Defect Engineering of Carbons for Energy Conversion and Storage Applications

Sustainable energy conversion and storage technologies are a vital prerequisite for neutral future carbon.To this end,carbon materials with attractive features,such as tunable pore architecture,good electrical conductivity,outstanding physicochemical stability,abundant resource,and low cost,have used as promising electrode materials for energy conversion and storage.Defect engineering could modulate the structures of carbon materials,thereby affecting their electronic properties.The presence of defects on carbons may lead to asymmetric charge distribution,change in geometrical configuration,and distortion of the electronic structure that may result in unexpected electrochemical performances.In this review,recent advances in defects of carbons used for energy conversion and storage were examined in terms of types,regulation strategies,and fine characterization means of defects.The applications of such carbons in supercapacitors,rechargeable batteries,and electrocatalysis were also discussed.The perspectives toward the development of defect engineering carbons were proposed.In all,novel insights related to improvement in high-performance carbon materials for future energy conversion and storage applications were provided.

Defect engineering of ternary Cu-In-Se quantum dots for boosting photoelectrochemical hydrogen generation

Heavy-metal-free ternary Cu–In–Se quantum dots(CISe QDs)are promising for solar fuel production because of their low toxicity,tunable band gap,and high light absorption coefficient.Although defects significantly affect the photophysical properties of QDs,the influence on photoelectrochemical hydrogen production is not well understood.Herein,we present the defect engineering of CISe QDs for efficient solar-energy conversion.Lewis acid–base reactions between metal halide–oleylamine complexes and oleylammonium selenocarbamate are modulated to achieve CISe QDs with the controlled amount of Cu vacancies without changing their morphology.Among them,CISe QDs with In/Cu=1.55 show the most outstanding photoelectrochemical hydrogen generation with excellent photocurrent density of up to 10.7 mA cm-2(at 0.6 VRHE),attributed to the suitable electronic band structures and enhanced carrier concentrations/lifetimes of the QDs.The proposed method,which can effectively control the defects in heavy-metal-free ternary QDs,offers a deeper understanding of the effects of the defects and provides a practical approach to enhance photoelectrochemical hydrogen generation.

Synergy mechanism of defect engineering in MoS_(2)/FeS_(2)/C heterostructure for high-performance sodium-ion battery

MoS_(2) is a promising anode material in sodium-ion battery technologies for possessing high theoretical capacity.However,the sluggish Na^(+) diffusion kinetics and low electronic conductivity hinder the promises.Herein,a unique MoS_(2)/FeS_(2)/C heterojunction with abundant defects and hollow structure(MFCHHS)was constructed.The synergy of defect engineering in MoS_(2),FeS_(2),and the carbon layer of MFCHHS with a larger specific surface area provides multiple storage sites of Na^(+)corresponding to the surface-controlled process.The MoS_(2)/FeS_(2)/C heterostructure and rich defects in MoS_(2) and carbon layer lower the Na^(+) diffusion energy barrier.Additionally,the construction of MoS_(2)/FeS_(2) heterojunction promotes electron transfer at the interface,accompanying with excellent conductivity of the carbon layer to facilitate reversible electrochemical reactions.The abundant defects and mismatches at the interface of MoS_(2)/FeS_(2) and MoS_(2)/C heterojunctions could relieve lattice stress and volume change sequentially.As a result,the MFCHHS anode exhibits the high capacity of 613.1 mA h g^(-1)at 0.5 A g^(-1) and 306.1 mA h g^(-1) at 20 A g^(-1).The capacity retention of 85.0%after 1400 cycles at 5.0 A g^(-1) is achieved.The density functional theory(DFT)calculation and in situ transmission electron microscope(TEM),Raman,ex-situ X-ray photon spectroscopy(XPS)studies confirm the low volume change during intercalation/deintercalation process and the efficient Na^(+)storage in the layered structure of MoS_(2) and carbon layer,as well as the defects and heterostructures in MFCHHS.We believe this work could provide an inspiration for constructing heterojunction with abundant defects to foster fast electron and Na^(+) diffusion kinetics,resulting in excellent rate capability and cycling stability.

