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Phosphorus-carbon anode materials for alkali-metal ion storage in rechargeable batteries can simultaneously achieve high-energy density and fast charging. The P-C-bonded structure in the phosphorus-carbon materials has been observed and acknowledged to be a critical structural feature that renders improved cycling stability and rate performance. However, the underlying mechanisms, especially the role played by P-C bonds, remain elusive. By combining computational simulations and spectroscopic characterizations, we reveal that the stability of P-C bonds is critical to the electrochemical performance. In the discharge process, P-P bonds are fragile, while the bonding state of the P-C bonds is almost unchanged since electrons were mainly received by the P atoms to form lone pairs. The preserved P-C clusters can effectively serve as a reunion center for the recovery of P-P bonds in the recharging process, leading to a moderate energy change and improved cycling reversibility and structural stability of the phosphorous for electrochemical energy storage.

This work reveals how the local electronic structures of single-site catalysts are tuned to enhance the performance for CO2 electroreduction.

Electrolyte freezing under low temperatures is a critical issue for the development of aqueous batteries (ABs). While lowering the freezing point of the electrolyte has caught major research efforts, limited attention has been paid to the structural evolution during the electrolyte freezing process and regulating the frozen electrolyte structure for low temperature ABs. Here, we reveal the formation process of interconnected liquid regions for ion transport in frozen electrolytes with various in situ variable-temperature technologies. More importantly, the low-temperature performance of ABs was significantly improved with the colloidal electrolyte design using graphene oxide quantum dots (GOQDs), which effectively inhibits the growth of ice crystals and expands the interconnected liquid regions for facial ion transport. This work provides new insights and a promising strategy for the electrolyte design of low-temperature ABs.

Appling an electrochemical catalyst is an efficient strategy for inhibiting the shuttle effect and enhancing the S utilization of Li-S batteries. Carbon-based materials are the most common conductive agents and catalyst supports used in Li-S batteries, but the correlation between the diversity of hybridizations and sulfur reduction reaction (SRR) catalytic activity remains unclear. Here, by establishing two forms of carbon models, i.e., graphitic carbon (GC) and amorphous carbon (AC), we observe that the nitrogen atom doped in the GC possesses a higher local charge density and a lower Gibbs free energy towards the formation of polysulfides than in the AC. And the GC-based electrode consistently inherits considerably enhanced SRR kinetics and superior cycling stability and rate capability in Li-S batteries. Therefore, the function of carbon in Li-S batteries is not only limited as conductive support but also plays an unignorable contribution to the electrocatalytic activities of SRR.

The thermal dispersion power depends on thermal conductivity and thickness of the thermal dispersion material that is a critical component of modern electronic devices due to the demands of high operating power in a miniaturized space. Films made of assembled graphene flakes have been becoming an emerging thermal dispersion material owing to their high thermal conductivity and tunable thickness up to millimeters, which outperform that of artificial graphite films made from polyimide. But the thermal conductivity typically decreases with the increase of film thickness. In our work, by pre-reducing the graphene oxide with Vitamin C and sequentially annealing the stacking films at 2950 °C, a 80 μm-thick graphene film (GF) with an in-plane thermal conductivity of above 1600 W/(m·K) is achieved. Detailed characterizations indicate that, the addition of Vitamin C is beneficial to the assembly ordering of graphene oxide platelets and the defect healing during the thermal annealing, which both contribute to the excellent thermal conductivity of the films. Our work provides an industrially scalable strategy towards high performance heat dissipation films for future electronic devices.

Na metal anodes have shown great promise for a low cost energy storage system but its practical application is hampered by the uncontrollable dendrite growth. Here, we present a sodiophobic–sodioph...

Amidst the material development for solar water splitting, silicon has been known as a promising photocatalyst candidate given its natural abundance and high processability toward future scale-up a...

Stable solid electrolyte interphase (SEI) has been well established to be critical for the reversible operation of Li (ion) batteries, yet our understanding of its mechanical properties currently remains incomplete. Here, we used an electrochemical quartz crystal microbalance combined with dissipation monitoring (EQCM-D) to investigate SEI formation. By quantitatively estimating in-situ, the change in mass, shear modulus, and viscosity of the SEI, we show that the SEI formation in propylene carbonate (PC)- and ethylene carbonate/diethyl carbonate (EC/DEC)-based electrolytes involves the growth of a rigid layer followed by a viscoelastic layer, whereas a distinct “one-layer” rigid model is applicable to the SEI formulated in tetraethylene glycol dimethyl ether (TEGDME)-based electrolyte. With the continuous formation of the SEI, its shear modulus decreases accompanied by an increase in viscosity. In TEGDME, the lightest/thinnest SEI (mass lower than in PC by a factor of nine) yet having the greatest stiffness (more than five times that in PC) is obtained. We attribute this behavior to differences in the chemical composition of the SEIs, which have been revealed by tracking the mass-change-per-mole-of-electron-transferred using EQCM-D and further confirmed by X-ray photoelectron spectroscopy.

