Advancing Applications of Black Phosphorus and BP-Analog Materials in Photo/Electrocatalysis through Structure Engineering and Surface Modulation

Rigid organic molecule pillared Ti3C2 towards high rate capability and fast sodium ion storage

MXenes are promising two-dimensional layered anode materials for rechargeable batteries due to their outstanding electrical conductivity, high specific surface area, and tunable surface functional groups. However, serious self-stacking of the layered structure and the sluggish sodium diffusion kinetics lead to inferior rate capability and cycling stability. Herein, an organic molecular pillaring strategy is reported to enlarge the interlayer spacing of Ti3C2 through a dehydration condensation reaction between the -COOH groups of 3,3',4,4'-benzene tetracarboxylic acid (BTCA) molecules and the -NH2 groups of Ti3C2-NH2, which enables rigid organic BTCA molecules to be chemically pillared into the interlayers of Ti3C2 (Ti3C2-BTCA). The rigid organic BTCA molecules not only play a dual role of pillar and strain effects in Ti3C2 layers, but also expand the interlayer spacing. Therefore, they can significantly enhance the rate capability and cycling stability of Ti3C2. Ti3C2-BTCA exhibits a reversible capacity of 182.3 mA h g-1 at a current density of 0.1 A g-1 after 2000 cycles and maintains a reversible capacity of 77.9%. Moreover, the sodium diffusion coefficient of Ti3C2-BTCA is 6.6 × 10-7 cm2 s-1. Ti3C2-BTCA shows a relatively low sodium diffusion barrier and a high sodium diffusion coefficient compared with Ti3C2. Interlayer engineering based on the organic molecular pillaring strategy is significant and meaningful for expanding the interlayer spacing of Ti3C2. This work provides theoretical guidance and new perspectives for the development of Na+ storage materials with high-rate capability.

Strategic design of emerging (K,Na)NbO3-based perovskites for high-performance piezocatalysis and photo-piezocatalysis

As a leading Pb-free perovskite material (ABO3-type), potassium sodium niobate (K,Na)NbO3 (KNN)-based ferroelectrics/piezoelectrics have been widely used in electronics, energy conversion, and storage due to their exceptional ability to interconvert mechanical and electrical energies. Beyond traditional applications, the piezoelectric potential generated by mechanical strain or stress modifies their energy band structures and facilitates charge carrier separation and transport, drawing increasing attention in emerging fields such as piezocatalysis and photo-piezocatalysis. With excellent piezoelectric properties, chemical/thermal stability, and strain-tuning capability, KNN-based materials show great promise for high-performance piezocatalytic applications. Coupling KNN with semiconductors exhibiting strong optical absorption to form heterojunctions further boosts performance by suppressing electron-hole recombination and promoting directed charge transfer, which is crucial for photo-piezocatalysis. The flexibility of KNN's perovskite structures also allows for modifications in chemical composition and crystal structure, enabling diverse design strategies such as defect engineering, phase boundary engineering, morphology control, and heterojunction formation. This review comprehensively explores the recent advancements in KNN-based piezocatalysis and photo-piezocatalysis, starting with an overview of their crystal structures and intrinsic properties. It then explores the role of piezoelectric potential in charge carrier dynamics and catalytic activity, followed by strategic design approaches to optimize efficiency in environmental remediation and energy conversion. Finally, the review addresses current challenges and future research directions aimed at advancing sustainable solutions using KNN-based materials in these applications.

Heterogeneous Interface Engineering of 2D Black Phosphorus-Based Materials for Enhanced Photocatalytic Performance

Photocatalysis has garnered significant attention as a sustainable approach for energy conversion and environmental management. 2D black phosphorus (BP) has emerged as a highly promising semiconductor photocatalyst owing to its distinctive properties. However, inherent issues such as rapid recombination of photogenerated electrons and holes severely impede the photocatalytic efficacy of single BP. The construction/stacking mode of BP with other nanomaterials decreases the recombination rate of carriers and extend its functionalities. Herein, from the perspective of atomic interface and electronic interface, the enhancement mechanism of photocatalytic performance by heterogeneous interface engineering is discussed. Based on the intrinsic properties of BP and corresponding photocatalytic principles, the effects of diverse interface characteristics (point, linear, and planar interface) and charge transfer mechanisms (type I, type II, Z-scheme, and S-scheme heterojunctions) on photocatalysis are summarized systematically. The modulation of heterogeneous interfaces and rational regulation of charge transfer mechanisms can enhance charge migration between interfaces and even maximize redox capability. Furthermore, research progress of heterogeneous interface engineering based on BP is summarized and their prospects are looked ahead. It is anticipated that a novel concept would be presented for constructing superior BP-based photocatalysts and designing other 2D photocatalytic materials.

