Fig 1

Overview of the possible reaction pathways for CO2RR towards different products. Black spheres, carbon; white spheres, hydrogen; red spheres, oxygen; blue spheres, catalyst. The orange arrows indicate proton or electron transfer 84. Adapted from Springer Nature 84."

Fig 2

Schematic illustration of the tandem mechanism towards CO2RR on Cu/M (M = Au, Ag, Zn, etc.) bimetallic catalysts."

Fig 3

(a) Top view of the calculation model (orange: Cu atoms; blue: top layer Ag or Au atoms; light blue: bottom layer Ag or Au atoms), the numbers represent the position of the binding sites; (b) binding energy for CO on Ag-Cu surface (blue) and Au-Cu surface (orange), hollow bullets indicate the sites nonadjacent to Cu surface; (c) kinetics and free energy diagrams of all possible pathways for the reduction of CO to C1 products on the Ag-Cu surface; (d, e) studies of CO adsorption on Cu, bare Ag and Ag-Cu thin films by Operando ATR-SEIRAS 102. Adapted from Springer Nature 102."

Fig 4

(a) Mechanism of electrochemical CO2RR to C2H5OH over CuxZn 111; (b) scheme of the Cu-Ag tandem catalysts for high-rate electrochemical CO2RR and C2+ products formation; (c) partial current density towards C2+ products on Cu500Ag1000, Cu500, and Ag1000 catalysts 117. Adapted from American Chemical Society 111 and Elsevier 117, respectively."

Fig 5

(a) CO2 reduction and CO production rates as a function of the potential; (b) reduction rates of CO2 to C1 and C2+ products on Cu, Au, and Au/Cu electrodes 125; (c) Ag/Cu interface for relay electrochemical CO2RR to C2H4 126; (d) FE of C2H4 over different Ag/Cu catalysts at ?1.1 V vs. RHE; (e) XPS spectra of different Ag/Cu catalysts 127; (f) schematic diagram of the cascade process of CO2 → CO → C2+ on the tandem electrode of the layered structure 133; (g) eelectrochemical CO2RR on oxide-derived Ag, Cu, Cu on Ag, and Ag on Cu foam catalysts. Black arrows indicate mass transport of CO2 from the solution bulk; grey arrows indicate mass transport CO; red arrows indicate electrochemical reaction 134; (h) schematic illustration of electrochemical CO2RR over Cu-Ag tandem catalysts 139; (i) schematic illustration of a plausible CO2RR mechanism on Ag65-Cu35 JNS-100 140. Adapted from Springer Nature 125, American Chemical Society 126, 127, 139, Elsevier 133 and John Wiley and Sons 134, 140, respectively."

Fig 6

(a) Schematic diagram of selective growth process of Au NBP-Cu heterojunction; (b) optimal FE of C2 over different catalysts 142; (c–h) HAADF-STEM images of (c) Au1Ag1Cu1 NSs, (d) Au1Ag1Cu5 NSs, (e) Au1Ag2Cu1 NSs, (f) Au1Ag2Cu5 NSs, (g) Au1Ag3Cu1 NSs, (h) Au1Ag3Cu5 NSs, and corresponding EDX elemental maps of Au (blue), Ag (green), and Cu (pink); (i) FE of the CO2RR products over Au1Ag1Cu5 NSs at a potential range from ?0.7 to ?1.3 V vs. RHE, Orange, H2; Green, CO; Purple, HCOOH; Yellow, C2H5OH; Blue, CH3COOH; (j) schematic illustration of the tandem mechanism for electrochemical CO2RR on asymmetric AuAgCu NSs 143. Adapted from John Wiley and Sons 142 and Springer Nature 143, respectively."

Fig 7

(a) EDS elemental mappings images for Cu@Ag-2; (b) FE of C2H4 over different Cu@Ag structures; (c) schematic illustration of tandem catalysis for electrochemical CO2RR on Cu/Ag core-shell structure 147; (d) schematic illustration of tandem catalysis for electrochemical CO2RR in the cavity of Au@Cu2O; (e) FE of different products over different catalysts under a range of potentials 148. Adapted from John Wiley and Sons 147 and Royal Society of Chemistry 148, respectively."

Fig 8

(a) Illustration of the preparation of Cu(111)@Cu-THQ via electro-reduction; (b) the energy barriers for CO2RR to *CO and *CHO intermediates. Red line indicates on CuO4 sites and blue line indicates on Cu(111) sites; (c) corresponding energy barriers for CORR to C2H4 over pure Cu(111) lattice facets on Cu(111)@Cu-THQ 160; (d) schematic illustration of the preparation of PTF (Ni)/Cu with well-dispersed Cu sites from Ni-TPPCN; (e) FE of C2H4 and CH4 over PTF (Ni)/Cu and PTF/Cu catalysts at a range of potentials; (f) free energies for the formation of CH4 and C2H4 of the rate-determined step at U = 0 V 161. Adapted from Royal Society of Chemistry 160 and John Wiley and Sons 161, respectively."

Fig 9

(a) The formation rate for C2H4 as a function of time under different feeding modes; (b) schematic illustration of tandem catalysis for electrochemical CO2RR on CuOx-NiNC catalyst. Grey, C; Blue, N; Yellow, Ni 177; (c) schematic illustration of Cu particles/N rich C formation during calcination; (d) FE of different products and current density over Cu30/N-CNF, Cu50/N-CNF, and Cu50/CNF catalysts under a range of potentials 178; (e) the mechanism for the production of CO on Cu-S1N3/Cux via electrochemical CO2RR, Orange, Cu; Yellow, S; Blue, N; Red, O; Gray, C; light blue, H 180. Adapted from Springer Nature 177, Royal Society of Chemistry 178 and John Wiley and Sons 180, respectively."

Fig 10

(a) HR-TEM images of Cu0@PIL@CuI-5. 5 refers to the molar percentage of CuCl to Cu NPs for the synthesis. Yellow, Cu2O; Orange, Cu; (b) CO2RR performance of Cu0@PIL@CuI-5 under different cathodic potentials; (c, d) energy diagrams of C－C coupling on Cu0-111 and Cu0-111-PIL, respectively 184. Adapted from John Wiley and Sons 184."

Table 1

Summary of some recently reported Cu-based tandem catalysts for electrochemical CO2RR."