Fluorinated Pr₂NiO_4+δ as high-performance air electrode for tubular reversible protonic ceramic cells

Reversible protonic ceramic cells (RPCCs) demonstrate increasingly potential for alleviating the worldwide energy crisis and environmental contamination through the efficient conversion between hydrogen and electricity. Reliable air electrode materials with high electrochemical activity and sufficient durability are imperatively desired for the commercialization process. Herein, the effort is targeted to improve electrochemical activity of Pr₂NiO_4+δ, a traditional triple conducting oxide with inherent durability. Through introducing the highly electronegative F⁻, the as-designed material demonstrates improved hydratability and protonic conductivity due to the attenuated the metal-oxygen bond energy which is beneficial for the diffusion of oxygen and protonic defects. As expected, the targeted material exhibits excellent performance as the air electrode of RPCCs, i.e. a peak power density of 0.58 W cm⁻² in the fuel cell mode and a current density of 2 A cm⁻² at 1.3 V in an electrolysis mode at 650 °C. Eventually, the tubular RPCCs are also successfully fabricated based on this designed material and exhibit promising performance. This work offers a substantial method to design superior air electrodes for RPCCs with excellent electrochemical activity and sufficient durability.