Defect Engineering Strategies Research Articles

Defects in Carbon-Based Materials for Electrocatalysis: Synthesis, Recognition, and Advances.

ConspectusOwing to climate change and over-reliance on fossil fuels, the study and development of sustainable energy is of essential importance in the next few decades. In recent years, rapid advances have been witnessed in various power to gas electrocatalysis technologies including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) for realizing the target of blue planet with carbon neutrality. Nevertheless, practical applications with superior performance and affordable cost are largely limited by the electrode materials because the reactions are regularly driven by precious metals such as platinum (Pt) or iridium (Ir) based catalysts. Therefore, it is of significance to develop novel electrocatalysts with high electroactivity and limited cost for boosting the commercialization of green hydrogen technology.Since nitrogen-doped carbon nanotubes were first reported for enhanced ORR performance in 2009, the exploitation of carbon-based metal-free catalysts (CMFCs) as potential replacements for the precious metal electrocatalysts has become an attractive research field. To date, great progress has been made in developing new dopant strategies for CMFCs; however, the details of the catalytic mechanism and identification of active sites remain unclear, owing to the complexity in controlling the dopants and their homogeneity in carbon-based materials. To tackle this issue, our group has presented a series of works on defects catalyzing electrochemical reactions and proposed a defect catalysis mechanism since 2015. This theory is now widely accepted by the research community and has become a very important area in electrocatalysis worldwide.In this Account, we first present the defect theory for the reasonable design of defective carbon-based materials (DCMs) and subsequently summarize our previous works on the state-of-the-art defect engineering strategies to design DCMs possessing high activity, with the particular emphasis on the conjunction between defect structures and electrochemical performances. We also categorize recent defect modulation approaches on active sites in DCMs as well as showcase the advanced characterization techniques to confirm the types and densities of defects in DCMs. Finally, several perspectives on the challenges and future research opportunities of this exciting field are proposed. Remarkably, rapid advances of DCMs possessing both high electrochemical activities and low cost as a new generation of electrode materials may greatly facilitate the deployment of sustainable energy infrastructures.

Photothermal Conversion Boosted Photocatalytic CO2 Reduction over S-Scheme CeO2@Cu-TCPP: In Situ Experiments and DFT Calculations

Herein, interfacial and defect-engineering strategies synergistically promote photocatalytic properties. Because of the matching energy levels and the close interfacial contact, the CeO2@Cu-TCPP S-scheme architecture is successfully constructed via the in situ wet chemistry route. Photothermal conversion assists abundant OVs on the CeO2 compartment. Strong evidence of an S-scheme charge transfer path is verified by density functional theory (DFT) calculations and in situ irradiated X-ray photoelectron spectroscopy (XPS). This S-scheme heterojunction system is more deep-seated in facilitating the separation and transfer of photogenerated carriers as well as acquiring strong photoredox ability. Meanwhile, the abundant OVs proved by XPS and electron paramagnetic resonance spectra (ESR) enhanced the light-harvesting capacity and conductivity and shortened the transfer route. As a result, this synergistic heterojunction could mostly promote photocatalytic CO2 activation. The typical 0.25CeO2@ Cu-NS exhibited the best photocatalytic CO2RR to form CO and CH4 (rate: 229.6 μmol·g–1), which is even 45.8- and 1.5-folds higher than those of pristine LA-CeO2 (5.0 μmol·g–1) and Cu-TCPP (152.2 μmol·g–1), respectively, higher than those of other reported CeO2-based photocatalysts. This study presents a reinforcement and matrix prospect for domain charge behaviors to accelerate CO2 activation.

The Precision Defect Engineering with Nonmetallic Element Refilling Strategy in g-C3 N4 for Enhanced Photocatalytic Hydrogen Production.

Traditional defect engineering and doping strategies are considered effective means for improving H2 evolution, but the uncontrollability of the modification process does not always lead to efficient activity. A defect-induced heteroatom refilling strategy is used here to synthesize heteroatoms introduced carbon nitride by precisely controlling the "introduction" sites on efficient N1 sites. Density functional theory calculations show that the refilling of B, P, and S sites have stronger H2 O adsorption and dissociation capacity than traditional doping, which makes it an optimal H2 production path. The large internal electric field strength of heteroatom-refilled catalysts leads to fast electron transfer and the hydrogen production of the best sample is up to 20.9mmolg-1 h-1 . This work provides a reliable and clear insight into controlled defect engineering of photocatalysts and a universal modification strategy for typical heteroatom and co-catalyst systems for H2 production.

