Defect-rich Surface Research Articles

Synergistic engineering of defects and architecture in Co3O4@C nanosheets toward Li/Na ion batteries with enhanced pseudocapacitances

Abstract Constructing robust 2D−based energy storage nanomaterials by well−defined pore architectures and rational surface modification are critical yet daunting challenges for rechargeable alkali−ion batteries. Herein, a new−type 2D interwoven multi pores decorated Co3O4@N−doped carbon nanosheet with rich surface defects is proposed as lithium/sodium ion anodes for the first time. The combining experimental researches, microscopic structure characterization and dynamics analysis demonstrate that the multi porous structure provides large numbers of channels to accelerate Li+/Na+ transport, rational surface design creates abundant active sites for fast ions reactions, while robust carbon shell offers excellent ionic/electrical conductivity and structural integrity. The obtained bifunctional composites deliver superior rate performance and long−term cycle stability (~529 mA h g−1 after 2000 cycles in LIBs and ~166 mA h g−1 after 1700 cycles in SIBs) due to the synergistic contribution of the unique structure and surface defects. Furthermore, it still remains a high reversible capacity (>610 mA h g−1 after 1000 cycles) in full cell. Kinetic analysis reveals the designed anode exhibits prominent pseudocapacitive behavior, enabling ultra−fast lithium/sodium storage and ultrahigh−rate capability. This work offers valuable insights for developing high performance energy storage devices.

Efficient visible and NIR light-driven photocatalytic CO2 reduction over defect-engineered ZnO/carbon dot hybrid and mechanistic insights

Photocatalytic CO2 reduction with H2O over wide bandgap semiconductor-based photocatalysts is significantly limited by the low light utilization efficiency and poor activation of CO2/H2O molecules on the photocatalyst’s surface. Herein, we demonstrate that oxygen-deficient ZnO/carbon dot (OD-ZnO/C) hybrid, rationally engineered with synergistically enhanced CO2/H2O activation ability and increased light utilization efficiency, showed excellent full spectrum (UV, visible and NIR light)-driven CO2 photoreduction. Under UV–Vis-NIR, Vis-NIR and NIR light separately, the optimized sample demonstrated high quantum yields of 0.26%, 0.13% and 0.05% for CO production, yields which are considerably superior to the reported values in the literature. The synergistic effects between OD-ZnO and carbon dots for visible- and NIR-driven CO2 reduction were systematically investigated. Experimental results showed that both the defect-induced sub-band in OD-ZnO and the upconverting emission from the carbon dots effectively increased the light utilization efficiency within the UV–Vis to NIR region, and the heterojunctions formed between OD-ZnO and carbon dots promoted the efficient separation of charge carriers. Meanwhile, the defect-rich surface ensures the efficient adsorption and activation of CO2/H2O into the key intermediate CO2–, formate, and hydroxyl species, which are effectively converted under light illumination from UV–Vis to NIR region. Based on the combined results of the CO2 photoreduction analysis and the material characterization, plausible CO2 photoreduction pathways under visible and NIR light irradiation are proposed.

Defects-rich porous carbon microspheres as green electrocatalysts for efficient and stable oxygen-reduction reaction over a wide range of pH values

Carbon materials are promising alternatives to noble metal catalysts for oxygen reduction reactions (ORR) in energy conversion devices. Here we report hierarchically porous carbon microspheres with a trace amount of encapsulated cobalt as highly active and stable electrocatalysts for the ORR under wide pH values ranged from high alkaline to high acidic conditions. We use renewable natural date pulp as the carbon precursor and a facile hydrothermal carbonization method with in situ formed recyclable cobalt as a template for the synthesis. These catalysts yield competitive catalytic activity (a small Tafel slope of 53 mV dec-1) as well as superb durability and methanol tolerance compared to the benchmark Pt/C catalyst in alkaline electrolyte. Even under harsh acidic conditions, the catalysts deliver a satisfactory catalytic performance and good stability, indicating their extensive applicability. This performance is mainly attributed to the rich surface defects and the hierarchically porous structure that provide abundant active sites for the ORR. In situ formed cobalt nanoparticles are critical to the creation of the abundant mesopores, high specific surface area, and catalytically active defect sites over the carbon material. The encapsulated cobalt residual further enhances the ORR activity of the catalysts, while having a negligible effect on the cost due to its trace level (0.2 at.%).

