# Nitrile Groups as Build-In Molecular Sensors for Interfacial Effects at Electrocatalytically Active Carbon–Nitrogen Materials

## TL;DR

This paper introduces a new method to study interfacial effects in electrocatalytic reactions using nitrile groups as molecular sensors in carbon-nitrogen materials.

## Contribution

The study introduces a carbon-based C2N-type electrocatalyst with nitrile groups for in situ electrochemical Stark spectroscopy.

## Key findings

- The ν(C≡N) peak shows a red-shift at more negative potentials under noncatalytic conditions.
- Catalytic conditions cause a semipermanent blue-shift in the ν(C≡N) peak, indicating restructuring of the electrochemical double layer.
- The nitrile groups act as effective Stark reporter groups for probing interfacial electric fields during electrocatalysis.

## Abstract

Electrocatalytic reactions are influenced by various
interfacial
phenomena including nonspecific interaction forces. For many examples,
their contributions to the catalytic cycle have yet to be identified.
Noncovalent interactions between the electrode and the electrolyte
can be described by the local electric field environment at the interface
and are experimentally accessible based on the Vibrational Stark Effect.
We herein present a carbon-based C2N-type electrocatalyst
that is active for the hydrogen evolution reaction and that contains
nitrile functions as Stark reporter groups. With this system, we expand
the range of electrocatalytically active systems suitable for electrochemical
Stark spectroscopy while taking a step away from pure model systems.
The stretching mode ν(C≡N) was analyzed via experimental
and calculated Raman spectroscopy, revealing a defect character of
the inherent CN groups. The ν(C≡N) peak position was
furthermore studied via in situ electrochemical Raman spectroscopy.
At noncatalytic conditions, a linear dependence between an applied
electric potential and ν(C≡N) peak shift is observed,
resulting in a red-shift at a more negative potential. At catalytic
conditions, deviations from the linearity occur, and a semipermanent
blue-shift of the CN peak is observed after electrocatalysis, implying
a restructuring of the electrochemical double layer and therefore
a change in the local electric field environment due to the catalytic
turnover and the associated interfacial processes.