Defect‐engineered two‐dimensional transition metal dichalcogenides towards electrocatalytic hydrogen evolution reaction

AbstractRecently, two‐dimensional transition metal dichalcogenides (TMDs) demonstrated their great potential as cost‐effective catalysts in hydrogen evolution reaction. Herein, we systematically summarize the existing defect engineering strategies, including intrinsic defects (atomic vacancy and active edges) and extrinsic defects (metal doping, nonmetal doping, and hybrid doping), which have been utilized to obtain advanced TMD‐based electrocatalysts. Based on theoretical simulations and experimental results, the electronic structure, intermediate adsorption/desorption energies and possible catalytic mechanisms are thoroughly discussed. Particular emphasis is given to the intrinsic relationship between various types of defects and electrocatalytic properties. Furthermore, current opportunities and challenges for mechanical investigations and applications of defective TMD‐based catalysts are presented. The aim herein is to reveal the respective properties of various defective TMD catalysts and provide valuable insights for fabricating high‐efficiency TMD‐based electrocatalysts.

Engineering metallenes for boosting electrocatalytic biomass-oxidation-assisted hydrogen evolution reaction.

Metallenes exhibit great potential for catalytic reaction, particularly for the hydrogen evolution reaction (HER) and biomass oxidation reaction, due to their favorable electronic configurations, ultrahigh specific surface areas, and highly accessible surface atoms. Therefore, metallenes can function as bifunctional electrocatalysts to boost the energy-saving biomass-oxidation-assisted HER, and have attracted great interest. Given the growing importance of green hydrogen as an alternative energy source in recent years, it is timely and imperative to summarize the recent progress and current status of metallene-based catalysts for the biomass-oxidation-assisted HER. Here, we review the recent advances in metallenes in terms of composition and structural regulations including alloying, nonmetal doping, defect engineering, surface functionalization, and heterostructure engineering strategies and their applications in driving electrocatalytic HER, with special focus on biomass-oxidation-assisted hydrogen production. The underlying structure-activity relationship and mechanisms are also comprehensively discussed. Finally, we also propose the challenges and future directions of metallene-based catalysts for the applications in biomass-oxidation-assisted HER.

A comprehensive insight into deep-level defect engineering in antimony chalcogenide solar cells

Antimony chalcogenides (Sb2X3, X = S and Se) are intriguing materials for flexible/wearable, lightweight, and tandem photovoltaic devices. This work highlights the deep-level defect engineering strategies for Sb2X3 thin-film solar cells.

Unlocking nanotubular bismuth oxyiodide toward carbon-neutral electrosynthesis

Defective ultrathin Bi5O7I nanotubes are designed by the combination of structure and defect engineering strategies to achieve highly active, selective, and stable performance for electrocatalytic reduction of CO2 to formate.

Cation-defect-induced self-reduction towards efficient mechanoluminescence in Mn2+-activated perovskites.

Mechanoluminescent (ML) materials have shown promising prospects for various applications, e.g. in stress sensing, information anti-counterfeiting and bio stress imaging fields. However, the development of trap-controlled ML materials is still limited, because the trap formation mechanism is not always clear. Here, inspired by a defect-induced Mn4+ → Mn2+ self-reduction process in suitable host crystal structures, a cation vacancy model is creatively proposed to determine the potential trap-controlled ML mechanism. Combined with the theoretical prediction and experimental results, both the self-reduction process and ML mechanism are clarified in detail, where the contribution of and defects dominates the ML luminescent process. Electrons/holes are mainly captured by the anionic/cationic defects, followed by the combination of electrons and holes to transfer energy to the Mn2+ 3d states under mechanical stimuli. Based on the multi-mode luminescent features excited by X-ray, 980 nm laser and 254 nm UV lamp, together with the excellent persistent luminescence and ML, a potential application in advanced anti-counterfeiting is demonstrated. These results will deepen the understanding of the defect-controlled ML mechanism, and inspire more defect-engineering strategies to develop more high-performance ML phosphors for practical application.

