Present approaches to use simple crystal electrodes for DEMS have certain disadvantages: Thin layer cells with defined diffusion and/or convection require large single discs of 1 cm diameter; also, a part of the crystal surface has to be pressed against a spacer. Other approaches, which allow the use of small bead crystals, have the disadvantage of ill-defined mass transport from the surface into the vacuum of the mass spectrometer. Here, we present a new approach which combines the advantage of defined convection of one dual thin layer cell with the possibility to use small bead crystals. The usual hanging meniscus is replaced by a cone-shaped capillary, through which electrolyte is flowing to a thin layer mass spectrometric detection compartment. In order to ensure a stable hanging meniscus at the electrode, the electrolyte level is maintained at constant height with the help of a second electrolyte pump adjusted to the same electrolyte flow as that sucked through the capillary. We demonstrate the quality of single-crystal voltammetry in this arrangement and its use for the examination of formic acid and methanol oxidation on Pt(100), Pt(15 1 1), and Pt(711). Current efficiencies for CO2 during methanol oxidation were also determined.
DEMS cellBead single-crystal electrodeHanging meniscusMethanol oxidationElectrochemical mass spectrometry