Atomically Dispersed Metal Atoms: Minimizing Interfacial Charge Transport Barrier for Efficient Carbon-Based Perovskite Solar Cells

Carbon-based perovskite solar cells (C-PSCs) exhibit notable stability and durability. However, the power conversion efficiency (PCE) is significantly hindered by energy level mismatches, which result in interfacial charge transport barriers at the electrode-related interfaces. Herein, we report a back electrode that utilizes atomically dispersed metallic cobalt (Co) in carbon nanosheets (Co1/CN) to adjust the interfacial energy levels. The electrons in the d-orbitals of Co atoms disrupt the electronic symmetry of the carbon nanosheets (CN), inducing a redistribution of the electronic density of states that leads to a downward shift in the Fermi level and a significantly reduced interfacial energy barrier. As a result, the C-PSCs using Co1/CN as back electrodes achieve a notable PCE of 22.61% with exceptional long-term stability, maintaining 94.4% of their initial efficiency after 1000 h of continuous illumination without encapsulation. This work provides a promising universal method to regulate the energy level of carbon electrodes for C-PSCs and paves the way for more efficient, stable, and scalable solar technologies toward commercialization.

Few-Layered Black Phosphorene as Hole Transport Layer for Novel All-Inorganic Perovskite Solar Cells

The CsPbBr3 perovskite exhibits strong environmental stability under light, humidity, temperature, and oxygen conditions. However, in all-inorganic perovskite solar cells (PSCs), interface defects between the carbon electrode and CsPbBr3 limit the carrier separation and transfer rates. We used black phosphorus (BP) nanosheets as the hole transport layer (HTL) to construct an all-inorganic carbon-based CsPbBr3 perovskite (FTO/c-TiO2/m-TiO2/CsPbBr3/BP/C) solar cell. BP can enhance hole extraction capabilities and reduce carrier recombination by adjusting the interface contact between the perovskite and the carbon layer. Due to the coordination of the energy structure related to interface charge extraction and transfer, BP, as a new type of hole transport layer for all-inorganic CsPbBr3 solar cells, achieves a power conversion efficiency (PCE) that is 1.43% higher than that of all-inorganic carbon-based CsPbBr3 perovskite solar cells without a hole transport layer, reaching 2.7% (Voc = 1.29 V, Jsc = 4.60 mA/cm2, FF = 48.58%). In contrast, the PCE of the all-inorganic carbon-based CsPbBr3 perovskite solar cells without a hole transport layer was only 1.27% (Voc = 1.22 V, Jsc = 2.65 mA/cm2, FF = 39.51%). The unencapsulated BP-based PSCs device maintained 69% of its initial efficiency after being placed in the air for 500 h. In contrast, the efficiency of the PSC without HTL significantly decreased to only 52% of its initial efficiency. This indicates that BP can effectively enhance the PCE and stability of PSCs, demonstrating its great potential as a hole transport material in all-inorganic perovskite solar cells. BP as the HTL for CsPbBr3 PSCs can passivate the perovskite interface, enhance the hole extraction capability, and improve the optoelectronic performance of the device. The subsequent doping and compounding of the BP hole transport layer can further enhance its photovoltaic conversion efficiency in PSCs.

