The rhombohedral α-GeTe can be approximated as a slightly distorted rock-salt structure along its [1 1 1] direction and possesses superb thermoelectric performance. However, the role of such a ferroelectric-like structural distortion on its transport properties remains unclear. Herein, we performed a systematic study on the crystal structure and electronic band structure evolutions of Ge1-xSnxTe alloys where the degree of ferroelectric distortion is continuously tuned. It is revealed that the band gap is maximized while multiple valence bands are converged at x = 0.6, where the ferroelectric distortion is the least but still works. Once undistorted, the band gap is considerably reduced, and the valence bands are largely separated again. Moreover, near the ferro-to-paraelectric phase transition Curie temperature, the lattice thermal conductivity reaches its minima because of significant lattice softening enabled by ferroelectric instability. We predict a peak ZT value of 2.6 at 673 K in α-GeTe by use of proper dopants which are powerful in suppressing the excess hole concentrations but meanwhile exert little influence on the ferroelectric distortion.
Efficient energy storage devices with suitable electrode materials, that integrate high power and high energy, are the crucial requisites of the renewable power source, which have unwrapped new possibilities in the sustainable development of energy and the environment. Herein, a facile collagen microstructure modulation strategy is proposed to construct a nitrogen/oxygen dual-doped hierarchically porous carbon fiber with ultrahigh specific surface area (2788 m2 g-1) and large pore volume (4.56 cm3 g-1) via local microfibrous breakage/disassembly of natural structured proteins. Combining operando spectroscopy and density functional theory unveil that the dual-heteroatom doping could effectively regulate the electronic structure of carbon atom framework with enhanced electric conductivity and electronegativity as well as decreased diffusion resistance in favor of rapid pseudocapacitive-dominated Li+-storage (353 mAh g-1 at 10 A g-1). Theoretical calculations reveal that the tailored micro-/mesoporous structures favor the rapid charge transfer and ion storage, synergistically realizing high capacity and superior rate performance for NPCF-H cathode (75.0 mAh g-1 at 30 A g-1). The assembled device with NPCF-H as both anode and cathode achieves extremely high energy density (200 Wh kg-1) with maximum power density (42 600 W kg-1) and ultralong lifespan (80% capacity retention over 10 000 cycles).
Rechargeable sodium-ion batteries usually suffer from accelerated electrode destruction at high temperatures and high synthesis costs of electrode materials. Therefore, it is highly desirable to explore novel organic electrodes considering their cost-effectiveness and large adaptability to volume changes. Herein, natural biomass, pristine lignin, is employed as the sodium-ion battery anodes, and their sodium storage performance is investigated at room temperature and 60 ℃. The lignin anodes exhibit excellent high-temperature sodium-ion battery performance. This mainly results from the generation of abundant reactive sites (C=O) due to the high temperature-induced homogeneous cleavage of the Cβ-O bond in the lignin macromolecule. This work can inspire researchers to explore other natural organic materials for large-scale applications and high-value utilization in advanced energy storage devices.
The development of freestanding and binder-free electrode is an effective approach to perform the inherent capacity of active materials and promote the mechanism study by minimizing the interference from additives. Herein, we construct a freestanding cathode composed of MoS3/PPy nanowires (NWs) deposited on porous nickel foam (NF) (MoS3/PPy/NF) through electrochemical methods, which can work efficiently as sulfur-equivalent cathode material for Li-S batteries. The structural stability of the MoS3/PPy/NF cathode is greatly enhanced due to its significant tolerance to the volume expansion of MoS3 during the lithiation process, which we ascribe to the flexible 3D framework of PPy NWs, leading to superior cycling performance compared to the bulk-MoS3/NF reference. Eliminating the interference of binder and carbon additives, the evolution of the chemical and electronic structure of Mo and S species during the discharge/charge was studied by X-ray absorption near-edge spectroscopy (XANES). The formation of lithium polysulfides was excluded as the driving cathode reaction mechanism, suggesting the great potential of MoS3 as a promising sulfur-equivalent cathode material to evade the shuttle effect for Li-S batteries. The present study successfully demonstrates the importance of structural design of freestanding electrode enhancing the cycling performances and revealing the corresponding mechanisms.
Hole transport material free carbon-based all-inorganic CsPbBr3 perovskite solar cells (PSCs) are promising for commercialization due to its low-cost, high open-circuit voltage (Voc) and superior stability. Due to the different solubility of PbBr2 and CsBr in conventional solvents, CsPbBr3 films are mainly obtained by multi-step spin-coating through the phase evolution from PbBr2 to CsPb2Br5 and then to CsPbBr3. The scalable fabrication of high-quality CsPbBr3 films has been rarely studied. Herein, an inkjet-printing method is developed to prepare high-quality CsPbBr3 films. The formation of long-range crystalline CsPb2Br5 phase can effectively improve phase purity and promote regular crystal stacking of CsPbBr3. Consequently, the inkjet-printed CsPbBr3 C-PSCs realized PCEs up to 9.09%, 8.59% and 7.81% with active areas of 0.09, 0.25, and 1 cm2, respectively, demonstrating the upscaling potential of our fabrication method and devices. This high performance is mainly ascribed to the high purity, strong crystal orientation, reduced surface roughness and lower trap states density of the as-printed CsPbBr3 films. This work provides insights into the relationship between the phase evolution mechanisms and crystal growth dynamics of cesium lead bromide halide films.
Thermal energy storage (TES) solutions offer opportunities to reduce energy consumption, greenhouse gas emissions, and cost. Specifically, they can help reduce the peak load and address the intermittency of renewable energy sources by time shifting the load, which are critical toward zero energy buildings. Thermochemical materials (TCMs) as a class of TES undergo a solid-gas reversible chemical reaction with water vapor to store and release energy with high storage capacities (600 kWh m-3) and negligible self-discharge that makes them uniquely suited as compact, stand-alone units for daily or seasonal storage. However, TCMs suffer from instabilities at the material (salt particles) and reactor level (packed beds of salt), resulting in poor multi-cycle efficiency and high-levelized cost of storage. In this study, a model is developed to predict the pulverization limit or Rcrit of various salt hydrates during thermal cycling. This is critical as it provides design rules to make mechanically stable TCM composites as well as enables the use of more energy-efficient manufacturing process (solid-state mixing) to make the composites. The model is experimentally validated on multiple TCM salt hydrates with different water content, and effect of Rcrit on hydration and dehydration kinetics is also investigated.
