To check if in acidic media CO is desorbed as such, i.e., as molecular CO, from the surface of nickel during a positive linear potential sweep, we have carried out a Fourier-transform infrared spectroscopic study of this system. We have found that, in the absence of dissolved CO, in a positive linear potential sweep at 1 mV s(-1) most, if not all, of the CO chemisorbed on Ni in GO-free 0.5 M Na2SO4 acidified to pH 3.0 is electrooxidized to CO2 instead of being electrodesorbed from the surface. Furthermore, we have found that a band at 2112 cm(-1) appears at potentials near the passivation maximum of nickel. We have assigned this band to CO adsorbed on Ni oxide or on Ni-0 sites perturbed by the oxidation of the neighboring Ni atoms. As far as we know, this is the first time that such a band has been found by FTIRS during the electrooxidation of a CO-covered metal.