As a consequence of the ongoing climate crisis and the resulting intensification of the use of environmentally friendly but volatile energy sources, technologies for energy conversion and storage are becoming increasingly relevant. Fuel and electrolysis cells, which convert chemical energy into electrical energy and vice versa, represent a promising option. Proton conducting fuel cells (PCFC), which currently still exhibit a relatively low technology readiness level, offer several advantages in terms of efficiency, costs and longevity. Current research is focused on developing new materials for the air electrode, as this is the primary factor limiting performance. The present work examines the fundamental material characteristics of acceptor-substituted self-generated composites with the objective of future utilisation in PCFC air electrodes. It is expected that the two perovskite phases of the composite will together fulfil the desired properties. These include sufficient proton uptake and conductivity, good electronic conductivity, and good catalytic activity for oxygen reduction. A substantial number of samples with varying compositions and substituted with different acceptors are synthesised and characterised in order to evaluate their suitability for the intended application. For this purpose, a variety of complementary methods are employed, including novel and innovative approaches. The crystal structure, lattice parameters and relative phase fractions are determined by X-ray diffraction. By annealing experiments, the miscibility gap is investigated as a function of the composition of the crystallographic B-site of the perovskite (ABO3), which is analysed employing ICP-OES and STEM. Thermogravimetry is used to determine the oxygen nonstoichiometry and the effective proton uptake capacity. As it is not possible to quantify the distribution of the proton uptake between the two phases of the composite, thermodynamic parameters can only be calculated for single phases. The mobility of the protons is determined using a novel approach, based on isotope exchange experiments and subsequent analysis of the resulting diffusion profiles. Conductivity and conductivity relaxation measurements are employed to analyse the electrical conductivity and oxygen exchange kinetics. The results of the present work demonstrate the existence of structure-property relationships, thereby providing design guidelines for optimising the materials with regard to the desired properties. Moreover, the fundamental relationships indicate the existence of limitations to the optimal distribution of acceptors within the selected material system. Based on these observations, suggestions are made regarding potential alternative material systems that could be considered in future research.