Methanol oxidation at platinum electrodes in alkaline solution: comparison between supported catalysts and model system

Abstract

Methanol oxidation was studied in 0.1 M NaOH at supported Pt electrodes, and compared with the single crystal Pt electrodes, Pt(1 1 1), Pt(1 1 0) and Pt(3 3 2), chosen as model systems, and with a polycrystalline Pt electrode. The supported Pt electrodes were obtained by chemical (Pt–C/GC) and electrochemical (Pt/GC) deposition of the catalyst layer on glassy carbon resulting in the same metal loading of 20 μgPt cm−2. Using STM in air, the average particle size distributions, 3–6 nm at Pt–C/GC and 4–32 nm at Pt/GC were determined. Both supported Pt catalysts were less active than polycrystalline Pt. Negligible differences in the kinetics observed between Pt–C/GC and Pt(1 1 0) and also Pt/GC and Pt(1 1 1) suggested that the activities of supported Pt electrodes could be correlated with the activities of single crystal Pt electrodes oriented as the sites dominating in the Pt particles in catalyst deposits. The electrocatalytic activities of the electrodes studied increase in the sequence: Pt(3 3 2) > polycrystalline Pt > Pt–C/GC ∼ Pt(1 1 0) > Pt/GC ∼ Pt(1 1 1). On the basis of diagnostic criteria obtained, the chemical reaction between HCOad and OHad giving formate was proposed as the rate limiting step in methanol oxidation.