Advanced Materials

2D oxide nanomaterials constitute a broad range of materials, with a wide array of current and potential applications, particularly in the fields of energy storage and catalysis for sustainable energy production. Despite the many similarities in structure, composition, and synthetic methods and uses, the current literature on layered oxides is diverse and disconnected. A number of reviews can be found in the literature, but they are mostly focused on one of the particular subclasses of 2D oxides. This review attempts to bridge the knowledge gap between individual layered oxide types by summarizing recent developments in all important 2D oxide systems including supported ultrathin oxide films, layered clays and double hydroxides, layered perovskites, and novel 2D‐zeolite‐based materials. Particular attention is paid to the underlying similarities and differences between the various materials, and the subsequent challenges faced by each research community. The potential of layered oxides toward future applications is critically evaluated, especially in the areas of electrocatalysis and photocatalysis, biomass conversion, and fine chemical synthesis. Attention is also paid to corresponding novel 3D materials that can be obtained via sophisticated engineering of 2D oxides.

An ABO₃‐type perovskite solid‐solution, (K_0.5Na_0.5)NbO₃ (KNN) doped with 2 mol% Ba(Ni_0.5Nb_0.5)O_3−δ (BNNO) is reported. Such a composition yields a much narrower bandgap (≈1.6 eV) compared to the parental composition—pure KNN—and other widely used piezoelectric and pyroelectric materials (e.g., Pb(Zr,Ti)O₃, BaTiO₃). Meanwhile, it exhibits the same large piezoelectric coefficient as that of KNN (≈100 pC N⁻¹) and a much larger pyroelectric coefficient (≈130 µC m⁻² K⁻¹) compared to the previously reported narrow‐bandgap material (KNbO₃)_1−x‐BNNO_x. The unique combination of these excellent ferroelectric and optical properties opens the door to the development of multisource energy harvesting or multifunctional sensing devices for the simultaneous and efficient conversion of solar, thermal, and kinetic energies into electricity in a single material. Individual and comprehensive characterizations of the optical, ferroelectric, piezoelectric, pyroelectric, and photovoltaic properties are investigated with single and coexisting energy sources. No degrading interaction between ferroelectric and photovoltaic behaviors is observed. This composition may fundamentally change the working principles of state‐of‐the‐art hybrid energy harvesters and sensors, and thus significantly increases the unit‐volume energy conversion efficiency and reliability of energy harvesters in ambient environments.

Low temperature solution processed planar‐structure perovskite solar cells gain great attention recently, while their power conversions are still lower than that of high temperature mesoporous counterpart. Previous reports are mainly focused on perovskite morphology control and interface engineering to improve performance. Here, this study systematically investigates the effect of precise stoichiometry, especially the PbI₂ contents on device performance including efficiency, hysteresis and stability. This study finds that a moderate residual of PbI₂ can deliver stable and high efficiency of solar cells without hysteresis, while too much residual PbI₂ will lead to serious hysteresis and poor transit stability. Solar cells with the efficiencies of 21.6% in small size (0.0737 cm²) and 20.1% in large size (1 cm²) with moderate residual PbI₂ in perovskite layer are obtained. The certificated efficiency for small size shows the efficiency of 20.9%, which is the highest efficiency ever recorded in planar‐structure perovskite solar cells, showing the planar‐structure perovskite solar cells are very promising.