Ex-situ surface preparation and analysis: Transfer between UHV and electrochemical cell

The further optimization of electrode materials for fuel cells in laboratory studies offers two main approaches: (i) improving the understanding of the microscopic electrode processes by observation with in-situ and ex-situ methods; and (ii) the systematic compositional and structural variation of surfaces to create model electrodes for electrocatalytic measurements. The ultra high vacuum (UHV) environment offers unique possibilities for both surface preparation and analysis and has thus been used extensively in recent electrocatalytical research work. At the same time, methods allowing the in-situ observation of electrochemical processes has also gone through impressive advances in recent years, and in many cases it has been found that earlier ex-situ results obtained in UHV needed to be revised due to changes of the electrode surfaces during the transfer into UHV. In the following we will discuss some of the most frequently applied ex-situ methods in electrocatalytic research and review some of the important aspects concerning the reliability of the resulting data. Utilizing a number of examples, we will demonstrate how such combined UHV electrochemistry experiments can be technically realized, including a discussion of commonly encountered practical problems. We will further point out the advantages offered by the electrocatalytical characterization of UHV designed and UHV characterized model electrodes. In our opinion, this is a very promising approach to UHV/electrochemistry experimentation: on the one hand, the uncertainties due to the transfer between UHV and electrochemical environment are less significant compared to emersion experiments of adsorbed adlayers; on the other hand, well-established UHV preparation techniques combined with structural characterization tools (atomic force microscopy (AFM)/scanning tunneling microscopy (STM)) provide the possibility of precisely tailoring defined model electrodes. Some examples from research on anode catalysts are given to illustrate this unique capability of UHV electrochemistry setups as powerful tool for the systematic tailoring of model electrodes. Keywords: electrocatalysis; bifunctional catalysts; morphology of catalysts; electrochemical mass spectroscopy; ex-situ measurements; electrochemical thermal desorption MS (ECTDMS); infrared spectroscopy; thin-layer electrochemical cell; scanning tunneling microscopy (STM); surface defects, auger electron spectroscopy (AES); emersion; ex-situ UHV analysis; electron spectroscopy for chemical analysis (ESCA); low energy electron diffraction (LEED); low energy ion scattering (LEIS); model surfaces, model electrodes; preparation of electrode surfaces; reflection high energy electron diffraction (RHEED); thermal desorption spectroscopy (TDS); UHV transfer of electrodes; ultra high vacuum (UHV); X-ray photoelectron spectroscopy (XPS)