265446 Modeling the Theoretical Limits of Solar-to-Hydrogen Efficiency for Photoelectrochemical Water Splitting Based On Realistic Assumptions of Material Performance
Photoelectrochemical (PEC) water splitting can be used to store solar energy in the form of chemical bonds, specifically those of hydrogen which can then be used as a fuel. The performance of a PEC water splitting device is best evaluated using the solar-to-hydrogen (STH) efficiency. Knowledge of practical limits can provide researchers with a means to assess and guide research directions in the field. Previous studies have calculated maximum efficiencies based on solar absorption limits with the framework used to study photovoltaic (PV) devices. While these numbers provide a starting point for understanding the limits of PEC water splitting devices, these studies neglect additional losses that are specific to PEC systems and thus can overestimate practical solar conversion efficiencies for this application. This work presents results of STH efficiency calculations for single and dual absorber systems over a wide range of band gaps that take into account the effects of various system losses including absorption limits, material defect losses, shunt losses, and reaction overpotentials. Comparing maximum STH values for devices with precious vs. non-precious metal catalysts or minimal vs. significant shunt losses illustrates the need for researchers to focus on these issues. Additionally, improvement in performance with the addition of a small bias is shown by calculating an applied bias photon conversion efficiency for each device configuration. Similarly to what has been accomplished in the PV field, an equivalent circuit diagram has been proposed to model the additional losses in a PEC system. These results provide insight into the intricacies of PEC device functioning as well as define obtainable efficiency values representative of the current state of materials research in the field.
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