Thin-Layer Diamond Coating on Si Wafer for Extended Alkaline ATR-SEIRAS Investigations†

Electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) plays an important role in deciphering interfacial reaction mechanisms at molecular level. However, the corrosive etching of Si internal reflection element by OH⁻ largely impedes reliable SEIRAS measurements in strong alkaline electrolytes. Herein, a dense and chemically inert nanocrystalline diamond (NCD) film is successfully fabricated at a thickness of ~120 nm through hot filament chemical vapor deposition on a micromachined Si wafer to insulate the OH⁻ etching. A reversible interfacial water feature without spectral interference of Si-O band is obtained in 1.0 mol·L^–1 KOH on Au/NCD/Si film electrode. Afterwards, electrochemical CO reduction reaction on Cu film electrode is explored in different KOH concentrations ranging from 0.1 to 3.0 mol·L^–1 as a model reaction. A redshift of CO_L band, as well as its lower intensity but faster depletion kinetics, is noted with increasing electrolyte pH, whereas CO_B is identified as an inert spectator accumulating on Cu surface. Our present work demonstrates the alkaline resistant feature of diamond/Si composite internal reflection element, which could be a powerful platform to study electrocatalytic reactions in strong alkaline media.