(171e) On-Sun Hydrogen Generation from Photoelectrochemical Water-Splitting Devices

Photoelectrochemical (PEC) water-splitting is a promising technology that uses sunlight to directly split water into hydrogen and oxygen, providing a storable form of chemical fuel.¹ While several semiconductor systems have shown the capability for unassisted solar hydrogen production, III-V semiconductors have demonstrated the highest solar-to-hydrogen (STH) conversion efficiencies and best device longevity.^2–4 However, to date, work in the field has focused almost exclusively on laboratory conditions, with very few PEC systems having been tested outdoors and on-sun.

In this work, we present unassisted PEC hydrogen generation under natural solar illumination using a tandem III-V semiconductor absorber device paired with a non-precious metal HER catalyst. An on-sun photoreactor platform was designed for PEC material testing and benchmarking that incorporates a 2-axis solar tracker to maximize sunlight utilization and a gas collection system.⁵ Nearby insolation and environmental monitoring instruments at the NREL Solar Radiation Research Laboratory provide a full record of the solar flux and environmental conditions that allow for more accurate comparisons of on-sun and in-lab performance. Tandem, lattice-matched GaInP₂/GaAs absorbers (1.8/1.4 eV bandgaps) that have been demonstrated with a high quality fabrication and yield >10 % STH efficiency^2,3 are coated with a MoS₂ HER catalytic and protective layer. Photoelectrochemical performance was characterized by current-voltage and chronoamperometric measurements under both simulated and natural sunlight illumination, while material structure is probed by XPS and SEM.

The MoS₂-protected tandem absorbers exhibit >10% STH efficiency under both laboratory and on-sun conditions. Over the course of a day of PEC testing under natural sunlight, >11 standard mL of hydrogen is generated with no external bias. We will discuss catalyst and semiconductor stability and cell design challenges that limit PEC durability and hydrogen yield.

(1) Seitz, L. C.; Chen, Z.; Forman, A. J.; Pinaud, B. A.; Benck, J. D.; Jaramillo, T. F. Modeling Practical Performance Limits of Photoelectrochemical Water Splitting Based on the Current State of Materials Research. ChemSusChem 2014, 7 (5), 1372–1385.

(2) Young, J. L.; Steiner, M. A.; Döscher, H.; France, R. M.; Turner, J. A.; Deutsch, T. G. Direct Solar-to-Hydrogen Conversion via Inverted Metamorphic Multi-Junction Semiconductor Architectures. Nat. Energy 2017, 2 (4), 17028.

(3) Khaselev, O.; Turner, J. A. A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production via Water Splitting. Science 1998, 280 (5362), 425–427.

(4) Cheng, W.-H.; Richter, M. H.; May, M. M.; Ohlmann, J.; Lackner, D.; Dimroth, F.; Hannappel, T.; Atwater, H. A.; Lewerenz, H.-J. Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Lett. 2018, 3 (8), 1795–1800.

(5) HydroGEN Consortium. On-Sun Photoelectrochemical Solar-to-Hydrogen Benchmarking https://www.h2awsm.org/capabilities/sun-photoelectrochemical-solar-hydro....