Developing a simple scalable method to fabricate electrodes with high capacity and wide voltage range is desired for the real use of electrochemical supercapacitors. Herein, we synthesized amorphous NiCo-LDH nanosheets vertically aligned on activated carbon cloth substrate, which was in situ transformed from Co-metal-organic framework materials nano-columns by a simple ion exchange process at room temperature. Due to the amorphous and vertically aligned ultrathin structure of NiCo-LDH, the NiCo-LDH/activated carbon cloth composites present high areal capacities of 3770 and 1480 mF cm-2 as cathode and anode at 2 mA cm-2, and 79.5% and 80% capacity have been preserved at 50 mA cm-2. In the meantime, they all showed excellent cycling performance with negligible change after >10 000 cycles. By fabricating them into an asymmetric supercapacitor, the device achieves high energy densities (5.61 mWh cm-2 and 0.352 mW cm-3). This work provides an innovative strategy for simplifying the design of supercapacitors as well as providing a new understanding of improving the rate capabilities/cycling stability of NiCo-LDH materials.
For microelectronic devices, the on-chip microsupercapacitors with facile construction and high performance, are attracting researchers' prior consideration due to their high compatibility with modern microsystems. Herein, we proposed interchanging interdigital Au-/MnO2/polyethylene dioxythiophene stacked microsupercapacitor based on a microfabrication process followed by successive electrochemical deposition. The stacked configuration of two pseudocapacitive active microelectrodes meritoriously leads to an enhanced contact area between MnO2 and the conductive and electroactive layer of polyethylene dioxythiophene, hence providing excellent electron transport and diffusion pathways of electrolyte ions, resulting in increased pseudocapacitance of MnO2 and polyethylene dioxythiophene. The stacked quasi-solid-state microsupercapacitors delivered the maximum specific capacitance of 43 mF cm-2 (211.9 F cm-3), an energy density of 3.8 μWh cm-2 (at a voltage window of 0.8 V) and 5.1 μWh cm-2 (at a voltage window of 1.0 V) with excellent rate capability (96.6% at 2 mA cm-2) and cycling performance of 85.3% retention of initial capacitance after 10 000 consecutive cycles at a current density of 5 mA cm-2, higher than those of ever reported polyethylene dioxythiophene and MnO2-based planar microsupercapacitors. Benefiting from the favorable morphology, bilayer microsupercapacitor is utilized as a flexible humidity sensor with a response/relaxation time superior to those of some commercially available integrated microsensors. This strategy will be of significance in developing high-performance on-chip integrated microsupercapacitors/microsensors at low cost and environment-friendly routes.
Thermoelectric power generators have attracted increasing interest in recent years owing to their great potential in wearable electronics power supply. It is noted that thermoelectric power generators are easy to damage in the dynamic service process, resulting in the formation of microcracks and performance degradation. Herein, we prepare a new hybrid hydrogel thermoelectric material PAAc/XG/Bi2Se0.3Te2.7 by an in situ polymerization method, which shows a high stretchable and self-healable performance, as well as a good thermoelectric performance. For the sample with Bi2Se0.3Te2.7 content of 1.5 wt% (i.e., PAAc/XG/Bi2Se0.3Te2.7 (1.5 wt%)), which has a room temperature Seebeck coefficient of -0.45 mV K-1, and exhibits an open-circuit voltage of -17.91 mV and output power of 38.1 nW at a temperature difference of 40 K. After being completely cut off, the hybrid thermoelectric hydrogel automatically recovers its electrical characteristics within a response time of 2.0 s, and the healed hydrogel remains more than 99% of its initial power output. Such stretchable and self-healable hybrid hydrogel thermoelectric materials show promising potential for application in dynamic service conditions, such as wearable electronics.
Herein, we report the design, fabrication, and performance of two wireless energy harvesting devices based on highly flexible graphene macroscopic films (FGMFs). We first demonstrate that benefiting from the high conductivity of up to 1 × 106 S m-1 and good resistive stability of FGMFs even under extensive bending, the FGMFs-based rectifying circuit (GRC) exhibits good flexibility and RF-to-DC efficiency of 53% at 2.1 GHz. Moreover, we further expand the application of FGMFs to a flexible wideband monopole rectenna and a 2.45 GHz wearable rectenna for harvesting wireless energy. The wideband rectenna at various bending conditions produces a maximum conversion efficiency of 52%, 46%, and 44% at the 5th Generation (5G) 2.1 GHz, Industrial Long-Term Evolution (LTE) 2.3 GHz, and Scientific Medical (ISM) 2.45 GHz, respectively. A 2.45 GHz GRC is optimized and integrated with an AMC-backed wearable antenna. The proposed 2.45 GHz wearable rectenna shows a maximum conversion efficiency of 55.7%. All the results indicate that the highly flexible graphene-film-based rectennas have great potential as a wireless power supplier for smart Internet of Things (IoT) applications.
Biaxially oriented polypropylene (BOPP) is one of the most commonly used commercial capacitor films, but its upper operating temperature is below 105 ℃ due to the sharply increased electrical conduction loss at high temperature. In this study, growing an inorganic nanoscale coating layer onto the BOPP film's surface is proposed to suppress electrical conduction loss at high temperature, as well as increase its upper operating temperature. Four kinds of inorganic coating layers that have different energy band structure and dielectric property are grown onto the both surface of BOPP films, respectively. The effect of inorganic coating layer on the high-temperature energy storage performance has been systematically investigated. The favorable coating layer materials and appropriate thickness enable the BOPP films to have a significant improvement in high-temperature energy storage performance. Specifically, when the aluminum nitride (AlN) acts as a coating layer, the AlN-BOPP-AlN sandwich-structured films possess a discharged energy density of 1.5 J cm-3 with an efficiency of 90% at 125 ℃, accompanying an outstandingly cyclic property. Both the discharged energy density and operation temperature are significantly enhanced, indicating that this efficient and facile method provides an important reference to improve the high-temperature energy storage performance of polymer-based dielectric films.
