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Subnanometer pores/channels (SNPCs) play crucial roles in regulating electrochemical redox reactions for rechargeable batteries. The delicately designed and tailored porous structure of SNPCs not only provides ample space for ion storage but also facilitates efficient ion diffusion within the electrodes in batteries, which can greatly improve the electrochemical performance. However, due to current technological limitations, it is challenging to synthesize and control the quality, storage, and transport of nanopores at the subnanometer scale, as well as to understand the relationship between SNPCs and performances. In this review, we systematically classify and summarize materials with SNPCs from a structural perspective, dividing them into one-dimensional (1D) SNPCs, two-dimensional (2D) SNPCs, and three-dimensional (3D) SNPCs. We also unveil the unique physicochemical properties of SNPCs and analyse electrochemical couplings in SNPCs for rechargeable batteries, including cathodes, anodes, electrolytes, and functional materials. Finally, we discuss the challenges that SNPCs may face in electrochemical reactions in batteries and propose future research directions. [ABSTRACT FROM AUTHOR]

Sodium (Na) metal anodes are promising candidates for various batteries with high energy density and high‐power density, however, the dendrite growth of Na metal is impeding their practical applications. The binary alloy Na–K is in the liquid state at room temperature with a wide composition range, which renders it inherently free from solid dendrite growth. Whereas the application of Na–K alloy is plagued by the lack of a wettable matrix to immobilize the liquid metal. Herein, a facile method is reported to introduce oxygen‐rich functional groups into carbon fiber cloth (O‐CFC), which is initially Na–K phobic yet turns into superwetting after the treatment. The superwetting behavior of the O‐CFC can be attributed to the favorable enthalpy changes as a result of the introduction of O‐rich functional groups. The superwetting property of the O‐CFC exhibits good universality, which can be extended to melting Na and K metals. By adopting the superwetting O‐CFC as a host for liquid Na–K alloy, the liquid metal can be well retained in the matrix and deliver a stable cycling for >1600 h. The concept of enthalpy‐driven wettability regulation can be enlightening for the host material design of other liquid metals and alloys. [ABSTRACT FROM AUTHOR]

Highlights: The LiNO3-implanted electroactive β phase polyvinylidene fluoride-co-hexafluoropropylene was built as an artificial solid electrolyte interphase layer for dendrite suppression. The electronegatively charged polymer layer can capture Li ion on its surface to form Li-ion charged channels and recompense the ionic flux of electrolytes via continuous supply of Li ion. The modified Li anode achieved a long cycle life over 2000 h under ultrahigh Li utilization of 50% in symmetric cell and worked in full cell for 100 cycles at harsh condition of extremely low N/P of 0.83. The concentration difference in the near-surface region of lithium metal is the main cause of lithium dendrite growth. Resolving this issue will be key to achieving high-performance lithium metal batteries (LMBs). Herein, we construct a lithium nitrate (LiNO3)-implanted electroactive β phase polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) crystalline polymorph layer (PHL). The electronegatively charged polymer chains attain lithium ions on the surface to form lithium-ion charged channels. These channels act as reservoirs to sustainably release Li ions to recompense the ionic flux of electrolytes, decreasing the growth of lithium dendrites. The stretched molecular channels can also accelerate the transport of Li ions. The combined effects enable a high Coulombic efficiency of 97.0% for 250 cycles in lithium (Li)||copper (Cu) cell and a stable symmetric plating/stripping behavior over 2000 h at 3 mA cm−2 with ultrahigh Li utilization of 50%. Furthermore, the full cell coupled with PHL-Cu@Li anode and LiFePO4 cathode exhibits long-term cycle stability with high-capacity retention of 95.9% after 900 cycles. Impressively, the full cell paired with LiNi0.87Co0.1Mn0.03O2 maintains a discharge capacity of 170.0 mAh g−1 with a capacity retention of 84.3% after 100 cycles even under harsh condition of ultralow N/P ratio of 0.83. This facile strategy will widen the potential application of LiNO3 in ester-based electrolyte for practical high-voltage LMBs. [ABSTRACT FROM AUTHOR]