Tuning the surface energy density of non-stoichiometric LaCoO3 perovskite for enhanced water oxidation

Tailoring the surface structure of Earth-abundant perovskite oxides can provide cost-effective, high-efficient, and durable electrocatalysts for oxygen evolution reaction (OER). However, the structural origin leading to high OER performance of perovskite is not fully understood. Here, we present a strategy of tuning the surface energy density of non-stoichiometric perovskite by creating surface defects in the 3D inverse opal LaCoO3-x (3DIO-LaCoO3-x) through a colloidal template strategy. The defective 3DIO-LaCoO3-x, which has an enhanced surface energy density and a shift in the d-band centre of Co relative to the Fermi level, demonstrates significantly improved intrinsic OER activity, with a TOF (0.21 s−1) ten-folder larger than that of conventional LaCoO3 nanoparticles (0.02 s−1). The defective surfaces of 3DIO-LaCoO3-x are theoretically proven to alter the rate determining step of OER and significantly reduce the adsorption energies of the intermediate species, resulting in dramatically enhanced OER activity. Moreover, rich surface defects with high electrical conductivity can mitigate structural corrosion by fast transfer of charge through defective conductive channels, and thus enables long-term stability for the defective 3DIO-LaCoO3-x. These results provide an effective approach for enhancing the intrinsic activity of perovskite for water oxidation towards understanding the surface structure engineering for perovskite-based materials.

Facile synthesis of holey lamellar CuO via ultrasonic chemical etching toward highly efficient hydrogenation of 4-nitrophenol under mild conditions

Rational engineering the structural and superficial characters of catalysts to tailor their properties is a pursuit for the catalyst design. In this work, via an ultrasonic-assisted H2O2 etching strategy, a kind of copper oxide catalyst (CuO-60) with a holey lamellar structure was prepared and structurally characterized by a series of characterization techniques including SEM, HRTEM, XRD, N2 adsorption, XPS and H2-TPR. Interestingly, this strategy can not only generate defect rich surface but also achieve morphology reconstruction, thereby affording high-density active sites on CuO-60. As a low-cost catalyst, CuO-60 displays exceptional high catalytic activity and stability for the hydrogenation of 4-nitrophenol (4-NP) under mild conditions (25 ​°C and 1 ​atm). The 4-NP conversion over CuO-60 reaches up to 99% within 12 ​min, which is nearly 43-fold faster than that of the pristine CuO control. The correlation between the microstructure of the catalyst and the enhanced catalytic performance was well established. The outstanding catalytic properties can be ascribed to the synergistic effects of structure porousness, which renders in more exposed active sites, and unique redox behavior of electropositive Cu sites during catalytic process. Additionally, a catalytic mechanism is also proposed and rationalized.

Field Dependence of Magnetic Disorder in Nanoparticles

The performance characteristics of magnetic nanoparticles towards application, e.g. in medicine, imaging, or as sensors, is directly determined by their magnetization relaxation and total magnetic moment. In the commonly assumed picture, nanoparticles have a constant overall magnetic moment originating from the magnetization of the single-domain particle core surrounded by a surface region hosting spin disorder. In contrast, this work demonstrates the significant increase of the magnetic moment of ferrite nanoparticles with applied magnetic field. At low magnetic field, the homogeneously magnetized particle core initially coincides in size with the structurally coherent grain of 12.8(2) nm diameter, indicating a strong coupling between magnetic and structural disorder. Applied magnetic fields gradually polarize the uncorrelated, disordered surface spins, resulting in a magnetic volume more than 20\% larger than the structurally coherent core. The intraparticle magnetic disorder energy increases sharply towards the defect-rich surface as established by the field-dependence of the magnetization distribution. In consequence, these findings illustrate how the nanoparticle magnetization overcomes structural surface disorder. This new concept of intraparticle magnetization is deployable to other magnetic nanoparticle systems, where the in-depth knowledge of spin disorder and associated magnetic anisotropies will be decisive for a rational nanomaterials design.

