| Powder XRD, Rietveld refinement | Sole crystalline product; space group: I4̅m2; a, b: 3.70(6) Å; c: 5.20(9) Å; α, β: 90°; γ: 90°; volume: 71.54(4) ų; Rwp: 2.7 %; reduced χ²: 0.07; image data were not transcribed |
|---|---|
| TEM | Polydisperse sample containing nanoparticles with sizes ranging from 50 to 200 nm; image data were not transcribed |
| HRTEM, SAED and STEM-HAADF | Consistent with the orthorhombic unit cell of CuSi₂P₃; brighter Cu-rich and darker Si-rich atomic columns with a superstructure along the [010] direction were observed; no adjacent Cu columns were detected by STEM-HAADF; image data were not transcribed |
| EELS | Homogeneous elemental distribution; the O-K signal was too low to be detected, even at the particle surface; image data were not transcribed |
| STEM-EDS and SEM-EDS | Homogeneous distribution of Cu, Si and P at the scale of one particle; STEM-EDS Cu:Si:P atomic ratio: 1:1.9:2.6; SEM-EDS Cu:Si:P atomic ratio: 1:2.1:2.7; image data were not transcribed |
| Cu K-edge XANES and EELS | Cu K-edge energy: 8980.1 eV, coincident with Cu₂O and indicating a copper oxidation state of +1; EELS average copper oxidation state: 1.3 ± 0.2; image data were not transcribed |
| Cu K-edge EXAFS | Cu-P apparent distance: 1.9 Å; image data were not transcribed |
| Cu 2p XPS and Cu LMM Auger spectroscopy | Cu 2p₃/₂ and Cu 2p₁/₂ peaks: 932.7 and 952.6 eV; no Cu²⁺ species were present at the particle surface; Cu⁺:Cu⁰ atomic ratio: 1:2; the apparent discrepancy with XAS was ascribed to partial reduction of Cu(I) in the XPS analysis chamber; image data were not transcribed |
| Si 2p XPS | Si 2p₃/₂ and Si 2p₁/₂ peaks: 100.3 and 100.9 eV, ascribed to silicon covalently bonded to phosphorus as in [SiP₄] units; signals at 101.5 and 103.3 eV correspond to SiOₓ (x < 4) species ascribed to inadvertent air exposure; image data were not transcribed |
| P 2p XPS | Broad phosphate-group signal at approximately 133.5 eV; P 2p₃/₂ and P 2p₁/₂ signals at 128.4 and 129.2 eV were assigned to a Cu-rich P environment; signals at 129.2 and 130.0 eV were assigned to a Si-rich P environment; image data were not transcribed |
| ²⁹Si MAS NMR (139.04 MHz, 20 kHz MAS, referenced to TMS) | δ = −26 ppm (single prominent peak); image data were not transcribed |
| ³¹P MAS NMR (282.3 MHz, 20 kHz MAS, referenced to H₃PO₄) | δ = −110, −150 ppm; image data were not transcribed |
| In situ Cu K-edge XANES (CO-saturated 1.0 M KOH, −0.83 V vs. RHE) | Spectra were identical before and during electrocatalysis, suggesting stability of the catalytic copper species and no oxidation-state change; image data were not transcribed |
| In situ Cu K-edge EXAFS (CO-saturated 1.0 M KOH, −0.83 V vs. RHE) | Constant apparent radial distance to near neighbours, consistent with Cu-P bonds at 1.87 Å in pristine CuSi₂P₃; Cu-Cu bonds expected for metallic Cu species were absent; image data were not transcribed |
| Post-catalysis TEM (CO reduction, −0.83 V vs. RHE) | No alteration in particle shape, size or surface crystallinity was detected; image data were not transcribed |
| In situ and post-catalysis Cu Kβ valence-to-core X-ray emission spectroscopy (CO reduction, −0.83 V vs. RHE) | No modification of the CuSi₂P₃ signal was observed; image data were not transcribed |