Hard carbon (HC) anodes have shown extraordinary promise for sodium‐ion batteries, but are limited to their poor initial coulombic efficiency (ICE) and low practical specific capacity due to the large amount of defects. These defects with oxygen containing groups cause irreversible sites for Na+ ions. Highly graphited carbon decreases defects, while potentially blocking diffusion paths of Na+ ions. Therefore, molecular‐level control of graphitization of hard carbon with open accessible channels for Na+ ions is key to achieve high‐performance hard carbon. Moreover, it is challenging to design a conventional method to obtain HCs with both high ICE and capacity. Herein, a universal strategy is developed as manganese ions‐assisted catalytic carbonization to precisely tune graphitization degree, eliminate defects, and maintain effective Na+ ions paths. The as‐prepared hard carbon has a high ICE of 92.05% and excellent cycling performance. Simultaneously, a sodium storage mechanism of "adsorption‐intercalation‐pore filling‐sodium cluster formation" is proposed, and a clear description given of the boundaries of the pore structure and the specific dynamic process of pore filling. [ABSTRACT FROM AUTHOR]

Sodium metal batteries are recognized as promising candidates for next‐generation energy storage devices, as a result of their high energy density, low redox potential, and cheap material price. Na metal anodes, however, generally exhibit notorious problems, including progressively thickened interfaces with active Na loss and Na metal dendrite growth with safety hazards. Herein, a lightweight aerogel consisting of MgF2 nanocrystals grown on a reduced graphene oxide (RGO) aerogel matrix (MgF2@RGO) is rationally designed as a multifunctional host material for Na metal anodes. The MgF2 nanocrystals can be electrochemically converted in situ into Mg and NaF nanograins during the first Na plating process, in which the Mg works as sodiophilic nucleation seeds for Na plating and NaF plays a key role in suppressing Na dendrite growth. Significantly, the Na metal anodes with the MgF2@RGO aerogel host deliver significantly enhanced Coulombic efficiency and dramatically improved cycling stability for more than 1600 h. The morphology evolution confirms the advantages of the Na metal anode with the MgF2@RGO host, which exhibits dense and flat interfaces. By pairing with the Na3V2(PO4)3 cathode, the Na metal batteries achieve stable cycling and good rate capability, suggesting the potential of the Na/MgF2@RGO anode for practical applications. [ABSTRACT FROM AUTHOR]

Biomass-derived materials offer low carbon approaches to energy storage. High surface area SiC w/wo 13 wt% hard carbon (SiC/HC, SiC/O), derived from carbothermal reduction of silica depleted rice hull ash (SDRHA), can function as Li+ battery anodes. Galvanostatic cycling of SiC/HC and SiC/O shows capacity increases eventually to >950 mA h g−1 (Li1.2–1.4SiC) and >740 mA h g−1 (Li1.1SiC), respectively, after 600 cycles. Post-mortem investigation via XRD and 29Si MAS NMR reveals partial phase transformation from 3C- to 6H-SiC, with no significant changes in unit cell size. SEMs show cycled electrodes maintain their integrity, implying almost no volume expansion on lithiation/delithiation, contrasting with >300% volume changes in Si anodes on lithiation. Significant void space is needed to compensate for these volume changes with Si in contrast to SiC anodes suggesting nearly competitive capacities. 6Li MAS NMR and XPS show no evidence of LixSi, with Li preferring all-C environments supported by computational modeling. Modeling also supports deviation from the 3C phase at high Li contents with minimal volume changes. [ABSTRACT FROM AUTHOR]

Hard carbon (HC) is recognized as a promising anode material with outstanding electrochemical performance for alkali metal‐ion batteries including lithium‐ion batteries (LIBs), as well as their analogs sodium‐ion batteries (SIBs) and potassium‐ion batteries (PIBs). Herein, a comprehensive review of the recent research is presented to interpret the challenges and opportunities for the applications of HC anodes. The ion storage mechanisms, materials design, and electrolyte optimizations for alkali metal‐ion batteries are illustrated in‐depth. HC is particularly promising as an anode material for SIBs. The solid‐electrolyte interphase, initial Coulombic efficiency, safety concerns, and all‐climate performances, which are vital for practical applications, are comprehensively discussed. Furthermore, commercial prototypes of SIBs based on HC anodes are extensively elaborated. The remaining challenges and research perspectives are provided, aiming to shed light on future research and early commercialization of HC‐based SIBs. [ABSTRACT FROM AUTHOR]

