Vertical-Channel Cathode Host Enables Rapid Deposition Kinetics toward High-Areal-Capacity Sodium-Chlorine Batteries.

Rechargeable sodium chloride (Na-Cl2) batteries have emerged as promising alternatives for next-generation energy storage due to their superior energy density and sodium abundance. However, their practical applications are hindered by the sluggish chlorine cathode kinetics related to the aggregation of NaCl and its difficult transformation into Cl2. Herein, the study, for the first time from the perspective of electrode level in Na-Cl2 batteries, proposes a free-standing carbon cathode host with customized vertical channels to facilitate the SOCl2 transport and regulate the NaCl deposition. Accordingly, electrode kinetics are significantly enhanced, and the deposited NaCl is distributed evenly across the whole electrode, avoiding the blockage of pores in the carbon host, and facilitating its oxidation to Cl2. With this low-polarization cathode, the Na-Cl2 batteries can deliver a practically high areal capacity approaching 4 mAh cm-2 and a long cycle life of over 170 cycles. This work demonstrates the significance of pore engineering in electrodes for mediating chlorine conversion kinetics in rechargeable alkali-metal-Cl2 batteries.

Unraveling the Catalyst-Solvent Interactions in Lean-Electrolyte Sulfur Reduction Electrocatalysis for Li-S Batteries.

Efficient catalyst design is important for lean-electrolyte sulfur reduction in Li-S batteries. However, most of the reported catalysts were focused on catalyst-polysulfide interactions, and generally exhibit high activity only with a large excess of electrolyte. Herein, we proposed a general rule to boost lean-electrolyte sulfur reduction by controlling the catalyst-solvent interactions. As evidenced by synchrotron-based analysis, in situ spectroscopy and theoretical computations, strong catalyst-solvent interaction greatly enhances the lean-electrolyte catalytic activity and battery stability. Benefitting from the strong interaction between solvent and cobalt catalyst, the Li-S battery achieves stable cycling with only 0.22 % capacity decay per cycle with a low electrolyte/sulfur mass ratio of 4.2. The lean-electrolyte battery delivers 79 % capacity retention compared with the battery with flooded electrolyte, which is the highest among the reported lean-electrolyte Li-S batteries.

Band Structure Engineering of Schiff-Base Microporous Organic Polymers for Enhanced Visible-Light Photocatalytic Performance.

Schiff-base networks (SBNs), as typical examples of nitrogen-doped microporous organic polymers (MOPs), exhibit promising application prospects owing to their stable properties and tunable chemical structures. However, their band structure engineering, which plays a key role in optical properties, remains elusive due to the complicated mechanisms behind energy level adjustment. In this work, a series of SBNs are fabricated by tailoring the ratio of p-phthalaldehyde and o-phthalaldehyde in the Schiff-base chemistry reaction with melamine, resulting in a straightforward as well as continuous tuning of their band gaps ranging from 4.4 to 1.4 eV. Consequently, SBNs can be successfully used as photocatalysts with excellent visible-light photocatalytic activity even under metal-free conditions. Significantly, electronic structures of SBNs are systematically studied by electrochemical and spectroscopic characterizations, demonstrating that the enhanced performance is ascribed to proper band structure and improved charge separation ability. More importantly, in combination with theoretical calculations, the band structure regulation mechanism and band structure-photocatalytic property relationship are deeply disclosed. The results obtained from this study will not only furnish SBN materials with excellent performance for solar energy conversion, but also open up elegant protocols for the molecular engineering of MOPs with desirable band structures.

Nitrogen-Enriched Carbon/CNT Composites Based on Schiff-Base Networks: Ultrahigh N Content and Enhanced Lithium Storage Properties.