Antimicrobial materials based on photothermal action and their application in wound treatment

Considering the increasing abundance of antibiotic-resistant bacteria, novel antimicrobial approaches need to be investigated. Photothermal therapy (PTT), an innovative noninvasive therapeutic technique, has demonstrated significant potential in addressing drug-resistant bacteria and bacterial biofilms. However, when used in isolation, PTT requires higher-temperature conditions to effectively eradicate bacteria, thereby potentially harming healthy tissues and inducing new inflammation. This study aims to present a comprehensive review of nanomaterials with intrinsic antimicrobial properties, antimicrobial materials relying on photothermal action, and nanomaterials using drug delivery antimicrobial action, along with their applications in antimicrobials. Additionally, the synergistic mechanisms of these antimicrobial approaches are elucidated. The review provides a reference for developing multifunctional photothermal nanoplatforms for treating bacterially infected wounds.

Dual-Atom P-Co-Dy Charge-Transfer Bridge on Black Phosphorus for Enhanced Photocatalytic CO2 Reduction

The synergistic effect of rare earth single-atoms and transition metal single-atoms may enable us to achieve some unprecedented performance and characteristics. Here, Co-Dy dual-atoms on black phosphorus with a P-Co-Dy charge-transfer bridge are designed and fabricated as the active center for the CO2 photoreduction reaction. The synergistic effect of Co-Dy on the performance of black phosphorus is studied by combining X-ray absorption spectroscopy, ultrafast spectral analysis, and in situ technology with DFT calculations. The results show that the Co and Dy bimetallic active site can promote charge transfer by the charge transfer bridge from P to Dy, and then to Co, thereby improving the photocatalytic activity of black phosphorus. The performance of catalysts excited at different wavelength light indicates that the 4G11/2/2I15/2/4F9/2→6H15/2 and 4F9/2→6H13/2 emissions of Dy can be absorbed by black phosphorus to improve the utilization of sunlight. The in situ DRIFTS and density functional theory (DFT) calculations are used to investigate the CO2 photoreduction pathway. This work provides an depth insight into the mechanism of dual-atom catalysts with enhanced photocatalytic performance, which helps to design novel atomic photocatalysts with excellent activity for CO2 reduction reactions.

Modification Strategies for Development of 2D Material-Based Electrocatalysts for Alcohol Oxidation Reaction

2D materials, such as graphene, MXenes (metal carbides and nitrides), graphdiyne (GDY), layered double hydroxides, and black phosphorus, are widely used as electrocatalyst supports for alcohol oxidation reactions (AORs) owing to their large surface area and unique 2D charge transport channels. Furthermore, the development of highly efficient electrocatalysts for AORs via tuning the structure of 2D support materials has recently become a hot area. This article provides a critical review on modification strategies to develop 2D material-based electrocatalysts for AOR. First, the principles and influencing factors of electrocatalytic oxidation of alcohols (such as methanol and ethanol) are introduced. Second, surface molecular functionalization, heteroatom doping, and composite hybridization are deeply discussed as the modification strategies to improve 2D material catalyst supports for AORs. Finally, the challenges and perspectives of 2D material-based electrocatalysts for AORs are outlined. This review will promote further efforts in the development of electrocatalysts for AORs.

Efficient photocatalytic hydrogen peroxide production over S-scheme In2S3/molten salt modified C3N5 heterojunction

Graphitic phase carbon nitride (g-C3N5), as a novel n-type metal-free material, is employed as a visible light-receptive catalyst because of its narrow band gap and abundant nitrogen. To overcome the low carrier mobility efficiency of g-C3N5, its modification by K ions was adopted. In addition, In2S3 was selected to couple with modified g-C3N5 to overcome the recombination of photogenerated e-/h+. As a novel photocatalytic material, it was proven to possess a high visible light absorption capacity and a strong H2O2 production ability (up to 3.89 mmol⋅L-1 in 2 h). Moreover, a S-scheme heterojunction structure was successfully constructed between the two materials, which was tested and confirmed to be successful in raising the photogenerated e-/h+ separation efficiency. Ultimately, the primary processes of photocatalytic H2O2 production were summarized by superoxide radical and rotating disc electron measurements. This research provides a fresh perspective for the synthesis of C3N5-based S-scheme heterojunction photocatalysts for producing H2O2.