Electrocatalysis enables the industrial transition to sustainable production of chemicals using abundant precursors and electricity from renewable sources. De-centralized production of hydrogen peroxide (H2O2) from water and oxygen of air is highly desirable for daily life and industry. We report an effective electrochemical refinery (e-refinery) for H2O2 by means of electrocatalysis-controlled comproportionation reaction (2HO+O→2HO), feeding pure water and oxygen only. Mesoporous nickel (II) oxide (NiO) was used as electrocatalyst for oxygen evolution reaction (OER), producing oxygen at the anode. Conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) drove the oxygen reduction reaction (ORR), forming H2O2 on the cathode. The reactions were evaluated in both half-cell and device configurations. The performance of the H2O2 e-refinery, assembled on anion-exchange solid electrolyte and fed with pure water, was limited by the unbalanced ionic transport. Optimization of the operation conditions allowed a conversion efficiency of 80%.
Myocardial damage resulting from acute myocardial infarction often leads to progressive heart failure and sudden death, highlighting the urgent clinical need for effective therapies. Recently, tanshinone IIA has been identified as a promising therapeutic agent for myocardial infarction. However, efficient delivery remains a major issue that limits clinical translation. To address this problem, an injectable thermosensitive poly (lactic acid-co-glycolic acid)-block-poly (ethylene glycol)-block-poly (lactic acid-co-glycolic acid) gel (PLGA-PEG-PLGA) system encapsulating tanshinone IIA-loaded reactive oxygen species-sensitive microspheres (Gel-MS/tanshinone IIA) has been designed and synthesized in this study. The thermosensitive hydrogel exhibits good mechanical properties after reaching body temperature. Microspheres initially immobilized by the gel exhibit excellent reactive oxygen species-triggered release properties in a high-reactive oxygen species environment after myocardial infarction onset. As a result, encapsulated tanshinone IIA is effectively released into the infarcted myocardium, where it exerts local anti-pyroptotic and anti-inflammatory effects. Importantly, the combined advantages of this technique contribute to the mitigation of left ventricular remodeling and the restoration of cardiac function following tanshinone IIA. Therefore, this novel, precision-guided intra-tissue therapeutic system allows for customized local release of tanshinone IIA, presenting a promising alternative treatment strategy aimed at inducing beneficial ventricular remodeling in the post-infarct heart.
Rh has been widely studied as a catalyst for the promising hydrazine oxidation reaction that can replace oxygen evolution reactions for boosting hydrogen production from hydrazine-containing wastewater. Despite Rh being expensive, only a few studies have examined its electrocatalytic mass activity. Herein, surface-limited cation exchange and electrochemical activation processes are designed to remarkably enhance the mass activity of Rh. Rh atoms were readily replaced at the Ni sites on the surface of NiOOH electrodes by cation exchange, and the resulting RhOOH compounds were activated by the electrochemical reduction process. The cation exchange-derived Rh catalysts exhibited particle sizes not exceeding 2 nm without agglomeration, indicating a decrease in the number of inactive inner Rh atoms. Consequently, an improved mass activity of 30 A mgRh-1 was achieved at 0.4 V versus reversible hydrogen electrode. Furthermore, the two-electrode system employing the same CE-derived Rh electrodes achieved overall hydrazine splitting over 36 h at a stable low voltage. The proposed surface-limited CE process is an effective method for reducing inactive atoms of expensive noble metal catalysts.
The Fe-N-C material represents an attractive oxygen reduction reaction electrocatalyst, and the FeN4 moiety has been identified as a very competitive catalytic active site. Fine tuning of the coordination structure of FeN4 has an essential impact on the catalytic performance. Herein, we construct a sulfur-modified Fe-N-C catalyst with controllable local coordination environment, where the Fe is coordinated with four in-plane N and an axial external S. The external S atom affects not only the electron distribution but also the spin state of Fe in the FeN4 active site. The appearance of higher valence states and spin states for Fe demonstrates the increase in unpaired electrons. With the above characteristics, the adsorption and desorption of the reactants at FeN4 active sites are optimized, thus promoting the oxygen reduction reaction activity. This work explores the key point in electronic configuration and coordination environment tuning of FeN4 through S doping and provides new insight into the construction of M-N-C-based oxygen reduction reaction catalysts.
Thermoelectric (TE) generators capable of converting thermal energy into applicable electricity have gained great popularity among emerging energy conversion technologies. Biopolymer-based ionic thermoelectric (i-TE) materials are promising candidates for energy conversion systems because of their wide sources, innocuity, and low manufacturing cost. However, common physically crosslinked biopolymer gels induced by single hydrogen bonding or hydrophobic interaction suffer from low differential thermal voltage and poor thermodynamic stability. Here, we develop a novel i-TE gel with supramolecular structures through multiple noncovalent interactions between ionic liquids (ILs) and gelatin molecular chains. The thermopower and thermoelectric power factor of the ionic gels are as high as 2.83 mV K-1 and 18.33 μW m-1 K-2, respectively. The quasi-solid-state gelatin-[EMIM]DCA i-TE cells achieve ultrahigh 2 h output energy density (E2h = 9.9 mJ m-2) under an optimal temperature range. Meanwhile, the remarkable stability of the supramolecular structure provides the i-TE hydrogels with a thermal stability of up to 80 ℃. It breaks the limitation that biopolymer-based i-TE gels can only be applied in the low temperature range and enables biopolymer-based i-TE materials to pursue better performance in a higher temperature range.