To improve the electrochemical performance of carbonaceous anodes for lithium ion batteries (LIBs), the incorporation of both well-defined heteroatom species and the controllable 3D porous networks are urgently required. In this work, a novel N-enriched carbon/carbon nanotube composite (NEC/CNT) through a chemically induced precursor-controlled pyrolysis approach is developed. Instead of conventional N-containing sources or precursors, Schiff-base network (SNW-1) enables the desirable combination of a 3D polymer with intrinsic microporosity and ultrahigh N-content, which can significantly promote the fast transport of both Li+ and electron. Significantly, the strong interaction between carbon skeleton and nitrogen atoms enables the retention of ultrahigh N-content up to 21 wt% in the resultant NEC/CNT, which exhibits a super-high capacity (1050 mAh g-1 ) for 1000 cycles and excellent rate performance (500 mAh g-1 at a current density of 5 A g-1 ) as the anode material for LIBs. The NEC/CNT composite affords a new model system as well as a totally different insight for deeply understanding the relationship between chemical structures and lithium ion storage properties, in which chemistry may play a more important role than previously expected.

Disassembly-Reassembly Approach to RuO2 /Graphene Composites for Ultrahigh Volumetric Capacitance Supercapacitor.

A porous, yet compact, RuO2 /graphene hybrid is successfully prepared by using a disassembly-reassembly strategy, achieving effective and uniform loading of RuO2 nanoparticles inside compact graphene monolith. The disassembly process ensures the uniform loading of RuO2 nanoparticles into graphene monolith, while the reassembly process guarantees a high density yet simultaneously unimpeded ion transport channel in the composite. The resulting RuO2 /graphene hybrid possesses a density of 2.63 g cm-3 , leading to a record high volumetric capacitance of 1485 F cm-3 at the current density of 0.1 A g-1 . When the current density is increased to 20 A g-1 , it remains a high volumetric capacitance of 1188 F cm-3 . More importantly, when the single electrode mass loading is increased to 12 mg cm-2 , it still delivers a high volumetric capacitance of 1415 F cm-3 at the current density of 0.1 A g-1 , demonstrating the promise of this disassembly-reassembly approach to create high volumetric performance materials for energy storage applications.

Iodine-induced self-depassivation strategy to improve reversible kinetics in Na-Cl2 battery.

Rechargeable sodium-chlorine (Na-Cl2) batteries show high theoretical specific energy density and excellent adaptability for extreme environmental applications. However, the reported cycle life is mostly less than 500 cycles, and the understanding of battery failure mechanisms is quite limited. In this work, we demonstrate that the substantially increased voltage polarization plays a critical role in the battery failure. Typically, the passivation on the porous cathode caused by the deposition of insulated sodium chloride (NaCl) is a crucial factor, significantly influencing the three-phase chlorine (NaCl/Na+, Cl-/Cl2) conversion kinetics. Here, a self-depassivation strategy enabled by iodine anion (I-)-tuned NaCl deposition was implemented to enhance the chlorine reversibility. The nucleation and growth of NaCl crystals are well balanced through strong coordination of the NaI deposition-dissolution process, achieving depassivation on the cathode and improving the reoxidation efficiency of solid NaCl. Consequently, the resultant Na-Cl2 battery delivers a super-long cycle life up to 2000 cycles.

Schottky Junction and D-A1 -A2 System Dual Regulation of Covalent Triazine Frameworks for Highly Efficient CO2 Photoreduction.

Covalent triazine frameworks (CTFs) are emerging as a promising molecular platform for photocatalysis. Nevertheless, the construction of highly effective charge transfer pathways in CTFs for oriented delivery of photoexcited electrons to enhance photocatalytic performance remains highly challenging. Herein, a molecular engineering strategy is presented to achieve highly efficient charge separation and transport in both the lateral and vertical directions for solar-to-formate conversion. Specifically, a large π-delocalized and π-stacked Schottky junction (Ru-Th-CTF/RGO) that synergistically knits a rebuilt extended π-delocalized network of the D-A1 -A2 system (multiple donor or acceptor units, Ru-Th-CTF) with reduced graphene oxide (RGO) is developed. It is verified that the single-site Ru units in Ru-Th-CTF/RGO act as effective secondary electron acceptors in the lateral direction for multistage charge separation/transport. Simultaneously, the π-stacked and covalently bonded graphene is regarded as a hole extraction layer, accelerating the separation/transport of the photogenerated charges in the vertical direction over the Ru-Th-CTF/RGO Schottky junction with full use of photogenerated electrons for the reduction reaction. Thus, the obtained photocatalyst has an excellent CO2 -to-formate conversion rate (≈11050 µmol g-1 h-1 ) and selectivity (≈99%), producing a state-of-the-art catalyst for the heterogeneous conversion of CO2 to formate without an extra photosensitizer.