Temperature dependent Raman spectroscopy and sensing performance of 2D black phosphorus

Temperature is an important parameter to be monitored in new wearable electronic devices. Layered black phosphorus (BP) has inherent good thermal stability and semiconductor properties and has a promising application as a temperature sensing layer. Here, we investigate the temperature sensing properties of BP, using in situ Raman spectroscopy and x-ray diffraction techniques. Flexible sensors are constructed, and temperature response is investigated in the range of 6-38 °C. The prospect application for monitoring the temperature of human body parts is demonstrated. The results show that the BP-based temperature sensors demonstrate good negative temperature coefficient characteristics and display high sensitivity and reproducible sensing performance. The temperature-dependent performance suggests the feasibility of BP as a sensitive layer in a wide temperature range. This work paves the way for exploring new applications of amazing layered materials, such as BP, in wearable electronic devices.

A win-win platform: Stabilized black phosphorous nanosheets loading gallium ions for enhancing the healing of bacterial-infected wounds through synergistic antibacterial approaches

Bacterial infection is the most common complication in wound healing, highlighting an urgent need for the development of innovative antibacterial technologies and treatments to address the growing threats posed by bacterial infections. Black phosphorus nanosheets (BPNSs), as a promising two-dimensional nanomaterial, have been utilized in treating infected wounds. However, BP's limited stability restricts its application. In this study, we enhance BP's stability and its antibacterial properties by anchoring gallium ions (Ga3+) onto BP's surface, creating a novel antibacterial platform. This modification reduces BP's electron density and enhances its antibacterial capabilities through a synergistic effect. Under near-infrared (NIR) irradiation, the BP/Ga3+ combination exerts antibacterial effects via photothermal therapy (PTT) and photodynamic therapy (PDT), while also releasing Ga3+. The Ga3+ employ a 'Trojan horse strategy' to disrupt iron metabolism, significantly boosting the antibacterial efficacy of the complex. This innovative material offers a viable alternative to antibiotics and holds significant promise for treating infected wounds and aiding skin reconstruction.

Black Phosphorus-Based Conductive Hydrogels Assisted by Electrical Stimulus for Skin Tissue Engineering

Conductive hydrogels have shown great potential in wound healing and skin tissue engineering, owing to their electroactive, mechanical, and chemical properties. However, it still remains as a challenge to incorporate other functions into conductive hydrogels, such as antibacterial ability, controllable drug release, and biodegradability. In this study, a black phosphorus-based conductive hydrogel (HA-DA@BP) is prepared by an amidation reaction coupled with a coordination of Fe3+ -catechol. The hydrogel could be changed from the sol phase to the gel phase under electrical stimulus (ES). The results show that BP could be released under slight acidity, which is cell compatible but could achieve synergistic electrical antibacterial action and promote wound healing. This study proves that BP is a strong candidate for electroactive materials and provides a new insight for the development of BP-based biomedical materials in skin tissue engineering.

Renaissance of elemental phosphorus materials: properties, synthesis, and applications in sustainable energy and environment

The polymorphism of phosphorus-based materials has garnered much research interest, and the variable chemical bonding structures give rise to a variety of micro and nanostructures. Among the different types of materials containing phosphorus, elemental phosphorus materials (EPMs) constitute the foundation for the synthesis of related compounds. EPMs are experiencing a renaissance in the post-graphene era, thanks to recent advancements in the scaling-down of black phosphorus, amorphous red phosphorus, violet phosphorus, and fibrous phosphorus and consequently, diverse classes of low-dimensional sheets, ribbons, and dots of EPMs with intriguing properties have been produced. The nanostructured EPMs featuring tunable bandgaps, moderate carrier mobility, and excellent optical absorption have shown great potential in energy conversion, energy storage, and environmental remediation. It is thus important to have a good understanding of the differences and interrelationships among diverse EPMs, their intrinsic physical and chemical properties, the synthesis of specific structures, and the selection of suitable nanostructures of EPMs for particular applications. In this comprehensive review, we aim to provide an in-depth analysis and discussion of the fundamental physicochemical properties, synthesis, and applications of EPMs in the areas of energy conversion, energy storage, and environmental remediation. Our evaluations are based on recent literature on well-established phosphorus allotropes and theoretical predictions of new EPMs. The objective of this review is to enhance our comprehension of the characteristics of EPMs, keep abreast of recent advances, and provide guidance for future research of EPMs in the fields of chemistry and materials science.

