In this study low energy ion scattering (LEIS) was used to analyse the surface of Co₂B catalysts, before and after being used for water electrolysis. During the electrolysis, the catalyst is activated, and Co is deposited at the surface. Scanning electron microscopy (SEM) shows morphological changes in the form of micrometre-sized platelets forming at the surface, but the chemical nature of this altered surface must be studied by other means.

 With its extreme surface sensitivity of a single monolayer, LEIS offers unique insights whenever the outermost atomic layer is important for the application. This is surely the case for heterogeneous catalysis, as the chemistry will be determined almost exclusively by the atoms exposed at the surface. The signals for other surface analytical techniques will always originate from a depth range of at least a few atomic layers, if not multiple nm. Any special properties of the top atomic layer will be difficult to identify when the signal is averaged over significant depth

LEIS achieves single-layer sensitivity by scattering noble gas ions off the surface atoms of the sample and analysing the energy of the backscattered ions. The energy after the collision is determined by the mass of the scattering partner, so that the outer atomic layer is analysed by identifying the elements in the surface by the energy of the peaks, and the composition by the intensities. Any ions penetrating the outer layer are preferentially neutralised and they lose additional kinetic energy via nuclear and electronic stopping, such that scattering from deeper layers is easily distinguished from top atomic layer scattering. On top of this surface signal from the outer layer, sub-surface scattering reveals additional information about the distribution of elements in the first few nm of the sample.

One crucial aspect of LEIS is sample cleaning, as surfaces are generally covered by undesired volatile organic compounds (VOCs) from exposure to ambient air. These VOCs must be removed prior to the analysis to reveal the actual surface of interest. Here we employed two different means of sample cleaning, namely exposure to atomic oxygen and thermal desorption. We show how these affect the measurement results, and how conclusions can be drawn about the chemical composition of the catalyst surface, both before and after the electrolysis has taken place.