A stable PdCu@Pd core-shell nanobranches with enhanced activity and methanol-tolerant for oxygen reduction reaction

Palladium-based catalyst represents one of the most promising candidates among all non-platinum oxygen reduction reaction (ORR) catalysts. However, it is still challenging to precisely engineering their morphology and composition. Herein, highly branched core-shell PdCu@Pd nanocrystals have been fabricated via a simple one-pot synthesis that co-directed by hydrogen gas and halide ions. Such unique PdCu@Pd nanocrystals exhibit prominent ORR activity, durability and methanol-tolerance in alkaline media owing to their core-shell composition, highly-branched structure and defect-rich surface. This work elucidates a facile strategy to design highly branched core-shell nanomaterials, shedding light on the exploration and optimization of novel non-platinum ORR catalysts.

Simple Method for Efficient Slot-Die Coating of MAPbI3 Perovskite Thin Films in Ambient Air Conditions.

Scalable methods for deposition of lead halide perovskite thin films are required to enable commercialization of the highly promising perovskite photovoltaics. Here, we have developed a slot-die coating process under ambient conditions for methylammonium lead iodide (MAPbI3) perovskite on heated substrates (about 90 °C on the substrate surface). Dense, highly crystalline perovskite films with large grains (100–200 μm) were obtained by careful adjustment of the deposition parameters, using solutions that are similar but more dilute than those used in typical spin-coating procedures. Without any further after treatments, such as antisolvent treatment or vapor annealing, we achieved power conversion efficiencies up of 14.5% for devices with the following structure: conducting tin oxide glass (FTO)/TiO2/MAPbI3/spiro-MeOTAD/Au. The performance was limited by the significant roughness of the deposited films, resulting from the hot-casting method, and the relatively high deposition temperature, which led to a defect-rich surface due to loss of MAI.

Template-free Synthesis of Mesoporous and Crystalline Transition Metal Oxide Nanoplates with Abundant Surface Defects

Summary Mesoporous transition metal oxides with crystalline walls show promising applications in catalysis and energy storage. Syntheses of those crystalline mesoporous oxides, however, currently remain as an unmet challenge because of the large volume shrinkage during crystallization in a sol-gel process. Here, we demonstrate a facile and general template-free method to prepare six mesoporous transition metal oxides, e.g., CuO, CoO, and spinel MCo2O4 (M = Co, Cu, Mn, Zn), with highly crystalline walls and continuous mesopores in the forms of two-dimensional nanoplates or nanosheets. The method is based on the thermal crystalline transformation from basic carbonates to mesoporous metal oxides. The crystal interconversion not only endows the crystallinity and mesoporosity of oxides but also generates abundant surface-step defects that show remarkable enhancement of the catalytic activity of porous oxides. Our method likely provides an alternative paradigm for cost-effective and universal synthesis of crystalline mesoporous oxides beyond the traditional templating methods.

Selective electrochemical reduction of carbon dioxide to ethylene on a copper hydroxide nitrate nanostructure electrode

Electrochemical carbon dioxide reduction (CO2 RR) is a promising technology to convert CO2 into valuable carbon-based fuels and chemicals. Copper (Cu) is a unique catalyst for this reaction as it yields substantial hydrocarbon products, but still suffers from low selectivity in aqueous solution. Here, we present a nanostructure Cu@Cu2(OH)3NO3 electrode using a facile molten salt decomposition method (MSDM). Both XPS and XRD data indicate that Cu2(OH)3NO3 is converted into metallic Cu when employed in CO2 electroreduction in KHCO3 solution, leaving abundant defects on the dendritic rough surface. Benefiting from the defects and rough surface, this electrode exhibited a high selectivity for C2H4 production with a faradaic efficiency (FE) of 31.80% and a high stability for 20 h.