Elaborating the Crystal Water of Prussian Blue for Outstanding Performance of Sodium Ion Batteries.

Prussian blue (PB) is one of the main cathode materials with industrial prospects for the sodium ion battery. The structural stability of PB materials is directly associated with the presence of crystal water within the open 3D framework. However, there remains a lack of consensus regarding whether all forms of crystal water have detrimental effects on the structural stability of the PB materials. Currently, it is widely accepted that interstitial water is the stability troublemaker, whereas the role of coordination water remains elusive. In this work, the dynamic evolution of PB structures is investigated during the crystal water (in all forms) removal process through a variety of online monitoring techniques. It can be inferred that the PB-130 °C retains trace coordination water (1.3%) and original structural integrity, whereas PB-180 °C eliminates almost all of crystal water (∼12.1%, including both interstitial and coordinated water), but inevitably suffers from structural collapse. This is mainly because the coordinated water within the PB material plays a crucial role in maintaining structural stability via forming the -N≡C-FeLS-C≡N- conjugate bridge. Consequently, PB-130 °C with trace coordination water delivers superior reversible capacity (113.6 mAh g-1), high rate capability (charge to >80% capacity in 3 min), and long cycling stability (only 0.012% fading per cycle), demonstrating its promising prospect in practical applications.

An orientated mass transfer in Ni-Cu tandem nanofibers for highly selective reduction of CO2 to ethanol.

Electrochemically reducing CO2 to ethanol is attractive but suffers from poor selectivity. Tandem catalysis that integrates the activation of CO2 to an intermediate using one active site and the subsequent formation of hydrocarbons on the other site offers a promising approach, where the control of the intermediate transfer between different catalytic sites is challenging. We propose an internally self-feeding mechanism that relies on the orientation of the mass transfer in a hierarchical structure and demonstrate it using a one-dimensional (1D) tandem core-shell catalyst. Specifically, the carbon-coated Ni-core (Ni/C) catalyzes the transformation of CO2-to-CO, after which the CO intermediates are guided to diffuse to the carbon-coated Cu-shell (Cu/C) and experience the selective reduction to ethanol, realizing the orientated key intermediate transfer. Results show that the Faradaic efficiency for ethanol was 18.2% at -1 V vs. RHE (VRHE) for up to 100 h. The following mechanism study supports the hypothesis that the CO2 reduction on Ni/C generates CO, which is further reduced to ethanol on Cu/C sites. Density functional theory calculations suggest a combined effect of the availability of CO intermediate in Ni/C core and the dimerization of key *CO intermediates, as well as the subsequent proton-electron transfer process on the Cu/C shell.

Chemically Induced Compatible Interface in Pyrolyzed Bacterial Cellulose/Graphene Sandwich for Electrochemical Energy Storage.

Herein, a three-step approach toward a multi-layered porous PBC/graphene sandwich has been developed, in which the chemical bonding interactions have been successfully enhanced via esterification between the layers of pyrolyzed bacterial cellulose (PBC) and graphene. Such a chemically induced compatible interface has been demonstrated to contribute significantly to the mass transfer efficiency when the PBC/graphene sandwich is deployed as electrode material for both supercapacitors and lithium-sulfur batteries. The high specific capacitance of the supercapacitors has been increased by three times, to 393 F g-1 at 0.1 A g-1. A high initial discharge specific capacity (~1100 mAhg-1) and high coulombic efficiency (99% after 300 cycles) of the rPG/S-based lithium-sulfur batteries have been achieved.

Scalable two-step annealing method for preparing ultra-high-density single-atom catalyst libraries.

