High Temperature Oxygen Sensors Based on Ruddlesden-Popper Type Oxides

There is a desire for oxygen gas sensors that are capable of high temperature operation and possibly in harsh environments of combustion processes. Sensor implementation would allow for combustion processes to be more efficient and more environmentally friendly. As a result, numerous studies have been done on different types of electrodes in an electrochemical sensor. In this study, praseodymium nickelate (Pr₂NiO₄) response to various oxygen environments at 750 °C was investigated. Pr₂NiO₄ was chosen due to its rapid diffusion and surface exchange coefficients of oxygen at elevated temperatures. Pr₂NiO₄ adopts a Ruddlesden-Popper structure and consists of oxygen octahedra between which there are rock-salt type layers allowing oxygen hopping via oxygen interstitial sites. Electrochemical impedance spectroscopy (EIS) was used to determine the transport resistance in an electrochemical cell. The evolution of electrode structure was determined by using X-ray diffraction (XRD). EIS results show that the electrode responds instantaneously to changes in oxygen partial pressure. Oxygen reduction reaction seems favored over oxygen evolution reaction at low potentials. In addition, EIS response was stable over the measurement period. XRD analysis shows the presence of phase transformation to higher ordered structures. Further research needs to be done in order to fully understand electrochemistry at low potentials.