Photocatalytic reduction of CO₂ using solar energy

Yimin Wu

Assistant professor, Department of Mechanical and Mechatronics Engineering, University of Waterloo

Development of sustainable and clean sources of energy, and mitigation of greenhouse gas emissions such as CO₂, is among the greatest challenges facing our planet. Recently, electroreduction of CO₂ has attracted considerable interest for removal of gaseous CO₂. However, it is associated with significant losses primarily due to a large overpotential and electrical energy input. In addition, the use of electricity as a secondary form of energy is inefficient due to significant losses associated with conversion from primary sources to chemical fuels. Solar energy is the largest primary energy source available. Photocatalytic reduction of CO₂ using solar energy offers an efficient way to convert solar energy into chemical energy and directly store it in the form of chemical fuels. Particular interest is its conversion directly into liquid fuels such as methanol. We will present CO₂ reduction in a metal oxide system, namely Cu₂O. It is very promising as photocatalysts with good multielectron transfer properties due to its loosely bonded d electrons. It is inexpensive materials with near ideal electronic properties for light energy conversion into fuels. Cu₂O shows intrinsic p type conductivity due to presence of negative charged Cu vacancies with one of the lowest electron affinities, identifying Cu₂O as an optimal candidate for reduction of CO₂. Here, we present atomic level understanding of active sites in Cu₂O that leads to the discovery of the facet specific adsorption and subsequent light induced of CO₂ into liquid fuel-methanol, and ethanol. The activity of these active sites was unraveled using operando multimodal correlative scanning fluorescence x-ray microscopy, environmental transmission electron microscopy, Bragg coherent diffractive imaging, ultrafast coherent diffractive imaging at atmospheric pressure, in operando, on a single particle level, we design nanoparticles with high active facet selective active sites, strain encoded active sites, and particles/thin film activity. This approach, referred to as “Integrated Imaging”, establishes an entirely new platform to understand interfaces, which provides design strategies for new materials and devices that may frame the next generation’s sustainable energy.

Dr. Wu, Yimin obtained his DPhil in Materials from the University of Oxford in 2013, focusing on two dimensional quantum materials, thin film devices, and aberration corrected (scanning) transmission electron microscopy. He went to work as a SinBeRise Postdoctoral Fellow at the Department of Materials Science and Engineering at the University of California, Berkeley, and Materials Science Division at Lawrence Berkeley National Laboratory, focusing on batteries and in situ multimodal characterizations using liquid phase transmission electron microscopy and synchrotron X-ray microscopy. Then, he joined the Center for Nanoscale Materials (CNM) at Argonne National Laboratory under Argonne Integrated Imaging Initiative, focusing on catalysis, battery and in situ multimodal characterizations using gas/liquid phase transmission electron microscopy, synchrotron X ray nanoprobe, and ultrafast X ray microscopy and spectroscopy. After that, he joined the faculty of University of Illinois at Chicago as an assistant professor of physics (research) and held a joint appointment at the Joint Center for Energy Storage Research (JCESR) at Argonne National Laboratory. In 2019, he joined the University of Waterloo as an assistant professor at Department of Mechanical and Mechatronics Engineering and Waterloo Institute for Nanotechnology. His research focuses on the design of new energy materials for solar fuels and batteries, and novel electronic, photonic, responsive materials for flexible electronics and soft robotics, and energy efficient neuromorphic computing through a deep understanding of energy transduction processes at interfaces.

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