In situ infrared spectroscopy and sum frequency generation spectroscopy in energy catalysis: fundamentals, challenges, and perspectives

Energy catalysis serves as a pivotal bridge to connect the energy revolution with sustainable development, which not only benefits to address the current energy and environmental challenges but also provides a solid technical foundation for the construction of a zero-carbon society in the future for humanity. The research of energy catalysis cannot be carried out without the role of catalysts. However, how to characterize the relationship between the physicochemical properties and catalytic performance of the catalysts during the in situ reactions is crucial for the rational design of catalysts. Fortunately, in situ molecular vibrational spectroscopic techniques hold the undeniable importance in energy catalysis due to providing more dynamic and transient information of energy catalytic system under the working conditions. In this review, we systematically introduce the fundamentals of in situ infrared (IR) spectroscopy and sum frequency generation (SFG) spectroscopy (a second-order nonlinear spectroscopy technique with surface-selectivity and sub-monolayer sensitivity), and their practical applications for energy catalysis. Finally, we propose the future potential applications and challenges of these in situ spectroscopic techniques, hoping that this review will better help researchers understand in situ spectroscopic techniques and expand their application scopes in energy catalysis.