Lithium-sulfur (Li-S) batteries have become prospective candidates for next-generation energy storage owing to the high energy density and low cost. However, the sluggish kinetics of the electrochemical reaction and shuttle effect result in a rapid capacity decay. Herein, a titanium nitride nanocrystal/N-doped graphene (TiN@NG) composite is developed to host elemental sulfur. The TiN nanoparticles decorated on graphene sheets attract Li polysulfides (LiPSx) and catalyze the electrochemical reduction and oxidation of LiPSx in the discharge and charge processes, respectively. These two effects effectively restrain the dissolution of the LiPSx and accelerate the electrochemical reactions, thereby, alleviating the shuttle effect. As a result, the cathode composed of TiN@NG/S delivers a remarkable reversible capacity (1390 mA h g−1 at 0.1 C) and excellent cycling performance (730 mA h g−1 after 300 cycles). We believe that this work can bring some inspiration for designing high-performance Li-S batteries.

Electrical double-layer capacitors are widely concerned for their high power density, long cycling life and high cycling efficiency. However, their wide application is limited by their low energy density. In this study, we propose a simple yet environmental friendly method to synthesize cobalt and nitrogen atoms co-doped porous carbon (CoAT-NC) material. Cobalt atoms connected with primarily pyridinic nitrogen atoms can be uniformly dispersed in the amorphous carbon matrix, which is benefit for improving electrical conductivity and density of states of the carbon material. Therefore, an enhanced performance is expected when CoAT-NC is served as electrode in a supercapacitor device. CoAT-NC displays a good gravimetric capacitance of 160 F/g at 0.5 A/g combing with outstanding capacitance retention of 90% at an extremely high current density of 100 A/g in acid electrolyte. Furthermore, a good energy density of 30 Wh/kg can be obtained in the organic electrolyte.

Because of its high theoretical specific capacity and low reduction potential, Li metal is considered to be key to reaching high energy density in rechargeable batteries. In this context, most of the research has focused on suppressing dendrite formation during Li deposition to improve the cycling reversibility and safety of the batteries. Here, covalent organic framework (COF) film coating on a commercial polypropylene separator is applied as an ion redistributor to eliminate Li dendrites. The COF crystallites consist of ordered nanochannels that hinder the movement of anions while allowing Li-ions to transport across, leading to a high Li-ion transference number of 0.77±0.01. The transport of Li-ions across the COF film can be considered to be analogous to beads passing through a Galton Board, a model that demonstrates a statistical concept of a normal distribution. Thus, an even distribution of Li-ions is obtained at the COF Li metal interface. The controlled Li-ion flux yields a smooth Li metal surface after 1,000 h (500 times) of cycling, leading to a significantly improved cycling stability and reversibility, as demonstrated by Cu||Li half cells, Li||Li symmetric cells, and LiFePO4||Li full cells. These results suggest that, following the principle of a Galton Board, nanopore insulators such as COF-based materials are effective ion distributors for the different energy storage or conversion systems.

In recent years, flexible pressure sensors have attracted much attention owing to their potential applications in motion detection and wearable electronics. As a result, important innovations have been reported in both conductive materials and the underlying substrates, which are the two crucial components of a pressure sensor. 1D materials like nanowires are being widely used as the conductive materials in flexible pressure sensors, but such sensors usually exhibit low performances mainly due to the lack of strong interfacial interactions between the substrates and 1D materials. In this paper, we report the use of graphene/graphene scrolls hybrid multilayers films as the conductive material and a micro-structured polydimethylsiloxane substrate using Epipremnum aureum leaf as the template to fabricate highly sensitive pressure sensors. The 2D structure of graphene allows to strongly anchor the scrolls to ensure the improved adhesion between the highly conductive hybrid films and the patterned substrate. We attribute the increased sensitivity (3.5 kPa \begin{document}$ ^{-1} $\end{document} ), fast response time ( \begin{document}$ 50 ms), and the good reproducibility during 1000 loading-unloading cycles of the pressure sensor to the synergistic effect between the 1D scrolls and 2D graphene films. Test results demonstrate that these sensors are promising for electronic skins and motion detection applications.