A Review of Phosphorus Structures as CO2 Reduction Photocatalysts

Effective photocatalytic carbon dioxide (CO₂ ) reduction into high-value-added chemicals is promising to mitigate current energy crisis and global warming issues. Finding effective photocatalysts is crucial for photocatalytic CO₂ reduction. Currently, metal-based semiconductors for photocatalytic CO₂ reduction have been well reviewed, while review of nonmetal-based semiconductors is almost limited to carbon nitrides. Phosphorus is a promising nonmetal photocatalysts with various allotropes and tunable band gaps, which has been demonstrated to be promising non-metallic photocatalysts. However, no systematic review about phosphorus structures for photocatalytic CO₂ reduction reactions has been reported. Herein, the progresses of phosphorus structures as photocatalysts for CO₂ reduction are reviewed. The fundamentals of photocatalytic CO₂ reduction, corresponding properties of phosphorus allotropes, photocatalysts with phosphorus doping or phosphorus-containing ligands, research progress of phosphorus allotropes as photocatalysts for CO₂ reduction have been reviewed in this paper. The future research and perspective of phosphorus structures for photocatalytic CO₂ reduction are also presented.

Unraveling the Role of Nickel Nanoparticles Functionalization in the Electronic Properties and Structural Features of 2D Black Phosphorene Exposed to Ambient Conditions

Layered black phosphorus (BP) is endowed with peculiar chemico-physical properties that make it a highly promising candidate in the field of electronics. Nevertheless, as other 2D materials with atomic scale thickness, it suffers from easy degradation under ambient conditions. Herein, it is shown that the functionalization of BP with preformed and in situ grown Ni NPs, affects the electronic properties of the material. In particular, Ni functionalization performed in situ leads to a narrowing of the average BP band gap from 1.15 to 0.95 eV and to a marked shift in the conduction band maximum from -0.33 V to -0.07 V, which, in turn, improve the ambient stability. Structural studies carried out by XAS can well distinguish the two nanohybrids and reveal that once Ni NPs are grown on BP nanosheets, a Ni-P coordinative bond is formed, featuring a short Ni-P distance of 2.27 Å, which is not observed when preformed Ni NPs are immobilized on BP. Comparing the XANES and EXAFS spectra of fresh and aged samples of both nanohybrids, suggests that the interaction between Ni and P atoms results in a stabilization effect exerted via a dual electronic and redox mechanism, that infers a much superior ambient stability to BP, even if the surface functionalization is far to achieve a full coverage.

Photoassisted Electrochemical Hydrogen Evolution Reaction of MFe2O4@Ultrathin Black Phosphorus Amorphous-Crystalline Interface

Exploring highly active, stable, and low-cost catalysts for photoelectrochemical hydrogen evolution reaction (PE-HER) is vital in the field of energy conversion. Herein, we construct a new amorphous crystalline interface that amorphous iron-based spinel oxide (A-MFe₂O₄ (M = Ni, Co, Zn)) is uniformly anchored on the crystalline exfoliated black phosphorus (C-EBP) nanosheets via electrochemical and solvothermal strategies. Among these A-MFe₂O₄@C-EBP catalysts, more oxygen defects of A-NiFe₂O₄@C-EBP interface provide a larger effective electrochemical active area of 32.33 mF cm^-2 as well as a turnover frequency of 0.44 s^-1 and allow for an optimum equilibrium of the hydrogen-containing adsorption intermediates. Furthermore, A-NiFe₂O₄@C-EBP exhibits significant PE-HER performance with an overpotential of 42 mV at 10 mA cm^-2 under visible-light irradiation. Density functional theory (DFT) calculations show that the amorphous-crystalline composite structure causes a large number of oxygen defects enhancing the intrinsic activity of A-NiFe₂O₄@C-EBP, which A-NiFe₂O₄@C-EBP significantly improves its adsorption capacity for H* for HER and has the lowest Gibbs free energy change for HER. This study not only provides a superior multifunctional amorphous-crystalline interface catalysts but also helps to understand the catalytic mechanism of PE-HER.

