Enhancing Electrochemical Performance of YBa0.95K0.05Co4O7+δ Cathode via Mn/Fe/Ni/Cu/Zn Doping at Co Sites for Proton-Conductor Solid Oxide Fuel Cells

The well-matched thermal expansion coefficient between YBa0.95K0.05Co4O7+δ and electrolyte materials makes it a highly promising electrode for proton-conducting solid oxide fuel cells (H-SOFCs). However, its limited electrochemical performance hampers the enhancement of the cell power density. In this study, we significantly improved the oxygen reduction reactivity and electrochemical properties of YBa0.95K0.05Co4O7+δ by introducing transition metal dopants (Mn/Fe/Ni/Cu/Zn) at the Co site, with a doping concentration of x = 0.05. Experimental results indicate that Mn doping yields the most substantial performance enhancement. Transition metal doping modulates the material’s band gap structure and conductivity, with Mn doping narrowing the band gap and enhancing conductivity by 105%. Conductivity relaxation tests further confirm that Mn doping accelerates oxygen ion transport, reducing the relaxation time. X-ray photoelectron spectroscopy analysis shows that the oxygen vacancy concentration in the Mn-doped systems increases by 72%. Symmetric cell tests reveal that Mn doping reduces cathodic polarization impedance by 33% at 700 °C, while Fe, Ni, and Zn doping results in varying impedance increases due to competitive mechanisms. The peak power density of a single cell with the Mn-doped cathode reaches 657 mW cm–2 at 700 °C, surpassing the 531 mW cm–2 obtained with the undoped sample. This work demonstrates the efficacy of a multielement doping strategy to optimize SOFC electrode materials, offering an approach for their design.