Photocatalytic CO₂ Reduction Using Water as an Electron Donor under Visible Light Irradiation by Z-Scheme and Photoelectrochemical Systems over (CuGa)_0.5ZnS₂ in the Presence of Basic Additives

Abstract

We demonstrated photocatalytic CO2 reduction using water as an electron donor under visible light irradiation by a Z-scheme photocatalyst and a photoelectrochemical cell using bare (CuGa)0.5ZnS2 prepared by a flux method as a CO2-reducing photocatalyst. The Z-scheme system employing the bare (CuGa)0.5ZnS2 photocatalyst and RGO-(CoO x /BiVO4) as an O2-evolving photocatalyst produced CO of a CO2 reduction product accompanied by H2 and O2 in a simple suspension system without any additives under visible light irradiation and 1 atm of CO2. When a basic salt (i.e., NaHCO3, NaOH, etc.) was added into the reactant solution (H2O + CO2), the CO formation rate and the CO selectivity increased. The same effect of the basic salt was observed for sacrificial CO2 reduction using SO3 2– as an electron donor over the bare (CuGa)0.5ZnS2 photocatalyst. The selectivity for the CO formation of the Z-schematic CO2 reduction reached 10–20% in the presence of the basic salt even in an aqueous solution and without loading any cocatalysts on the (CuGa)0.5ZnS2 metal sulfide photocatalyst. It is notable that CO was obtained accompanied by reasonable O2 evolution, indicating that water was an electron donor for the CO2 reduction. Moreover, the present Z-scheme system also showed activity for solar CO2 reduction using water as an electron donor. The bare (CuGa)0.5ZnS2 powder loaded on an FTO glass was also used as a photocathode for CO2 reduction under visible light irradiation. CO and H2 were obtained on the photocathode with 20% and 80% Faradaic efficiencies at 0.1 V vs RHE, respectively.

CO2 Reduction Using Water as an Electron Donor over Heterogeneous Photocatalysts Aiming at Artificial Photosynthesis

“…39 When the fine particulate (CuGa) 0.5 ZnS 2 is applied to a Zscheme system, photocatalytic water splitting and CO 2 reduction are much enhanced (Figure 4B). 4 The Z-scheme CO 2 reduction activity strongly depends on the reactant solution conditions (Table 4, entries 5−8). Addition of a basic salt not only stabilizes but also enhances Z-scheme CO 2 reduction because of efficient supply of hydrated CO 2 to the photocatalyst surface.…”

“…The bare (CuGa) 0.5 ZnS 2 photocathode reduces CO 2 to CO with high stability under visible light with application of an external bias (Figure 5B). 4 Faradaic efficiencies for CO and H 2 formation are 20% and 80%, respectively, being almost 100% of total Faradaic efficiency. It is stressed that high CO formation is observed even without cocatalyst and surface modification on the photocathode.…”

A review on ZnS-based photocatalysts for CO2 reduction in all-inorganic aqueous medium

“…(b) and (c) Reproduced with permission. 57 Copyright 2022, American Chemical Society. apparent quantum yields of 59.1% and 5.6%, respectively, at 340 nm and 420 nm for CO 2 reduction to HCOOH (Fig.…”

“…10b and c). 57 Thus, band engineering is a useful strategy for both HER and CO 2 RR photocatalyst design. It can also be found that (CuGa) 0.5 ZnS 2 shows better performance than CuGaS 2 in reducing CO 2 to CO under the same reaction conditions (Fig.…”

“…29,58–61 Kudo et al used a (CuGa) 0.5 ZnS 2 solid solution as the CO 2 RR photocatalyst and RGO–(CoO x /BiVO 4 ) as the oxygen evolution photocatalyst to construct a Z-scheme system. 57 This system realized CO 2 reduction with water as the electron donor under visible light irradiation. NaHCO 3 has a positive effect on enhancing Z-schematic CO 2 reduction due to “pH regulation” and “efficient supply of hydrated CO 2 ”.…”