Numerical Simulation of Performance and Solar-to-Fuel Conversion Efficiency for Photoelectrochemical Devices

Citation

Chen, Yikai (Katie) (2021) Numerical Simulation of Performance and Solar-to-Fuel Conversion Efficiency for Photoelectrochemical Devices. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/65pq-7d93. https://resolver.caltech.edu/CaltechTHESIS:06082021-054649127

Abstract

The Industrial Revolution was energized by coal, petroleum, and natural gas. It is clear that fossil fuels, which drive steam and electrical engines, made possible a monumental increase in the amount of productive energy available to humans. But in the meantime, the constant burning of fossil fuels has changed the natural greenhouse, intensified global warming, deteriorated air quality, and eventually caused irreversible environmental damage on our planet. Renewable energy especially solar energy offers a desirable approach toward meeting our growing energy needs while largely reducing fossil fuel burning. The major problems in terms of harvesting energy directly from sunlight turn out to be low energy concentration and intermittency. Building solar-fuel generators, which stores solar energy in chemical bonds, similar to photosynthesis in nature, provides a possible solution to these two problems. Carbon-free chemicals, such as hydrogen gas, which are produced by solar-driven water-splitting, or carbon-neutral chemicals, such as methane and ethylene, which are produced by solar-driven CO₂ reduction, are all promising clean fuels for solar storage.

This thesis is focused on studying the performance and solar to fuel conversion efficiency of existing and hypothetical test-bed photoelectrochemical prototypes using multi-physics modeling and simulation to lay a foundation for future implementation and scale-up of the integrated, solar-driven systems. For water-splitting systems, a sensitivity analysis has been made to assess the relative importance of improvements in electrocatalysts, light absorbers, and system geometry on the efficiency of solar-to-hydrogen generators. Besides, an integrated photoelectrolysis system sustained by water vapor is designed and modeled. Under concentrated sunlight, the performance of the photoelectrochemical system with 10× solar concentrators was simulated and the impact of hydrogen bubbles that are generated inside the cathodic chamber on the performance of the photoelectrolysis system was evaluated. For CO₂ reduction systems, operational constraints and strategies for systems to effect the sustainable, solar-driven reduction of atmospheric CO₂ were investigated. The spatial and light-intensity dependence of product distributions in an integrated photoelectrochemical CO₂ reduction system was modeled and simulated. Finally, the performance a flow-through gas diffusion electrode for electrochemical reduction of CO or CO₂ was evaluated.

This thesis can be divided into three parts. The first part discusses the importance of solar energy. The second part includes Chapter II, Chapter III, Chapter IV, and Chapter V, which deals with solar-driven water-splitting cells, and the third part includes Chapter VI, Chapter VII, and Chapter VIII, which deals with solar-driven CO₂ reduction cells.

Thesis Files