To successfully scale photo-electrochemical water-splitting technologies from bench to demonstration size requires addressing predictable and unpredictable complications. This talk will identify the challenges and describe solutions for successful scaling of the absorber area of inverted metamorphic multijunction III-V cells 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. Despite using Comsol multiphysics to model our photoreactor and identify suitable specifications for a prototype, several practical issues that were uncovered during testing led to multiple iterations between the initial and final photoreactor design. Several bottlenecks that ranged from counter electrode composition and orientation to bubble removal 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.
 NATURE ENERGY 2, 17028 (2017)