Advanced <i>In Situ</i> Spectroscopic Techniques for Probing the Acidic Oxygen Evolution Reaction

Proton exchange membrane water electrolysis (PEMWE) is a promising technology for sustainable hydrogen production. However, the anodic oxygen evolution reaction (OER) is a critical bottleneck restricting the power-to-gas efficiency and the widespread application of PEMWE devices because the harsh acidic and oxidative environment causes drastic catalyst structural evolution and thus severe catalyst dissolution/corrosion as well as performance degradation. Currently, the lack of deep insight for identifying the real catalytic sites during the structural evolution and the distinctions of reaction mechanisms have hindered the development of highly active and durable OER catalysts for PEMWE. Therefore, elucidating the OER-induced structure evolution and understanding the underlying mechanisms are recognized as the foundations for PEMWE technology. Against this backdrop, in situ spectroscopic characterization techniques serve as powerful tools for achieving this goal by enabling the real-time monitoring of the catalytic structure and the capture of key intermediates. This Account summarizes the recent advances in cutting-edge in situ spectroscopy techniques for probing the acidic OER process. The fundamentals and device configurations of these techniques are briefly introduced, and the advantages of each technique for monitoring the catalyst structural evolution and identifying the intermediates to unveil the underlying mechanisms have also been discussed. Finally, the challenges, development trends, and prospects in this field are presented.