Si-Based Metal-Insulator-Semiconductor Structures with RuO2-(IrO2) Films for Photoelectrochemical Water Oxidation

We report on the properties of metal-insulator-semiconductor (MIS) photoanodes for water oxidation employing a thin RuO2-(IrO2) film as a top catalytic layer. In this study, MIS photoanodes with the configurations RuO2/SiO2/n-Si and IrO2-RuO2/SiO2/n-Si were prepared and their photoelectrochemical (PEC) oxygen evolution under solar irradiation has been discussed. The thin SiO2 layers were prepared by the atomic layer deposition method and the RuO2-(IrO2) thin layers were deposited by the metal-organic chemical vapor deposition method. The photocurrent and photovoltage of these MIS photoanodes were studied in 1 M aq. H2SO4 (pH = 0), 0.5 M aq. Na2SO4 (pH = 6), and 1 M aq. KOH (pH = 14) electrolytes showing the trend acidic > alkaline > near-neutral pH conditions for both RuO2- and IrO2-RuO2-based structures. The RuO2/SiO2/n-Si photoanode exhibited a photovoltage of 0.49 V and was able to generate a photocurrent of similar to 10 mA/cm(2) at a thermodynamic water oxidation potential (1.23 V vs the normal hydrogen electrode, NHE) in 1 M aq. H2SO4 solution under 1 Sun intensity with AM 1.5 spectrum. A photovoltage of 0.42 V and a photocurrent of similar to 4 mA/cm(2) were achieved for the IrO2-RuO2/SiO2/n-Si photoanode under acidic conditions. The stability of the photoanodes was examined in 1 M aq. H2SO4 and 1 M aq. KOH solutions. Chronoamperometry measurements on the RuO2/SiO2/n-Si photoanode in acidic solution under an applied voltage of 1.23 V versus NHE showed the deterioration of the photoanode after 2 h of operation. Similarly, stability measurements were performed on IrO2-RuO2/SiO2/n-Si photoanodes in 1 M aq. H2SO4 solution. Under acidic conditions, at an applied bias of 1.23 V versus NHE, a photocurrent of similar to 2 mA/cm(2) was observed, which was stable for 24 h for the IrO2-RuO2-based photoanodes. The preparation, PEC activity, stability, and characterization of the RuO2/SiO2/n-Si and IrO2-RuO2/SiO2/n-Si have been discussed in our study.

Automated summary

This study investigated the properties of metal-insulator-semiconductor (MIS) photoanodes with RuO2/SiO2/n-Si and IrO2-RuO2/SiO2/n-Si configurations for water oxidation. The results showed that both structures exhibited better oxygen evolution performance under acidic conditions compared to alkaline or near-neutral pH conditions.