Electrochemical performance and degradation behaviour of Ni–YSZ anode-supported SOFC operated with pre-processed biogas

Solid Oxide Fuel Cells (SOFCs) offer high efficiency and fuel flexibility, yet their long-term stability under biogas-derived fuels remains insufficiently understood. This work investigates the electrochemical behaviour and degradation mechanisms of a Ni–YSZ anode-supported cell operated sequentially in dry hydrogen (DH), cold recirculation of biogas before reformer (CB), and hot recirculation of biogas before reformer (HB). The study combines voltage monitoring, IV curves, electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT) analysis, and complex nonlinear least-squares (CNLS) fitting to elucidate the evolution of anodic and cathodic processes under each fuel composition. Voltage measurements reveal distinct stability windows for the three environments, with CB showing the largest voltage decay. DRT analysis identifies six electrochemical processes, whose relative contributions vary with fuel composition. CNLS fitting confirms that the Ni–YSZ interface retains its electrochemical activity throughout the test sequence. Overall, this study provides a comprehensive interpretation of SOFC degradation under realistic biogas-derived fuels, highlighting that performance losses are primarily driven by gas-transport and cathodic polarisation processes, while the catalytic activity of Ni–YSZ anode remains largely preserved. These insights contribute to a clearer understanding of SOFC operation under renewable and pre-processed biogas feeds and provide guidance for future durability-oriented system design.