Photo-Electrochemical Hydrogen Production Systems using III-V Semiconductors: Challenges in Scaling-up from an Electrode to a Device
Todd Deutsch a, James Young a, Walter Klein a, Myles Steiner a
a Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting19 (NFM19)
#SolFuel19. Solar Fuel Synthesis: From Bio-inspired Catalysis to Devices
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Roel van de Krol and Erwin Reisner
Invited Speaker, Todd Deutsch, presentation 161
DOI: https://doi.org/10.29363/nanoge.nfm.2019.161
Publication date: 18th July 2019

While III-V semiconductors have achieved the highest photo-electrochemical solar-to-hydrogen conversion efficiencies, they are remarkably unstable during operation in a harsh electrolyte. The first part of this talk will focus on the degradation mechanism of inverted metamorphic multijunction (IMM) III-V cells and surface modification strategies aimed at protecting them from photocorrosion. We applied noble metal catalysts, oxide coatings by atomic layer deposition, and MoSin an effort to protect the GaInP2 surface that was in contact with acidic electrolyte. We also grew epitaxial capping layers from III-V alloys that should be more intrinsically stable than GaInP2. The ability of the various modifications to protect the IMM’s surface was evaluated by operating at each electrode at short circuit for extended periods of time.

The second part of this talk will identify the challenges encountered while scaling the IMM III-V absorber areas of from ~0.15 cm2 up to 16 cm2 and incorporating them in a photoreactor capable of generating 3 standard liters of hydrogen in 8 hours under natural sunlight. To successfully scale photo-electrochemical water-splitting technologies from bench to demonstration size requires addressing predictable and unpredictable complications. Despite using Comsol multiphysics to model our photoreactor and identify suitable specifications for a prototype, several practical issues were uncovered during testing that led to multiple iterations of photoreactor design between the initial and final generations. Several bottlenecks that ranged from counter electrode composition and orientation to bubble management needed redress in order to meet our performance targets. Ultimately, the demonstration-scale system was able to generate nearly twice the target volume of hydrogen in an 8-hour outdoor trial.

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