Activity of a PtBi alloy in the electrochemical oxidation of formic acid

Formic acid oxidation in acid solution was examined on a PtBi alloy characterized by X-ray photoelectron spectroscopy. Three chemical states of Bi, i.e., PtBi or Bi(0), Bi2O3 and BiO(OH) were found. Electrochemical characterization revealed that PtBi follows the behavior of its constituents, as well as that Bi is not stable in the PtBi alloy. It was established that the activity of PtBi is highly dependent of the reduction/oxidation of Bi species. Oxidation of formic acid does not occur on Bi covered PtBi. Rotated PtBi showed impressive activity relative to polycrystalline Pt, with the onset potential shifted by 0.25 V towards more negative potentials, and attained steady state current densities at 0.05 V, higher by two and half orders of magnitude. The activity of PtBi is caused by UPD phenomena of Bi on Pt, which was electrochemically detected. In addition, based on XPS analysis, it is proposed that the activity of PtBi could also be caused by the bifunctional action of hydroxylated Bi species.