Lithium metal batteries are vital devices for high-energy-density energy storage, but the Li metal anode is highly reactive with electrolyte and forms uncontrolled dendrite that can cause undesirable parasitic reactions and, thus, poor cycling stability and raise safety concerns. Despite remarkable progress to partially solve these issues, the Li metal still plates at the electrode/electrolyte interface where the parasitic reactions and dendrite formation invariably occur. Here, we demonstrate the inward-growth plating of Li atoms into a metal foil of thickness of tens of micrometers while avoiding surface deposition, which is driven by the reversible solid-solution-based alloy phase change. Lithiation of the solid-solution alloy phase allows the freshly generated Li atoms at the surface to sink into the metal foil, while the reversible alloy phase change is companied by the dealloying reaction during delithiation, which extracts Li atoms from inside of the metal foil. The yielded dendrite free Li anode produces an enhanced Coulombic efficiency of 99.5 ± 0.2% with a reversible capacity of 1660 mA h g-1 (3.3 mA h cm-2).

The rechargeable aluminium-sulfur (Al-S) battery is regarded as a potential alternative beyond lithium-ion battery system owing to its safety, promising energy density, and the high earth abundance of the constituent electrode materials, however, sluggish kinetic response and short life-span are the major issues that limit the battery development towards applications. In this article, we report CoII,III as an electrochemical catalyst in the sulfur cathode that renders a reduced discharge-charge voltage hysteresis and improved capacity retention and rate capability for Al-S batteries. The structural and electrochemical analysis suggest that the catalytic effect of CoII,III is closely associated with the formation of cobalt sulfides and the changes in the valence states of the CoII,III during the electrochemical reactions of the sulfur species, which lead to improved reaction kinetics and sulfur utilization in the cathode. The Al-S battery, assembled with the cathode consisting of CoII,III decorated carbon matrix, demonstrates a considerably reduced voltage hysteresis of 0.8 V, a reversible specific capacity of ≈500 mAh g-1 at 1 A g-1 after 200 discharge-charge cycles and of ≈300 mAh g-1 at 3 A g-1 .

Graphene oxide (GO) suspensions in solvents are the most important feedstocks for preparing GO based composites, and the dispersion state of GO on the microscale in solvent is a dominating factor in determining the physical properties of GO based composites. However, the morphology of GO sheets in solvents has hardly been reported due to the limitation of the characterization methods. Here, we report that the sheet thickness and lateral size of GO in solution can be identified using optical microscopy (OM) within a couple of minutes. The dispersion states of GO, including stretched flakes, scrolls, crumbles, and agglomerates, can also be distinguished. Moreover, the dispersion states, which change with the pH value and ionic strength of the solvent, are closely related to the dispersion stability of the GO suspension and the morphology of the GO/PVA composite. We believe that the fast observation and identification of GO sheets and their structural features in solvents, enabled by OM, opens up a new avenue to studying GO based composite materials in liquids.

Carbon-based single metal atom catalysts (SACs) are being extensively investigated to improve the kinetics of the Li-S redox reaction, which is greatly important for batteries with cell-level energy densities500 W h kg

Na metal anode (NMA) is one of the most promising candidate materials for next-generation low-cost sodium metal batteries. However, the preferred deposition of Na metal at the anode/separator interface increases the risk of dendrite penetration of the separator, consequently, reduces safety and life of batteries with NMA. In this study, a Na deposition-regulating strategy is shown by designing a gradiently graphitized 3D carbon fiber (CF) framework as host (grad-CF), whereby Na is guided to deposit preferentially at the bottom of the anode, safely away from the separator. The obtained Na anode significantly reduces the probability of dendrite-induced short circuits. The grad-CF host enables NMA stable cycling at a high current density of 6 mA cm

Graphite oxide and its exfoliated counterpart, graphene oxide, are important precursors for the large-scale production of graphene-based materials and many relevant applications. The current batch-style preparation of graphite oxide suffers from safety concern, long reaction time, and nonuniform product quality, due to the large volume of reactors and slow energy exchange. Reaction in microchannels can largely enhance the oxidization efficiency of graphite due to the enhanced mass transfer and extremely quick energy exchange, by which the controllable oxidization of graphite is achieved in ≈2 min. Comprehensive characterizations show that the graphene oxide obtained through the microfluidic strategy has features like those prepared in laboratory beakers and industrial reactors, yet with the higher oxidization degree and more epoxy groups. More importantly, the microfluidic preparation allows for on-line monitoring of the oxidization by Raman spectroscopy, ready for the dynamical control of reaction condition and product quality. The capability of continuous preparation is also demonstrated by showing the assembly of fibers and reduction of graphene oxide in microfluidic channels, and the applicability of graphene oxide prepared from the microfluidic strategy for thermally and electrically conductive films.