N-doped carbon nanofiber embedded with TiN nanoparticles: A type of efficient microwave absorbers with lightweight and wide-bandwidth

In this work, TiN-embedded in N-doped carbon nanofiber (TiN/NCNF) composites were synthesized by the electrospinning method and heat treatment process subsequently. The TiN/NCNF composites possess different TiN nanoparticles (TiNNPs) content, which can acquire by tuning the percentage of TiNNPs in the polyacrylonitrile precursor solutions. The study shows that TiN/NCNF composites hold more intense and tunable electromagnetic wave (EMW) absorption capabilities, as the embedded TiNNPs with more defects lead to enhanced electrical conductivity and cause room-temperature ferromagnetic. As a result, TiN/NCNF composites can achieve the well-matched impedance and contribute to significant electromagnetic wave attenuation capabilities due to their more interfacial polarization, defect dipole relaxation polarization, enhanced conductance loss, and magnetic loss caused by the defect, resulting in excellent microwave absorbing performance. When the mass fraction of the TiN/NCNF composites (S2 sample with nominal 3 wt% TiNNPs content) was only 30% in the absorbing coating, the optimal reflection loss (RL) value was achieved in − 45.19 dB at 15.6 GHz with a thickness of 1.91 mm, corresponding efficient absorption bandwidth (RL≤−10 dB) of 4.93 GHz. This work provides a novel method of realizing lightweight, wide-bandwidth, and efficient microwave absorbing characteristics of carbon fiber absorbents, using obtained particles from defect engineering strategies as loaded ones. As may be expected, the TiN/NCNF composites would have a significant potential application prospect as microwave absorbing materials.

Integrated nickel/polymer dual catalytic system for visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides

By merging transition metal and heterogeneous photocatalyst, a metal-photoredox system has attracted more attention for cross-coupling of various dual photoredox catalysis. However, there is a grand challenge for the attenuated nucleophilicity of sulfonamides relative to alkyl amines. Herein, an integrated dual catalytic system of porous carbon nitride nanosheet with nitrogen vacancies (N V -P-C 3 N 4 ) as a conjugated polymer semiconductor host in combination with transition-metal nickel (Ni) was constructed by a defect and morphology regulation strategy toward visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides. The excellent nickel/photoredox-catalyzed C–N coupling reaction performance is ascribed to the large specific surface area, abundant active sites, long carrier lifetime, and efficient transfer and separation of photoexcited electrons and holes. This work highlights the opportunity to cooperate with heterogeneous catalysts and active metal sites for challenging cross-coupling reactions. • Dual catalytic system of photoredox and transition metal • Carbon nitride with defect and morphology characteristics • C–N cross-coupling • Heterogeneous catalysts are used for sulfonamidation reactions For the fine chemical and pharmaceutical synthesis communities, it is crucial to determine the formation of anilines through C–N bond transformation approach. Considerable progress has been reported on dual catalytic systems of homogeneous photocatalysts combined with transition metals. However, the progress of heterogeneous catalysts for dual catalysis has not been satisfactory. Carbon nitride (C 3 N 4 ) is a class of metal-free conjugated polymer semiconductor with great potential for photoredox/Ni dual catalytic cross-couplings due to its thermal and chemical stability, facile fabrication, and cheapness. Herein, porous carbon nitride nanosheets with nitrogen vacancies (N V -P-C 3 N 4 ) were fabricated by a defect and morphology regulation strategy for visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides. This work highlights the opportunity to cooperate with heterogeneous catalysts and active metal sites for challenging cross-coupling reactions. An integrated dual catalytic system of N V -P-C 3 N 4 in combination with transition-metal Ni was constructed toward visible-light-driven sulfonamidation between aryl halides and aryl sulfonamides. This work not only realizes the sulfonamidation reaction in a heterogeneous catalytic system for the first time but also demonstrates that defect engineering and morphology strategies are effective for enhancing photoredox dual catalytic performance.

First-principles investigation of a-line Shockley partial dislocations in wurtzite GaN: core reconstruction and electronic structure

Αtomistic simulations based on density functional theory were performed to investigate Shockley partial dislocations, parallel to the <11–20> direction, in wurtzite gallium nitride. The cores of both 30° and 90° Shockley partial dislocations, their possible reconstructions and their electronic structures were analyzed and compared systematically. Shockley partial dislocations were found to have a variety of core structures while exhibiting different bonding states like: deformed Ga–N bonds, Ga–Ga and N–N homo-nuclear bonds, as well as Ga– and N–dangling bonds. We have demonstrated that the core reconstruction of these dislocations is not always energetically favourable in wurtzite GaN, as it is the case in elemental semiconductors. It results from interplay between the energy gain from eliminating dangling and forming homo-nuclear bonds and the energy excess from the induced strain of hetero-nuclear Ga–N bonds within the core. Depending on their core configurations, Shockley partial dislocations are expected to have different electronic behaviours in wurtzite GaN, as they can act either as sources of parasitic luminescence or non-radiative recombination centres, or give pathways to leakage currents. We have demonstrated that deep states associated with dislocations are not due to the dangling bonds, as generally believed, but rather to Ga–Ga bonds in their cores, and that N–N bonds do not lead to any gap states. These results are of high relevance as guidelines in defect engineering strategies aiming at producing dislocations with a particular electronic behaviour in wurtzite GaN.

