In situ copper faceting enables efficient CO2/CO electrolysis

The copper (Cu)-catalyzed electrochemical CO2 reduction provides a route for the synthesis of multicarbon (C2+) products. However, the thermodynamically favorable Cu surface (i.e. Cu(111)) energetically favors single-carbon production, leading to low energy efficiency and low production rates for C2+ products. Here we introduce in situ copper faceting from electrochemical reduction to enable preferential exposure of Cu(100) facets. During the precatalyst evolution, a phosphate ligand slows the reduction of Cu and assists the generation and co-adsorption of CO and hydroxide ions, steering the surface reconstruction to Cu (100). The resulting Cu catalyst enables current densities of > 500 mA cm−2 and Faradaic efficiencies of >83% towards C2+ products from both CO2 reduction and CO reduction. When run at 500 mA cm−2 for 150 hours, the catalyst maintains a 37% full-cell energy efficiency and a 95% single-pass carbon efficiency throughout.


Supplementary
95% not available †This value is calculated based on the XRD pattern of Cu-CO2 catalyst (63s) reported in Supplementary Fig. 18a of Ref. 3 .10 | EXAFS fitting results for CuP0.4 during CO2R over the course of 30-min reduction time.Data range k = 3-11 Å -1 , amplitude reduction factor  0 2 = 0.8.We referred to a previous work 22 for the fitting principle.Briefly, the coordination numbers (N) were fixed to the expected values listed in cif files of Cu2(OH)3Cl and Cu foil, bond distances (R) and the Debye Waller factor (σ 2 ) for each cell were determined.Then the Debye Waller values were fixed to calculate N. Numbers marked with * are fixed according to the information in the cif file.Bolded and unbolded scatter paths are from Cu2(OH)3Cl and metallic Cu, respectively.

Fig. |
Fig. | Model structure of Cu(100) and Cu(111).Fig. | E avg of *CO and OH − on Cu(111) and Cu(100) at various coverage.Fig. | The adsorption structure of Cu(100) with different *CO coverage.Fig. | The adsorption structure of Cu(100) with different OH − coverage.Fig. | The adsorption structure of Cu(111) with different *CO coverage.Fig. | The adsorption structure of Cu(111) with different OH − coverage.Fig. | The work function of Cu(100) with different OHˉ coverage.Fig. | PDOS of Cu atom on Cu(111) and Cu(100) with different*CO and OH − coverage.Fig. | P/Cu atomic ratio in the precatalysts measured by EDX and ICP-OES.Fig. | SEM images of precatalysts.Fig. | Characterization of the CuP0 precatalyst.Fig. | Characterization of the CuP0.4 precatalyst.Fig. | The Cu K-edge XANES derivative spectra of Cu precatalyst and standards.Fig. | High-resolution XPS spectra of CuP0.4 and CuP0 precatalysts.Fig. | XRD patterns for precatalysts and corresponding derived Cu catalysts.Fig. | FTIR spectra for precatalysts.Fig. | Possible geometry structures of phosphate-copper complexes.Fig. | High-resolution XPS spectra of the precatalyst and derived Cu-based catalysts.Fig. | High-resolution and dark-field TEM images for Cu(100)-rich catalyst.Fig. | Dark-field microscope images and SEM images of CuP0 precatalyst and derived Cu catalysts.Fig. | High-resolution and dark-field TEM images for Cu catalyst.Fig. | CV curves for Cu(100)-rich and Cu catalysts and the corresponding facet ratio.Fig. | A photograph of the in-situ Raman setup.Fig. | Raman spectra of CuP0 and CuP0.4 precatalysts.Fig. | Time-dependent in-situ ATR-SEIRAS spectra for CuP0.4 and CuP0 precatalysts.Fig. | Time-dependent Cu K-edge XAFS spectra before normalized of CuP0.4 precatalys.Fig. | Time-dependent Cu K-edge XANES and EXAFS of control CuP0 precatalyst.Fig. | Performance comparison for the Cu-based catalysts tested in MEA-CO2R systems.Fig. | CV curves for Cu and Cu(100)-rich catalyst and ECSA-normalized jC2+.Fig. | In-situ Raman spectra for Cu(100)-rich catalyst derived from CO2R and COR.Fig. | Performance comparison for the Cu-based catalysts tested in MEA-COR systems.