Here, furfural oxidation was performed to replace the kinetically sluggish O2 evolution reaction (OER). Pt-Co3O4 nanospheres were developed via pulsed laser ablation in liquid (PLAL) in a single step for the paired electrocatalysis of an H2 evolution reaction (HER) and furfural oxidation reaction (FOR). The FOR afforded a high furfural conversion (44.2%) with a major product of 2-furoic acid after a 2-h electrolysis at 1.55 V versus reversible hydrogen electrode in a 1.0-M KOH/50-mM furfural electrolyte. The Pt-Co3O4 electrode exhibited a small overpotential of 290 mV at 10 mA cm-2. As an anode and cathode in an electrolyzer system, the Pt-Co3O4 electrocatalyst required only a small applied cell voltage of ∼1.83 V to deliver 10 mA cm-2, compared with that of the pure water electrolyzer (OER||HER, ∼1.99 V). This study simultaneously realized the integrated production of energy-saving H2 fuel at the cathode and 2-furoic acid at the anode.
Nitrogen-doped three-dimensional graphene (N-doped 3D-graphene) is a graphene derivative with excellent adsorption capacity, large specific surface area, high porosity, and optoelectronic properties. Herein, N-doped 3D-graphene/Si heterojunctions were grown in situ directly on silicon (Si) substrates via plasma-assisted chemical vapor deposition (PACVD), which is promising for surface-enhanced Raman scattering (SERS) substrates candidates. Combined analyses of theoretical simulation, incorporating N atoms in 3D-graphene are beneficial to increase the electronic state density of the system and enhance the charge transfer between the substrate and the target molecules. The enhancement of the optical and electric fields benefits from the stronger light-matter interaction improved by the natural nano-resonator structure of N-doped 3D-graphene. The as-prepared SERS substrates based on N-doped 3D-graphene/Si heterojunctions achieve ultra-low detection for various molecules: 10-8 M for methylene blue (MB) and 10-9 M for crystal violet (CRV) with rhodamine (R6G) of 10-10 M. In practical detected, 10-8 M thiram was precisely detected in apple peel extract. The results indicate that N-doped 3D-graphene/Si heterojunctions based-SERS substrates have promising applications in low-concentration molecular detection and food safety.
As an emerging technology to convert environmental high-entropy energy into electrical energy, triboelectric nanogenerator (TENG) has great demands for further enhancing the service lifetime and output performance in practical applications. Here, an ultra-robust and high-performance rotational triboelectric nanogenerator (R-TENG) by bearing charge pumping is proposed. The R-TENG composes of a pumping TENG (P-TENG), an output TENG (O-TENG), a voltage-multiplying circuit (VMC), and a buffer capacitor. The P-TENG is designed with freestanding mode based on a rolling ball bearing, which can also act as the rotating mechanical energy harvester. The output low charge from the P-TENG is accumulated and pumped to the non-contact O-TENG, which can simultaneously realize ultralow mechanical wear and high output performance. The matched instantaneous power of R-TENG is increased by 32 times under 300 r/min. Furthermore, the transferring charge of R-TENG can remain 95% during 15 days (6.4 × 106 cycles) continuous operation. This work presents a realizable method to further enhance the durability of TENG, which would facilitate the practical applications of high-performance TENG in harvesting distributed ambient micro mechanical energy.
The realization of a stable lithium-metal free (LiMF) sulfur battery based on amorphous carbon anode and lithium sulfide (Li2S) cathode is here reported. In particular, a biomass waste originating full-cell combining a carbonized brewer's spent grain (CBSG) biochar anode with a Li2S-graphene composite cathode (Li2S70Gr30) is proposed. This design is particularly attractive for applying a cost-effective, high performance, environment friendly, and safe anode material, as an alternative to standard graphite and metallic lithium in emerging battery technologies. The anodic and cathodic materials are characterized in terms of structure, morphology and composition through X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron and Raman spectroscopies. Furthermore, an electrochemical characterization comprising galvanostatic cycling, rate capability and cyclic voltammetry tests were carried out both in half-cell and full-cell configurations. The systematic investigation reveals that unlike graphite, the biochar electrode displays good compatibility with the electrolyte typically employed in sulfur batteries. The CBSG/Li2S70Gr30 full-cell demonstrates an initial charge and discharge capacities of 726 and 537 mAh g-1, respectively, at 0.05C with a coulombic efficiency of 74%. Moreover, it discloses a reversible capacity of 330 mAh g-1 (0.1C) after over 300 cycles. Based on these achievements, the CBSG/Li2S70Gr30 battery system can be considered as a promising energy storage solution for electric vehicles (EVs), especially when taking into account its easy scalability to an industrial level.
The emerging of single-atom catalysts (SACs) offers a great opportunity for the development of advanced energy storage and conversion devices due to their excellent activity and durability, but the actual mass production of high-loading SACs is still challenging. Herein, a facile and green boron acid (H3BO3)-assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan, cobalt salt and H3BO3 as precursor, and the effect of H3BO3 is deeply investigated. The results show that molten boron oxide derived from H3BO3 as ideal high-temperature carbonization media and blocking media play important role in the synthesis process. As a result, the acquired Co/N/B tri-doped porous carbon framework (Co-N-B-C) not only presents hierarchical porous structure, large specific surface area and abundant carbon edges but also possesses high-loading single Co atom (4.2 wt.%), thus giving rise to outstanding oxygen catalytic performance. When employed as a catalyst for air cathode in Zn-air batteries, the resultant Co-N-B-C catalyst shows remarkable power density and long-term stability. Clearly, our work gains deep insight into the role of H3BO3 and provides a new avenue to synthesis of high-performance SACs.