Abstract: The reformate gas is one of the commonest solutions to the problem of fuel supply for proton exchange membrane fuel cell systems. Thus, it is important to understand the behaviors of a fuel cell using reformate gases. In this work, effects of nitrogen and carbon monoxide concentrations on unsteady characteristics of a proton exchange membrane fuel cell with the Pt–Ru anodic catalyst are investigated experimentally. Simulated reformate gases with hydrogen, nitrogen and carbon monoxide are employed as the fuel. The experimental data show that a larger dilution effect of nitrogen is noted for cases with lower hydrogen stoichiometric ratios. Furthermore, increasing the carbon monoxide concentration reduces the cell performance because the elevated carbon monoxide adsorption rate results in a severer poison effect. The voltage fluctuating phenomenon is observed at high CO ppm and is due to a periodical change of coverage on the catalyst surface. Meanwhile, it is verified that the voltage fluctuation is accompanied with a periodical change of the anode outlet carbon monoxide concentration. Furthermore, the fluctuating phenomena of voltage and the anode outlet carbon monoxide concentration are more easily triggered in diluted hydrogen than in non-diluted hydrogen. [Copyright &y& Elsevier]

This paper discusses the effects of humidification and temperature differences of the anode and cathode on water transport in a proton exchange membrane fuel cell. Heaters are used to cause a difference in gas temperature between two electrodes before the gases enter the fuel cell. The results show that when the temperature of the cathode is higher than that of the anode, the electro-osmotic drag is suppressed. In contrast, when the temperature of the anode is higher than that of cathode, it is enhanced. These effects are more significant when the temperature difference between the anode and cathode is greater. The same trends are seen with back diffusion. Three cases are tested, and the results show that the suppression due to the temperature difference occurs even when the relative humidity is low at the hotter side. The water transport tendencies of electro-osmotic drag and back diffusion in different situations can be expressed as dominant percentages calculated by the water masses collected at the anode and cathode. The suppression effect due to the temperature difference is relatively insignificant with regard to back diffusion compared to electro-osmosis, so water tends to accumulate on the anode rather than the cathode side. [ABSTRACT FROM AUTHOR]

Abstract: The electrolytic deposition of TiO2 thin films on platinum for lithium batteries is carried out in TiCl4 alcoholic solution and the films are subsequently annealed. The as-prepared films are amorphous TiO(OH)2·H2O, transformed into anatase TiO2 at 350°C, and then gradually into rutile TiO2 at 500°C. Cyclic voltammograms show oxidation and reduction peaks at 2.20 and 1.61V, respectively, corresponding to charge and discharge plateaus at 1.98 and 1.75V vs. Li+/Li. The specific capacity decreases with increasing current density for film of 128-nm thickness in the initial discharge. It is observed that the diffusion flux of Li+ insertion/extraction into/from TiO2 controls the reaction rate at higher current densities. Consequently, at low film thickness, high discharge capacity (per weight) is found for the initial cycle at a current density of 10μAcm−2. However, the capacity of prepared films in various thicknesses approach 103±5mAhg−1 after 50cycles, since the formation of cracks for thicker films offers shorter diffusion paths for Li+. In addition, TiO2 films show electrochromic properties during lithiation and delithiation. [Copyright &y& Elsevier]

Composites of few-layer transition metal oxides and graphene nanosheets with strong interfacial connection hold great promise as high-performance anodes for lithium-ion batteries, but it is highly challenging to realize full interfacial properties. Herein, we report an ultra-refined layer-by-layer mesoporous CoO/reduced graphene oxide (CoO/RGO) architecture synthesized via a facile method. The CoO/RGO has stacked interfaces between the CoO nanosheets and the graphene nanosheets via Co–O–C bonds, which has been proposed to have an important role in achieving excellent performance in lithium ion batteries with high initial capacity and good rate capability. It is shown that the CoO/RGO exhibits a high initial discharge capacity of 2189.4 mAh g−1 at a current density of 100 mA g−1. Furthermore, the CoO/RGO exhibits a high reversible capacity retention of 70% after prolonged 300 cycles at a high rate of 2 A g−1. Significantly, it delivers an ultrahigh reversible capacity of 1167 mAh g−1 at 5 A g−1 with an excellent reversible capacity retention of 76% over 40 cycles. • Layered transition metal oxide and graphene nanosheets composite with interfacial Co–O–C bonding has been developed. • CoO/RGO electrode exhibits a discharge capacity of 2189.4 mAh g−1 at 100 mA g−1 and stablizes 300 cycles at 2 A g−1. • CoO/RGO delivers a reversible rate capability of 1167 mAh g−1 at 5 A g−1 with capacity retention of 76%. [ABSTRACT FROM AUTHOR]