Defect engineering of vanadium-based electrode materials for zinc ion battery

With the quick development of sustainable energy sources, aqueous zinc-ion batteries (AZIBs) have become a highly potential energy storage technology. It is a crucial step to construct desired electrode materials for improving the total performance of AZIBs. In recent years, considerable efforts have focused on the modification of vanadium-based cathode materials. In this review, we summarized defect engineering strategies of vanadium-based cathodes, including oxygen defects, cation vacancies and heterogeneous doping. Then, we discussed the effect of various defects on the electrochemical performance of electrode materials. Finally, we proposed the future challenges and development directions of V-based cathode materials.

Advances on Defect Engineering of Vanadium‐Based Compounds for High‐Energy Aqueous Zinc–Ion Batteries

AbstractAqueous zinc–ion batteries (ZIBs) have been promptly developed as a competitive and promising system for future large‐scale energy storage. In recent years, vanadium (V)‐based compounds, with diversity of valences and high electrochemical‐activity, have been widely studied as cathodes for aqueous ZIBs because of their rich reserves and high theoretical capacity. However, the stubborn issues including low conductivity and sluggish kinetics, plague their smooth application in aqueous ZIBs. Among various countermeasures, defect engineering is believed as an effective method to alleviate the above limitations. This review highlights the challenges of different V‐based cathode materials (e.g., vanadium oxides and vanadates) and summarizes the advances in defect engineering strategies including types and effects of the defects, designed strategies, and characterization techniques for high‐energy ZIBs. Finally, several sound prospects in this fervent field are also rationally proposed for fundamental research and practical application.

Morphology control in nickel cobaltite synthesised via solution routes for electrochemical applications

Research on the synthesis of electrode materials has seen a transition from a “mix and try” approach to a systematic design of nanostructures resulting in exciting morphologies and architectures. Recent research efforts delve rigorously into utilizing the exquisite shape dependant and defect-induced property of electrode materials for phenomenal enhancements in the device performance. Among various strategies for the morphology control at the nano/micro level, the solution-based chemical processes offer pathways for the growth of various morphologies enabling the utility of materials chemistry for enhanced properties. Nickel cobaltite has been explored as an active electrode material for various energy storage and conversion devices, including batteries, supercapacitors, and electrocatalysts. Synthesis of an impressive range of composite structures of nickel cobaltite has already been reviewed and reported. In this article, we collate and review the approaches for morphology control and defect engineering strategies adopted for nickel cobaltite nanostructures. The effect of synthetic parameters such as precursor effects, type of precipitant and additives, calcination temperature etc. On the morphology tuning and defect engineering are analysed. This review aims to establish a structure-property correlation based on the synthesis conditions and the electrochemical properties of nickel cobaltite for meeting the desired needs in various application areas.

Defect engineering on SnO2 nanomaterials for enhanced gas sensing performances

Although defect engineering opens up new opportunities in the field of gas sensors, the introduction of defects to enhance the gas sensing properties of metal oxide semiconductors (MOSs) has long been neglected. In this review, defect engineering strategies have been systematically introduced, with a focus on employing them for improved gas sensing performances. To keep the subject focused, we take SnO 2 nanomaterials as an example. Various synthesis methods for defective SnO 2 , including ion/electron/ray/laser-beam irradiation, plasma treatment, heating protocol, chemical reduction, tailoring specially exposed crystal facets and atoms doping, are emphasized. Different roles of defects on the gas sensing process of SnO 2 are discussed. Finally, critical issues and future directions of defect engineering are presented. This paper provides a platform for better understanding the relationships between synthesis, defect types and gas sensing performances of MOSs. It is also expected to unpack an important research direction for controlled synthesis of defective nanomaterials with other applications, including advanced energy conversion and storage. Defect engineering strategies have been utilized to optimize the gas sensing properties of SnO 2 nanomaterials. • The significant roles of defects in enhancing the gas sensing behavior of SnO 2 are proposed. • Typical approaches for defects implantation on SnO 2 are comprehensively investigated. • The underlying mechanisms of improved gas sensing performance based on SnO 2 via defect engineering are discussed in detail.

