In the present work, the well-known proton conducting oxide La_0.9Sr_0.1ScO_3-δ (LSS) is modified by the introduction of transition metal cations into a Sc sublattice in order to enhance the electronic conductivity of the material. Introduced cations of transition metal are selected on the basis of their ion radii and the variety of oxidation state, thus the compositions under study are La_0.9Sr_0.1Sc_1-xMe_xO_3–α (LSSMe) (where Me is Ti, Fe, Co, Ni, or Mo). Introduction of more than 5 mol.% of a dopant leads to a change in conductivity behaviour on pO₂ which means that the predominant disorder type shifts from ionic to electronic. Electrochemical performance is studied on both symmetric and fuel cells. Impedance spectra are analysed by means of the distribution of relaxation time (DRT) technique. Both cathodes and anodes have shown great electrochemical performance with polarization resistance at 800 °C as low as 0.005 Ohm*cm² for the cathode and 0.039 Ohm*cm² for the anode in wet (water vapour pressure (pH2O) = 2.5*10⁻² atm) air and hydrogen respectively.