Temperature effects on the kinetics of formic acid electrooxidation are studied on Pt(111) and on Pt(111) modified by irreversibly adsorbed Bi under both potentiodynamic and potentiostatic conditions. We propose two modes of action of irreversibly adsorbed Pi on the kinetics of HCOOH oxidation: (i) the inhibiting effect due to a blocking of active Pt sites and (ii) the catalytic effect due to the enhanced adsorption of OHad on the Pt sites adjacent to Bi. This counteracting behavior led to the fact that under steady-state conditions no difference in the overall activity was observed between Pt(111) and Pt(111)/Bi. Therefore, Pt(111)/Bi does not represent a catalytically active system of technological relevance.