Imaging of catalytic activity of platinum on p-InP for photocathodical hydrogen evolution

Platinum was deposited photocathodically on single-crystalline p-type indium phosphide from aqueous hexachloroplatinic acid. The laser-induced deposition was performed with a scanning optical microscope set-up equipped with a He/Ne-laser. This technique allowed the formation of deposits at different positions of the electrode along laser scanned lines in a single combinatorial experiment under variation of potential, light intensity and time of exposure. Subsequent spatially resolved photocurrent measurements in sulphuric acid at different potentials and comparison with optical micrographs of the deposits revealed the different catalytic activity for hydrogen evolution of platinum deposits precipitated under different conditions. The catalytically most active deposits were formed at low light intensity (45 mW/cm2) and relatively negative potentials (−0.3 V vs. SCE). With increasing light intensity and negative potentials corrosion of p-InP dominated platinum deposition, while high light intensities and more positive potentials resulted in more densely deposited platinum of low catalytic activity.