Platinum border atoms as dominant active site during the carbon monoxide electrooxidation reaction

Active site is a concept that is widely applied in heterogeneous catalysis. However, this concept is difficult to achieve for experimental analysis. Low coordinated atoms located in step, edge, and corner sites act as active sites for several catalytic reactions on catalytic metal surfaces. The study of carbon monoxide electrooxidation on stepped single crystal surfaces is normally adopted for assessing the role of defects in heterogeneous electrocatalysis. For this approach, it has been observed that steps of (110) orientation act as active sites for electrooxidation of carbon monoxide adsorbed on platinum electrodes in an acidic medium.

Dr. Gonzalo García and colleagues from the University of La Laguna in Spain proposed a new approach that involved platinum nanodiscs adsorbed in gold surface as source of low-coordinated atoms in order to observe their catalytic abilities compared to carbon monoxide oxidation. Their aim was to develop a concept of catalytic materials prepared with a control on surface defect occurrence.  From that they would discern the catalytic behavior of lowly and highly coordinated atoms. Their work is published in peer-reviewed journal, international journal of hydrogen energy.

The authors prepared platinum planar clusters via micro-emulsion method. They prepared two micro-emulsions one containing 100% excess hydrazine while the other contained hexachloroplatinic acid in an aqueous state. The solutions were then stirred for some hours and mixed together to form a single homogeneous micro-emulsion.

Micelles with platinum clusters were deposited on gold surface and washed in acetone in order to obtain a monolayer of micelles with platinum coated on the gold surface. The authors deposited a secondary monolayer on the first sample and followed the same procedure, and the sample was heat treated.

The authors controlled the annealing process in a bid to finely tune the presence of lowly and highly coordinated platinum atoms. They confirmed this by carbon monoxide stripping voltammetry together with x-ray photoelectron spectroscopy and scanning tunneling microscopy.  This way, the authors were in a position to individualize the effects of materials rich and free of catalytic defects site on the carbon monoxide electrochemical oxidation state. The researchers were also capable of correlating low-coordinated platinum atoms and the appearance of carbon monoxide peaks compared to highly-coordinated platinum atoms.

This study successfully investigated the concept of active sites in electrocatalysis. It developed an approach to investigate platinum sites with varied activity in carbon monoxide oxidation. The catalytic material was synthesized with a high control on defect abundance. In this way, the authors were capable of analyzing the catalytic activity of lowly and highly coordinated platinum atoms.  They finally proved that boarder sites of platinum and platinum-gold solution were the principle causes of the improved catalytic activity towards the electrooxidation of adsorbed carbon monoxide.