Fig 1

Schematic illustration of three different PEC CO2 reduction systems with two compartment cells seperatred by a proton-exchange membrane. (a) p-type semiconductor as photocathode and dark anode, (b) n-type semiconductor as a photoanode and dark cathode, (c) n-type semiconductor as photoanode and p-type semiconductor as photocathode. Adapted from Royal Society of Chemistry publisher 23."

Fig 2

(A) Linear sweep voltammetry of Mg-doped CuFeO2 using chopped light in 0.1 mol?L?1 NaHCO3 (scan rate = 100 mV?s?1); (B) the incident photon-to-current efficiency (IPCE) obtained at ?0.4 V vs SCE in 0.1 mol?L?1 NaHCO3 in air, and measured from 780 to 340 nm. Adapted from ACS Publications publisher 29."

Fig 3

UV-Vis spectra of commercial SrTiO3 and as prepared SiTiO3?δ samples reduced in Ar at different temperatures. Adapted from Royal Society of Chemistry publisher 30."

Fig 4

Photoelectrochemical CO2 reduction with plasmonic Au/p-GaN photocathodes. (a) Time-course of gas evolution from plasmonic Au/p-GaN photocathode during controlled potential electrolysis under dark conditions. (b) Time-course of gas evolution from plasmonic Au/p-GaN photocathode during controlled potential electrolysis under plasmon excitation (λ > 495 nm). All electrolysis experiments were performed at ?1.8 VRHE in CO2-saturated 50 mmol?L?1 K2CO3 electrolyte without sacrificial reagents. Adapted from ACS Publications publisher 34."

Fig 5

(a) Schematic representation of the Cu-Co3O4 NTs fabrication; (b) schematic mechanism of PEC reduction of CO2 on Cu-Co3O4 NTs. Adapted from ACS Publications publisher 37."

Fig 6

Schematic diagram of action principle of titanium dioxide photocathode composites. Adapted from Elsevier publisher 38."

Fig 7

Schematic illustration of: (a) electron-hole recombination on a single photocatalyst; (b) Type-Ⅱ heterojunction. CB, VB, PC Ⅰ and PC Ⅱ stand for the conduction band, valence band, photocatalyst Ⅰ and photocatalyst Ⅱ, respectively. Adapted from Elsevier publisher 41."

Fig 8

Proposed mechanisms for (a) EC-CO2RR, (b) PC-CO2RR and (c) PEC-CO2RR on ZnPc/carbon nitride nanosheets. Adapted from Elsevier publisher 42."

Fig 9

Charge transfer mechanism diagram of SnO2/InP/TiO2 NTs (a) and InP/SnO2/TiO2 NTs (b). Adapted from Elsevier publisher 44."

Fig 10

ZIF-8 formation on Ti/TiO2NT. Adapted from Elsevier publisher 45."

Fig 11

dppz-Co3O4/CA concerted photoelectrocatalytic interface. Adapted from Elsevier publisher 47."

Fig 12

Schematic plots of the CO2 adsorption-enhanced Ru(bpy)2dppzCo3O4/CA interface together with its energy level diagram and the possible reaction pathways for CO2 conversion on this photocathode. Adapted from Elsevier publisher 47."

Fig 13

(a–c) SEM images of the as-prepared catalysts with Fe : Cu atomic fraction of 1.3 (panel (a)), 0.5 (panel (b)), and 0.1 (panel (c)), as determined by ICP-MS; (d) cross-sectional SEM image of the catalyst with a Fe : Cu atomic fraction of 1.3; (e, f) concentration of acetate and formate in post-reaction electrolyte (panel (e)) and corresponding Faradaic efficiencies (panel (f)). Adapted from ACS Publications publisher 51."

Fig 14

The EIS responses (Nyquist plots) of (a) TiO2 and (b) graphene-TiO2 film electrodes. Adapted from Elsevier publisher 54."

Fig 15

Photocurrent characterization (a) TiO2, RGO-TiO2 and Cu-RGO-TiO2 electrodes under illumination and (b) the CuRGO-TiO2 electrode in the dark and under illumination. Adapted from Royal Society of Chemistry publisher 55."