FePc and FePcF16 on Rutile TiO2(110) and (100): Influence of the Substrate Preparation on the Interaction Strength.

Interface properties of iron phthalocyanine (FePc) and perfluorinated iron phthalocyanine (FePcF16) on rutile TiO2(100) and TiO2(110) surfaces were studied using X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and low-energy electron diffraction (LEED). It is demonstrated that the interaction strength at the interfaces is considerably affected by the detailed preparation procedure. Weak interactions were observed for all studied interfaces between FePc or FePcF16 and rutile, as long as the substrate was exposed to oxygen during the annealing steps of the preparation procedure. The absence of oxygen in the last annealing step only had almost no influence on interface properties. In contrast, repeated substrate cleaning cycles performed in the absence of oxygen resulted in a more reactive, defect-rich substrate surface. On such reactive surfaces, stronger interactions were observed, including the cleavage of some C–F bonds of FePcF16.

Shape-controlled synthesis of golf-like, star-like, urchin-like and flower-like SrTiO3 for highly efficient photocatalytic degradation and H2 production

As a typical perovskite-type metal oxide, SrTiO3 has emerged as prospective candidate for many fields. However, the synthesis of SrTiO3 with controlled morphology, high surface area, and enhanced photocatalytic activity are still lacking. Herein, a series of porous SrTiO3 with well-controlled morphologies including assembled nanoparticles (ANPs), golf-like particles (GLPs), star-like microspheres (SLMs), urchin-like microspheres (ULMs), and flower-like microspheres (FLMs) were successfully prepared via an ethylene glycol-water mixed solvothermal route. The ratio of VEG/VH2O play an important role in the shape-evolution during the solvothermal reaction. A comparative study of photocatalytic H2 production and photodegradation was performed, and a possible photocatalysis mechanism of SrTiO3 has been proposed. Significantly, the ULMs and FLMs photocatalysts of SrTiO3 with optimized low Pt loading amount (0.075 wt%) exhibited outstanding H2 production rates (8.21 and 7.29 mmol g−1 h−1) due to its unique structure of high-surface area and defect-rich surface. The facile and shape-controlled synthesis of varied SrTiO3 structures is believed to be useful for the design and application of perovskite.

The UV Plasmonic Behavior of Rhodium Tetrahedrons—A Numerical Analysis

Rhodium (Rh) nanoparticles have attracted a lot of attention due to their strong and ambient-stable UV plasmonic response. Very recently, the synthesis of Rh tetrahedra with and without concave defect-rich surfaces serving in plasmon assisted photocatalytic energy conversion has been reported. In this work, we perform a systematic numerical study on plasmonic behavior and surface charge distribution in order to optimize the use of Rh tetrahedra in surface-enhanced spectroscopies and photocatalysis. We analyze the effect of the edges and corners reshaping, a deformation already reported to appear in Rh nanocubes which have been repeatedly re-used in photocatalytic processes. It is demonstrated that rounding the edges and corners weakens both the near-field enhancement and surface charge densities in these locations, which in turn are the more reactive regions due to the presence of uncoordinated sites. In addition, we study how the near-field and charge density is redistributed on the surface of the tetrahedra when concavities of different sizes and depths are introduced. Through this study, we show that, in order to simultaneously maximize the near-field enhancement and surface charge densities in the concavity and at external edges and corners, medium size deep concavities are needed.

