# The Characteristically Slow Proton Transfer Coupled to Platinum Oxidation in Alkaline Polyelectrolyte as Elucidated at the Molecular Level

## TL;DR

This study reveals that proton transfer at platinum interfaces in alkaline polyelectrolyte membranes is slower than expected, affecting electrochemical reactions.

## Contribution

The paper introduces a molecular-level understanding of slow proton transfer in APEM/Pt interfaces using advanced spectroscopy and quantum-chemical calculations.

## Key findings

- Proton transfer in APEM/Pt interfaces is characteristically slow compared to conventional NaOH solutions.
- OH– in APEM is hydrated by more water molecules, reducing the driving force for proton transfer.
- The slow proton transfer is universally coupled to electrochemical reactions in devices with APEMs.

## Abstract

The proton transfer
in alkaline polyelectrolyte membrane (APEM)/electrode
interfaces is significantly coupled to the electrochemical reactions
in energy conversion and green synthesis. The OH– in APEM/electrode interfaces is characteristically without cations
in the surroundings but ambiguous in proton-transfer-coupled electrochemical
reactions at the molecular level. Here we employed in situ electrochemical surface-enhanced Raman spectroscopy and high-level
quantum-chemical calculations to elucidate the proton transfer in
the APEM/Pt interface by using electrochemical Pt oxidation as an
indicator. To manifest the characters in APEM, a comparison to that
in conventional NaOH solution was made. With the similar electron
transfer of Pt oxidation in both APEM and NaOH, the driving force
and rate of proton transfer were distinguished respectively according
to the onset oxidation potential and morphology of Pt nanoparticles,
which suggested the slow proton transfer in an APEM/Pt interface.
The similar vibrational fingerprints of subsurface oxygenated intermediates
in both APEM and NaOH solution evidenced the characteristically slow
proton transfer in an APEM/Pt interface. The high-level quantum-chemical
calculations combined with molecular dynamics simulation showed that
the driving force of proton transfer in APEM was reduced since OH– was coordinated by more water molecules in its hydration
shell. The characteristically slow interfacial proton transfer may
be universally coupled to electrochemical reactions in devices with
APEMs.