Infrared spectra of carbon monoxide adsorbed on a smooth gold electrode Part I. EMIRS spectra in acid and alkaline solutions

Electrochemically modulated infrared spectroscopy (EMIRS) was applied to the study of adsorption of CO on gold in 0.5 M sulfuric acid and 1 M sodium hydroxide solutions. A CO stretch band was observed with a peak intensity of ca. 0.2 % between 1850 and 2000 cm⁻¹ in 1 M NaOH, while a very weak band was detected between 1950 and 2050 cm⁻¹ in 0.5 M H₂SO₄. The bands were assigned to linear CO species adsorbed on the gold surface. In 1 M NaOH, electrooxidation of the strongly adsorbed CO species, which was detected by EMIRS, starts from ca. 0.5 V (RHE) with a sharp voltammetric current peak at 1.0 V at 50 mV/s, while electrooxidation of the bulk CO starts from ca. 0 V in the absence of the strongly adsorbed CO species on Au. The strongly adsorbed CO species acts as a poison for the electrooxidation of CO in the lower potential region.