Optimizing the high-temperature energy storage characteristics of energy storage dielectrics is of great significance for the development of pulsed power devices and power control systems. Selecting a polymer with a higher glass transition temperature (Tg) as the matrix is one of the effective ways to increase the upper limit of the polymer operating temperature. However, current high-Tg polymers have limitations, and it is difficult to meet the demand for high-temperature energy storage dielectrics with only one polymer. For example, polyetherimide has high-energy storage efficiency, but low breakdown strength at high temperatures. Polyimide has high corona resistance, but low high-temperature energy storage efficiency. In this work, combining the advantages of two polymer, a novel high-Tg polymer fiber-reinforced microstructure is designed. Polyimide is designed as extremely fine fibers distributed in the composite dielectric, which will facilitate the reduction of high-temperature conductivity loss for polyimide. At the same time, due to the high-temperature resistance and corona resistance of polyimide, the high-temperature breakdown strength of the composite dielectric is enhanced. After the polyimide content with the best high-temperature energy storage characteristics is determined, molecular semiconductors (ITIC) are blended into the polyimide fibers to further improve the high-temperature efficiency. Ultimately, excellent high-temperature energy storage properties are obtained. The 0.25 vol% ITIC-polyimide/polyetherimide composite exhibits high-energy density and high discharge efficiency at 150 ℃ (2.9 J cm-3, 90%) and 180 ℃ (2.16 J cm-3, 90%). This work provides a scalable design idea for high-performance all-organic high-temperature energy storage dielectrics.
As a critical role in battery systems, polymer binders have been shown to efficiently suppress the lithium polysulfide shuttling and accommodate volume changes in recent years. However, preparation processes and safety, as the key criterions for Li-S batteries' practical applications, still attract less attention. Herein, an aqueous multifunction binder (named PEI-TIC) is prepared via an easy and fast epoxy-amine ring-opening reaction (10 min), which can not only give the sulfur cathode a stable mechanical property, a strong chemical adsorption and catalytic conversion ability, but also a fire safety improvement. The Li-S batteries based on the PEI-TIC binder display a high discharge capacity (1297.8 mAh g-1), superior rate performance (823.0 mAh g-1 at 2 C), and an ultralow capacity decay rate of 0.035% over more than 800 cycles. Even under 7.1 mg cm-2 S-loaded, the PEI-TIC electrode can also achieve a high areal capacity of 7.2 mA h g-1 and excellent cycling stability, confirming its application potential. Moreover, it is also noted that TG-FTIR test is performed for the first time to explore the flame-retardant mechanism of polymer binders. This work provides an economically and environmentally friendly binder for the practical application and inspires the exploration of the flame-retardant mechanism of all electrode components.
LiNixCoyAlzO2(NCA) cathode materials are drawing widespread attention, but the huge gap between the ideal and present cyclic stability still hinders their further commercial application, especially for the Ni-rich LiNixCoyAlzO2 (x > 0.8, x + y + z = 1) cathode material, which is owing to the structural degradation and particles' intrinsic fracture. To tackle the problems, Li0.5La2Al0.5O4 in situ coated and Mn compensating doped multilayer LiNi0.82Co0.14Al0.04O2 was prepared. XRD refinement indicates that La-Mn co-modifying could realize appropriate Li/Ni disorder degree. Calculated results and in situ XRD patterns reveal that the LLAO coating layer could effectively restrain crack in secondary particles benefited from the suppressed internal strain. AFM further improves as NCA-LM2 has superior mechanical property. The SEM, TEM, XPS tests indicate that the cycled cathode with LLAO-Mn modification displays a more complete morphology and less side reaction with electrolyte. DEMS was used to further investigate cathode-electrolyte interface which was reflected by gas evolution. NCA-LM2 releases less CO2 than NCA-P indexing on a more stable surface. The modified material presents outstanding capacity retention of 96.2% after 100 cycles in the voltage range of 3.0-4.4 V at 1C, 13% higher than that of the pristine and 80.8% at 1 C after 300 cycles. This excellent electrochemical performance could be attributed to the fact that the high chemically stable coating layer of Li0.5La2Al0.5O4 (LLAO) could enhance the interface and the Mn doping layer could suppress the influence of the lattice mismatch and distortion. We believe that it can be a useful strategy for the modification of Ni-rich cathode material and other advanced functional material.
Owing to the intrinsically sluggish kinetics of urea oxidation reaction (UOR) involving a six-electron transfer process, developing efficient UOR electrocatalyst is a great challenge remained to be overwhelmed. Herein, by taking advantage of 2-Methylimidazole, of which is a kind of alkali in water and owns strong coordination ability to Co2+ in methanol, trace Co (1.0 mol%) addition was found to induce defect engineering on α-Ni(OH)2 in a dual-solvent system of water and methanol. Physical characterization results revealed that the synthesized electrocatalyst (WM-Ni0.99Co0.01(OH)2) was a kind of defective nanosheet with thickness around 5-6 nm, attributing to the synergistic effect of Co doping and defect engineering, its electron structure was finely altered, and its specific surface area was tremendously enlarged from 68 to 172.3 m2 g-1. With all these merits, its overpotential to drive 10 mA cm-2 was reduced by 110 mV. Besides, the interfacial behavior of UOR was also well deciphered by operando electrochemical impedance spectroscopy.
How to achieve synergistic improvement of permittivity (εr) and breakdown strength (Eb) is a huge challenge for polymer dielectrics. Here, for the first time, the π-conjugated comonomer (MHT) can simultaneously promote the εr and Eb of linear poly(methyl methacrylate) (PMMA) copolymers. The PMMA-based random copolymer films (P(MMA-co-MHT)), block copolymer films (PMMA-b-PMHT), and PMMA-based blend films were prepared to investigate the effects of sequential structure, phase separation structure, and modification method on dielectric and energy storage properties of PMMA-based dielectric films. As a result, the random copolymer P(MMA-co-MHT) can achieve a maximum εr of 5.8 at 1 kHz owing to the enhanced orientation polarization and electron polarization. Because electron injection and charge transfer are limited by the strong electrostatic attraction of π-conjugated benzophenanthrene group analyzed by the density functional theory (DFT), the discharge energy density value of P(MMA-co-PMHT) containing 1 mol% MHT units with the efficiency of 80% reaches 15.00 J cm-3 at 872 MV m-1, which is 165% higher than that of pure PMMA. This study provides a simple and effective way to fabricate the high performance of polymer dielectrics via copolymerization with the monomer of P-type semi-conductive polymer.
