Analysis of the hydrogen electrode reaction mechanism in thin-layer cells. 3. Study of hydrogen electro-oxidation by scanning electrochemical microscopy

- An analytical SECM model to study reaction mechanisms on substrates is presented.
- The analytical SECM model was validated with numerical simulations.
- The hydrogen oxidation reaction (hor) was analyzed by SECM on Pt substrates.
- The optimal experimental conditions to study the hor on Pt were determined.

Scanning electrochemical microscopy (SECM) in the feedback mode was used to analyze the complete mechanism of the hydrogen oxidation reaction (hor). A general SECM equation was proposed to carry out the kinetic analysis of the dependences of the tip current (iT) on the substrate potential (ES) and on the tip-substrate distance (d). This SECM equation involves the contribution of a thin-layer cell (TLC) with no aprioristic restrictions about the reaction mechanism. A dependence of the TLC current on ES previously developed for the hor operating through the Tafel-Heyrovsky-Volmer mechanism was included in the proposed SECM model. The domain of conditions where the equation properly reproduces the SECM responses was determined by contrasting the calculated iT(ES, d) dependences with simulated curves obtained by a numerical method using varied kinetic and geometric parameters. The experimental conditions where the model can be used were explored by analyzing the hor on Pt. The present treatment provides a versatile tool for the application of SECM to the kinetic and mechanistic analysis of the hor, which can be easily adapted for the analysis of any multi-step electrocatalyzed reaction on infinite substrates.