Electrochemical Performance and Degradation Mechanisms of BaCe _0.7 Zr _0.1 Y _0.2 O _3‐δ /BaZr _0.8 Y _0.2 O _3‐δ Based Tubular Protonic Ceramic Electrolysis Cells and Stacks for

Protonic Ceramic Electrolysis Cells (PCECs) attract much attention for efficient green hydrogen production in recent years, however, their application is still limited due to the lack of stable and robust large area single cells. In this paper, small batch production of large area tubular PCEC single cells with 10-31 cm² effective area is reported, and PCEC stacks are assembled and evaluated. The assembled 4-cell-stack in parallel based on BaZr_0.8Y_0.2O_3-δ (BZY) electrolyte cells achieves 26 W and 257 mA cm^-2 at 1.4 V, and it maintains hydrogen production for 15 200 h at 700 °C with a degradation rate of 1.4% 1000 h^-1. Ni agglomeration and BaCO₃ formation are found to be the main degradation mechanisms by post-mortem analysis. The added BaCe_0.7Zr_0.1Y_0.2O_3-δ (BCZY) electrolyte interlayer improves the electrochemical performance and the 15 cm² single cell can get an electrolysis current density of 200 mAcm^-2 at 1.3 V and 550 °C. The assembled 4-cell-stack in combined serial and parallel connections achieves 58 W at 650 °C. Several thermal cycles to room temperature of the single cell and stack are both achieved to show structural stability and reliability. All these results show excellent stability of BZY material and Ni-BCZY electrode supported tubular structure for PCEC applications.