Spatial Mapping of Methanol Oxidation Activity on a Monolithic Variable-Composition PtNi Alloy Using Synchrotron Infrared Microspectroscopy

The use of synchrotron-sourced infrared radiation to map the electrochemical activity of a binary metal (Pt and Ni) alloy is demonstrated. The alloy is created in such a way that its metal concentration varies along one of its dimensions thus creating a continuum of electrocatalyst compositions on a single electrode. Localized methanol oxidation activity is determined spectroscopically by measuring the rate of CO₂ production at variable positions along the alloy concentration gradient using an infrared microscope. Numerical simulations of the kinetically controlled reaction demonstrate that qualitative assessment of relative reaction rates is possible as long as the reaction is followed on time scales smaller than those that lead to diffusional broadening. Characterization of the alloy before and after electrochemical experiments reveals significant levels of base metal leaching. Highly dealloyed regions of the sample show the highest rates of methanol activity and have a final Ni atomic composition of approximately 5%. Surface roughening from the dealloying process is shown to be at least partially responsible for enhanced activity