ZrO₂‑Supported Fe₂O₃ for Chemical-Looping-Based Hydrogen Production: Effect of pH on Its Structure and Performance As Probed by X‑ray Absorption Spectroscopy and Electrical Conductivity Measurements

Chemical looping is a promising process to produce high purity H₂ while simultaneously capturing CO₂. The key requirement for this process is the availability of oxygen carriers that possess a high cyclic redox stability, resistance to carbon deposition, and thermal sintering. In this study, ZrO₂-supported Fe₂O₃-based oxygen carriers were developed using a coprecipitation technique. We assess in detail the influence of the key synthesis parameter, i.e., the pH value at which the precipitation was performed, on the morphological properties, chemical composition, local structure, and cyclic redox stability. The performance of the new oxygen carriers was compared to unsupported Fe₂O₃ and Al₂O₃-supported Fe₂O₃. A higher degree of disorder in the local structure of oxygen carriers precipitated at low pH values was confirmed by X-ray absorption spectroscopy (XAS) measurements. Electrical conductivity measurements showed that supporting Fe₂O₃ on ZrO₂ lowered significantly the activation energy for charge transport when compared to pure Fe₂O₃. In line with this observation, ZrO₂-supported oxygen carriers displayed a very high and stable H₂ yield over 15 redox cycles when precipitation was performed at pH > 5