Gas-involved electrochemical reactions provide feasible solutions to the worldwide energy crisis and environmental pollution. It has been recognized that various elements of the reaction system, including catalysts, intermediates, and products, will undergo real-time variations during the reaction process, which are of significant meaning to the in-depth understanding of reaction mechanisms, material structure, and active sites. As judicious tools for real-time monitoring of the changes in these complex elements, in situ techniques have been exposed to the spotlight in recent years. This review aims to highlight significant progress of various advanced in situ characterization techniques, such as in situ X-ray based technologies, in situ spectrum technologies, and in situ scanning probe technologies, that enhance our understanding of heterogeneous electrocatalytic carbon dioxide reduction reaction, nitrogen reduction reaction, and hydrogen evolution reaction. We provide a summary of recent advances in the development and applications of these in situ characterization techniques, from the working principle and detection modes to detailed applications in different reactions, along with key questions that need to be addressed. Finally, in view of the unique application and limitation of different in situ characterization techniques, we conclude by putting forward some insights and perspectives on the development direction and emerging combinations in the future.

Nitrogen chemisorption is a prerequisite for efficient ammonia synthesis under ambient conditions, but promoting this process remains a significant challenge. Here, by loading yttrium clusters onto a single-atom support, an electronic promoting effect is triggered to successfully eliminate the nitrogen chemisorption barrier and achieve highly efficient ammonia synthesis. Density functional theory calculations reveal that yttrium clusters with abundant electron orbitals can provide considerable electrons and greatly promote electron backdonation to the N₂ antibonding orbitals, making the chemisorption process exothermic. Moreover, according to the “hot atom” mechanism, the energy released during exothermic N₂ chemisorption would benefit subsequent N₂ cleavage and hydrogenation, thereby dramatically reducing the energy barrier of the overall process. As expected, the proof-of-concept catalyst achieves a prominent NH₃ yield rate of 48.1 μg·h⁻¹·mg⁻¹ at −0.2 V versus the reversible hydrogen electrode, with a Faradaic efficiency of up to 69.7%. This strategy overcomes one of the most serious obstacles for electrochemical ammonia synthesis, and provides a promising method for the development of catalysts with high catalytic activity and selectivity.