Semiconductors, that can be used as photocatalysts to convert solar energy in different applications of environmental and technological interest, were employed in gas diffusion electrodes (GDEs) resulting in an innovative strategy for electrochemical reactions involving gases as reactants in aqueous media. The light-responsive GDEs, assembled with p-type semiconductors and porous conductive structures, were then used as photocathodes in photoreactors for water remediation and CO2 conversion. The solar-driven photoreactor for water remediation was assembled with a photoactive GDE that in situ produces H2O2 from the O2 reduction reaction (ORR). The photoactive GDE was prepared with graphite sintered with PTFE and the multiphasic Ag/AgBiW2O8/Bi2WO6 (Ag/ABW/BW), a photocatalyst for ORR. The irradiated GDE|Ag/ABW/BW photocathode under air flow (21 % of O2) was associated with a photoanode and externally connected with a silicon solar cell. The initial studies, performed using a TiO2 photoanode, revealed excellent performance for remediation of 150 mL of amoxicillin (AMX) aqueous solution (removal of 53 % of AMX after 3 h under irradiation). Ongoing studies using the iron titanate FeTiO3 as photoanode and the GDE|Ag/ABW/BW photocathode also revealed promising results for removal of the antibiotic ciprofloxacin from aqueous solution. Furthermore, GDEs consisted of Cu2WO4 on carbon paper, with Pt counter-electrode, were used for light-assisted CO2 reduction reaction (CO2RR) in NaHCO3 aqueous solution. Under CO2 flow and polarized at -0.25 V (vs Ag/AgCl), the GDE|Cu2WO4 exhibited intense cathodic photocurrent and, after 2 h, produced ethanol and methanol with 70 % of Faradaic Efficiency. Currently, we are improving a two-compartment photoelectrochemical cell where the Pt counter-electrode was replaced by a photoactive BiVO4 anode for O2 evolution reaction. The cell will be connected to a solar cell and we will investigate the efficiency and long-term stability of this solar-driven photoreactor for solar fuels production from CO2.

Solar-driven photoreactors with light-responsive electrodes for CO2 reduction and for water decontamination

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ACS Fall 2022

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