Anissa Ghoridi, Carlos V. M. Inocêncio, Hong Phong Duong, Ngoc-Huan Tran, Isabel Gómez-Recio, Maria Luisa Ruiz-Gonzàlez, Stephan Steinmann, Preeti Verma, Antoine Miche, Sandra Casale, Christel Gervais, Cristina Coelho Diogo, Isabelle Génois, Andrea Zitolo, Christoph Sahle, Alessandro Longo, José Maria González-Calbet, Marc Fontecave, David Portehault. “Tuning covalence for phosphorus-mediated C-C coupling in carbon monoxide electroreduction to multicarbon oxygenates.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15007881/v1
| Powder XRD, Rietveld refinement | Sole crystalline phase; space group: P2₁3; a, b: 9.66(8) Å; c: 9.66(8) Å; α, β: 90°; γ: 90°; volume: 903.67(0) ų; Rwp: 6.6 %; reduced χ²: 0.12; image data were not transcribed |
|---|---|
| TEM and SEM | Microparticles were observed; image data were not transcribed |
| Cu K-edge XANES | Cu K-edge energy: 8980.7 eV; average copper oxidation state: approximately +1.4, according to linear interpolation from Cu(0), Cu(I) and Cu(II) reference species; image data were not transcribed |
| Cu K-edge EXAFS | Cu-S apparent distance: 1.9 Å; image data were not transcribed |
| Cu 2p XPS and Cu LMM Auger spectroscopy | Cu 2p₃/₂ and Cu 2p₁/₂ peaks: 932.7 and 952.6 eV; Cu⁰:Cu⁺ atomic ratio: 1:39; Cu⁺ species: 96–98 at.%; image data were not transcribed |
| S 2p XPS | S 2p₃/₂ and S 2p₁/₂ signals at 161.5 and 162.7 eV were assigned to S(−II) bonded to copper; signals at 162.4 and 163.6 eV were assigned to S(−I) bonded to phosphorus; sulfate groups were detected with a broad signal at 164 eV, indicating surface oxidation upon air exposure; image data were not transcribed |
| P 2p XPS | No phosphate groups with oxidation state +5 were found; P 2p₃/₂ and P 2p₁/₂ peaks at 132.0 and 132.8 eV were assigned to phosphorus bonded to sulfur; image data were not transcribed |
| In situ Cu K-edge XANES (CO-saturated 1.0 M KOH, −0.83 V vs. RHE) | Cu K-edge downshifted from 8980.7 to 8979.0 eV during electrocatalysis, indicating an average copper oxidation state of +0.2 and reduction of 80 % of the initial Cu⁺ species to Cu⁰; image data were not transcribed |
| In situ and post-catalysis Cu K-edge EXAFS (CO-saturated 1.0 M KOH, −0.83 V vs. RHE) | Cu-S bonds at an apparent radial distance of 1.79 Å progressively disappeared in favour of Cu-Cu bonds at 2.16 Å; post-catalysis EXAFS indicated only Cu-O distances, mostly as Cu₂O; image data were not transcribed |
| Post-catalysis TEM and SAED (CO reduction, −0.83 V vs. RHE) | Spherical Cu nanoparticles with diameters of 50–70 nm were surrounded by an amorphous layer consistent with a copper oxide layer; image data were not transcribed |
| Cu K-edge XANES | Cu K-edge energy coincided with the 8980.1 eV value measured for Cu₂O, indicating a copper oxidation state of +1; image data were not transcribed |
|---|---|
| Cu K-edge EXAFS | Apparent distance of 1.9 Å, consistent with Cu-P bonds; image data were not transcribed |
| In situ Cu K-edge XANES and EXAFS (CO-saturated 1.0 M KOH, −0.83 V vs. RHE) | Cu⁺ species and distances from copper atoms to their near neighbours remained stable; image data were not transcribed |
| In situ Cu Kβ valence-to-core X-ray emission spectroscopy (CO reduction, −0.83 V vs. RHE) | A minor change of the Kβ₂,₅ line was observed compared with pristine CuP₂ powder; the source states that the slight variation could be ascribed to a poorer signal-to-noise ratio; image data were not transcribed |