Modulating of MoSe_(2)functional plane via doping-defect engineering strategy for the development of conductive and electrocatalytic mediators in Li-S batteries

The lithium polysulfide shuttle and sluggish sulfur reaction kinetics still pose significant challenges to lithium-sulfur(Li-S)batteries.The functional plane of Fe-MoSe_(2)@r GO nanohybrid with abundant defects has been designed and applied in Li-S batteries to develop the functional separator and multi-layer sulfur cathode.The cell with a functional separator exhibits a retention capacity of 462 m Ah g^(-1)after the 1000th at 0.5 C and 516 m Ah g^(-1)after the 600th at 0.3 C.Even at low electrolyte conditions(7.0μL_(mgsulfur)^(-1)and 15μL_(mgsulfur)^(-1))under high sulfur loadings(3.46 mg cm^(-2)and 3.73 mg cm^(-2)),the cell still presents high reversible discharge capacities 679 and 762 m Ah g^(-1)after 70 cycles,respectively.Further,at sulfur loadings up to 8.26 and 5.2 mg cm^(-2),the cells assembled with the bi-layers sulfur cathode and the tri-layers sulfur cathode give reversible capacities of 3.3 m Ah cm^(-2)after the 100th cycle and 3.0 m Ah cm^(-2)after the 120th cycle,respectively.This research not only demonstrates that the FeMoSe_(2)@r GO functional plane is successfully designed and applied in Li-S batteries with superior electrochemical performances but also paves the novel way for developing a unique multi-layer cathode technique to enhance and advance the electrochemical behavior of Li-S cells at a high-sulfur-loading cathode under lean electrolyte/sulfur(E/S)ratio.

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.

Defect engineering endows NiTi stents with photothermal-enhanced catalytic activity for high-efficiency tumor therapy

NiTi stents are widely used in clinic for palliative care to relieve obstruction caused by Gastrointestinal(GI)cancers,which have high morbidity and mortality rates.However,tumor invasion and tumor overgrowth around the stent after surgery may lead to re-obstruction of the lumen.Thus,it is urgent to endow NiTi stents with excellent tumor suppressive ability and good biocompatibility.In this study,Ce-BTC was firstly prepared on the surface of NiTi pretreated by alkaline heat,followed by pyrolysis in Ar atmosphere at 450℃.Then,a composite coating consisting of defective cerium oxide and black Ni-Ti hydroxide/oxide was constructed on NiTi surface,which exhibited tumor microenvironment-response and hyperthermia-enhanced catalytic ability.Under near-infrared light irradiation,the photothermal performance of black Ni-Ti hydroxide/oxide and hyperthermia-enhanced catalytic activity of defective cerium oxide can achieve a synergistic effect of photothermal therapy and tumor catalytic therapy.Thereafter,defective cerium oxide can sustainably inhibit the proliferation of residual tumor cells by the generation of reactive oxygen species.Moreover,the composite coating has no obvious cytotoxicity to normal cells.This work provides a new insight for the preparation of stimulus-responsive antitumor stents for palliative treatment of gastrointestinal cancer.

Defect engineering for advanced electrocatalytic conversion of nitrogen-containing molecules

Electrocatalytic conversion of nitrogen-containing molecules into valuable chemicals is a promising strategy to alleviate anthropogenic imbalances in the global nitrogen cycle,but developing efficient electrocatalysts remains a formidable challenge.In recent years,the exploration of high-performance electrocatalysts has achieved significant progress by resorting to defect engineering strategy,which encouraged the researchers to understand the relationship between defects in catalysts and electrocatalytic performance.In this review,recent advances in defect engineering for advanced electrocatalytic conversion of nitrogen-containing molecules are systematically summarized,with special focus on electrocatalytic nitrogen oxidation and reduction,electrocatalytic nitric oxide oxidation and reduction,electrocatalytic nitrate reduction,and the construction of C–N bonds.Defects can effectively tune the electronic structure of catalysts,facilitate species diffusion,and provide more adsorption/active sites for reaction intermediates,thereby enhancing the electrocatalytic performance.Moreover,objective issues and future trends for optimizing electrocatalyst by defect engineering are proposed,which will contribute to the further development of advanced electrocatalytic conversion of nitrogen-containing molecules.

Defect engineering of two-dimensional materials towards nextgeneration electronics and optoelectronics

The ultrathin body of two-dimensional(2D)materials provides potential for next-generation electronics and optoelectronics.The unavoidable atomic defects substantially determine the physical properties of atomic-level thin 2D materials,thus enabling new functionalities that are impossible in three-dimensional semiconductors.Therefore,rational design of atomic defects provides an alternative approach to modulate the physical properties of 2D materials.In this review,we summarize the recent progress of defect engineering in 2D materials,particularly in device performance enhancement.Firstly,the common defects in 2D materials and approaches for generating and repairing defects,including synthesis and post-growth treatments,are systematically introduced.The correlations between defects and optical,electronic,and magnetic properties of 2D materials are then highlighted.Subsequently,defect engineering for high performance electronics and optoelectronics is emphasized.At last,we provide our perspective on challenges and opportunities in defect engineering of 2D materials.