Defect Engineering Strategies Toward Controlled Functionalization of Solution‐Processed Transition Metal Dichalcogenides

Defect Engineering of Transition Metal Dichalcogenides The great variety of defects in solution-processed transition metal dichalcogenides (TMDs) and their crucial influence on the physicochemical properties have recently prompted worldwide scientists to master their inherent features. In article number 2100122, Stefano Ippolito and Paolo Samorì review some of the most enlightening advances regarding defect engineering strategies in solution-processed TMDs, highlighting the future directions, challenges, and opportunities.

Metal Oxides for the Electrocatalytic Reduction of Carbon Dioxide Active Sites, Composites, Interface and Defect Engineering Strategies

Metal Oxides for the Electrocatalytic Reduction of Carbon Dioxide Active Sites, Composites, Interface and Defect Engineering Strategies

Defect engineering in semiconductor-based SERS.

Semiconductor-based surface enhanced Raman spectroscopy (SERS) platforms take advantage of the multifaceted tunability of semiconductor materials to realize specialized sensing demands in a wide range of applications. However, until quite recently, semiconductor-based SERS materials have generally exhibited low activity compared to conventional noble metal substrates, with enhancement factors (EF) typically reaching 103, confining the study of semiconductor-based SERS to purely academic settings. In recent years, defect engineering has been proposed to effectively improve the SERS activity of semiconductor materials. Defective semiconductors can now achieve noble-metal-comparable SERS enhancement and exceedingly low, nano-molar detection concentrations towards certain molecules. The reason for such success is that defect engineering effectively harnesses the complex enhancement mechanisms behind the SERS phenomenon by purposefully tailoring many physicochemical parameters of semiconductors. In this perspective, we introduce the main defect engineering approaches used in SERS-activation, and discuss in depth the electromagnetic and chemical enhancement mechanisms (EM and CM, respectively) that are influenced by these defect engineering methods. We also introduce the applications that have been reported for defective semiconductor-based SERS platforms. With this perspective we aim to meet the imperative demand for a summary on the recent developments of SERS material design based on defect engineering of semiconductors, and highlight the attractive research and application prospects for semiconductor-based SERS.

Probing lattice defects in crystalline battery cathode using hard X-ray nanoprobe with data-driven modeling

Lattice defects, e.g., dislocations and grain boundaries, critically impact the properties of crystalline battery cathode materials. A longstanding challenge is to probe the meso‑scale heterogeneity and evolution of lattice defects with sensitivity to atomic-scale details. Herein, we tackle this issue with a unique combination of X-ray nanoprobe diffractive imaging and advanced machine learning techniques. The domains with different lattice defect configuration within a single-crystalline LiCoO2 cathode particle are faithfully revealed using our approach. We further visualize the rearrangement of grain boundaries and local crystallinity upon mild thermal annealing. These results pave a direct way to the understanding of crystalline battery materials’ response under external stimuli with high fidelity, which provides valuable empirical guidance to defect-engineering strategies for improving the cathode materials against aggressive battery operation.

Role of Defect Engineering and Surface Functionalization in the Design of Carbon Nanotube-Based Nitrogen Oxide Sensors.

Nitrogen oxides (NOx) are among the main atmospheric pollutants; therefore, it is important to monitor and detect their presence in the atmosphere. To this end, low-dimensional carbon structures have been widely used as NOx sensors for their outstanding properties. In particular, carbon nanotubes (CNTs) have been widely used as toxic-gas sensors owing to their high specific surface area and excellent mechanical properties. Although pristine CNTs have shown promising performance for NOx detection, several strategies have been developed such as surface functionalization and defect engineering to improve the NOx sensing of pristine CNT-based sensors. Through these strategies, the sensing properties of modified CNTs toward NOx gases have been substantially improved. Therefore, in this review, we have analyzed the defect engineering and surface functionalization strategies used in the last decade to modify the sensitivity and the selectivity of CNTs to NOx. First, the different types of surface functionalization and defect engineering were reviewed. Thereafter, we analyzed experimental, theoretical, and coupled experimental–theoretical studies on CNTs modified through surface functionalization and defect engineering to improve the sensitivity and selectivity to NOx. Finally, we presented the conclusions and the future directions of modified CNTs as NOx sensors.