Effects of Barium Excess on the Performance of Multilayer Microtubular Proton Ceramic Electrochemical Hydrogen Pumps with BaxCe0.7Zr0.1Y0.1Yb0.1O3−δ (x = 1.05, 1.10, 1.15)

A series of Ba-excess BaxCe0.7Zr0.1Y0.1Yb0.1O3−δ (BxCZYYb, x = 1.05, 1.10, 1.15) was employed as electrolytes. Multilayer microtubular protonic ceramic electrochemical hydrogen pumps (PCEHPs) with a current collector/anode/electrolyte/cathode/current collector architecture were fabricated by a triple-layer one-step co-spinning and co-sintering method. Their hydrogen separation performance was systematically investigated over the temperature range of 200–400 °C. The results show that the hydrogen pump employing the B1.05CZYYb electrolyte delivers the optimal performance. At 250 °C and a feed H2 concentration of 30 vol%, the hydrogen permeation flux achieves 1.01 mL min−1 cm−2, with Faradaic efficiency maintained above 95%. EDS line-scan results reveal the presence of Ni-rich precipitates on grain surfaces in the co-sintered electrolyte layer. It is speculated that, under the co-sintering conditions, excessive Ba may induce lattice distortion and reduce Ni solubility in the perovskite lattice, thereby promoting Ni exsolution at grain surfaces; the precipitated Ni could, in turn, hinder proton conduction and increase the ohmic resistance. These findings suggest that the hydrogen-permeation performance of multilayer PCEHPs is governed by the combined effect of Ba excess and Ni rather than by Ba doping alone. This work provides a valid experimental basis and theoretical reference for component optimization and structural design of high-performance co-sintered microtubular PCEHP devices.