Direct Conversion of Natural Date Pulp to Hierarchically Porous Carbon Spheres As Efficient and Stable Oxygen-Reduction Electrocatalysts

The impending global energy crisis and environmental concerns associated with the excessive use of fossil fuels have prompted us to explore highly sustainable alternative energy sources as well as highly efficient eco-friendly energy conversion and storage technologies. Fuel cells are electrochemical energy conversion devices with energy conversion efficiencies two times greater than those of conventional fire powered plants. Such electrochemical devices normally involve an oxygen reduction reaction (ORR) over their positive electrode; unfortunately, the sluggish ORR kinetics at room temperature significantly limit their efficiency and performance, and thus have become a major obstacle towards their practical applications. The development of efficient electrocatalysts for promoting the ORR is the key to realize the practical use of such advanced technologie. Carbon materials are promising alternatives to noble metal catalysts for oxygen reduction reactions (ORR) in energy conversion devices. Here we report hierarchically porous carbon spheres with a trace amount of encapsulated cobalt as highly active and stable electrocatalysts for the ORR under both alkaline and acidic conditions. We use renewable natural date pulp as the carbon precursor and a facile hydrothermal carbonization method with in situ formed cobalt as a template for the synthesis. These catalysts yield competitive catalytic activity (a small Tafel slope of 53 mV dec-1) and superb durability and methanol tolerance compared to the benchmark Pt/C catalyst in alkaline electrolyte. Even under harsh acidic conditions, the catalysts deliver a satisfactory catalytic performance and good stability, indicating their extensive applicability. This performance is mainly attributed to the rich surface defects and the hierarchically porous structure that provide abundant active sites for the ORR. In situ formed cobalt nanoparticles are critical to the creation of the abundant mesopores, high specific surface area, and catalytically active defect sites over the carbon material. The encapsulated cobalt residual further enhances the ORR activity of the catalysts, while having a negligible effect on the cost due to its trace level (0.2 at.%).

Octahedral gold-silver nanoframes with rich crystalline defects for efficient methanol oxidation manifesting a CO-promoting effect

Three-dimensional bimetallic nanoframes with high spatial diffusivity and surface heterogeneity possess remarkable catalytic activities owing to their highly exposed active surfaces and tunable electronic structure. Here we report a general one-pot strategy to prepare ultrathin octahedral Au3Ag nanoframes, with the formation mechanism explicitly elucidated through well-monitored temporal nanostructure evolution. Rich crystalline defects lead to lowered atomic coordination and varied electronic states of the metal atoms as evidenced by extensive structural characterizations. When used for electrocatalytic methanol oxidation, the Au3Ag nanoframes demonstrate superior performance with a high specific activity of 3.38 mA cm−2, 3.9 times that of the commercial Pt/C. More intriguingly, the kinetics of methanol oxidation on the Au3Ag nanoframes is counter-intuitively promoted by carbon monoxide. The enhancement is ascribed to the altered reaction pathway and enhanced OH− co-adsorption on the defect-rich surfaces, which can be well understood from the d-band model and comprehensive density functional theory simulations.

Activation of persulfate by CO2-activated biochar for improved phenolic pollutant degradation: Performance and mechanism

Environment-friendly and low-cost catalysts are important for persulfate based advanced oxidation processes. In this study, we reported a CO2-activated biochar (AC) as a low-cost and efficient catalyst for persulfate (PS) activation and the degradation of phenol and chlorophenols. The AC950 showed the best catalytic performance for PS with an oxidant utility of 0.5 mol/mol oxidant/h/g with an activation energy of 15.86 kJ/mol owing to its large surface area, rich surface defects, and well-modified oxygen functional groups. In contrast to a radical-based mechanism, this novel biochar/persulfate system works through a non-radical mechanism that includes singlet state oxygen generation and an electron transfer reaction pathway. The major degradation intermediate of the phenolic pollutant was identified to be benzoquinone; moreover, amongst chlorophenols, the para-chlorine substituent was the first to degrade. The durability of the catalyst was low, it was deactivated primarily because of the oxidation of the carbon surface, and thermal regeneration was determined to be efficient for its recovery. Furthermore, HCO3− and HPO42− were found to considerably inhibit the performance of the catalytic oxidation system.