Anchoring Black Phosphorus Quantum Dots on Fe-Doped W18 O49 Nanowires for Efficient Photocatalytic Nitrogen Fixation

Herein, we demonstrate that the surface anchoring of black phosphorus quantum dots (BPQDs) and bulk iron-doping in W₁₈ O₄₉ nanowires significantly promotes the photocatalytic activity toward N₂ fixation into NH₃ . More specifically, a NH₃ production rate of up to 187.6 μmol g^-1  h^-1 could be achieved, nearly one order of magnitude higher than that of pristine W₁₈ O₄₉ (18.9 μmol g^-1  h^-1 ). Comprehensive experiments and density-functional theory calculations reveal that Fe-doping could enhance the reducing ability of photo-generated electrons by decreasing the work function and elevating the defect band (d-band) centers. Additionally, the surface BPQDs anchoring could facilitate the N₂ adsorption/activation owing to the increased adsorption energy and advantaged W-P dimer bonding-mode. Therefore, synergizing the surface BPQD anchoring and bulk Fe-doping remarkably enhanced the photocatalytic activity of W₁₈ O₄₉ nanowires for NH₃ production.

2D BP/InSe Heterostructures as a Nonlinear Optical Material for Ultrafast Photonics

The BP/InSe heterojunction has attracted the attention of many fields in successful combined high hole mobility of black phosphorus (BP) and high electron mobility of indium selenide (InSe), and enhanced the environmental stability of BP. Nevertheless, photonics research on the BP/InSe heterostructure was insufficient, while both components are considered promising in the field. In this work, a two-dimensional (2D) BP/InSe heterostructure was fabricated using the liquid-phase exfoliation method. Its linear and non-linear optical (NLO) absorption was characterized by ultraviolet-visible-infrared and Open-aperture Z-scan technology. On account of the revealed superior NLO properties, an SA based on 2D BP/InSe was prepared and embedded into an erbium-doped fiber laser, traditional soliton pulses were observed at 1.5 μm with the pulse duration of 881 fs. Furthermore, harmonic mode locking of bound solitons and dark-bright soliton pairs were also obtained in the same laser cavity due to the cross-coupling effect. The stable mode-locked operation can be maintained for several days, which overcome the low air stability of BP. This contribution further proves the excellent optical properties of 2D BP/InSe heterostructure and provides new probability of developing nano-photonics devices for the applications of double pulses laser source and long-distance information transmission.

Site dependent catalytic water dissociation on an anisotropic buckled black phosphorus surface

Black phosphorus (BP) is unique among 2D materials due to its anisotropic puckered structure. It has been used as a multifunctional catalyst for various purposes. In this study, we performed first principles molecular dynamics simulations to understand the water-splitting reaction on a bi-layer BP surface. We focused on the site-specific aqueous reactivity of the buckled surface. A difference in the axis-dependent reactivity is observed owing to edge defects and exposed sites. Thus, we believe that BP edges, which significantly affect the interfacial water or organic solvent molecules, must exhibit very different edge-dependent reactivity. Experiments suggested the increasing catalytic efficiency of undisturbed BP in the order bulk, few-layered BP, and BP quantum dots. We choose three active sites to investigate the mechanistic details of the OER: the zigzag (ZZ), armchair (AC), and bulk sites. This study will provide insight into the enhanced catalytic activity when more edges are exposed as the active surface. We hope to clarify the reactive pathway in an aqueous solution supported by bi-layer BP by exploring the two different mechanisms for forming the OOH* complex. We explore and report two mechanisms: a simple push-pull reaction for oxygen-oxygen bond formation, the nucleophilic attack by formed OH^- and an attack by a water molecule. The free energy barriers procured for mechanism 1 taking place at the zigzag, armchair, and bulk sites are 7.59 ± 0.33, 9.04 ± 0.01, and 12.80 ± 0.09 kcal mol^-1, respectively. For mechanism 2 the free energy barriers are 7.62 ± 0.11, 9.15 ± 0.16, and 11.63 ± 0.11 kcal mol^-1 for the ZZ, AC, and bulk sites. The interlink between both the mechanisms is established concerning the reported free energy barriers for OOH* formation. The ZZ site is found to lower the activation barrier for the rate-determining step, followed by the AC and bulk.

