In Situ Infrared (FTIR) Study of the Mechanism of the Borohydride Oxidation Reaction on Smooth Pt Electrode

Although Pt has been thoroughly studied regarding its activity for the borohydride oxidation reaction (BOR), the BOR mechanism at Pt remains unclear: Depending on the applied potential, spontaneous BH 4 – hydrolysis can compete with the direct BOR. The goal of the present work is to provide more insight into the behavior of smooth Pt electrodes toward the BOR, by coupling in situ infrared reflectance spectroscopy with electrochemistry. The measurements were performed on a Pt electrode in 1 M NaOH/1 M NaBH 4, so as to detect the reaction intermediate species generated as a function of the applied potential. Several bands were monitored in the B—H (ν̅ ≈ 1180, 1080, and 972 cm –1 ) and B—O (ν̅ = 1325 and ∼1425 cm –1 ) bond regions upon increased electrode polarization. These absorption bands, which appear sequentially and were already detected for similar measurements on Au electrodes, are assigned to BH 3, BH 2, and BO 2 – species. In light of these experimental data and previous results obtained in our group for Pt- or Au-based electrodes, possible initial elementary steps of the BOR on platinum electrodes are proposed and discussed according to the relevant literature data.