Poly (ethylene oxide) (PEO)-based polymer electrolytes show the prospect in all-solid-state lithium metal batteries; however, they present limitations of low room-temperature ionic conductivity, and interfacial incompatibility with high voltage cathodes. Therefore, a salt engineering of 1, 1, 2, 2, 3, 3-hexafluoropropane-1, 3-disulfonimide lithium salt (LiHFDF)/LiTFSI system was developed in PEO-based electrolyte, demonstrating to effectively regulate Li ion transport and improve the interfacial stability under high voltage. We show, by manipulating the interaction between PEO matrix and TFSI--HFDF-, the optimized solid-state polymer electrolyte achieves maximum Li+ conduction of 1.24 × 10-4 S cm-1 at 40 ℃, which is almost 3 times of the baseline. Also, the optimized polymer electrolyte demonstrates outstanding stable cycling in the LiFePO4/Li and LiNi0.8Mn0.1Co0.1O2/Li (3.0-4.4 V, 200 cycles) based all-solid-state lithium batteries at 40 ℃.
In designing efficient perovskite solar cells (PSCs), the selection of suitable electron transport layers (ETLs) is critical to the final device performance as they determine the driving force for selective charge extraction. SnO2 nanoparticles (NPs) based ETLs have been a popular choice for PSCs due to superior electron mobility, but their relatively deep-lying conduction band energy levels (ECB) result in substantial potential loss. Meanwhile, TiO2 NPs establish favorable band alignment owing to shallower ECB, but their low intrinsic mobility and abundant surface trap sites impede the final performance. For this reason, constructing a cascaded bilayer ETL is highly desirable for efficient PSCs, as it can rearrange energy levels and exploit on advantages of an individual ETL. In this study, we prepare SnO2 NPs and acetylacetone-modified TiO2 (Acac-TiO2) NPs and implement them as bilayer SnO2/Acac-TiO2 (BST) ETL, to assemble cascaded energy band structure. SnO2 contributes to rapid charge carrier transport from high electron mobility while Acac-TiO2 minimizes band-offset and effectively suppresses interfacial recombination. Accordingly, the optimized BST ETL generates synergistic influence and delivers power conversion efficiency (PCE) as high as 23.14% with open-circuit voltage (VOC) reaching 1.14 V. Furthermore, the BST ETL is transferred to a large scale and the corresponding mini module demonstrates peak performance of 18.39% PCE from 25 cm2 aperture area. Finally, the BST-based mini module exhibit excellent stability, maintaining 83.1% of its initial efficiency after 1000 h under simultaneous 1 Sun light-soaking and damp heat (85 ℃/RH 85%) environment.
The orthorhombic CuNb2O6 (O-CNO) is established as a competitive anode for lithium-ion capacitors (LICs) owing to its attractive compositional/structural merits. However, the high-temperature synthesis (>900 ℃) and controversial charge-storage mechanism always limit its applications. Herein, we develop a low-temperature strategy to fabricate a nano-blocks-constructed hierarchical accordional O-CNO framework by employing multilayered Nb2CTx as the niobium source. The intrinsic stress-induced formation/transformation mechanism of the monoclinic CuNb2O6 to O-CNO is tentatively put forward. Furthermore, the integrated phase conversion and solid solution lithium-storage mechanism is reasonably unveiled with comprehensive in(ex) situ characterizations. Thanks to its unique structural merits and lithium-storage process, the resulted O-CNO anode is endowed with a large capacity of 150.3 mAh g-1 at 2.0 A g-1, along with long-duration cycling behaviors. Furthermore, the constructed O-CNO-based LICs exhibit a high energy (138.9 Wh kg-1) and power (4.0 kW kg-1) densities with a modest cycling stability (15.8% capacity degradation after 3000 consecutive cycles). More meaningfully, the in-depth insights into the formation and charge-storage process here can promote the extensive development of binary metal Nb-based oxides for advanced LICs.
Crystalline γ-Ga2O3@rGO core-shell nanostructures are synthesized in gram scale, which are accomplished by a facile sonochemical strategy under ambient condition. They are composed of uniform γ-Ga2O3 nanospheres encapsulated by reduced graphene oxide (rGO) nanolayers, and their formation is mainly attributed to the existed opposite zeta potential between the Ga2O3 and rGO. The as-constructed lithium-ion batteries (LIBs) based on as-fabricated γ-Ga2O3@rGO nanostructures deliver an initial discharge capacity of 1000 mAh g-1 at 100 mA g-1 and reversible capacity of 600 mAh g-1 under 500 mA g-1 after 1000 cycles, respectively, which are remarkably higher than those of pristine γ-Ga2O3 with a much reduced lifetime of 100 cycles and much lower capacity. Ex situ XRD and XPS analyses demonstrate that the reversible LIBs storage is dominant by a conversion reaction and alloying mechanism, where the discharged product of liquid metal Ga exhibits self-healing ability, thus preventing the destroy of electrodes. Additionally, the rGO shell could act robustly as conductive network of the electrode for significantly improved conductivity, endowing the efficient Li storage behaviors. This work might provide some insight on mass production of advanced electrode materials under mild condition for energy storage and conversion applications.
The rational design of metal single-atom catalysts (SACs) for electrochemical nitrogen reduction reaction (NRR) is challenging. Two-dimensional metal-organic frameworks (2DMOFs) is a unique class of promising SACs. Up to now, the roles of individual metals, coordination atoms, and their synergy effect on the electroanalytic performance remain unclear. Therefore, in this work, a series of 2DMOFs with different metals and coordinating atoms are systematically investigated as electrocatalysts for ammonia synthesis using density functional theory calculations. For a specific metal, a proper metal-intermediate atoms p-d orbital hybridization interaction strength is found to be a key indicator for their NRR catalytic activities. The hybridization interaction strength can be quantitatively described with the p-/d- band center energy difference (∆d-p), which is found to be a sufficient descriptor for both the p-d hybridization strength and the NRR performance. The maximum free energy change (ΔGmax) and ∆d-p have a volcanic relationship with OsC4(Se)4 located at the apex of the volcanic curve, showing the best NRR performance. The asymmetrical coordination environment could regulate the band structure subtly in terms of band overlap and positions. This work may shed new light on the application of orbital engineering in electrocatalytic NRR activity and especially promotes the rational design for SACs.