CO2 reduction to CH4 on Cu-doped phosphorene: a first-principles study

Optimizing the electrochemical carbon dioxide reduction reaction (CRR) to fuels is one of the most significant challenges in materials science and chemistry. Recently, single metal atom catalysts based on 2D materials have shown promise to improve the electroreduction performance of pristine 2D materials in the CRR. The physical origins of such performance enhancements are still poorly understood. Herein, we report the potential of a single Cu atom doped phosphorene catalyst for CO₂ electroreduction based on density functional theory (DFT) calculations. The doping sites (hollow, bridge, and on-top) of Cu on phosphorene are investigated first. Phosphorene with a Cu atom anchored on the hollow site is chosen for further study. The pathways for different CRR products, including HCOOH, CO, CH₃OH, and CH₄, are examined via constructing free energy diagrams and via comparing the limiting potentials. CH₄ is the most likely product after analysis of the adsorption energies and free energy pathways. Cu-Doped phosphorene in general shows improved CRR performance with lower limiting potential values. Cu doping leads to a decrease in the band gap value (about 0.2 eV), which is likely to be the physical origin of the CRR performance enhancement. Our study provides a novel promising CRR candidate catalyst based on phosphorene.

Surface-Dependent Intermediate Adsorption Modulation on Iridium-Modified Black Phosphorus Electrocatalysts for Efficient pH-Universal Water Splitting

2D black phosphorus (BP) is one promising electrocatalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysis. The too strong adsorption of oxygen intermediates during OER, while the too weak adsorption of hydrogen intermediate during HER, however, greatly compromise its practical water splitting applications with overpotentials as high as 450 mV for OER and 420 mV for HER to achieve 10 mA cm^-2 under alkaline conditions. Herein, by rationally introducing the nanosized iridium (Ir) modifier together with optimized exposing surface toward electrolytes, an efficient Ir-modified BP electrocatalyst with much favorable adsorption energies toward catalytic intermediates possesses an outstanding pH-universal water splitting performance, surpassing the nearly all reported BP-based catalysts and the commercial noble-metal catalysts. The Ir-modified BP catalyst with the optimized exposed surfaces only requires an overall cell voltage of 1.54 and 1.57 V to achieve 10 mA cm^-2 in acidic and alkaline electrolysers, respectively. This design uncovers the potential applications of 2D BP in practical electrocatalysis fields via decreasing reaction intermediate adsorption energy barriers and promoting the interfacial electron coupling for heterostructured catalysts, and offers new insights into the surface-dependent activity enhancement mechanism.

Photocatalytic Z-Scheme Overall Water Splitting: Recent Advances in Theory and Experiments

Photocatalytic water splitting is considered one of the most important and appealing approaches for the production of green H₂ to address the global energy demand. The utmost possible form of artificial photosynthesis is a two-step photoexcitation known as "Z-scheme", which mimics the natural photosystem. This process solely relies on the effective coupling and suitable band positions of semiconductors (SCs) and redox mediators for the purpose to catalyze the surface chemical reactions and significantly deter the backward reaction. In recent years, the Z-scheme strategies and their key role have been studied progressively through experimental approaches. In addition, theoretical studies based on density functional theory have provided detailed insight into the mechanistic aspects of some breathtakingly complex problems associated with hydrogen evolution reaction and oxygen evolution reaction. In this context, this critical review gives an overview of the fundamentals of Z-scheme photocatalysis, including both theoretical and experimental advancements in the field of photocatalytic water splitting, and suggests future perspectives.

