We report the first results in which ALD-TiO2 layers electronically couple silicon to an overlying catalyst coating while inhibiting corrosion during brine splitting, a reaction that is capable of generating not only a fuel (H2) but also a disinfectant (Cl2 or NaOCl). An n-type silicon photoanode, and a p+-silicon anode are protected by a 1.7 nm coating of amorphous TiO2 and 2 nm coating of Ir. The p+-Si/TiO2/Ir anode is able to effect the oxidation of chloride (0.5 M H2SO4, 3.5 M NaCl) in the dark with a low overpotential compared to that for oxidation of water (0.5 M H2SO4). The 0.294 V overpotential difference occurs despite the difference in standard redox potentials, ΔE = (E°(Cl2/Cl−) - E°(O2/H2O)), of 130 mV. Under 1 sun irradiation a photovoltage of ca. 0.566 V is achieved by comparing the illuminated n-Si/TiO2/Ir photoanode with the dark p+-silicon anode. Although the n-Si/TiO2/Ir photoanode is only one half of an eventual tandem cell needed for photosynthetic brine splitting, its ABPE for chloride oxidation is 1.42%, ca. 28 times that for water oxidation. The illuminated n-Si/TiO2/Ir photoanode remained stable at 1 mA cm−2 during a six-day chronopotentiometry test.
Silicon Photoanodes for Solar-Driven Oxidation of Brine: A Nanoscale, Photo-Active Analog of the Dimensionally-Stable Anode