Perovskites are mixed-metal oxides that are attracting much scientific and application interest owing to their low price, adaptability, and thermal stability, which often depend on bulk and surface characteristics. These materials have been extensively explored for their catalytic, electrical, magnetic, and optical properties. They are promising candidates for the photocatalytic splitting of water and have also been extensively studied for environmental catalysis applications. Oxygen and cation non-stoichiometry can be tailored in a large number of perovskite compositions to achieve the desired catalytic activity, including multifunctional catalytic properties. Despite the extensive uses, the commercial success for this class of perovskite-based catalytic materials has not been achieved for vehicle exhaust emission control or for many other environmental applications. With recent advances in synthesis techniques, including the preparation of supported perovskites, and increasing understanding of promoted substitute perovskite-type materials, there is a growing interest in applied studies of perovskite-type catalytic materials. We have studied a number of perovskites based on Co, Mn, Ru, and Fe and their substituted compositions for their catalytic activity in terms of diesel soot oxidation, three-way catalysis, N2O decomposition, low-temperature CO oxidation, oxidation of volatile organic compounds, etc. The enhanced catalytic activity of these materials is attributed mainly to their altered redox properties, the promotional effect of co-ions, and the increased exposure of catalytically active transition metals in certain preparations. The recent lowering of sulfur content in fuel and concerns over the cost and availability of precious metals are responsible for renewed interest in perovskite-type catalysts for environmental applications.

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In photocatalysis, imperative photoredox behavior and narrow band gap are important properties to exploit solar light for water splitting reaction. Nanostructured ceria (cerium dioxide/CeO2) with Ce3+/Ce4+ (photoredox couple) shows significant enhancement in photocatalytic activity, however, no significant activity for water splitting reaction. The present study mainly focuses on incorporation of Pt on nanostructured mesoporous ceria by wet-impregnation method and its evaluation for donor assisted photocatalytic water splitting reaction. The BET analysis shows much higher surface area (119–131 m2 g–1) for unmodified as well as Pt modified mesoceria samples as compared to commercial ceria (24.4 m2 g–1), although structure was not ordered. The incorporation of Pt on mesoceria shows remarkable influence on photocatalytic hydrogen generation activity, and 1 wt % Pt was found to be optimized content, with broader light absorption. This photocatalyst was optimized with respect to photocatalyst dose, use of different sacrificial donors and their concentrations as well as other experimental parameters, with 34 h time course evaluation, yielding cumulative 1.52 mmol of hydrogen, under visible-NIR light irradiation and using ethanol as a sacrificial donor. The XPS, BET and photoluminescence studies imply that the enhanced photocatalytic hydrogen evolution in the case of mesoceria is due to the unison of high surface area, reduced recombination of photogenerated charge carrier and lower Ce3+ concentration in the case of mesoceria.

As a group of large-surface-area nonmetal materials, polymeric carbon nitride (C x N y ) and its hybrid structures are nowadays of ever-increasing interest for use in energy devices involved in energy conversion and storage, offering low expenses and facile production processes. With the growing requirement for clean and renewable energy generation and storage systems, progress in the replacement of expensive noble-metal catalysts with C x N y -based materials as efficient electrocatalysts has expanded considerably, and the demand for these materials has increased. The modified C x N y architectures are beneficial to electrocatalytic applications, improving their moderate electrical conductivities and capacity loss. The present review strives to highlight the recent advances in the research on the aforementioned identities of C x N y -derived materials and their structurally modified polymorphs. This review also discusses the use of C x N y -based materials in fuel cells, metal–air batteries, water splitting cells, and supercapacitor applications. Herein, we deal with electrocatalytic oxidation and reduction reactions such as hydrogen evolution, oxygen evolution, oxygen reduction, CO2 reduction, nitrogen reduction, etc. Each device has been studied for a clearer understanding of the patent applications, and the relevant experiments are reviewed separately. Additionally, the role of C x N y -derived materials in some general redox reactions capable of being exploited in any of the relevant devices is included.