Bernal-stacked bilayer graphene is uniquely suited for application in electronic and photonic devices because of its tunable band structure. Even though chemical vapor deposition (CVD) is considered to be the method of choice to grow bilayer graphene, the direct synthesis of high-quality, large-area Bernal-stacked bilayer graphene on Cu foils is complicated by overcoming the self-limiting nature of graphene growth on Cu. Here, we report a facile H2O-assisted CVD process to grow bilayer graphene on Cu foils, where graphene growth is controlled by injecting intermittent pulses of H2O vapor using a pulse valve. By optimizing CVD process parameters fully covered large area graphene with bilayer coverage of 77 ± 3.6% and high AB stacking ratio of 93 ± 3% can be directly obtained on Cu foils, which presents a hole concentration and mobility of 4.5 × 1012 cm–2 and 1100 cm2 V–1 s–1, respectively, at room temperature. The H2O selectively etches graphene edges without damaging graphene facets, which slows down the ...

Although atomically dispersed Fe-N species as electrocatalysts often exhibit high activity for oxygen reduction reaction (ORR), the rational design and facile fabrication of single-atom Fe-N species-based catalysts remains a great challenge because of their easy aggregation. Herein, a new precursor of host-guest Fe-TPP⊂rho-ZIF (Fe-TPP = tetraphenylporphyrin iron; rho-ZIF = zeolitic imidazolate framework with the rho topology) for the first time was elaborately designed and readily prepared by one-pot mechanochemical method, and then was pyrolyzed into Fe-N/C catalysts with no need of solution-based steps and post-ammonia/acid treatments, which greatly simplified the preparation procedures. Owing to the host-guest confinement at the molecular level, the encapsulated Fe centers within interior cavities of rho-ZIF host matrice can be effectively isolated during pyrolysis to afford atomically dispersed Fe-N4 moieties anchored on the carbon matrice. Such a well-elaborated precursor not only endows the final product with the single-atom characteristic, but also with high Fe loading (up to 3.8 wt%) and specific surface area. Benefitting from the outstanding compositional and structural advantages, the resultant Fe-N/C exhibits highly efficient ORR activity with E1/2 of 0.895 V in 0.1 M KOH, ~ 50 mV more positive than that of the commercial Pt/C, which is among the top-level ORR electrocatalysts to date. It has excellent stability and displays a negligible change after a 10000-cycle accelerated durability test. Moreover, rechargeable Zn-air batteries were also assembled to demonstrate the practical application of the as-obtained Fe-N/C as air cathode catalyst. Our work may provide an insight into the facile and large-scale production of high-performance and durable non-precious metal catalysts with atomic-level dispersion.

Three-dimensional carbon materials combining excellent mechanical, electrical and thermal properties with very good electrochemical resistance have shown great potential for electrochemical energy storage. Building up a three-dimensional current collector can simultaneously optimize the conductive network in the electrochemically active layers and mitigate the volume change at the electrode level during cycling, which leads to enhanced energy density, power density and cycle stability. This review aims to provide an overview of the recent key progress on 3D carbon current collector for Li-ion batteries. According to the type of the connections at the junctions between the nano/micro-scale constituents, we categorize 3D carbon materials into two aspects: 3D carbon networks based on covalent connection and 3D carbon networks based on non-covalent connection. The requirements and the challenges of the 3D carbon based current collector’s design are discussed, which provide inspiration for further exploitation of the current collectors for Li-ion batteries and shed light on batteries based on other electrochemistry.

Graphene sponge (GS) with microscale size, high mechanical elasticity and electrical conductivity has attracted great interest as a sensing material for piezoresistive pressure sensor. However, GS offering a lower limit of pressure detection with high gauge factor, which is closely dependent on the mechanical and electrical properties and determined by the fabrication process, is still demanded. Here, γ-ray irradiation reduced GS is reported to possess a gauge factor of 1.03 kPa–1 with pressure detection limit of 10 Pa and high stress retention of 76% after 800 cycles of compressing/relaxation at strain of 50%. Compared with the carbon nanotube (CNT) reinforced GS, the improved lower limit of pressure detection and gauge factor of the GS prepared by γ-ray irradiation is due to the low compression stress (0.9 kPa at stain of 50%). These excellent physical properties of the GS are ascribed to the mild, residual free, and controllable reduction process offered by γ-ray irradiation.