Exploring noble metal-free catalyst materials for high efficient electrochemical water splitting to produce hydrogen is strongly desired for renewable energy development. In this article, a novel bifunctional catalytic electrode of insitu-grown type for alkaline water splitting based on FeCoNi alloy substrate has been successfully prepared via a facile one-step hydrothermal oxidation route in an alkaline hydrogen peroxide medium. It shows that the matrix alloy with the atom ratio 4:3:3 of Fe:Co:Ni can obtain the best catalytic performance when hydrothermally treated at 180℃ for 18 h in the solution containing 1.8 M hydrogen peroxide and 3.6 M sodium hydroxide. The as-prepared Fe0.4Co0.3Ni0.3-1.8 electrode exhibits small overpotentials of only 184 and 175 mV at electrolysis current density of 10 mA cm-2 for alkaline OER and HER processes, respectively. The overall water splitting at electrolysis current density of 10 mA cm-2 can be stably delivered at a low cell voltage of 1.62 V. These characteristics including the large specific surface area, the high surface nickel content, the abundant catalyst species, the balanced distribution between bivalent and trivalent metal ions, and the strong binding of in-situ naturally growed catalytic layer to matrix are responsible for the prominent catalytic performance of the Fe0.4Co0.3Ni0.3-1.8 electrode, which can act as a possible replacement for expensive noble metal-based materials.
Here, a novel fabrication method for making free-standing 3D hierarchical porous carbon aerogels from molecularly engineered biomass-derived hydrogels is presented. In situ formed flower-like CaCO3 molecularly embedded within the hydrogel network regulated the pore structure during in situ mineralization assisted one-step activation graphitization (iMAG), while the intrinsic structural integrity of the carbon aerogels was maintained. The homogenously distributed minerals simultaneously acted as a hard template, activating agent, and graphitization catalyst. The decomposition of the homogenously distributed CaCO3 during iMAG followed by the etching of residual CaO through a mild acid washing endowed a robust carbon aerogel with high porosity and excellent electrochemical performance. At 0.5 mA cm-2, the gravimetric capacitance increased from 0.01 F g-1 without mineralization to 322 F g-1 with iMAG, which exceeds values reported for any other free-standing or powder-based biomass-derived carbon electrodes. An outstanding cycling stability of ~104% after 1000 cycles in 1 M HClO4 was demonstrated. The assembled symmetric supercapacitor device delivered a high specific capacitance of 376 F g-1 and a high energy density of 26 W h kg-1 at a power density of 4000 W kg-1, with excellent cycling performance (98.5% retention after 2000 cycles). In combination with the proposed 3D printed mold-assisted solution casting (3DMASC), iMAG allows for the generation of free-standing carbon aerogel architectures with arbitrary shapes. Furthermore, the novel method introduces flexibility in constructing free-standing carbon aerogels from any ionically cross-linkable biopolymer while maintaining the ability to tailor the design, dimensions, and pore size distribution for specific energy storage applications.
Gravure printing is a promising large-scale fabrication method for flexible organic solar cells (FOSCs) because it is compatible with two-dimension patternable roll-to-roll fabrication. However, the unsuitable rheological property of ZnO nanoinks resulted in unevenness and looseness of the gravure-printed ZnO interfacial layer. Here we propose a strategy to manipulate the macroscopic and microscopic of the gravure-printed ZnO films through using mixed solvent and poly(vinylpyrrolidone) (PVP) additive. The regulation of drying speed effectively manipulates the droplets fusion and leveling process and eliminates the printing ribbing structure in the macroscopic morphology. The additive of PVP effectively regulates the rheological property and improves the microscopic compactness of the films. Following this method, large-area ZnO:PVP films (28 × 9 cm2) with excellent uniformity, compactness, conductivity, and bending durability were fabricated. The power conversion efficiencies of FOSCs with gravure-printed AgNWs and ZnO:PVP films reached 14.34% and 17.07% for the 1 cm2 PM6:Y6 and PM6:L8-BO flexible devices. The efficiency of 17.07% is the highest value to date for the 1 cm2 FOSCs. The use of mixed solvent and PVP addition also significantly enlarged the printing window of ZnO ink, ensuring high-quality printed thin films with thicknesses varying from 30 to 100 nm.
Dendritic mesoporous silica nanoparticles own three-dimensional center-radial channels and hierarchical pores, which endows themselves with super-high specific surface area, extremely large pore volumes, especially accessible internal spaces, and so forth. Dissimilar guest species (such as organic groups or metal nanoparticles) could be readily decorated onto the interfaces of the channels and pores, realizing the functionalization of dendritic mesoporous silica nanoparticles for targeted applications. As adsorbents and catalysts, dendritic mesoporous silica nanoparticles-based materials have experienced nonignorable development in CO2 capture and catalytic conversion. This comprehensive review provides a critical survey on this pregnant subject, summarizing the designed construction of novel dendritic mesoporous silica nanoparticles-based materials, the involved chemical reactions (such as CO2 methanation, dry reforming of CH4), the value-added chemicals from CO2 (such as cyclic carbonates, 2-oxazolidinones, quinazoline-2,4(1H,3H)-diones), and so on. The adsorptive and catalytic performances have been compared with traditional silica mesoporous materials (such as SBA-15 or MCM-41), and the corresponding reaction mechanisms have been thoroughly revealed. It is sincerely expected that the in-depth discussion could give materials scientists certain inspiration to design brand-new dendritic mesoporous silica nanoparticles-based materials with superior capabilities towards CO2 capture, utilization, and storage.
