Perovskites are used in many applications such as electrode materials in fuel cells or as catalysts e.g. in syngas conversion, CO oxidation, N2O decomposition, or oxygen/hydrogen evolution reactions.Chemical composition and crystal structures govern physical and chemical properties. We plan a systematic structure evaluation of simple and complex substituted perovskites of type ABO3 (A=La,Ca,Sr; B=Ni,Co,Fe,Mn) which show deviations from the ideal crystal bulk structures. By means of neutron scattering combined with synchrotron data, oxygen vacancies, elemental distribution on A and B sites as well as locally distorted structures will be analyzed. The results with then be related to the catalytic performance of the perovskites which have been tested as cathode materials for the oxygen evolution reaction (OER) in the electrochemical water splitting.