Abstract
The competition between the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) on a polycrystalline Pt (pc-Pt) electrode in weakly acidic solutions (pH ≈ 3) under the condition when both reactions are thermodynamically allowed is investigated using the rotating ring disk 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 and (ii) at potentials negative of the onset of Had formation, the H2O2 production rate first increases and then decreases with the increasing overpotential. Possible origins for the H2O2 yield in the 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.
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