The stabilization of transition metals as isolated centres with high areal density on suitably tailored carriers is crucial for maximizing the industrial potential of single-atom heterogeneous catalysts. However, achieving single-atom dispersions at metal contents above 2 wt% remains challenging. Here we introduce a versatile approach combining impregnation and two-step annealing to synthesize ultra-high-density single-atom catalysts with metal contents up to 23 wt% for 15 metals on chemically distinct carriers. Translation to a standardized, automated protocol demonstrates the robustness of our method and provides a path to explore virtually unlimited libraries of mono- or multimetallic catalysts. At the molecular level, characterization of the synthesis mechanism through experiments and simulations shows that controlling the bonding of metal precursors with the carrier via stepwise ligand removal prevents their thermally induced aggregation into nanoparticles. The drastically enhanced reactivity with increasing metal content exemplifies the need to optimize the surface metal density for a given application. Moreover, the loading-dependent site-specific activity observed in three distinct catalytic systems reflects the well-known complexity in heterogeneous catalyst design, which now can be tackled with a library of single-atom catalysts with widely tunable metal loadings.

Performance demonstration of gas-assisted gravity drainage in a heterogeneous reservoir using a 3D scaled model.

Gas-assisted gravity drainage (GAGD) is an effective method for oil recovery. Gravity increases the stability of the Gas-Oil Contact (GOC), thus delaying gas breakthrough and promoting crude oil production. Studying the effects of fluid and reservoir parameters on the stability of GOC could help understand the mechanism of GAGD. In this study, a series of high-pressure GAGD tests were conducted on a 3D heterogeneous scaled model established according to the heterogeneity of the oil reservoir. During the tests, GOC was monitored with electrical resistivity tomography (ERT) to study the effects of gas injection rate, gas type, and gas injection direction on GOC and oil recovery factor (RF). The results showed that N2-GAGD achieved the most stable GOC, the largest sweep volume but a poor RF. CO2-GAGD achieved the best RF of 63.33% at the injection rate of 0.15 m d-1 under 15 MPa. CO2 and CH4 could interact with crude oil and reduce the advancing rate and transverse swept area of GOC. CO2 and CH4 could lead to a higher RF as they reduce the viscosity of crude oil, cause swelling when dissolved, and have low tension. Therefore, the effects of gas dissolution, swelling, and viscosity reduction must be considered in addition to those of gravity, viscous force, and the capillary force so that RF could be increased while ensuring the stability of the displacement front. Accordingly, a new non-dimensional number N new was proposed with comprehensive considerations of gravity, viscous force, capillary force, gas-oil viscosity ratio, the viscosity reduction by gas, and reservoir properties. Finally, a prediction model was proposed, which could accurately predict the RF of heterogeneous reservoirs applying GAGD.

Study on Pressure Propagation in Tight Oil Reservoirs with Stimulated Reservoir Volume Development.

The stimulated reservoir volume fracturing development in tight oil reservoirs is characterized by multiscale flow of the reservoir matrix, fracture network, and hydraulic fracture. Therefore, the flow field structure is extremely complex. Multiscale flow characteristics have been revealed through the systematical experiments including the threshold pressure gradient and the stress sensitivity. Based on the theory of elliptical flow, a comprehensive and practical mathematical model of multiregion coupling flow is established to characterize the multiscale flow, and the pressure distribution equation is derived. The calculation method of moving boundary is established to simulate the dynamic supply boundary and the dynamic pressure distribution by using the steady-state sequential replacement method. The characteristics of multiscale flow, multistage development state, and stress sensitivity are considered, especially the different stress sensitivity characteristics in different regions. Finally, the pressure propagation in tight reservoirs is clarified and the influence of matrix permeability, stress sensitivity characteristics, and drawdown pressure on the distance at the dynamic supply boundary are revealed. The research results provide theoretical basis for the development effect evaluation.

A template oriented one-dimensional Schiff-base polymer: towards flexible nitrogen-enriched carbonaceous electrodes with ultrahigh electrochemical capacity.

