The greatest challenges of the solid oxide fuel cell (SOFC) technology are its reliability and durability, both of them considering a variety of possible fuels. To address those issues, understanding of the ongoing processes in SOFCs is of crucial importance. The ability to monitor electrochemical processes online and to identify fast alternating operating conditions offers a possibility to determine degradation-inducing processes at their preliminary stage. Thus, their early identification would provide timely counteractions and inhibit irreversible SOFC degradation. To guarantee the safe SOFC operation, the present study focuses on: (1) investigation of SOFC behavior during feeding with different fuels, (2) development and application of non-conventional tools for online-monitoring, and (3) identification of failure modes at the early stage.