Efficiency Limits for Hydrogen and Formate Production via Fully-Integrated Photoelectrochemical Devices

Abstract

Limiting efficiencies play a critical role in determining the viability of proposed technologies and, consequently, in motivating and guiding device development. Herein we present an analytic, unified framework for fully-integrated photoelectrochemical device performance and apply it to water-splitting and CO_2 reduction reactions for hydrogen and formate production, respectively. An analytic form for the current-voltage relationship of a photoelectrochemical device is used to calculate limiting efficiencies under specific ideal and realistic conditions for single, dual and triple junction photodiode units. Differences in realistic limiting efficiencies for hydrogen and formate production arise not only from disparate catalyst performance but also from design considerations for liquid vs. gas products and realistic operating pH. The results indicate that dual junction devices are sufficient for water-splitting devices, while triple junction devices are more ideal for CO_2 reduction devices with current high performance components.