(707f) Optimizing Operating Conditions for Solar Driven CO2 Reduction Using High Performance GaAs and Silicon-Based Photocathodes

Integrated solar-fuels devices have gained significant attention as they allow for the co-designing of devices to maximize solar and catalytic efficiency towards electrochemical systems, such as CO₂ reduction (CO₂R). Effective design of integrated solar fuels devices aims to maximize photovoltage towards solar-driven CO₂R improve CO₂R selectivity for higher value products (i.e., ethanol, propanol), improve system durability, and maximize photocurrent. In this report, we have designed and characterized a high-performance integrated solar-fuels device for determining optimal fabrication and experimental conditions for CO₂R photocathodes under diurnal conditions. This involved the construction of an electrochemical cell which allows for direct comparison of solar-driven electrocatalysis and “dark” electrocatalysis. High-performance III-V GaAs-based photocathodes, and Si-based photocathodes, with Cu catalytic layers were fabricated for C₂₊ product formation at low overpotentials.

We conducted an analysis of the photovoltaic (PV) behavior of the photocathodes and compared this to their photoelectrochemical behavior under solar-driven conditions. This photoelectrochemical behavior was also compared to the electrochemical behavior of the catalyst layer to evaluate the solar-driven system for any unique photo-effect, outside of the light absorption of the PV, which could enable improved I-V behavior with respect to a purely electrochemical system, or a ‘PV + electrolyzer’ architecture. To achieve this, we tested I-V points in both the light-limited and reaction-kinetics limited regions of the photoelectrochemical curve and compared their CO₂R behavior to equivalent current points on the electrochemical I-V curve.

Finally, we modeled the diurnal output of an integrated solar-driven CO₂R system by compiling data points collected at different light intensities to inform the conditions that must be controlled to maximize C₂₊ product selectivity over the course of a day. This model can be used to identify ‘target’ operating conditions (i.e., high voltage, low current vs. low voltage, high current) for solar-driven CO₂R systems operating under ‘real’ conditions.