Ammonia is a commodity chemical that is manufactured worldwide and supports a growing population. Industrially, ammonia synthesis is dominated by the energy-intensive Haber−Bosch process, thus necessitating the development of a greener approach. Recently, two-dimensional transition-metal carbides/nitrides/carbonitrides, MXenes are emerging as optimistic prospects for the environmentally benign electro-and photocatalytic nitrogen fixation to ammonia. MXenes exhibit excellent hydrophilicity, large specific surface area, superior electrical conductivity, and abundant active sites. Their promising properties for functionalization prosper efficacious enhancement strategies such as co-catalyst loading as well as the formation of MXene-based composites and MXenederived hybrids. In this Review, the characteristics, fabrication strategies, and applications of MXene-based materials in electrocatalytic and photocatalytic nitrogen fixation, relative to their roles and features, are systematically reviewed. Finally, the current challenges and future directions toward sustainable ammonia generation are provided. This work is expected to deliver valuable insights for the rational engineering of MXene catalysts toward a greener route of ammonia synthesis.

Photocatalytic conversion of carbon dioxide (CO2) into value‐added fuels is a vastly promising anthropogenic chemical carbon cycle to combat the greenhouse effect while meeting the ever‐increasing energy demand. Recently, lead‐based halide perovskites have demonstrated great potential in various applications including photochemical reduction of CO2. However, in view of lead toxicity, the exploration of a lead‐free alternative is crucial for long term application. Herein, a series of lead‐free mixed halide perovskites Cs3Sb2ClxBr9−x (0 ≤ x ≤ 9) is prepared via a facile antisolvent recrystallization technique, where the incorporation of a secondary halide enhances the charge transfer and separation while allowing precise tuning of bandgap between 2.59 and 2.90 eV. Theoretical calculations further reveal that the formation of mixed Cl/Br halides engenders favorable charge redistribution due to lower octahedral distortion, which in turn strengthens CO2 adsorption and activation. Under visible light illumination, the optimal dual halide perovskite, Cs3Sb2Cl4Br5 manifests substantial twofold and fourfold enhancements of CH4 yield over the single halide perovskite, Cs3Sb2Br9 and Cs3Sb2Cl9, respectively. In brief, this study provides a compelling demonstration of lead‐free mixed halide perovskites for photocatalytic CO2 reduction, and it is anticipated to drive further application of perovskite‐based photocatalysts toward a diverse range of artificial photoredox reactions.

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