Oxygen reduction reaction is an extensively researched area in the fields of catalysis and electrochemistry due to its relevance to storage devices technologies and electrochemical energy conversion. In the last few years, several platinum-based heterogeneous electro-catalyst methods have been investigated. It has been identified that nano- and micro- structuring of plain platinum surfaces enhances the electrochemically active surface area.
In this study, direct surface structuring method was applied to produce micro and nano-dimensioned surface topographies achieved by an ultra-short pulse laser beam incident on the platinum metal surface without re-deposition of ejected particles on special substrates. Laser treatment allows for modification of materials by focusing a huge amount of energy on a selected surface area of a material in a controlled process.
Two processes have been identified to increase the surface area: through ablation, the surface roughness of the platinum metal is observed to increase, and the precipitated metal droplets develop a porous coating. Karsten Lange and Juergen Caro at Leibniz University Hannover and in collaboration with Malte Schulz-Ruhtenberg from LPKF Laser& Electronics AG in Germany demonstrated for the first time, the catalytic attributes of varying laser-induced surface structures using platinum plates as electrode material. They applied powder X-ray diffraction to determine changes in the crystal structure generated by laser structuring. In addition, they obtained scanning electron microscopy images in order to characterize the surface topology. Their work is published in peer-reviewed journal, ChemElectroChem.
The authors polished platinum plates before laser treatment. Laser structuring with linear polarized laser radiation with 1-picosecond pulses at 100 kHz repetition rate was done on the plates. In order to generate the desired texture, the authors changed two parameters such as the mean power of the laser beam and the spatial overlap of the laser pulses.
The authors identified and discussed various parameters for picosecond laser structuring of platinum, and enumerated their impact on the electrochemical attributes. Direct ultrashort pulse laser structuring method was identified as a straightforward way to generate nano and micro-sized surface topographies.
The researchers then conducted electrochemical characterization of the samples after laser treatment. A three-electrode configuration was applied with graphite counter electrode and a silver-silver chloride reference electrode.
Laser treatment was observed to allow for material surface modification and enlargement of amount of accessible active sites for catalysis by over 1500 times as compared to polished surface. Owing to the rapid quenching, it was impossible to build up large surface area modification with definite crystal structures. Aging experiments confirmed an electrochemical sinter process in the laser-induced structures, which slightly reduced the catalytic activity. X-ray diffraction analyses indicated no change of the crystalline attributes of the platinum by the electrochemical sintering.
Platinum was picked as a case study only, in view of its excellent electrochemical properties. Practically, all metal surfaces can be modified through ultra-short pulse laser structuring. For this reason, a good number of applications in the areas of hydrogen and oxygen production from electro catalytic splitting of water by hydrogen evolution reaction as well as oxygen evolution reaction are practical. In addition, selected applications in heterogeneous catalysis are conceivable.
Karsten Lange, Malte Schulz-Ruhtenberg, and Jurgen Caro. Platinum Electrodes for Oxygen Reduction Catalysis Designed by Ultrashort Pulse Laser Structuring. ChemElectroChem 2017, 4, 570–576.Go To ChemElectroChem