The aim of this paper was to investigate an influence of the nanocrystalline Ce(0.8)A(0.02)O(2)(-delta) (A = Mn, Fe, Co, Ni, Cu) materials on the direct internal reforming of biogas in SOFC. Structural analysis of fabricated compounds has been done. An in-situ analysis of a composition of outlet gases from operating SOFC was performed using FTIR spectroscopy with simultaneous electrical tests. It was found out, that type of dopant strongly affects biogas reforming process. The differences in absolute values of current density resulted mostly from a microstructure and probably phase composition of a deposited layers. Fuel cells with Ce0.8Co0.2O2-delta and Ce0.8Ni0.2O2-delta additional layers presented the highest drop of current density after switching from hydrogen to biogas, but simultaneously they were the most stable in time. Additional chemical analysis revealed that steam reforming and methane pyrolysis might be dominating reactions while working in biogas atmosphere. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.