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A mixed ionic−electronic conducting (MIEC) double perovskite, PrBaCo 2 O 5+δ (PBC), was synthesized and evaluated as the heterogeneous catalyst to generate radicals from peroxymonosulfate (PMS) for the oxidative degradation of organic wastes in aqueous solution. A superior catalytic activity was obtained for PBC, which was much higher than that of the most popular Co 3 O 4 nanocatalyst. More importantly, a detailed mechanism of PMS activation on the MIEC perovskite was proposed. Electron paramagnetic resonance (EPR) and radical competitive reactions suggested that both sulfate radicals (SO 4 •−) and hydroxyl radicals ( • OH) participated in and played important roles in the catalytic oxidation processes. Oxygen temperature-programmed desorption (O 2 -TPD) demonstrated that the PBC perovskite oxide is capable of facilitating an easier valence-state change of the B-site cation (cobalt ions) to mediate a redox process. Additionally, the oxygen vacancies could facilitate the bonding with PMS molecules and promote the reactivity of cobalt ions for PMS activation. Electrochemical impedance spectroscopy (EIS) was also performed to evidence charge transfer and surface reaction rates of the PBC catalyst that are much faster than those of Co 3 O 4 . Additionally, suppressed cobalt leaching was also achieved through tailoring the pH value of the reaction solution. This study provides insight into MIEC perovskites in catalytic reactions and applications.

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Oxygen production by air separation is of great importance in both environmental and industrial processes as most large scale clean energy technologies require oxygen as feed gas. Currently the conventional cryogenic air separation unit is a major economic impediment to the deployment of these clean energy technologies with carbon capture (i.e. oxy-fuel combustion). Dense ceramic perovskite membranes are envisaged to replace the cryogenics and reduce O 2 production costs by 35% or more; which can significantly cut the energy penalty by 50% when integrated in oxy-fuel power plant for CO 2 capture. This paper reviews the current progress in the development of dense ceramic membranes for oxygen production. The principles, advantages or disadvantages, and the crucial problems of all kinds of membranes are discussed. Materials development, optimisation guidelines and suggestions for future research direction are also included. Some areas already previously reviewed are treated with less attention.

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Reversible protonic ceramic cells (RePCCs) can facilitate the global transition to renewable energy sources by providing high efficiency, scalable, and fuel‐flexible energy generation and storage at the grid level. However, RePCC technology is limited by the lack of durable air electrode materials with high activity toward the oxygen reduction/evolution reaction and water formation/water‐splitting reaction. Herein, a novel nanocomposites concept for developing bifunctional RePCC electrodes with exceptional performance is reported. By harnessing the unique functionalities of nanoscale particles, nanocomposites can produce electrodes that simultaneously optimize reaction activity in both fuel cell/electrolysis operations. In this work, a nanocomposite electrode composed of tetragonal and Ruddlesden–Popper (RP) perovskite phases with a surface enriched by CeO2 and NiO nanoparticles is synthesized. Experiments and calculations identify that the RP phase promotes hydration and proton transfer, while NiO and CeO2 nanoparticles facilitate O2 surface exchange and O2‐ transfer from the surface to the major perovskite. This composite also ensures fast (H+/O2‐/e‐) triple‐conduction, thereby promoting oxygen reduction/evolution reaction activities. The as‐fabricated RePCC achieves an excellent peak power density of 531 mW cm‐2 and an electrolysis current of −364 mA cm‐2 at 1.3 V at 600 °C, while demonstrating exceptional reversible operation stability of 120 h at 550 °C.

Electrochemical energy storage systems with high power output, large energy density, and stable performance are urgently needed. Zn-air batteries are one of the most promising candidates owing to abundant and inexpensive resources used, decent energy density, and the high reduction potential of Zn. The most significant challenge of primary and rechargeable aqueous Zn-air batteries is the relatively high overpotential due to the sluggish kinetics of oxygen reactions on the air cathode. Highly efficient oxygen catalysts derived from metal-organic framework (MOF) precursors have demonstrated remarkable capabilities for facilitating the oxygen reactions. In this contribution, we review the recent progress in state-of-the-art MOF-derived materials for use as oxygen catalysts in primary and rechargeable Zn-air batteries. We first summarize the development of several important MOF derivatives, including transition metal-nitrogen-carbon (TMÀNÀC) composites, carbon-based transition metal compounds, and metal-free carbons. The advantages and disadvantages of these MOF-derived catalysts are also discussed. Strategies for optimization of the gas-liquid diffusion and the long-range electronic transportation on the air cathode with these MOF-derived catalysts are also demonstrated. Finally, the main challenges and some perspectives for developing advanced MOF-derived catalysts applied in Zn-air batteries are provided.