CAREER: Scale Dependent Property-Performance Relationships in Individual Heterojunction Nanowire Photocatalysts

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NON-TECHNICAL DESCRIPTION: Efficiently converting sunlight and water into hydrogen is an attractive approach to producing 'green' fuels that could help support the future US economy. Commercially realizing this goal requires improved scientific understanding of the associated processes and the development of human capital capable of addressing the engineering challenges. A variety of catalysts have been known to perform photolysis (converting water to hydrogen) for several decades, but many remain too inefficient or expensive for commercial application. The properties of photocatalysts may be improved most effectively by controlling their electronic structure, which depends on variables such as particle size, shape, chemistry, defect structure, or their interactions with adjoining materials. The resultant photocatalytic performance is typically characterized over an ensemble of millions of particles, whose individual properties could vary significantly. Averaging over the entire system obscures the fundamental relationships between the electronic properties and the photocatalytic performance at the nanoparticle level. This project develops and utilizes new approaches to measuring the electronic properties and photocatalytic performance of individual nanoparticles in order to develop improved scientific understanding of the effects of size, defects, and interfaces on both the electronic structure and the associated photocatalytic performance. The activity integrates research and education through a research experience for education majors program while promoting diversity. It will enable Illinois teachers to bring authentic scientific research experience into the K-12 classroom, research experience for undergraduate students, and research support for a graduate student. As well, inquiry-based and active-learning approaches to education will be fostered by working closely with the Illinois Foundry for Innovation in Engineering Education (IFoundry). This multifaceted approach will have impact at all levels of the STEM pipeline. TECHNICAL DETAILS:The project is seeking to develop improved scientific underpinnings for nanostructural design of optimized high-efficiency low-cost heterojunction photocatalysts. The electronic properties and photocatalytic performance of individual heterojunction nanowires are being characterized as a function of size. The experiments utilize a geometry that enables electrical measurements, ex situ structural and chemical characterization, and subsequent in situ photocatalysis by environmental transmission electron microscopy (TEM). In situ TEM provides appropriate spatial resolution, temporal resolution, and geometric flexibility necessary to quantify the rate of photocatalytic gas evolution at individual nanostructures. Special emphasis is being placed on elucidating the role of characterized defects and defect states in affecting the variation in performance of individual nanoscale photocatalysts. The experiments target ZnO-Pt and ZnO-Fe2O3, which will serve as model oxide-metal and model low-cost oxide-oxide systems that exhibit the desired physics and fulfill experimental requirements.