Defect engineering of electrocatalysts for organic synthesis

Electrocatalytic organic synthesis has attracted considerable research attention because it is an efficient and eco-friendly strategy for converting energy sources to value-added chemicals.Defect engineering is a promising strategy for regulating the electronic structure and charge density of electrocatalysts.It endows electrocatalysts with excellent physical and physicochemical properties and optimizes the adsorption energy of the reaction intermediates to reduce the kinetic barriers of the electrosynthesis reaction.Herein,the recent advances related to the use of electrocatalysts for organic synthesis with respect to defects are systematically reviewed.The roles of defects in anodic and cathodic reactions,such as the syntheses of alkanes,alkenes,alcohols,aldehydes,amides,and carboxylic acids,are reviewed.Furthermore,the relationship between the defective structure and electrocatalytic activity is discussed by combining experimental results and theoretical calculations.Finally,the challenges,opportunities,and development prospects of defective electrocatalysts are examined to promote the development of the field of electrocatalytic organic synthesis.This review is expected to help understand the vital role of defects in catalytic processes and the controllable synthesis of efficient electrocatalysts for the production of high-value chemicals.

Dielectric barrier discharge-based defect engineering method to assist flash sintering

Oxygen vacancy OV plays an important role in a flash sintering (FS) process. In defect engineering, the methods of creating oxygen vacancy defects include doping, heating, and etching, and all of them often have complex processes or equipment. In this study, we used dielectric barrier discharge (DBD) as a new defect engineering technology to increase oxygen vacancy concentrations of green billets with different ceramics (ZnO, TiO_(2), and 3 mol% yttria-stabilized zirconia (3YSZ)). With an alternating current (AC) power supply of 10 kHz, low-temperature plasma was generated, and a specimen could be treated in different atmospheres. The effect of the DBD treatment was influenced by atmosphere, treatment time, and voltage amplitude of the power supply. After the DBD treatment, the oxygen vacancy defect concentration in ZnO samples increased significantly, and a resistance test showed that conductivity of the samples increased by 2–3 orders of magnitude. Moreover, the onset electric field (E) of ZnO FS decreased from 5.17 to 0.86 kV/cm at room temperature (RT);while in the whole FS, the max power dissipation decreased from 563.17 to 27.94 W. The defect concentration and conductivity of the green billets for TiO_(2) and 3YSZ were also changed by the DBD, and then the FS process was modified. It is a new technology to treat the green billet of ceramics in very short time, applicable to other ceramics, and beneficial to regulate the FS process.

Outstanding electromechanical performance in piezoelectric ceramics via synergistic effects of defect engineering and domain miniaturization

Piezoelectric ceramics with high mechanical quality factor Q_(m) and large piezoelectric coefficient d_(33) are urgently required for advanced piezoelectric applications.However,obtaining both of these prop-erties simultaneously remains a difficult challenge due to their mutually restrictive relationship.Here 0.5Pb(Ni_(1/3)Nb_(2/3))O_(3)-0.5Pb(Zr_(0.3)Ti_(0.7))O_(3) piezoceramic with tetragonal(T)-rich MPB is designed as a matrix to construct the defect engineering by doping low-valent Mn ions.The strong coupling of defect dipole and T-rich phase can effectively hinder the rotation of P_(s),restrict domain wall motion and improve Q_(m).At the same time,the substituted Mn ions will introduce local random field,destroying the long-range or-dering of ferroelectric domain and reducing domain size.The miniaturized domain structure can increase poling efficiency and inhibit the reduction of d_(33).Guided by this strategy,Q_(m) has increased by more than 10 times and d_(33) has only decreased by about 25%.The optimized electromechanical performance with Q_(m)=822,d_(33)=502 pC/N,k_(p)=0.55 and tanδ=0.0069 can be obtained in the present study.

Recent progress in defect engineering for kesterite solar cells

Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)thin film solar cells have been regarded as one of the most promising thin film photovoltaic technologies,offering a low-cost and environmentally friendly solar energy option.Although remarkable advances have been achieved in kesterite solar cells,the performance gap relative to mature thin film photovoltaic technologies such as CIGSe and Cd Te remains large.Significant open-circuit voltage(V_(OC))deficit has been recognized as the main limiting factor to performance improvement,with undesirable intrinsic defects being a key culprit contributing to the low V_(OC).To realize the promise inherent in kesterite CZTS to become an earth-abundant alternative to existing thin film photovoltaic technologies with comparable performance,significant research effort has been invested to tackle the challenging defect issues.In this review,recent progress and achievements relevant to engineering improvements to the defect properties of the semiconductor have been examined and summarized.Promising strategies include:(i)manipulating the synthesis process to obtain a desirable reaction pathway and chemical environment;(ii)introducing cation substitution to increase the ionic size difference and supress the related band tailing deep-level defects;(iii)applying post deposition treatment(PDT)with alkaline elements to passivate the detrimental defects.These advances obtained from work on kesterite solar cells may lead to future high performance from this material and may be further extended to other earth-abundant chalcogenide photovoltaic technologies.

