(Invited) Techno-Economics of Photoelectrochemical Water Splitting and Progress in Cost Reduction of High-Efficiency III-V Photoabsorbers

Abstract

Photoelectrochemical (PEC) water splitting is a potentially promising route to direct solar-driven hydrogen production. Challenging targets for solar-to-hydrogen (STH) efficiency, durability, and semiconductor absorber costs must be realized for this approach to be economically competitive with other hydrogen production pathways. The first part of this talk will focus on the cost and performance metrics that go into techno-economic analysis and their status.Research on PEC hydrogen production at the National Renewable Energy Laboratory (NREL) has focused on III-V semiconductor absorber materials because their tunable bandgaps, high photon conversion efficiencies, and ability to make multi-junction structures that have resulted in the highest STH efficiencies yet demonstrated. However, to achieve the U.S. DOE’s hydrogen production target of $2/kg, in addition to high STH efficiency, the semiconductor absorber synthesis cost must come down 1-2 orders of magnitude from the current metal organic vapor phase epitaxial route. Hydride vapor phase epitaxy (HVPE) is a technique that has the potential to lower tandem III-V synthesis costs. The second part of this talk will describe experimental photoelectrochemical characterizations of HVPE-grown GaInP/GaAs tandem photoelectrodes with 1.85/1.38 eV bandgaps. Their incident photon-to-current efficiency, photocurrent vs. circuit bias, and unbiased chronoamperometry will be presented and discussed. Upon illumination, the HVPE-grown structures were able to drive water electrolysis spontaneously (e.g., without an external bias) at STH efficiencies up to 10%. The durability of III-V photoelectrodes remains an unresolved challenge for cost effective hydrogen production via photoelectrolysis.