Hierarchical Co0.85 Se-CdSe/MoSe2 /CdSe Sandwich-Like Heterostructured Cages for Efficient Photocatalytic CO2 Reduction

Fabricating efficient photocatalysts with rapid charge carrier separation and high visible light harvesting is an advisable strategy to improve CO₂ reduction performance. Herein, hierarchical Co_0.85 Se-CdSe/MoSe₂ /CdSe cages with sandwich-like heterostructure are prepared to act as efficient photocatalysts for CO₂ reduction. In this study, the structure and composition of the final products can be regulated through the cation-exchange reaction in the presence of ascorbic acid. In the Co_0.85 Se-CdSe/MoSe₂ /CdSe cages, MoSe₂ nanosheets function as a bridge to integrate Co_0.85 Se-CdSe and CdSe on both sides of the MoSe₂ nanosheet shell into a sandwich-like heterostructured catalyst system, which possesses multiple positive merits for photocatalysis, including accelerated transport and separation of photogenerated carriers, improved visible light utilization, and increased catalytic active sites. Thus, the optimized Co_0.85 Se-CdSe/MoSe₂ /CdSe cages exhibit remarkable visible-light photocatalytic performance and outstanding stability for CO₂ reduction with a high CO average yield of 15.04 µmol g^-1 h^-1 and 90.14% selectivity, which are much higher than those of other control samples including single-component catalysts and binary hybrid catalysts. This study provides a promising way for the design and fabrication of high-efficiency photocatalysts.

Interfacial Covalent Bonds Regulated Electron-Deficient 2D Black Phosphorus for Electrocatalytic Oxygen Reactions

Developing resource-abundant and sustainable metal-free bifunctional oxygen electrocatalysts is essential for the practical application of zinc-air batteries (ZABs). 2D black phosphorus (BP) with fully exposed atoms and active lone pair electrons can be promising for oxygen electrocatalysts, which, however, suffers from low catalytic activity and poor electrochemical stability. Herein, guided by density functional theory (DFT) calculations, an efficient metal-free electrocatalyst is demonstrated via covalently bonding BP nanosheets with graphitic carbon nitride (denoted BP-CN-c). The polarized PN covalent bonds in BP-CN-c can efficiently regulate the electron transfer from BP to graphitic carbon nitride and significantly promote the OOH* adsorption on phosphorus atoms. Impressively, the oxygen evolution reaction performance of BP-CN-c (overpotential of 350 mV at 10 mA cm-2 , 90% retention after 10 h operation) represents the state-of-the-art among the reported BP-based metal-free catalysts. Additionally, BP-CN-c exhibits a small half-wave overpotential of 390 mV for oxygen reduction reaction, representing the first bifunctional BP-based metal-free oxygen catalyst. Moreover, ZABs are assembled incorporating BP-CN-c cathodes, delivering a substantially higher peak power density (168.3 mW cm-2 ) than the Pt/C+RuO2 -based ZABs (101.3 mW cm-2 ). The acquired insights into interfacial covalent bonds pave the way for the rational design of new and affordable metal-free catalysts.

Molecular-Level Control of the Intersheet Distance and Electronic Coupling between 2D Semiconducting and Metallic Nanosheets: Establishing Design Rules for High-Performance Hybrid Photocatalysts

Hybridization with conductive nanospecies has attracted intense research interest as a general effective means to improve the photocatalytic functionalities of nanostructured materials. To establish universal design rules for high-performance hybrid photocatalysts, correlations between versatile roles of conductive species and interfacial interaction between hybridized species are systematically investigated through fine-control of intersheet distance between photocatalytically active TiO2 and metallic reduced graphene oxide (rGO)/RuO2 nanosheets. Molecular-level tailoring of intersheet distance and electronic coupling between 2D nanosheets can be successfully achieved by restacking of colloidal nanosheet mixture with variable-sized organic intercalants. While the shortest intersheet distance between restacked TiO2 and rGO nanosheets leads to the highest visible-light-driven photocatalytic activity, the best UV-vis photocatalyst performance occurs for moderate intersheet spacing. These results highlight the greater sensitivity of photoinduced electronic excitation to the intersheet distance than that of interfacial charge transfer. The rGO nanosheet can function as effective charge transport pathway and cocatalyst within ≈1.7 nm distance from the semiconducting nanosheet, and as efficient stabilizer for hybridized photocatalyst within ≈1.8 nm. The present study underscores that the intercalative restacking of colloidal nanosheet mixture with intercalants enables molecular-level control of distance between 2D inorganic/graphene nanosheets, which provides a rational design strategy for high-performance hybrid photocatalysts.