Collaborative Research: Bandgap Engineering of Dilute Antimonide III-Nitride Nanostructures for Efficient and Stable Photocatalytic Overall Water Splitting

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Energy from the sun offers a sustainable alternative to conventional energy sources such as fossil fuels. This project focuses on using sunlight to split water into hydrogen and oxygen, for direct use of hydrogen as a fuel, or for further chemical reactions to generate a broad range of fuels and chemicals. Specifically, the project will investigate a new class of semiconductor materials that have potential to significantly increase the efficiency of solar-to-fuel energy conversion, thereby achieving more cost-effective catalysts and energy conversion devices. The project will contribute to our Nation's energy security and future energy needs while also building a highly-trained workforce and providing STEM-related outreach to undergraduate students, underrepresented minorities, and K-12 students.The research will explore dilute antimonide nitrides, e.g. InGaSbN nanowires to overcome the limitations of conventional photocatalyst materials for achieving photocatalytic overall water splitting under light illumination up to 700 nm in wavelength, which has remained a grand challenge in renewable energy and in artificial photosynthesis. The research team has recently shown, both theoretically and experimentally, that the energy bandgap (approximately 3.4 eV) of GaN can be substantially reduced to about 2 eV with the incorporation of a small amount of antimony (Sb). Significantly, the reduction of energy bandgap of GaN with Sb incorporation is primarily due to the upward shift of the valence band edge, which is in direct contrast to the downward shift of the conduction band edge by alloying with indium (In). The project will start with first-principles calculations of the energy band structure and electronic, optical and photocatalytic properties of InGaSbN. Experimentally, the predicted nanoscale photocatalyst compositions will be grown on low cost, large area Si substrates, and will be characterized using a broad range of techniques. The bandgap energy and band edge positions of InGaSbN will be tuned by independently varying In and Sb incorporation, and their photocatalytic performance in overall water splitting and half reactions will be thoroughly investigated. In addition, the surfaces of InGaSbN nanowires will be engineered to be nitrogen-rich to protect against photocorrosion and oxidation, with the goal to achieve high efficiency, long-term stable operation. Success of this project will also provide an ideal 1.7 eV top light absorber to pair with a Si bottom light absorber to achieve high efficiency, low cost, and highly stable photoelectrochemical water splitting. The education and outreach program includes 1) encouraging underrepresented minorities and women in careers in science and engineering, 2) involving undergraduate students in research, and 3) communicating the research to the general public. This project will reach out to the broader public, particularly underrepresented groups on the science and technology of nanostructured materials, catalysis, and solar energy devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.