Exploring Fast Room Temperature Oxygen Diffusion in Pr₂NiO_4+δStand-Alone Single-Crystalline Electrodes

Performant solid-state oxygen ion conductors are of utmost importance for current and future energy applications. A significant enhancement of oxygen mobility has been recently established in the intermediate temperature range from 500 to 700 °C, but materials showing notable room temperature oxygen diffusion are still rare. While devices for energy storage or transformation generally employ polycrystalline electrodes, we report here on the electrochemical oxygen permeation capacity of single-crystalline Pr2NiO4+δ electrodes, showing remarkably high oxygen diffusion under ambient conditions, with 60 μm thickness. The electrochemically performed oxygen reduction was followed up by in situ single-crystal synchrotron diffraction, revealing oxygen mass transport corresponding to a chemical diffusion coefficient of D∗ = 6.3 × 10-11 cm2 s-1. Rapid oxygen diffusion becomes possible due to the predominant absence of grain boundaries, as revealed from the evolution of the individual twin domains. For the first time, the formation of anti-phase domains, organized on a length scale of 7 nm, could be evidenced during a chemical reaction, indicated by sharp satellite reflections of the second order. Our results demonstrate the yet unexplored potential of single crystals as stand-alone electrodes for high-throughput solid oxygen ion conductors under already ambient conditions.