Understanding the Modulated Electrocatalytic H₂ Generation Activity of Surface Functionalized Ti₂C MXenes Using the Potential of Zero Charge and Electron Transfer Coefficient as Electrochemical Descriptors

The electrochemical parameters, viz., potential of zero charge (EPZC) and electron transfer coefficient (α) are directly linked to the various intrinsic interfacial parameters. The proper extraction, analysis, and correlation of EPZC and α are important for using them as descriptors to understand the microkinetic aspects of electrocatalysis reactions. Herein, we present our attempts to use these descriptors for understanding the activity trend of the hydrogen evolution reaction (HER) over Ti2C MXenes terminated with varying surface functionalities (viz., *OH-dominant, *F-dominant, and mixture of *OH and *F). The HER activity is found to be closely related to EPZC (estimated via differential capacitance measurements) and α (estimated from the Tafel plots under steady-state conditions), which, in turn, are tuned via surface termination of MXenes. The potential screening effect derived from α explains the facile formation of the transition state and the favorable electron transfer distance. This methodology can be extended to other electrocatalytic systems, providing a practical tool to screen materials and refine the interfacial properties through quantitative correlations between surface structure, interfacial energetics, and reaction kinetics.