High-crystalline and high-aspect-ratio hematite nanotube photoanode for efficient solar water splitting

Hematite (ɑ-Fe2O3) nanotube arrays with high aspect ratio and well-defined crystalline structures are highly attractive for photoelectrochemical water splitting. However, their design and fabrication remain a great challenge resulted from the poor thermal stability. Herein, we demonstrate that the high-crystalline Fe2O3 nanotube arrays with average length of 2 μm and high density of 2.5×107 tubes/cm2 could survive extended calcination temperatures up to ∼800 °C without any sintering. Owing to the well-oriented tubular structure, high light absorption and rich surface defects, this Fe2O3 nanotube photoanode exhibits a significantly improved PEC activity for water oxidation, and the photocurrent could be achieved up to 1.2 mA cm−2 at 1.23 V (vs. reversible hydrogen electrode, RHE). The decoration of FeOOH/NiOOH dual-cocatalysts not only caused a negative shift on onset-potential (170 mV), but also increased the photocurrent density up to 2.0 mA cm−2 (1.23 VRHE), which is the highest value among the reported hematite nanotube photoanodes.

In situ construction of surface defects of carbon-doped ternary cobalt-nickel-iron phosphide nanocubes for efficient overall water splitting

The ternary cobalt-nickel-iron phosphide nanocubes (P-Co0.9Ni0.9Fe1.2 NCs) with high intrinsic activity, conductivity, defect concentration and optimized ratio have been realized through a facile phosphorization treatment using ternary cobalt-nickel-iron nanocubes of Prussian blue analogs (PBA) as a precursor. The scanning electron microscopy and transmission electron microscopy results show that the P-Co0.9Ni0.9Fe1.2 NCs maintain a cubic structure with a rough surface, implying the rich surface defects as exposed active sites. The thermal phosphorization of the ternary PBA precursor not only provids carbon doping but also leads to the in situ construction of surface defects on the NCs. The carbon doping from the PBA precursor lowers the charge transfer resistance and optimizes the electronic transformation. The synergistic effect among the ternary metal ions and rich defects contributes to the enhanced electrocatalytic performance. The P-Co0.9Ni0.9Fe1.2 NCs achieve low overpotentials of −200.7 and 273.1 mV at a current density of 10 mA cm−2 for the hydrogen evolution reaction and the oxygen evolution reaction, respectively. The potential of overall water splitting reaches 1.52 V at a current density of 10 mA cm−2. The long-term stability of the electrocatalysts was also evaluated. This work provides a facile method to design efficient transition-metal-based bifunctional electrocatalysts for overall water splitting.

All-in-one surface engineering strategy on nickel phosphide arrays towards a robust electrocatalyst for hydrogen evolution reaction

Efficient hydrogen evolution reaction electrocatalysts based on inexpensive and earth-abundant elements could enable low-cost water splitting and H2 production, thus are compelling for the conversion of renewable electricity to fuels. In this work, we showcase the combinations of multiple surface engineering routes in a Ni2P electrocatalyst that achieves significantly enhanced catalytic performance. The surface roughness and structure disordering of the Ni2P arrays on carbon foil are precisely regulated by altering the annealing condition, resulting in a surface area-enlarged, defect-rich and superaerophobic catalytic surface. Density functional theory calculations are used to identify the effect of defective sites on the free energy for hydrogen adsorption in hydrogen evolution. Meanwhile, the superaerophobic surface is proved to accelerate removing gas bubbles on the electrode, thus facilitate the catalytic process. In addition, the enlarged surface area of material is considered to elevate the catalytic performance by providing more active sites in reaction. The designed catalyst obtained through a moderate treatment exhibits optimal electrocatalytic activity in acidic media: a low overpotential of 63 mV at 10 mA cm−2, small Tafel slope of 67 mV dec−1 and outstanding stability over 10 h. The synthetic strategy shows great promise to design efficient catalysts via subtle surface engineering.

Phosphide protected FeS2 anchored oxygen defect oriented CeO2NS based ternary hybrid for electrocatalytic and photocatalytic N2 reduction to NH3

A nitrogenase mimicking iron-based ceria heterostructured material with a defect rich surface was fabricated for application in the nitrogen reduction reaction.