Simultaneous Photoelectrocatalytic Water Oxidation and Oxygen Reduction for Solar Electricity Production in Alkaline Solution.

The photoelectrochemical (PEC) method offers an alternative approach to photovoltaic devices for solar electricity generation. The water oxidation reaction (WOR) on the anode and oxygen reduction reaction (ORR) on the cathode is an ideal design for energy transfer owing to their superiority in terms of cleanliness, eco-friendliness, and natural abundance. However, solar electricity production based on O2 circulation by a fuel-free PEC cell is very challenging because it is extremely hard to extract electrons from water molecules owing to the uphill and sluggish WOR together with enormous overpotential for the cathodic ORR. Herein, a PEC cell based on the OH- /O2 redox pair is reported for efficient and sustainable solar electricity production by using two photoelectrodes of TiO2 and polyterthiophene in alkaline electrolyte. This fuel-free PEC cell delivers an open-circuit voltage up to 0.90 V and a maximum power density of 222 µW cm-2 with O2 -saturated NaOH electrolyte under AM 1.5 G solar irradiation. A record solar-to-electricity conversion efficiency of 0.22 % is achieved in the case of tandem illumination of the two photoelectrodes. In addition, the dual photoelectrode remains robust in accelerated and day-night cycling operation under natural atmosphere for more than a week. This PEC cell is free of fuel, separating membranes, and cocatalyst, which may guide future designs for clean and simple devices for solar energy conversion.