We seek to describe how defects and interfaces impact the atomic and electronic structure of extended semiconducting materials relevant to energy sustainability.
We use methods based on density functional theory, molecular dynamics, and many-body perturbation theory to achieve a microscopic understanding of optoelectronic materials properties.
Past relevant papers:
- H. Ma, W. Wang, S. Kim, M.H. Cheng, M. Govoni, G. Galli. “PyCDFT: a Python package for constrained density functional theory.” J. Comp. Chem. 41, 1859 (2020) [doi: 10.1002/JCC.26354] [open-source code]
- W. Wang, Y. Kang, H. Peelaers, K. Krishnaswamy, C.G. Van de Walle. “First-principles study of transport in WO3.” Phys. Rev. B. 101, 045116 (2020). [doi: 10.1103/PhysRevB.101.045116]
Mixed transition metal systems in electrocatalysts
Hydrogen fuel is considered to be a promising candidate to replace fossil fuels. Water splitting via electrolysis is a promising avenue for generating hydrogen fuel in an efficient manner. The transition metal oxyhydroxides (MOOH, M = Fe, Ni, Co, …) have been shown to have one of the highest activities of all known electrocatalysts. Interestingly, only certain compositions of transition metals have shown enhanced electrocatalytic performance. Many of these systems are also known to structurally change after cycling in operation. Nevertheless, there is limited understanding as to how or why performance is so dependent on composition and structure at the atomic level.
Our goal is to elucidate the microscopic impact of the presence of mixed transition metals on (1) charge transfer and charge recombination and (2) rationalize structure-composition-property-relationships.
Chemoselectivity in aqueous environments for photoelectrode materials
Harnessing solar energy to drive water splitting reactions is a sustainable and clean strategy to hydrogen generation. In order to realize a hydrogen economy at scale and avoid stressing freshwater resources, we must look to using ocean/sea water. However, ocean/sea water contains a medley of salts and ions, in particular chloride ions, that can inhibit water-splitting reactions and corrode the active material. Many multicomponent systems have shown the ability to split water in a salty aqueous environment, but no systematic understanding of which features of material systems work or why exists.
Thus our goal is to establish a holistic picture of the interfacial interactions between semiconductor surfaces and (salty) aqueous environments and their impact on electronic structure and provide engineering guidelines for more robust systems capable of selective and efficient generation of water splitting reactions.
Past relevant papers:
- D. Lee,* W. Wang*, C, Zhou *, X. Tong, M. Liu, G. Galli, K.-S. Choi. “The impact of surface composition on the interfacial energetics and photoelectrochemical properties of BiVO4 .” Nature Energy. 6, 287 (2021)[doi: 10.1038/s41560-021-00777-x] [UChicago News release][BNL news release]
- W. Wang, P. Strohbeen, D. Lee, C. Zhou, J. Kawasaki, K.-S. Choi, M. Liu, G. Galli. “The role of surface oxygen vacancies in BiVO4.” Chemistry of Materials. 32, 2899-2909 (2020). [doi: 10.1021/acs.chemmater.9b05047]
Past relevant papers:
- W. Wang, P. Strohbeen, D. Lee, C. Zhou, J. Kawasaki, K.-S. Choi, M. Liu, G. Galli. “The role of surface oxygen vacancies in BiVO4.” Chemistry of Materials. 32, 2899-2909 (2020). [doi: 10.1021/acs.chemmater.9b05047]
- W. Wang, A. Janotti, C.G. Van de Walle. “Phase transformations upon doping in WO3.” J. Chem. Phys., 146, 214504 (2017), [doi: 10.1063/1.4984581]
Oxygen vacancies and electric fields in perovskites for neuromorphic computing
As conventional materials such as silicon are approaching quantum mechanical limits, a new paradigm beyond Moore’s law is needed. One promising solution is neuromorphic computing, which aims to develop devices based on our own brain capable of learning and making nuanced decisions. Neurons operate with up to a 1000 times smaller power dissipation compared to devices based on conventional semiconductors, and thus offer a sustainable model for the next-generation of computing infrastructure.
We study the migration of oxygen vacancies and how this changes in the presence of an external field in perovskite compounds as one way to achieve memristive behavior (i.e., the resistance depends on the previous state of the system). Perovskites offer fantastic compositional and structural variations, and will help elucidate fundamental aspects of metal-to-insulator transitions.