Structure and Charge Carrier Separation Promotion Effects of Antiphase Boundaries in Cesium Lead Bromide

Defects in lead halide perovskites (LHPs) may have a significant impact on charge carrier separation, but the roles of the defects are not fully understood. Here, using aberration-corrected scanning transmission electron microscopy (STEM), different types of antiphase boundaries (APBs) are discovered in CsPbBr3 platelets. APBs with a displacement vector of 1/4[111] are characterized by double layers of CsBr layers at the (110) or (001) planes, while APBs at the (112) planes are formed through edge sharing of PbBr6 ̵octahedra. Significant lattice distortions are determined at (001) and (110) APBs on the basis of quantitative analyses of STEM images. Density functional theory calculations demonstrate that all three types of APBs can induce band offsets at their valence bands and conduction bands. The APBs are intended to promote the separation of photogenerated charge carriers in LHPs. These findings provide a crystal engineering technique for enhancing the optoelectronic properties of LHPs by controlling defects

Bifunctional HER/OER or OER/ORR Catalytic Activity of Two-Dimensional TM₃(HITP)₂ with TM = Fe–Zn

The designability of metal–organic frameworks (MOFs) offers a promising platform for development of multifunctional electrocatalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) which are long-desired in wide-range applications, such as overall water splitting, fuel cells, and metal–air batteries. On the basis of the recent experimental progresses, we proposed from first-principles a family of two-dimensional (2D) MOFs, consisting of transition metal (TM) atoms (TM = Fe–Zn) and 2,3,6,7,10,11-hexaiminotriphenylene (C18H12N6) functional group (HITP), namely TM3(HITP)2, with versatile multifunctional catalytic activity, which can be ascribed to synergistic effects of TM and organic ligands. Cu3(HITP)2 can serve as a bifunctional catalyst for HER and OER, while Fe3(HITP)2, Co3(HITP)2, and Zn3(HITP)2 are promising for both OER and ORR. The overpotentials of these TM3(HITP)2 monolayers are comparable or even superior to those of the well-developed noble catalysts. The tunable catalytic activity in the TM3(HITP)2 opens an avenue for design of low-cost and multifunctional catalysts and may find applications in the fields of clean and renewable energy

Nitrogen-Doped Triphenylene-Graphdiyne as Metal-Free Multifunctional (Photo)Electrocatalysts for Overall Water Splitting

Hydrogen (H2) produced by electrochemical (EC) and photoelectrochemical (PEC) overall water splitting is regarded as promising clean energy technologies, while exploring low-cost and high-efficient catalysts remains a challenging task. Herein, we demonstrate the catalytic activities of nitrogen-doped triphenylene-graphdiyne (N@TP-GDY) monolayers using first principles calculations in combination with nonadiabatic molecular dynamics. Our results show that the introduction of sp/sp2-hybridized N atoms can greatly regulate the electronic structures of TP-GDY monolayer, presenting appealing bifunctional EC performance with low overpotentials of 0.06 and 0.49 V for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Meanwhile, the redox ability of the photogenerated electrons and holes in the N@TP-GDY systems is strong enough to drive HER and OER processes at acid and alkaline conditions, respectively. Moreover, the lifetime of the photogenerated carriers is greatly improved up to 729 ps in the N@TP-GDY structures compared with that of pristine TP-GDY monolayers (110 ps). This means that the N@TP-GDY monolayers can serve as a promising photocathode or photoanode in the PEC cells. These intriguing results highlight the role of N-atom doping in the TP-GDY systems for overall water splitting, providing useful insights into the rational design of metal-free catalysts for sustainable production of H2

Rational Design of Black Phosphorus-Based Direct Z‑Scheme Photocatalysts for Overall Water Splitting: The Role of Defects

Black phosphorus (BP) has received increasing interest as a promising photocatalyst for water splitting. Nevertheless, exploring the underlying hydrogen evolution reaction (HER) mechanism and improving the water oxidizing ability remains an urgent task. Here, using first-principles calculations, we uncover the role of point defects in improving the HER activity of BP photocatalysts. We demonstrate that the defective phosphorene can be effectively activated by the photoinduced electrons under solar light, exhibiting high HER catalytic activity in a broad pH range (0–10). Besides, we propose that the direct Z-scheme in the defective BP/SnSe2 heterobilayer is quite feasible for photocatalytic overall water splitting. This mechanism could be further verified based on the excited state dynamics method. The role of point defects in the photocatalytic mechanism provides useful insights for the development of BP photocatalysts

Carrier Separation Enhanced by High Angle Twist Grain Boundaries in Cesium Lead Bromide Perovskites

Grain boundaries (GBs) have a profound impact on mechanical, chemical, and physical properties of polycrystalline materials. Comprehension of atomic and electronic structures of different GBs in materials can help to understand their impact on materials’ properties. Here, with aberration-corrected scanning transmission electron microscopy (STEM), the atomic structure of a 90° twist GB s in CsPbBr3 is determined, and its impact on electron–hole pair separation is predicted. The 90° twist GB has a coherent interface and the same chemical composition as the bulk except for the lattice twist. Density functional theory (DFT) calculation results indicate that the twist GB has an electronic structure similar to that of the bulk CsPbBr3. An electronic potential at the GBs enhances the separation of photogenerated carriers and promotes the motion of electrons across the GBs. These results extend the understanding of atomic and electronic structure of GBs in halide perovskites and propose a potential strategy to eliminate the influence of GBs by GB engineering

Bifunctional Electrocatalytic Activity of Bis(iminothiolato)nickel Monolayer for Overall Water Splitting

The bifunctional catalysts for the hydrogen and oxygen evolution reactions (HER and OER) with high efficiency, low cost, and easy integration for future renewable energy systems are highly desirable. Here, on the basis of first-principles calculations, we predicted a two-dimensional (2D) metal–organic framework (MOF) bifunctional electrocatalyst, namely, bis­(iminothiolato)nickel (NiIT) monolayer, for overall water splitting. The semi-metallic properties and low HER/OER overpotentials (−0.15/0.50 V) ensure the remarkable electrocatalytic performance of the 2D MOF electrocatalyst. The spatially separated HER and OER active sites with different electronegativities facilitate the electrocatalytic processes. Our findings highlight a promising precious-metal-free bifunctional electrocatalyst for efficient overall water splitting, as well as a novel strategy in catalyst design

Insights into Photoinduced Carrier Dynamics and Overall Water Splitting of Z‑Scheme van der Waals Heterostructures with Intrinsic Electric Polarization

Using first-principles calculations in combination with nonadiabatic molecular dynamics (NAMD), we propose novel heterostructures of carbon nitride (C7N6) and the Janus GaSnPS monolayer as promising direct Z-scheme photocatalysts for solar-driven overall water splitting. The out-of-plane electric field due to the electric polarization which is dependent on the stacking pattern alters the band alignment and catalytic activity of the heterostructures. The relatively strong interfacial nonadiabatic coupling and long quantum coherence time accelerate the interlayer carrier recombination, enabling a direct Z-scheme photocatalytic mechanism. More importantly, the redox ability of the remanent photogenerated carriers in the Z scheme is strong enough to trigger both the hydrogen evolution reaction (HER) and oxygen reduction reaction (OER) simultaneously without the help of sacrificial agents. Our work reveals a fundamental understanding of ultrafast charge carrier dynamics at vdW heterointerfaces as well as new design prospects for highly efficient direct Z-scheme photocatalysts