Study On The Electrocatalytic Oxidation Of Hydrogen By Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is an in-situ electrochemical technology with both high special resolution and chemical sensitivity. The SECM can be used to study the electrocatalytic activities of noble metals (e.g. Pt, Ru, Rh and Ir etc) and get important kinetic information which can not be obtained using the conventional electrochemical methods. Using the scanning electrochemistry microscope technique, it is possible to study the electrochemical inhomogeneity of metal surface and metal/solution interface, explore the interface reaction mechanism and kinetics of heterogeneous electron transfer, and deeply investigates the effects of the composition and surface morphology of metallic electrocatalysts, temperature and the solution pH value, etc on the electrocatalytic activities of metals. Therefore, the SECM technique can promote the electrochemical catalysis research to more microscopic and comprehensive levels.In this work, the SECM tip is made of a platinum wires sealed in glass capillary, the substrate electrode is pure platinum (99.99%) or platinum particulate-modified glass carbon (GC)/polyaniline (PAni) electrode. The feedback and generation-collection modes are the characteristics of SECM methods. By the combination of traditional electrochemical methods, such as cyclic voltammogram (CV) and chronoamperometry, and SECM's approach curve and area scanning imaging, the electrocatalytic activity of platinum for hydrogen oxidation in acidic and alkaline solutions can be investigated.The main work is as follows:1) Based on the unique feedback mode of scanning electrochemistry microscopy, the Faraday current image of microprobe at different substrate surfaces can be measured by means of approach curve and the area scanning in the acidic solution system. At the same time, the surface morphology and the electrochemical activeness distribution of substrate electrode have been characterized. Moreover, compared to use traditional electrochemical methods, this technique can be applied to directly prove the effect of factors on the electrocatalytic activity of Pt at different potentials.2) The area scanning to the substrate can be obtained by selecting the tip generation-substrate collection (TG-SC) mode of scanning electrochemistry microscope in alkaline system. The magnitude of substrate current reflects the rate of hydrogen oxidation reaction. On the basis of the reaction rate, the influence of substrate potential and the concentration of OH~- on the electrocatalytic activity of Pt have been determined. It is found that the electrocatalytic activity of Pt for hydrogen oxidation reaction is highest at the substrate potential of -0.4V. The electrocatalytic activity of Pt increases with the concentration of OH~- in solution. However, the electrocatalytic activity of Pt decreases greatly when the concentration of OH~- is higher than 0.5 M.3) The electrocatalytic activity of platinum particulate modified GC/ PAni electrode for hydrogen oxidation has been investigated by using the feedback mode of SECM in acidic solution. The rate constants of hydrogen oxidation at different potentials have been calculated according to the data obtained from the approach curve. It is seen that, compared with the Pt particles directly deposited on the GC electrode, the platinum particulate modified GC/PAni electrode has not only much higher dispersion of Pt particles in a porous PAni structure but also higher electrocatalytic activity for hydrogen oxidation.