Developing stable and efficient nonprecious-metal-based oxygen evolution catalysts in the neutral electrolyte is a challenging but essential goal for various electrochemical systems. Particularly, cobalt-based spinels have drawn a considerable amount of attention but most of them operate in alkali solutions. However, the frequently studied Co-Fe spinel system never exhibits appreciable stability in nonbasic conditions, not to mention attract further investigation on its key structural motif and transition states for activity loss. Herein, we report exceptional stable Co-Fe spinel oxygen evolution catalysts (~30% Fe is optimal) in a neutral electrolyte, owing to its unique metal ion arrangements in the crystal lattice. The introduced iron content enters both the octahedral and tetrahedral sites of the spinel as Fe2+ and Fe3+ (with Co ions having mixed distribution as well). Combining density functional theory calculations, we find that the introduction of Fe to Co3O4 lowers the covalency of metal-oxygen bonds and can help suppress the oxidation of Co2+/3+ and O2-. It implies that the Co-Fe spinel will have minor surface reconstruction and less lattice oxygen loss during the oxygen evolution reaction process in comparison with Co3O4 and hence show much better stability. These findings suggest that there is still much chance for the spinel structures, especially using reasonable sublattices engineering via multimetal doping to develop advanced oxygen evolution catalysts.
Metal oxide charge transport materials are preferable for realizing long-term stable and potentially low-cost perovskite solar cells (PSCs). However, due to some technical difficulties (e.g., intricate fabrication protocols, high-temperature heating process, incompatible solvents, etc.), it is still challenging to achieve efficient and reliable all-metal-oxide-based devices. Here, we developed efficient inverted PSCs (IPSCs) based on solution-processed nickel oxide (NiOx) and tin oxide (SnO2) nanoparticles, working as hole and electron transport materials respectively, enabling a fast and balanced charge transfer for photogenerated charge carriers. Through further understanding and optimizing the perovskite/metal oxide interfaces, we have realized an outstanding power conversion efficiency (PCE) of 23.5% (the bandgap of the perovskite is 1.62 eV), which is the highest efficiency among IPSCs based on all-metal-oxide charge transport materials. Thanks to these stable metal oxides and improved interface properties, ambient stability (retaining 95% of initial PCE after 1 month), thermal stability (retaining 80% of initial PCE after 2 weeks) and light stability (retaining 90% of initial PCE after 1000 hours aging) of resultant devices are enhanced significantly. In addition, owing to the low-temperature fabrication procedures of the entire device, we have obtained a PCE of over 21% for flexible IPSCs with enhanced operational stability.
Hyperfluorescent organic light-emitting diodes (HF-OLEDs) approach has made it possible to achieve excellent device performance and color purity with low roll-off using noble-metal-free pure organic emitter. Despite significant progress, the performance of HF-OLEDs is still unsatisfactory due to the existence of a competitive dexter energy transfer (DET) pathway. In this contribution, two boron dipyrromethene (BODIPY)-based donor-acceptor emitters (BDP-C-Cz and BDP-N-Cz) with hybridized local and charge transfer characteristics (HLCT) are introduced in the HF-OLED to suppress the exciton loss by dexter mechanism, and a breakthrough performance with low-efficiency roll-off (0.3%) even at high brightness (1000 cd m-2) is achieved. It is demonstrated that the energy loss via the DET channel can be suppressed in HF-OLEDs utilizing the HLCT emitter, as the excitons from the dark triplet state of such emitters are funneled to its emissive singlet state following the hot-exciton mechanism. The developed HF-OLED device has realized a good maximum external quantum efficiency (EQE) of 19.25% at brightness of 1000 cd m-2 and maximum luminance over 60 000 cd m-2, with an emission peak at 602 nm and Commission International de L'Eclairage (CIE) coordinates (0.57, 0.41), which is among the best-achieved results in solution-processed HF-OLEDs. This work presents a viable methodology to suppress energy loss and achieve high performance in the HF-OLEDs.
This paper reports a multifunctional magnetic-photoelectric laminate device based on the integration of spintronic material (La0.7Sr0.3MnO3) and multiferroic (Ni-doped BiFeO3), in which the repeatable modulation effect on the photoelectric properties were achieved by applying external magnetic fields. More obviously, photocurrent density (J) of the laminate was largely enhanced, the change rate of J up to 287.6% is obtained. This sensing function effect should be attributed to the low-field magnetoresistance effect in perovskite manganite and the scattering of spin photoelectron in multiferroic material. The laminate perfectly combines the functions of sensor and controller, which can not only reflect the intensity of environmental magnetic field, but also modulate the photoelectric conversion performance. This work provides an alternative and facile way to realize multi-degree-of-freedom control for photoelectric conversion performances and lastly miniaturize multifunction device.
To demonstrate flexible and tandem device applications, a low-temperature Cu2ZnSnSe4 (CZTSe) deposition process, combined with efficient alkali doping, was developed. First, high-quality CZTSe films were grown at 480 ℃ by a single co-evaporation, which is applicable to polyimide (PI) substrate. Because of the alkali-free substrate, Na and K alkali doping were systematically studied and optimized to precisely control the alkali distribution in CZTSe. The bulk defect density was significantly reduced by suppression of deep acceptor states after the (NaF + KF) PDTs. Through the low-temperature deposition with (NaF + KF) PDTs, the CZTSe device on glass yields the best efficiency of 8.1% with an improved VOC deficit of 646 mV. The developed deposition technologies have been applied to PI. For the first time, we report the highest efficiency of 6.92% for flexible CZTSe solar cells on PI. Additionally, CZTSe devices were utilized as bottom cells to fabricate four-terminal CZTSe/perovskite tandem cells because of a low bandgap of CZTSe (~1.0 eV) so that the tandem cell yielded an efficiency of 20%. The obtained results show that CZTSe solar cells prepared by a low-temperature process with in-situ alkali doping can be utilized for flexible thin-film solar cells as well as tandem device applications.