Interface evolution unlocks the anti-poisoning capability of trace B-site excessive medium-entropy air electrodes for tubular reversible solid oxide cells

Sluggish oxygen exchange kinetics and poor robustness are critical challenges for the air electrode materials reversible solid oxide cells (RSOCs), closely related to the poisoning reaction brought by alkaline earth metal segregation and high-acidity impurities. Herein, different weight ratios of NiO are introducing with medium-entropy material SrCo_0.5Fe_0.2Ti_0.1Ta_0.1Nb_0.1O_3-δ (ME-SCF) electrode through one-pot fabrication to accelerate the oxygen exchange process, forming the trace B-site excessive medium-entropy material SrCo_0.5Fe_0.2Ti_0.1Ta_0.1Nb_0.1Ni_xO_3-δ (ME-SCFNx). With a higher oxygen surface exchange coefficient, ME-SCFN5 electrode achieves a lower polarization resistance value of 0.031Ω cm² at 700 °C, which is better than that of ME-SCF (0.037Ω cm²). More importantly, with the in-situ interfacial self-evolution, the acid-base reaction between high-acidity Cr vapor and SrO segregation with high basicity is significantly suppressed. Under Cr-containing atmosphere, the current density of the button cell with ME-SCFN5 electrode decreases at a rate of 0.052 % h⁻¹, smaller than that of the cell with ME-SCF electrode (0.084 % h⁻¹), which is attributed to the high acidic NiO protective layer formed by self-dissolution on the electrode surface. The tubular type RSOC with ME-SCFN5 electrode reaches 1280.2 mW cm⁻² at 800 °C in fuel cell mode and 1.039 A cm² at 20 % H₂O concentrations in electrolysis cell mode (1.3 V, 700 °C), with brilliant reversible cycle stability in 130 h, making the obtained material a promising air electrode candidate for advanced RSOCs.