Nanocrystalline CuGaS2-based photoelectrodes for photoelectrocatalytic reduction of CO2
Juliana Brito a b, Marcos Júnior a, Maria Zanoni b, Lúcia Mascaro a
a UFSCAR- Federal University of São Carlos, Brazil
b Institute of Chemistry, São Paulo State University (UNESP), Brazil., Jardim Quitandinha, Araraquara - Estado de São Paulo, 14800-060, Brasil, Brazil
Poster, Juliana Brito, 018
Publication date: 7th June 2020

CuGaS2-based photocatalysts were studied for CO2 reduction under photoelectrocatalysis (PEC) technique. The CuGaS2 was modified with small amounts of In or Bi to analyze the interference of these metals in the products generation. The doped and non-doped CuGaS2 were deposited by spray coating on Mo using inks comprised by the respective salts of each cations, and thiourea as the source of sulfur. A CdS and TiO2 thin films were deposited by a chemical bath deposition method on the spray-coated CuGaS2 films. The photoelectrodes were characterized by XRD, Raman, SEM, EDS, Diffuse Reflectance and XPS. The photoelectrocatalytic reductions of CO2 were performed in a one-compartment glass reactor (50 mL) equipped with quartz window, at 20 oC, and three electrodes: Pt foil (counter electrode), Ag/AgCl (KCl sat) (reference electrode), and the semiconductors as working electrode, with 0.1 mol L-1 Na2SO4 saturated with CO2, irradiated by a 150 W commercial solar simulator lamp (Newport 66902) and submitted to a controlled potential (potentiostat/galvanostat - Autolab PGSTAT 302, Metrohm). Aliquots of the solution were evaluated by CG-FID[1]. The CuGaS2 and Cu(In,Ga)S2 electrodes presented a more stable photocurrent along the time analyzed, indicating a better stability of the material compared to Cu(Ga,Bi)S2 electrode. The CO2 reduction was performed under -0.7 V and light incidence (one sun) with the three electrodes. Comparing the amount of methanol (the main product for all the electrodes), it was higher employing Cu(In,Ga)S2 electrode than under CuGaS2 and Cu(Ga,Bi)S2. However, the formation of other products that require a higher number of electrons and protons (ethanol and acetone) was higher under the CuGaS2 catalyst. In addition, the stability and, consequently, repeatability of the products concentration formed using CuGaS2 for consecutive reactions of CO2 reduction is better than the observed for the catalysts modified with In or Bi. In fact, the Bi presence did not improve the CuGaS2 activity for CO2 reduction. After 240 min of CO2 reduction using CuGaS2 semiconductor under -0.7 V and light incidence (one sun) were quantified 1.30 mmol L-1 methanol, 0.45 mmol L-1 ethanol and 0.25 mmol L-1 acetone. So, despite the improvement for methanol production obtained in the first 4h of reaction with the addition of In in the semiconductor surface, the results obtained under CuGaS2 electrode without further modification showed to be superior for CO2 reduction using PEC technique.


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