Switching on the Photocatalysis of Metal–Organic Frameworks by Engineering Structural Defects

Defect engineering is a versatile approach to modulate band and electronic structures as well as materials performance. Herein, metal–organic frameworks (MOFs) featuring controlled structural defects, namely UiO‐66‐NH₂‐X (X represents the molar equivalents of the modulator, acetic acid, with respect to the linker in synthesis), were synthesized to systematically investigate the effect of structural defects on photocatalytic properties. Remarkably, structural defects in MOFs are able to switch on the photocatalysis. The photocatalytic H₂ production rate presents a volcano‐type trend with increasing structural defects, where Pt@UiO‐66‐NH₂‐100 exhibits the highest activity. Ultrafast transient absorption spectroscopy unveils that UiO‐66‐NH₂‐100 with moderate structural defects possesses the fastest relaxation kinetics and the highest charge separation efficiency, while excessive defects retard the relaxation and reduce charge separation efficiency.     

Unravelling the Synergy between Oxygen Vacancies and Oxygen Substitution in BiO2−x for Efficient Molecular-Oxygen Activation

Defects in nanomaterials often lead to properties that are absent in their pristine counterparts. To date, most studies have focused on the effect of single defects, while ignoring the synergy of multiple defects. In this study, a model of photocatalytic O₂ activation was selected to unravel the role of dual defects by decorating bismuth oxide with surface O vacancies and bulk O substitution simultaneously. The introduction of dual defects led to a spatial and electronic synergistic process: i) O substitution induced a local electric field in the bulk of BiO_2−x, which promoted bulk separation of electrons and holes immediately after their generation; ii) O vacancies efficiently lowered the conduction band, served as the capture center for electrons, and thus facilitated the adsorption and activation of O₂. This effect was greatly promoted by the coexistence of bulk O substitution, and DFT calculations showed that only O substitution near an O vacancy could have this effect.     

Coagulated SnO2 Colloids for High‐Performance Planar Perovskite Solar Cells with Negligible Hysteresis and Improved Stability

Organic–inorganic perovskite solar cells with a planar architecture have attracted much attention due to the simple structure and easy fabrication. However, the power conversion efficiency and hysteresis behavior need to be improved for planar‐type devices where the electron transport layer is vital. SnO₂ is a promising alternative for TiO₂ as the electron transport layer owing to the high charge mobility and chemical stability, but the hysteresis issue can still remain despite the use of SnO₂. Now, a facile and effective method is presented to simultaneously tune the electronic property of SnO₂ and passivate the defects at the interface between the perovskite and SnO₂. The perovskite solar cells with ammonium chloride induced coagulated SnO₂ colloids exhibit a power conversion efficiency of 21.38 % with negligible hysteresis, compared to 18.71 % with obvious hysteresis for the reference device. The device stability can also be significantly improved.     

Understanding the Activity of Co-N4−xCx in Atomic Metal Catalysts for Oxygen Reduction Catalysis

Atomic metal catalysis (AMC) provides an effective way to enhance activity for the oxygen reduction reaction (ORR). Cobalt anchored on nitrogen-doped carbon materials have been extensively reported. The carbon-hosted Co-N₄ structure was widely considered as the active site; however, it is very rare to investigate the activity of Co partially coordinated with N, for example, Co-N_4−xC_x. Herein, the activity of Co-N_4−xC_x with tunable coordination environment is investigated as the active sites for ORR catalysis. The defect (di-vacancies) on carbon is essential for the formation of Co-N_4−xC_x. N species play two important roles in promoting the intrinsic activity of atomic metal catalyst: N coordinated with Co to manipulate the reactivity by modification of electronic distribution and N helped to trap more Co to increase the number of active sites.     

Soft Lattice and Defect Covalency Rationalize Tolerance of β-CsPbI3 Perovskite Solar Cells to Native Defects

Although all-inorganic metal halide perovskites (MHPs) have shown tremendous improvement, they are still inferior to the hybrid organic–inorganic MHPs in efficiency. Recently, a conceptually new β-CsPbI₃ perovskite reached 18.4 % efficiency combined with good thermodynamic stability at ambient conditions. We use ab initio non-adiabatic molecular dynamics to show that native point defects in β-CsPbI₃ are generally benign for nonradiative charge recombination, regardless of whether they introduce shallow or deep trap states. These results indicate that MHPs do not follow the simple models used to explain defect-mediated charge recombination in the conventional semiconductors. The strong tolerance is due to the softness of the perovskite lattice, which permits separation of electrons and holes upon defect formation, and only allows carriers to couple to the low-frequency vibrations. Both factors decrease notably the non-adiabatic coupling and slow down the dissipation of energy to heat.     

Interfacial Defect Engineering for Improved Portable Zinc–Air Batteries with a Broad Working Temperature

Atomic‐thick interfacial dominated bifunctional catalyst NiO/CoO transition interfacial nanowires (TINWs) with abundant defect sites display high electroactivity and durability in the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations show that the excellent OER/ORR performance arises from the electron‐rich interfacial region coupled with defect sites, thus enabling a fast‐redox rate with lower activation barrier for fast electron transfer. When assembled as an air‐electrode, NiO/CoO TINWs delivered the high specific capacity of 842.58 mAh g_Zn^?1, the large energy density of 996.44 Wh kg_Zn^?1 with long‐time stability of more than 33 h (25 °C), and superior performance at low (?10 °C) and high temperature (80 °C).     

Observing Defect Passivation of the Grain Boundary with 2-Aminoterephthalic Acid for Efficient and Stable Perovskite Solar Cells

Metal halide perovskite solar cells (PSCs), with their exceptional properties, show promise as photoelectric converters. However, defects in the perovskite layer, particularly at the grain boundaries (GBs), seriously restrict the performance and stability of PSCs. Now, a simple post-treatment procedure involves applying 2-aminoterephthalic acid to the perovskite to produce efficient and stable PSCs. By optimizing the post-treatment conditions, we created a device that achieved a remarkable power conversion efficiency (PCE) of 21.09 % and demonstrated improved stability. This improvement was attributed to the fact that the 2-aminoterephthalic acid acted as a cross-linking agent that inhibited the migration of ions and passivated the trap states at GBs. These findings provide a potential strategy for designing efficient and stable PSCs regarding the aspects of defect passivation and crystal growth.