Photoelectrochemical (PEC) water-splitting directly splits water into hydrogen and oxygen using solar energy, providing a storable form of chemical fuel. Of the semiconductor material classes that have shown promise for unassisted solar hydrogen production, III-V semiconductors have demonstrated the best reported device longevity and highest solar-to-hydrogen (STH) conversion efficiencies and best device longevity. However, work in the field has mostly focused on laboratory conditions, with very few PEC systems having been tested outdoors under natural sunlight illumination. In this work, we present molybdenum disulfide-protected tandem III-V semiconductor absorber systems that produce unassisted PEC hydrogen generation on-sun. Tandem, lattice-matched GaInP2/GaAs absorbers (1.8/1.4 eV bandgaps) incorporate window and encapsulating layers to improve device efficiency and longevity, respectively and are also coated with a MoS2 HER catalytic and protective layer. These durability and efficiency improvements allow for more meaningful outdoor measurements. A photoreactor platform was designed for PEC material testing and benchmarking that incorporates a 2-axis solar tracker and a gas collection system. Insolation and environmental monitoring instruments at the nearby NREL Solar Radiation Research Laboratory provide a full record of the solar irradiance and environmental conditions to allow for more accurate benchmarking of on-sun performance. PEC performance was characterized via current-voltage and chronoamperometric measurements under both simulated and natural sunlight illumination, while material structure is probed by XPS and SEM. Under both laboratory and on-sun conditions, the MoS2-protected tandem absorbers exhibit &gt;10% STH efficiency. In addition, &gt;11 standard mL of hydrogen is generated with no external bias during a day of PEC testing under natural sunlight. We will discuss catalyst and semiconductor stability and cell design challenges that limit PEC durability and hydrogen yield.

On-sun photoelectrochemical water-splitting with molybdenum disulfide-protected III-V tandem absorbers

ACS Fall 2020 Virtual Meeting

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