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

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.