Exfoliated black phosphorus (BP), as a monolayer or few-layer material, has attracted tremendous attention owing to its unique physical properties for applications ranging from optoelectronics to photocatalytic hydrogen production. Approaching intrinsic properties has been, however, challenged by chemical reactions and structure degradation of BP under ambient conditions. Surface passivation by capping agents has been proposed to extend the processing time window, yet contamination or structure damage rise challenges for BP applications. Here, we report experiments combined with first-principle calculations that address the degradation chemistry of BP. Our results show that BP reacts with oxygen in water even without light illumination. The reaction follows a pseudo-first-order parallel reaction kinetics, produces PO23–, PO33–, and PO43– with reaction rate constants of 0.019, 0.034, and 0.023 per day, respectively, and occurs preferentially from the P atoms locating at BP edges, which yields structural de...

Chemical vapor deposition (CVD) on Cu foils emerged as an important method for preparing high-quality and large-area graphene films for practical applications. However, to date it remains challenging to rapidly identify the structural features, especially the layer numbers, of CVD-graphene directly on Cu substrate. Herein, we report an O2-plasma-assisted approach for identifying the coverage, wrinkles, domain size, and layer number of large-area graphene films on Cu foils by optical microscopy. The wrinkles and grain boundaries of five-layer graphene can be observed with a grayscale increment of ∼23.4% per one graphene layer after O2-plasma treatment for only 15 s, which allows for checking graphene on Cu foils with a sample size of 17 cm × 20 cm in a few minutes. The Raman spectroscopy and X-ray photoelectron spectroscopy presents a strong layer number dependence of both the plasma induced graphene defects and Cu oxides, which, as indicated by molecular dynamic simulation, is responsible for the improved...

NS codoped carbon nanorods (NS-CNRs) were prepared using crab shell as template and polyphenylene sulfide (PPS) as both the C and S precursor, followed by carbonization in NH3. The as-obtained NS-CNRs had a diameter of ∼50 nm, length of several micrometers, and N and S contents of 12.5 at.% and 3.7 at.%, respectively, which can serve as anodes for both lithium-ion batteries (LIBs) and sodium ion batteries (SIBs). When serving as an anode of LIB, the NS-CNRs delivered gravimetric capacities of 2154 mAh g−1 at current densities of 0.1 A g−1 and 625 mAh g−1 at current densities of 5.0 A g−1 for 1000 cycles. When serving as an anode of SIB, the NS-CNRs delivered gravimetric capacities of 303 mAh g−1 at current densities of 0.1 A g−1 and 230 mAh g−1 at current densities of 1.0 A g−1 for 3000 cycles. The excellent electrochemical performance of NS-CNRs could be ascribed to the one-dimensional nanometer structure and high level of heteroatom doping. We expect that the obtained NS-CNRs would benefit for the future development of the doped carbon materials for lithium ion batteries and other extended applications such as supercapacitor, catalyst and hydrogen storage.

A three-dimensional (3D) architectural hybrid, composed of reduced graphene oxide (RGO) and ultrathin MoS2 layers, is fabricated by a facile spray-freezing method. The spray-freezing to liquid nitrogen rapidly freezes the precursor droplets which avoids phase separation and restacking of MoS2 and RGO platelets, and the following drying/annealing results in the porous 3D structure. The as-prepared 3D architectural RGO/MoS2 hybrid has a high surface area of 128 m2 g−1, a porous structure and a good electrical conductivity. In LIBs, the capacity of RGO/MoS2 anode (with an optimized MoS2 content of 55 wt%) remains 1197 mAh g−1 after 400 cycles of measurement at a current density of 1 A g−1 and it remains 892 mAh g−1 over 400 cycles at a current density of 2 A g−1. A capacity of 723 mAh g−1 is obtained at a current of 10 A g−1. As for the anode (with an optimized MoS2 content of 74 wt%) in SIBs, a high initial discharge capacity of 1315 mAh g−1, a superior rate capacity of 470 mAh g−1 at 1 A g−1 and an excellent cycling stability (518 mAh g−1 after 200 cycles at 0.5 A g−1) are demonstrated.

The application of supercapacitors has been restricted partially due to the high self-discharge rate and large leakage current. In this paper, a nematic hybrid liquid crystal, E7, is adopted as an additive to the electrolyte, and the self-discharge of activated carbon-based supercapacitors is evaluated by tuning various parameters such as initial voltage, current density, temperature and thickness of electrodes. Our results show that the supercapacitors exhibit an obviously lower self-discharge rate due to the contribution of E7, evidenced by the 24 h open circuit potential (OCP) drop from 3 V to 1.4 V with E7, compared to the 24 h OCP drop to 1.1 V in the situation without E7. The leakage current is also reduced from 10 to 2.2 µA with the existence of E7.