Photo-Electrochemical Scanning Droplet Cell for Screening of Photocatalysts

Reasearch on photocatalysts is rapidly increasing. They will hopefully help us solving or at least reducing our energy problems. Heterogeneous and homogeneous catalysts are considered in various approaches. The preparation of modified or entirely new photoactive materials requires an effective screening of the material. This is performed using the photo-electrochemical scanning droplet cell PE-SDC that was introduced in its initial form some 10 years ago [1]. The basic idea is using a glass capillary with a tip diameter of e.g. 100 µm that is wetting a small part of a substrate. An in build reference electrode guarantees a full 3 electrode arrangement. In the set up presented here various light sources can be randomly used to illuminate the investigated small spot. The light sources are either diode lasers with fixed wavelength or a continuous emitter for which the wavelength of interest is chosen using a monochromator [2].

            The performance of this system is demonstrated using traditional semi conductors such as n-Si, p-Si and III-IV semiconductors proving that:

      photo potential (continuous or chopped)

      photo current (continuous or chopped)

      photo impedance (full spectra and/or fixed frequency bias scanning)

can be automatically performed.

            Material libraries of transition metal oxides have been prepared by multi source co-deposition and have been screened using the PE-SDC. This class of materials produces promising candidates for water splitting photo electrodes. In the comparison of MeOx-WOx libraries in which the metal Me is a ferrous metal like Fe, Ni or Co differences in the mechanisms are explained. There are striking differences which results form the differences in the watersplitting capacity of compositions within these libraries. What they do have in common is that they all show successful applications of a combinatorial photo-electrochemical approach in which samples are prepared and investigated in the CALMAR.

            Screening of homogeneous or immobilized catalysts is an alternative application. Complex bi-functional materials with an intramolecular donor acceptor pair are rather difficult to synthesize and therefore may exist only in several 10 mg amounts in the beginning. Here it is necessary to have an efficient method for fully characterizing such materials under these limited conditions [3]. Examples will be given to prove the effectiveness of PE-SDCs

[1] A. W. Hassel, M. Seo, Localised Photoelectrochemical Measuremnets with the Scanning Droplet Cell in Passivity and Localised Corrosion, Proc. Electrochem. Soc. (1999) 337

[2] J. P. Kollender, A. I. Mardare, A. W. Hassel, “Photoelectrochemical Scanning Droplet Cell Microscopy (PE-SDCM)”, ChemPhysChem 14 (2013) 560-567

[3] J. Gasiorowski, A. I. Mardare, N. S. Sariciftci, A. W. Hassel, “Electrochemical characterization of sub-micro-gram amounts of organic semiconductors using scanning droplet cell microscopy”, J. Electroanal. Chem. 691 (2013) 77-82