Scanning electrochemical microscopy of a fuel-cell electrocatalyst deposited onto highly oriented pyrolytic graphite

The hydrogen evolution reaction (HER) has been examined on a platinum electrocatalysts (Johnson Matthey HSA platinum black) dispersed onto a flat highly oriented pyrolytic graphite (HOPG) electrode using an atomic force microscope (AFM) modified to perform scanning tunneling microscopy (STM) and scanning electrochemical microscopy (SECM). For both STM and SECM experiments the same Pt/Ir tips produced by electrochemical etching of Pt/Ir wire followed by coating with varnish have been used. The coating process leaves only the very end of the tip exposed. Positioning the SECM tip 42 nm from one of the particles allows monitoring of hydrogen evolution from that particle as a function of substrate potential. In a separate experiment the substrate has been polarized at a potential at which hydrogen evolution occurs and the SECM tip rastered over the surface to obtain images of the local concentration of hydrogen. This map indicates the activity of hydrogen production as a function of position. (C) 2000 Elsevier Science Ltd. All rights reserved.