Semiconductor/Mixed-Conducting-Oxide Heterojunction for Photo-electrochemical H2O & CO2 Splitting at Elevated Temperatures

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PI: Chueh, WilliamProposal Number: 1336835Institution: Stanford UniversityTitle: Semiconductor/Mixed-Conducting-Oxide Heterojunction for Photo-electrochemical H2O and CO2 Splitting at Elevated TemperaturesMaking solar energy available when and where it is required is crucial towards increasing its utilization. Dissociating steam and/or carbon dioxide to chemical fuels is a promising route for storing solar energy. The objective of this work is to design a new class of photo-electrochemical cells that operates at 500 to 700 deg. C rather than at room temperature by utilizing an all solid-state design. Using an oxide heterojunction consisting of a semiconducting light absorber and a mixed oxygen ion and electron conducting oxide, incident solar energy above and below the band gap of the light absorber is converted to thermal energy, which in turn increases the solar-to-fuel efficiency. Unlike conventional photovoltaic-based approaches, here the solar-to-fuel efficiency increases, rather than decreases, with temperature. Thin-film heterojunctions consisting of oxides such as iron, vanadium, and titanium oxides will be evaluated for their potential in elevated temperature photo-electrochemical water and carbon dioxide splitting. The specific objective is to identify a combination of materials that delivers high solar-to-fuel efficiency and reliability over thousands of hours.The central component of this research is understanding and controlling charge generation, separation, and recombination at the heterojunction between a semiconducting oxide and a mixed ionic and electronic conducting oxide, at temperatures significantly above ambient. In photo-electrochemistry involving oxides, ionic defects such as vacancies must play an important role, yet it is not well understood. By combining rapid material screening, opto-electrochemical and in-situ synchrotron X-ray characterizations of oxide heterojunctions, this research aims to understand the interfacial chemistry and electronic properties at the junction of dissimilar solids under extreme conditions.This research seeks to enhance the viability of storing intermittent solar energy in chemical bonds, and increase the global utilization of solar energy. Beyond energy generation and storage, advanced understanding of charge transport at heterojunctions will benefit scientific fields such as catalysis and high temperature electronics, and applications such as solid-oxide fuel cells and sensors in extreme environments. The project work also provides research opportunities for one graduate student over the duration of the project. In addition to incorporating the results into undergraduate and graduate curriculums, the PI will develop a unique "Solar After Dark" outreach program. Human interaction with sunlight is one of the most ubiquitous phenomena in daily life and is an excellent vehicle to raise student interest in science and engineering.