Insights into the Redox Behavior of Pr0.5Ba0.5MnO3−δ-Derived Perovskites for CO2 Valorization Technologies

In situ temperature-programmed (TP) analyses in a multianalytical approach including X-ray diffractometry (XRD), temperature-programmed reduction (TPR), thermogravimetry (TGA), near-edge X-ray absorption fine structure spectroscopy (NEXAFS) are used to study the relationship between redox properties and structural changes in PrBaMnO(m-PBM), PrBaMnO(r-PBM), and PrBaMnO(o-PBM) when exposed to reduction/oxidation cycles. TP-XRD analysis shows that under reducing conditions, between 300 and 850 °C, the biphase perovskite m-PBM turns into the monolayered perovskite r-PBM. Stabilization of the latter phase at room temperature requires early oxidation in air at a high temperature (850 °C) to avoid segregation, resulting in the formation of the oxidized layered phase (o-PBM). The o-PBM layered perovskite is characterized by the H-TPR profile, showing two reduction peaks at temperatures below 500 °C. TP-NEXAFS characterization reveals the copresence of Mn(IV) (60%), Mn(III) (30%), and Mn(II) (10%) and helps to interpret the reduction profile: Mn(IV) converts to Mn(III) at ~300 °C (I pk), Mn(III) to Mn(II) at ~450 °C (II pk). The TGA characterization confirms the reversibility of the o-PBM <-> r-PBM process at 800 °C; in addition, it shows that the r-PBM can be oxidized almost completely (~99%) also by COwithout accumulation of carbonates. This study sheds light on the peculiar redox behavior of PBM-based materials and paves the way for their application as oxygen carriers and catalytic promoters in different COenhancement technologies. Here, we discuss the results obtained to develop versatile and redox-resistant electrodes for solid oxide electrochemical cell/solid oxide fuel cell applications.