4 |SupplementaryFig. 8 |
The top and side views of adsorption structure of Cu(100) with different OH − coverage.The projected density of state (PDOS) of top Cu atom on Cu(111) with different (a) *CO coverage and (b) OH − coverage; PDOS of top Cu atom on Cu(100) with different (c) *CO coverage and (d) OH − coverage.Supplementary Fig. 13 | a, The Cu K-edge XANES derivative spectra of Cu precatalyst and standards (Cu foil, Cu2O, CuO, and Cu(OH)2), in which the blueshift of XANES derivative maximum in the precatalyst is due to the ligand effect from phosphate doping.b,c, Wavelet transform of the Cu K-edge EXAFS of (b) precatalyst and (c) CuO standard.Supplementary Fig. 24 | Raman spectra of CuP0 and CuP0.4 precatalysts in 0.1 M KHCO3 electrolyte at open circuit potential.For the CuP0 precatalyst, the lower frequency peak at 512 cm -1 was assigned to the Cu-O bond, which became widened after P-doping, likely due to the symmetric bending mode of PO4 (ν2) at 472 cm -1 .For the CuP0.4 precatalyst, P-O vibrations in phosphate anions showed the antisymmetric stretching mode (ν3) at 1019 cm -1 , the symmetric stretching mode (ν1) at 998 cm -1 , and the peak at 298 cm -1 attributable to the [PO4] species in reichenbachite and libethenite 1 .Supplementary Fig. 26 | Time-dependent Cu K-edge XAFS spectra (before normalization) of Cu precatalyst with phosphate addition, in which the edge jump of XAFS spectrum drastically decreases at the first 15 mins and then remains steady at the later stage, indicating that the catalyst is dissolved and re-deposited.The test was performed in CO2flowed 0.1 M KHCO3 electrolyte at -1.1 V vs RHE over the course of 30-min reduction time; ocp stands for open-circuit potential.Supplementary Fig. 29 | a,b, CV curves collected in N2-saturated 1.0 M KOH with scan rates from 40 mV/s to 100 mV/s for (a) Cu catalyst and (b) Cu(100)-rich catalyst.c, Correlation between the absolute current density difference and the scan rate, double-layer capacitance (Cdl) is equal to half of the linear slope.d, ECSA-normalized C2+ current densities for Cu(100)-rich catalyst and Cu catalysts.

Table 1 |
Surface energies for Cu(100) and Cu(111) facets at different coverages of CO* and OH -.Table | The dipole moment of Cu(100) and Cu(111) with different OHˉ coverage.Table | Work function of Cu(100) with 1/9 ML and 2/9 ML of OHˉ coverage.Table | The energy of 1/9 ML of OHˉ coverage on Cu(100) with/without spin polarization.Table | Calculated area proportion of Cu(100) and Cu(111) facets at different coverages of CO* and OH -from the Wulff construction analysis.Table | Atomic percentages of elements in precatalysts measured by EDX and ICP-OES.Table | Comparison of this work with a previous work that growth of Cu(100) using *CO.Table | The Cu(100)/(Cu(100)+Cu(111)) ratio of different Cu catalysts.Table | Linear combination fit analysis of CuP0.4 precatalyst at different reduction times.Table | EXAFS fitting results of CuP0.4 precatalyst at different reduction times.Table | Performance comparison for the Cu-based catalysts in MEA-CO2R systems.Table | Double-layer capacitance and ECSA for Cu and Cu(100)-rich catalysts.Table | Performance comparison for the Cu-based catalysts in MEA-COR systems.

Table 1 |
Calculated surface energies for Cu(100) and Cu(111) facets at different coverages of CO* and OH -.

Table 5 |
Calculated area proportion of Cu(100) and Cu(111) facets at different coverages of CO* and OH -from the Wulff construction analysis.

Table 6 |
Atomic percentages of different elements in precatalysts as measured by EDX and a comparison of the P/Cu atomic ratios extracted from EDX and ICP-OES.