Lithium-ion capacitors (LICs) have attracted much attention considering their efficient combination of high energy density and high-power density. However, to meet the increasing requirements of energy storage devices and the flexible portable electronic equipment, it is still challenging to develop flexible LIC anodes with high specific capacity and excellent rate capability. Herein, we propose a delicate bottom-up strategy to integrate unique Schiff-base-type polymers into desirable one-dimensional (1D) polymeric structures. A secondary-polymerization-induced template-oriented synthesis approach realizes the 1D integration of Schiff-base porous organic polymers with appealing characteristics of a high nitrogen-doping level and developed pore channels, and a further thermalization yields flexible nitrogen-enriched carbon nanofibers with high specific capacity and fast ion transport. Remarkably, when used as the flexible anode in LICs, the NPCNF//AC LIC demonstrates a high energy density of 154 W h kg-1 at 500 W kg-1 and a high power density of 12.5 kW kg-1 at 104 W h kg-1. This work may provide a new scenario for synthesizing 1D Schiff-base-type polymer derived nitrogen-enriched carbonaceous materials towards promising free-standing anodes in LICs.

1000 Wh L-1 lithium-ion batteries enabled by crosslink-shrunk tough carbon encapsulated silicon microparticle anodes.

Microparticulate silicon (Si), normally shelled with carbons, features higher tap density and less interfacial side reactions compared to its nanosized counterpart, showing great potential to be applied as high-energy lithium-ion battery anodes. However, localized high stress generated during fabrication and particularly, under operating, could induce cracking of carbon shells and release pulverized nanoparticles, significantly deteriorating its electrochemical performance. Here we design a strong yet ductile carbon cage from an easily processing capillary shrinkage of graphene hydrogel followed by precise tailoring of inner voids. Such a structure, analog to the stable structure of plant cells, presents 'imperfection-tolerance' to volume variation of irregular Si microparticles, maintaining the electrode integrity over 1000 cycles with Coulombic efficiency over 99.5%. This design enables the use of a dense and thick (3 mAh cm-2) microparticulate Si anode with an ultra-high volumetric energy density of 1048 Wh L-1 achieved at pouch full-cell level coupled with a LiNi0.8Co0.1Mn0.1O2 cathode.

A thick yet dense silicon anode with enhanced interface stability in lithium storage evidenced by in situ TEM observations.

Increasing the density and thickness of electrodes is required to maximize the volumetric energy density of lithium-ion batteries for practical applications. However, dense and thick electrodes, especially high-mass-content (>50 wt%) silicon anodes, have poor mechanical stability due to the presence of a large number of unstable interfaces between the silicon and conducting components during cycling. Here we report a network of mechanically robust carbon cages produced by the capillary shrinkage of graphene hydrogels that can contain the silicon nanoparticles in the cages and stabilize the silicon/carbon interfaces. In situ transmission electron microscope characterizations including compression and tearing of the structure and lithiation-induced silicon expansion experiments, have provided insight into the excellent confinement and buffering ability of this interface-strengthened graphene-caged silicon nanoparticle anode material. Consequently, a dense and thick silicon anode with reduced thickness fluctuations has been shown to deliver both high volumetric (>1000 mAh cm-3) and areal (>6 mAh cm-2) capacities together with excellent cycling capability.

Vertical Graphenes Grown on a Flexible Graphite Paper as an All-Carbon Current Collector towards Stable Li Deposition.

Lithium (Li) metal has been regarded as one of the most promising anode materials to meet the urgent requirements for the next-generation high-energy density batteries. However, the practical use of lithium metal anode is hindered by the uncontrolled growth of Li dendrites, resulting in poor cycling stability and severe safety issues. Herein, vertical graphene (VG) film grown on graphite paper (GP) as an all-carbon current collector was utilized to regulate the uniform Li nucleation and suppress the growth of dendrites. The high surface area VG grown on GP not only reduces the local current density to the uniform electric field but also allows fast ion transport to homogenize the ion gradients, thus regulating the Li deposition to suppress the dendrite growth. The Li deposition can be further guided with the lithiation reaction between graphite paper and Li metal, which helps to increase lithiophilicity and reduce the Li nucleation barrier as well as the overpotential. As a result, the VG film-based anode demonstrates a stable cycling performance at a current density higher than 5 mA cm-2 in half cells and a small hysteresis of 50 mV at 1 mA cm-2 in symmetric cells. This work provides an efficient strategy for the rational design of highly stable Li metal anodes.

