Unravelling Complex Electrode Processes by Differential Electrochemical Mass Spectrometry and Rotating Ring Disk Electrode Technique

The competition of oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) on pc-Pt electrode in weakly acidic solution (pH~3) under condition when both reactions are thermodynamically allowed are investigated using the rotating ring disc electrode (RRDE) technique and differential electrochemical mass spectrometry (DEMS). The partial currents of HER and ORR producing H2O2 or H2O are quantified. The results show that: i) ORR occurs preferentially in a diffusion-limited manner (either limited by the mass transfer of O2 or H+) and only the excess H+ not being consumed by the ORR can be converted to Had and H2; ii) At potentials negative of the onset for Had formation, the H2O2 production rate first increases then decreases with the increasing overpotential. Possible origins for H2O2 yield in HER region are suggested. Present results demonstrate that combining DEMS and RRDE techniques can be powerful for deriving the intrinsic kinetics of individual processes in a complex electrochemical system.