Ni-doped cobalt-free perovskite as the cathode for proton ceramic fuel cells

Proton ceramic fuel cells (PCFCs), as a clean energy technology with broad application prospects, hold tremendous potential in the field of energy conversion. The development of PCFCs is limited by air electrode due to the slow kinetics at below 700°C. This paper introduces novel cobalt-free cathode Ba_0.5Sr_0.375Fe_0.875-xZr_0.125Ni_xO_3-δ (D-BSFZNx, x = 0, 0.125, 0.25) for PCFCs. Among them, D-BSFZ exhibits a second phase, which transfers to a pure phase after Ni doping. Based on the first-principles calculations (Density Functional Theory (DFT)), the oxygen vacancy formation energy decreases from 0.37 eV for D-BSFZ to 0.04 eV for D-BSFZN0.125. The research results indicate that Ni doping favors the formation of $V_O^{..}$. The Density of States (DOS) and energy band diagram indicate a reduction in the band gap from 0.0065 eV to 0.0017 eV. The maximum conductivity increases from 43.20 to 64.59 S cm⁻¹ within the temperature range of 300–800 °C, suggesting that Ni doping can enhance the conductivity of D-BSFZ. The polarization resistance of D-BSFZN electrode on BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ (BZCYYb) electrolyte at 650 °C is 0.06 Ω cm² in air, and the polarization resistance stability test at 550 °C can reach 100 h without significant degradation. The maximum power densities (MPD) of the single cell with D-BSFZN0.125 as air electrode at 650 °C reaches 779 mW cm⁻².