Stable high-capacity and high-rate silicon-based lithium battery anodes upon two-dimensional covalent encapsulation.

Silicon is a promising anode material for lithium-ion and post lithium-ion batteries but suffers from a large volume change upon lithiation and delithiation. The resulting instabilities of bulk and interfacial structures severely hamper performance and obstruct practical use. Stability improvements have been achieved, although at the expense of rate capability. Herein, a protocol is developed which we describe as two-dimensional covalent encapsulation. Two-dimensional, covalently bound silicon-carbon hybrids serve as proof-of-concept of a new material design. Their high reversibility, capacity and rate capability furnish a remarkable level of integrated performances when referred to weight, volume and area. Different from existing strategies, the two-dimensional covalent binding creates a robust and efficient contact between the silicon and electrically conductive media, enabling stable and fast electron, as well as ion, transport from and to silicon. As evidenced by interfacial morphology and chemical composition, this design profoundly changes the interface between silicon and the electrolyte, securing the as-created contact to persist upon cycling. Combined with a simple, facile and scalable manufacturing process, this study opens a new avenue to stabilize silicon without sacrificing other device parameters. The results hold great promise for both further rational improvement and mass production of advanced energy storage materials.

Rational Design of Carbon-Rich Materials for Energy Storage and Conversion.

Carbon-rich materials have drawn tremendous attention toward a wide spectrum of energy applications due to their superior electronic mobility, good mechanical strength, ultrahigh surface area, and more importantly, abundant diversity in structure and components. Herein, rationally designed and bottom-up constructed carbon-rich materials for energy storage and conversion are discussed. The fundamental design principles are itemized for the targeted preparation of carbon-rich materials and the latest remarkable advances are summarized in terms of emerging dimensions including sp2 carbon fragment manipulation, pore structure modulation, topological defect engineering, heteroatom incorporation, and edge chemical regulation. In this respect, the corresponding structure-property relationships of the resultant carbon-rich materials are comprehensively discussed. Finally, critical perspectives on future challenges of carbon-rich materials are presented. The progress highlighted here will provide meaningful guidance on the precise design and targeted synthesis of carbon-rich materials, which are of critical importance for the achievement of performance characteristics highly desirable for urgent energy deployment.

Enhanced Roles of Carbon Architectures in High-Performance Lithium-Ion Batteries.

Lithium-ion batteries (LIBs), which are high-energy-density and low-safety-risk secondary batteries, are underpinned to the rise in electrochemical energy storage devices that satisfy the urgent demands of the global energy storage market. With the aim of achieving high energy density and fast-charging performance, the exploitation of simple and low-cost approaches for the production of high capacity, high density, high mass loading, and kinetically ion-accessible electrodes that maximize charge storage and transport in LIBs, is a critical need. Toward the construction of high-performance electrodes, carbons are promisingly used in the enhanced roles of active materials, electrochemical reaction frameworks for high-capacity noncarbons, and lightweight current collectors. Here, we review recent advances in the carbon engineering of electrodes for excellent electrochemical performance and structural stability, which is enabled by assembled carbon architectures that guarantee sufficient charge delivery and volume fluctuation buffering inside the electrode during cycling. Some specific feasible assembly methods, synergism between structural design components of carbon assemblies, and electrochemical performance enhancement are highlighted. The precise design of carbon cages by the assembly of graphene units is potentially useful for the controlled preparation of high-capacity carbon-caged noncarbon anodes with volumetric capacities over 2100 mAh cm-3. Finally, insights are given on the prospects and challenges for designing carbon architectures for practical LIBs that simultaneously provide high energy densities (both gravimetric and volumetric) and high rate performance.