Varying heterojunction thickness within space charge region for photocatalytic water splitting

Summary: Photocatalytic overall water splitting for converting solar energy into hydrogen is a potential means of pursuing a renewable, scalable, and eco-friendly energy source. It is challenging to achieve the 5%–10% solar-to-hydrogen (STH) efficiency needed to be economically viable for renewable solar hydrogen production. Here, we report a heterojunction in which the thickness within the space charge region can be precisely adjusted to enhance the redox capacity, increase light absorption, and reduce carrier transport distance. The fully stacked two catalysts and aqueous-solution-exposed surfaces exhibit advantages of an enhanced built-in-electric field and a highly effective surface area. Based on that, an Ag3PO4/CdS/Pt photocatalyst exhibits overall water splitting with an STH efficiency, dramatically improving from zero to 0.75% under visible light at ambient pressure by tuning CdS/Ag3PO4 thickness from 200 nm/120 nm to 60 nm/30 nm. The STH efficiency can be further enhanced to 2% under visible light in 0.01 mol L−1 Na2S solution.