The main topic of this master thesis is the electrochemical characterization of electrolyte supported single cell SOFCs in terms of performance and long-term stability, focusing on improved preparation of the cells and development of new methods for in-operando state diagnosis. Within this thesis, a semi-automatic screen printing machine was put into operation. The optimal way of performing cell installation, screen adjustment and printing parameters, such as squeegee pressure, were determined. Flooding the screen manually provided better print results compared to automatic flooding. The adjustable squeegee pressure is important for reproducibility of the layer thickness, but the printing quality depends mainly on the properties of the paste. One aim of this thesis was to evaluate the feasibility of early artefact detection using intermodulation products in fast Fourier transforms during continuous or intermittent intermodulation analysis, such that deviations in the operating state caused by degradation mechanisms or by suboptimal process management (i.e. fuel depletion) may be detected in time. For this purpose a separate program for the evaluation of electrochemical measurements on solid oxide single cells was developed, using the principle of intermodulation analysis with Matlab as computing environment. First, experiments were conducted under conditions of accelerated aging (“chromium poisoning” of the cathode) on a symmetrical button cell. Investigations were carried out to examine whether damage diagnosis based on nonlinearities in the system response (current/voltage characteristics) is possible by means of software algorithms. Linear and nonlinear regions were successfully identified in the I/V cell characteristics. Data obtained during chromium poisoning show that intermodulation products are most pronounced at low input signal frequencies and thus grounds the method for early detection of anomalies during fuel cell operation. In addition, a new test setup was built to investigate the influence of silicon species in the gas supply of the cathode using impedance spectroscopy and current/voltage measurements in combination with intermodulation analysis. During the silicon poisoning experiment, the influence of the time-dependent degradation on I/V-characteristics, impedance spectra and intermodulation analyses were investigated. In principle, the detection of operational deviations is feasible by means of IMA.