Research on intermediate-temperature protonic ceramic electrolysis cells as ammonia synthesis reactors

Ammonia is a carbon-free fuel with high energy density, offering advantages over hydrogen due to its easier liquefaction, which facilitates storage and transportation. This makes it a promising candidate for future applications in energy storage and transportation. Currently, traditional ammonia production relies primarily on the Haber-Bosch process, which requires high temperatures and pressures, leading to significant fossil fuel consumption and carbon emissions. Thus, it is necessary to develop low-carbon technological pathway for ammonia synthesis, making green ammonia synthesis a critical research area under the “dual carbon” goals. Protonic ceramic electrolysis cells (PCECs) can utilize renewable electricity to electrolyze steam at the oxygen electrode, generating protons that are then used at the fuel electrode to synthesize ammonia. This process offers higher energy efficiency, positioning PCECs as potential reactors for green ammonia synthesis. In this study, a porous Ni-BaCe_0.7Zr_0.1Y_0.2O_3−δ (BCZY) composite ceramic was employed to investigate the material properties of the composite fuel electrode and the working conditions for ammonia synthesis. At 650 ℃, with a nitrogen-to-hydrogen partial pressure ratio of 1∶3, an ammonia synthesis rate of 1.04×10⁻¹⁰ mol/(s·cm²) was achieved. Building on these results, a tubular protonic ceramic electrolysis cell with an active area of 10 cm² was fabricated using isostatic pressing-impregnation-co-sintering method. Each part of cell was firmly bonded without delamination. The tubular cell demonstrated excellent hydrogen production performance, achieving an electrolysis current of 3 A at 650 ℃ under a 1.4 V applied voltage, and operated stably under ammonia synthesis conditions. The significant voltage-dependent response in ammonia synthesis rate confirmed that the in-situ hydrogen production within the tubular cell effectively facilitated the ammonia synthesis process on the Ni-BCZY fuel electrode, with an enhanced ammonia synthesis rate reaching 7.02×10⁻¹⁰ mol/(s·cm²). Long-term test of electrochemical ammonia synthesis using the tubular cell showed that both the electrochemical performance and the ammonia synthesis rate remained stable. The post-test cell morphology exhibited no significant changes, indicating stability in the presence of a complex atmosphere containing N₂, H₂ and NH₃. These findings demonstrate the potential of tubular PCECs as reactors for green ammonia synthesis.