Decade Milestone Advancement of Defect-Engineered g-C_(3)N_(4) for Solar Catalytic Applications

Over the past decade, graphitic carbon nitride(g-C_(3)N_(4)) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C_(3)N_(4) is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the “all-in-one” defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultraactive coordinated environment(M–N_(x), M–C_(2)N_(2), M–O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra(fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C_(3)N_(4) “customization”, motivating more profound thinking and flourishing research outputs on g-C_(3)N_(4)-based photocatalysis.

Anion Defects Engineering of Ternary Nb-Based Chalcogenide Anodes Toward High-Performance Sodium-Based Dual-Ion Batteries

Sodium-based dual-ion batteries(SDIBs) have gained tremendous attention due to their virtues of high operating voltage and low cost, yet it remains a tough challenge for the development of ideal anode material of SDIBs featuring with high kinetics and long durability. Herein, we report the design and fabrication of N-doped carbon film-modified niobium sulfur–selenium(NbSSe/NC) nanosheets architecture, which holds favorable merits for Na^(+) storage of enlarged interlayer space, improved electrical conductivity, as well as enhanced reaction reversibility, endowing it with high capacity, high-rate capability and high cycling stability. The combined electrochemical studies with density functional theory calculation reveal that the enriched defects in such nanosheets architecture can benefit for facilitating charge transfer and Na+ adsorption to speed the electrochemical kinetics. The NbSSe/NC composites are studied as the anode of a full SDIBs by pairing the expanded graphite as cathode, which shows an impressively cyclic durability with negligible capacity attenuation over 1000 cycles at 0.5 A g^(-1), as well as an outstanding energy density of 230.6 Wh kg^(-1) based on the total mass of anode and cathode.

Defect engineering of two-dimensional materials for efficient electrocatalysis

Exploring high-activity and earth-abundant electrocatalysts for electrochemical reactions,including the hydrogen evolution reaction(HER),oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),etc.are crucial for building future large-scale green energy conversion and storage systems.Recently,some low-cost and resourceful two-dimensional(2D)semiconductor materials such as transition metal dichalcogenides(TMDCs)and layered oxides,have attracted increasing attention in electrocatalysis applications in virtue of their comparable catalytic activity and long-term stability to conventional noble metal-based catalysts(e.g.Pt/C,RuO_(2),IrO_(2),etc.).However,the intrinsic activity of some 2D materials still cannot meet the increasing requirement for highly efficient and reliable eletrocatalysts for future energy conversion and storage systems.In this context,designing elctrocatalysts with sufficient amount of active sites accessible for electrolyte,high activity of each active sites,and excellent conductivity is of great significance.To this end,defect engineering is a powerful strategy for tailoring the physical and chemical properties of 2D materials for efficient electrocatalysis.In this article,an overview of recent progress on defect engineering in 2D eletrocatalysts for HER,ORR and OER is presented.The effects of defects on the structure and tuned properties of 2D materials in eletrocatalysts applications are also summarized.Additionally,the challenges and opportunities ahead in this emerging field are also proposed.

Defect engineering on carbon black for accelerated Li-S chemistry

Rationally designing sulfur hosts with the functions of confining lithium polysulfides(LiPSs)and promoting sulfur reaction kinetics is critically important to the real implementation of lithium-sulfur(Li-S)batteries.Herein,the defect-rich carbon black(CB)as sulfur host was successfully constructed through a rationally regulated defect engineering.Thus-obtained defect-rich CB can act as an active electrocatalyst to enable the sulfur redox reaction kinetics,which could be regarded as effective inhibitor to alleviate the LiPS shuttle.As expected,the cathode consisting of sulfur and defect-rich CB presents a high rate capacity of 783.8 mA·h·g^−1 at 4 C and a low capacity decay of only 0.07% per cycle at 2 C over 500 cycles,showing favorable electrochemical performances.The strategy in this investigation paves a promising way to the design of active electrocatalysts for realizing commercially viable Li-S batteries.

