites are rationally synthesized via a co-eletropolymerization strategy, in which uniformly dispersed metal nanocluster and single-atom co-entrenched on the poly-carbazole matrix. Systematic characterization and theoretical modeling reveal that functionalizing single-atoms enable altering the electronic structures of Au8 clusters, which amplifies their electrocatalytic reduction of CO2 to CO activity by ~18.07 fold compared to isolated Au8 metal clusters. The rearrangements of the electronic structure not only strengthen the adsorption of the key intermediates *COOH, but also establish a favorable reaction pathway for the CO2 reduction reaction. Moreover, this strategy fixing nanoclusters and single-atoms on cross-linked polymer networks efficiently deduce the performance deactivation caused by agglomeration during the catalytic process. This work contribute to explore the intrinsic activity and stability improvement of metal clusters.

Characterization: Single-crystal X-ray diffraction (SCXRD) was performed on a Rigaku XtaLAB Pro diffractometer using Cu Kα radiation (λ = 1.54184Å).Powder Xray diffraction (PXRD) were collected on a Riguku D / Max-2500PC X-ray diffractometer with Cu sealed tub (λ = 1.54178Å).Morphology of all samples were carried out using Zeiss Sigma 500 on a scanning electron microscopy (SEM) measurement.The Poly-(Au8-DCP@M), Poly-(Au8-DCP), Poly-Au8 and Poly-DCP@Fe were prepared by employing the CH660E B14145 electrochemical workstation.Fourier transform infrared (FT-IR) spectra were recorded on a Bruker ALPHA II FT-IR spectrometer. 1 H nuclear magnetic resonance (NMR) spectra were recorded on a Bruker DRX spectrometer operating at 400 MHz.Transmission electron microscopy (TEM) images were obtained in FEI TalosF200S.Aberration-corrected HAADF-STEM (AC HAADF-STEM) images were obtained in FEI Titan cubed Themis G2 300 STEM with aspherical aberration corrector.The produced gas was monitored by Agilent GC7820 Gas Chromatograph (N2 as gas carrier, and the columns of GC are Porapak Q and MolSieve 5A).The CO2RR reaction pathways of as-prepared catalysts were detected via in situ ATR-FTIR spectrometer (BRUKER INVENIO S).
Computational Calculation.2][3][4] The cutoff energy for the plane-wave basis set was set to 450 eV.The Brillouin zone of the surface unit cell was sampled by Monkhorst-Pack (MP) grids, with k-point mesh density of 2π × 0.04 Å -1 for structures optimizations.The convergence criterion for the electronic self-consistent iteration and force was set to 10 −5 eV and 0.01 eV/Å, respectively.The vacuum layer of 15 Å was introduced to avoid interactions between periodic images.
The free energies of adsorbates at temperature T were estimated according to the harmonic approximation, and the entropy is evaluated using the following equation: where KB is Boltzmann's constant and DOF is the number of harmonic energies (εi) used in the summation denoted as the degree of freedom, which is generally 3N, where N is the number of atoms in the adsorbates.Meanwhile, the free energies of gas phase species are corrected as: where Cp is the gas phase heat capacity as a function of temperature derived from Shomate equations and the corresponding parameters in the equations were obtained from NIST.

Supplementary
a CN: coordination numbers; b R: bond distance; c σ 2 : Debye-Waller factors; d ΔE0: the inner potential correction.R factor: goodness of fit.The obtained XAFS data was processed in Athena (version 0.9.26) for background, preedge line and post-edge line calibrations.Then Fourier transformed fitting was carried out in Artemis (version 0.9.26).The k 2 weighting, k-range of 3 -~11.5Å -1 and R range of 1 -3 Å were used for the fitting of Au foil and Sample.The four parameters, coordination number, bond length, Debye-Waller factor and E0 shift (CN, R, ΔE0) were fitted without anyone was fixed, the σ 2 was set.Supplementary Fig. 12 Wavelet transform of Poly-(Au8-DCP@Fe) and control materials.Wavelet transform of Fe K-edge EXAFS for (a) Poly-(Au8-DCP@Fe), (b) FePc and (c) Fe foil.

Table 1 .
Crystal data and structure refinements.

Table 5 .
EXAFS fitting parameters at the Au L3-edge and Fe K-edge

Table 6
Comparison of CO2RR performance of Poly-(Au8@DCP@Fe) with other representative Au nanoclusters catalysts.