(Invited) In-Situ/Operando Monitoring of Mechanisms of Catalytic Reaction Using X-Rays

Abstract

Global climate warming and environment pollution have spurred scientists to develop new high-efficient and environmental-friendly energy technologies. Hydrogen plays a key role in deep decarbonization for realization of net-zero carbon dioxide emission by 2050. Presently, the most popular and economical commercial process for H2 production is steam–methane reforming, which uses fossil fuels as the raw material and produces comparable amounts of CO2 as the by–product. It is definitely an environmental unfriendly and a non–sustainable H2 production process, and development of green H2 production is in urgent need. Sunlight is a clean, renewable and abundant energy source on the earth. Its conversion to hydrogen has been considered an ideal solution to counter the depletion and environmental problems of fossil fuels. Hydrogen is an ideal fuel for fuel cell applications. Hydrogen has to be produced from renewable and carbon-free resources using nature energies such as sunlight if one thinks of clean energy and environmental issues. In this regard, a photoelectrochemical cell consisting of semiconductor photoelectrodes that can harvest light and use this energy directly for splitting water is a more promising way for hydrogen generation. Photocatalysis utilizes the energy delivered by light and enables chemical reactions that otherwise cannot take place. When used to power thermodynamically uphill reactions, photocatalysis offers a solution to large-scale solar energy storage. Despite over four decades of intense research, however, photocatalysis remains either too expensive or too inefficient or both. Poor understanding of the mechanisms behind the low performance is a key reason that limits the progress of this important field. To address this critical challenge, I will overview a number of the experimental studies that successfully revealed the catalytic reactions at solid/liquid interfaces in real time, e.g. electrochemical interface of photocatalysis and electrocatalysis. The experimental results demonstrate that the operando X-ray characterization provides the unique information for understanding the real reaction mechanism.