Defect and interface engineering for electrochemical nitrogen reduction reaction under ambient conditions

Electrochemical nitrogen reduction reaction(e-NRR)under ambient conditions is an emerging strategy to tackle the hydrogen-and energy-intensive operations for traditional Haber-Bosch process in industrial ammonia(NH_(3))synthesis.However,the e-NRR performance is currently impeded by the inherent inertness of N_(2) molecules,the extremely slow kinetics and the overwhelming competition from the hydrogen evolution reaction(HER),all of which cause unsatisfied yield and ammonia selectivity(Faradaic efficiency,FE).Defect and interface engineering are capable of achieving novel physical and chemical properties as well as superior synergistic effects for various electrocatalysts.In this review,we first provide a general introduction to the NRR mechanism.We then focus on the recent progress in defect and interface engineering and summarize how defect and interface can be rationally designed and functioned in NRR catalysts.Particularly,the origin of superior NRR catalytic activity by applying these approaches was discussed from both theoretical and experimental perspectives.Finally,the remaining challenges and future perspectives in this emerging area are highlighted.It is expected that this review will shed some light on designing NRR electrocatalysts with excellent activity,selectivity and stability.

Surface defect engineering of metal oxides photocatalyst for energy application and water treatment

Despite metal oxides offer excellent characteristics in the field of photocatalysis,they often suffer from charge carrier recombination as well as limited visible response,which indeed reduce the charge kinetics process and ultimately reduce the photocatalytic output.Defect engineering is a sophisticated technique to manufacture defects and alter the geometric structure and chemical environment of the host.The present study provides an all-inclusive outline of recent developments on the classification of metal oxide defects based on the dimensions of a host crystal lattice.Precisely,surface modification of metal oxides through 0D(point),1D(line),2D(planar),and 3D(volume)defects with their subsequent mechanism and impact on photocatalytic performance are presented.By wisely amending the morphology(cores along with the shells)and electronic structure of metal oxide photocatalysts(TiO_(2),ZnO,Bi_(2)O_(3),Fe_(2)O_(4) etc.)through different attuned and veritable approaches,their photocatalytic activity can be substantially improved.Optimal studies on defect engineering not only expose the altered physicochemical features but also modulate the electron-hole pair dynamics,stability,and active radical production for various photoredox reactions.Altered atomic,as well as electronic configuration,facilitated a photocatalyst material to have different optical features,adsorption properties along with improved carrier transfer as well as isolation rate.Thus,the systematic exploration of photocatalytic rudiments of defect rich metal oxide for various applications such as H_(2) evolution,CO_(2) reduction,pollutant degradation,and bacterial disinfection could bring significant research advancement in this field.

Photocatalytic nitrogen reduction to ammonia:Insights into the role of defect engineering in photocatalysts

Engineering of defects in semiconductors provides an effective protocol for improving photocatalytic N_(2) conversion efficiency.This review focuses on the state-of-the-art progress in defect engineering of photocatalysts for the N_(2) reduction toward ammonia.The basic principles and mechanisms of thermal catalyzed and photon-induced N_(2) reduction are first concisely recapped,including relevant properties of the N_(2) molecule,reaction pathways,and NH3 quantification methods.Subsequently,defect classification,synthesis strategies,and identification techniques are compendiously summarized.Advances of in situ characterization techniques for monitoring defect state during the N_(2) reduction process are also described.Especially,various surface defect strategies and their critical roles in improving the N_(2) photoreduction performance are highlighted,including surface vacancies(i.e.,anionic vacancies and cationic vacancies),heteroatom doping(i.e.,metal element doping and nonmetal element doping),and atomically defined surface sites.Finally,future opportunities and challenges as well as perspectives on further development of defect-engineered photocatalysts for the nitrogen reduction to ammonia are presented.It is expected that this review can provide a profound guidance for more specialized design of defect-engineered catalysts with high activity and stability for nitrogen photochemical fixation.

Enhanced thermoelectric performance of ternary compound Cu_(3)PSe_(4)by defect engineering

The diamond-like compound Cu_(3)PSe_(4)with low lattice thermal conductivity is deemed to be a promising thermoelectric material,which can directly convert waste heat into electricity or vice versa with no moving parts and greenhouse emissions.However,its performance is limited by its low electrical conductivity.In this study,we report an effective method to enhance thermoelectric performance of Cu_(3)PSe_(4)by defect engineering.It is found that the carrier concentrations of Cu_(3-x)PSe_(4)(x=0,0.03,0.06,0.09,0.12)compounds are increased by two orders of magnitude as x>0.03,from 1×10^(17)to 1×10^(19)cm^(-3).Combined with the intrinsically low lattice thermal conductivities and enhanced electrical transport performance,a maximum zT value of 0.62 is obtained at 727 K for x=0.12 sample,revealing that Cu defect regulation can be an effective method for enhancing thermoelectric performance of Cu_(3)PSe_(4).