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Flexible zinc-air batteries (ZABs) are expected to become a promising candidate in energy storage equipment for wearable electronic devices. However, the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have impeded the development of ZABs. Herein, an FeCo- and N-codoped bifunctional electrocatalyst (FeCoNCF) is fabricated by simple one-pot and pyrolysis strategies. Concretely, the bacterial cellulose (BC) and Prussian blue analogue (PBA) derived transition metal and nitrogen doped carbon (M-N-C) composites provide ORR and OER active sites. FeCoNCF exhibits outstanding ORR and OER activities. It displays a favorable high half-wave potential (0.81 V) and a low overpotential at 10 mA cm

Halide perovskites have attracted great attention owing to their outstanding performance in optoelectronic applications and solar cells. Recently, two-dimensional (2D) Cs3Sb2I9 nanocrystals (NCs) have attracted sustained interest due to their potentially useful photovoltaic behavior. However, their practical application is impeded by the large bandgap. In this study, the bandgap of 2D Cs3Sb2I9 NCs is successfully narrowed from 2.05 eV to 1.36 eV by means of a high pressure with a measurable rate of 33.7%. Optical changes of 2D Cs3Sb2I9 NCs originate from Sb–I bond contraction and I–Sb–I bond angle changes within the [SbI6]3− octahedra, which determines the overlap of orbitals. Angle dispersive synchrotron X-ray diffraction spectra and Raman spectra of Cs3Sb2I9 NCs indicate that the structural amorphization gradually begins at about 14.0 GPa and the changes are reversible once pressure is completely released. The band gap is slightly smaller after decompression than that under the initial ambient conditions, resulting from the incomplete recrystallization process. First-principles calculations further elucidate that variations in band gaps are mainly governed by the orbital interactions associated with the distortion of the Sb–I octahedral network upon compression. The research enhances the fundamental understanding of 2D Cs3Sb2I9 NCs and is expected to greatly advance the research progress of perovskites in band gap interception at high pressures. Meanwhile, this study demonstrates that pressure processing can be used as a robust strategy to improve materials-by-design in applications.

Lead-free double halide perovskite nanocrystals (NCs) are attracting increasing attention due to their non-toxic nature and exceptional stability as a substitute material for lead-based perovskites. Herein, we investigate the relationship between the structural and optical properties of double halide perovskite Cs2AgBiBr6 NCs under high pressure. In situ synchrotron high-pressure powder X-ray diffraction and Raman experiments indicated that the structure of Cs2AgBiBr6 NCs transformed into a tetragonal from a cubic system at 2.3 GPa. Pressure-dependent absorption demonstrated that the band gap changes in the sequence red-shift → blue-shift. First-principles calculations further indicated that the band gap evolution was highly related to the orbital interactions, associated with the tilting and distortion of [AgBr6]5− and [BiBr6]3− octahedra under pressure. It is worth noting that the quenched absorption peak of Cs2AgBiBr6 NCs was slightly blue-shifted compared with that of the initial one under ambient conditions, which is in stark contrast to that of the corresponding bulk counterparts. This is because the structure of the sample was not yet recovered and maintained a certain degree of distortion after fully releasing the pressure. What's more, the NCs after decompression are a mixture of cubic and tetragonal phases, which leads to a larger quenched band gap than that of the initial value. Our results improve the understanding of the structural and optical properties of nanostructured double halide perovskites, thus providing a basis for their application in optoelectronic devices.

Halide perovskites have attracted great attention owing to their outstanding performance in optoelectronic applications and solar cells. Recently, two-dimensional (2D) Cs3Sb2I9 nanocrystals (NCs) have attracted sustained interest due to their potentially useful photovoltaic behavior. However, their practical application is impeded by the large bandgap. In this study, the bandgap of 2D Cs3Sb2I9 NCs is successfully narrowed from 2.05 eV to 1.36 eV by means of a high pressure with a measurable rate of 33.7%. Optical changes of 2D Cs3Sb2I9 NCs originate from Sb-I bond contraction and I-Sb-I bond angle changes within the [SbI6]3- octahedra, which determines the overlap of orbitals. Angle dispersive synchrotron X-ray diffraction spectra and Raman spectra of Cs3Sb2I9 NCs indicate that the structural amorphization gradually begins at about 14.0 GPa and the changes are reversible once pressure is completely released. The band gap is slightly smaller after decompression than that under the initial ambient conditions, resulting from the incomplete recrystallization process. First-principles calculations further elucidate that variations in band gaps are mainly governed by the orbital interactions associated with the distortion of the Sb-I octahedral network upon compression. The research enhances the fundamental understanding of 2D Cs3Sb2I9 NCs and is expected to greatly advance the research progress of perovskites in band gap interception at high pressures. Meanwhile, this study demonstrates that pressure processing can be used as a robust strategy to improve materials-by-design in applications.

Lead-free double halide perovskite nanocrystals (NCs) are attracting increasing attention due to their non-toxic nature and exceptional stability as a substitute material for lead-based perovskites. Herein, we investigate the relationship between the structural and optical properties of double halide perovskite Cs2AgBiBr6 NCs under high pressure. In situ synchrotron high-pressure powder X-ray diffraction and Raman experiments indicated that the structure of Cs2AgBiBr6 NCs transformed into a tetragonal from a cubic system at 2.3 GPa. Pressure-dependent absorption demonstrated that the band gap changes in the sequence red-shift → blue-shift. First-principles calculations further indicated that the band gap evolution was highly related to the orbital interactions, associated with the tilting and distortion of [AgBr6]5- and [BiBr6]3- octahedra under pressure. It is worth noting that the quenched absorption peak of Cs2AgBiBr6 NCs was slightly blue-shifted compared with that of the initial one under ambient conditions, which is in stark contrast to that of the corresponding bulk counterparts. This is because the structure of the sample was not yet recovered and maintained a certain degree of distortion after fully releasing the pressure. What's more, the NCs after decompression are a mixture of cubic and tetragonal phases, which leads to a larger quenched band gap than that of the initial value. Our results improve the understanding of the structural and optical properties of nanostructured double halide perovskites, thus providing a basis for their application in optoelectronic devices.