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Supercapacitors based on activated carbon electrodes and ionic liquids as electrolytes are capable of storing charge through the electrosorption of ions on porous carbons and represent important energy storage devices with high power delivery/uptake. Various computational and instrumental methods have been developed to understand the ion storage behavior, however, techniques that can probe various cations and anions of ionic liquids separately remain lacking. Here, we report an approach to monitoring cations and anions independently by using silica nanoparticle-grafted ionic liquids, in which ions attaching to silica nanoparticle cannot access activated carbon pores upon charging, whereas free counter-ions can. Aided by this strategy, conventional electrochemical characterizations allow the direct measurement of the respective capacitance contributions and acting potential windows of different ions. Moreover, coupled with electrochemical quartz crystal microbalance, this method can provide unprecedented insight into the underlying electrochemistry. Quantifying the individual capacitance contributions of in-pore ions during charging remains a challenge. Here the authors design silica-grafted ionic liquids to reveal the charging behaviors of cations and anions separately, providing fresh insight into the storage mechanism of supercapacitors.

Owing to their unique nanosize effect and surface effect, pseudocapacitive quantum dots (QDs) hold considerable potential for high‐efficiency supercapacitors (SCs). However, their pseudocapacitive behavior is exploited in aqueous electrolytes with narrow potential windows, thereby leading to a low energy density of the SCs. Here, a film electrode based on dual‐confined FeOOH QDs (FQDs) with superior pseudocapacitive behavior in a high‐voltage ionic liquid (IL) electrolyte is put forward. In such a film electrode, FQDs are steadily dual‐confined in a 2D heterogeneous nanospace supported by graphite carbon nitride (g‐C3N4) and Ti‐MXene (Ti3C2). Probing of potential‐driven ion accumulation elucidates that strong adsorption occurs between the IL cation and the electrode surface with abundant active sites, providing sufficient redox reaction of FQDs in the film electrode. Furthermore, porous g‐C3N4 and conductive Ti3C2 act as ion‐accessible channels and charge‐transfer pathways, respectively, endowing the FQDs‐based film electrode with favorable electrochemical kinetics in the IL electrolyte. A high‐voltage flexible SC (FSC) based on an ionogel electrolyte is fabricated, exhibiting a high energy density (77.12 mWh cm−3), a high power density, a remarkable rate capability, and long‐term durability. Such an FSC can also be charged by harvesting sustainable energy and can effectively power various wearable and portable electronics. A unique electrode based on dual‐confined FeOOH quantum dots (FQDs) is proposed, in which FQDs are confined in a 2D heterogeneous nanospace supported by g‐C3N4 and Ti3C2. Such an electrode exhibits superior energy‐storage behavior in a high‐voltage ionic liquid electrolyte, introducing a new avenue for breaking the bottleneck of the low energy density of quantum‐dot‐based supercapacitors.

Sudden air pollution accidents (explosions, fires, leaks, etc.) in chemical industry parks may result in great harm to people’s lives, property, and the ecological environment. A gas tracking network can monitor hazardous gas diffusion using traceability technology combined with sensors distributed within the scope of a chemical industry park. Such systems can automatically locate the source of pollutants in a timely manner and notify relevant departments to take major hazards into their control. However, tracing the source of the leak in a large area is still a tough problem, especially within an urban area. In this paper, the diffusion of 79 potential leaking sources with consideration of different weather conditions and complex urban terrain is simulated by AERMOD. Only 61 sensors are used to monitor the gas concentration within such a large scale. A fully connected network trained with a hybrid strategy is proposed to trace the leaking source effectively and robustly. Our proposed model reaches a final classification accuracy of 99.14%.

Nanosizing is the fashionable method to obtain a desirable electrode material for energy storage applications, and thus, a question arises: do smaller electrode materials exhibit better electrochemical performance? In this context, theoretical analyses on the particle size, band gap and conductivity of nano-electrode materials were performed; it was determined that a critical size exist between particle size and electrochemical performance. To verify this determination, for the first time, a scalable formation and disassociation of nickel-citrate complex approach was performed to synthesize ultra-small Ni(OH) 2 nanoparticles with different average sizes (3.3, 3.7, 4.4, 6.0, 6.3, 7.9, 9.4, 10.0 and 12.2 nm). The best electrochemical performance was observed with a specific capacity of 406 C g −1 , an excellent rate capability was achieved at a critical size of 7.9 nm and a rapid decrease in the specific capacity was observed when the particle size was <7.9 nm. This result is because of the quantum confinement effect, which decreased the electrical conductivity and the sluggish charge and proton transfer. The results presented here provide a new insight into the nanosize effect on the electrochemical performance to help design advanced energy storage devices. Electrochemical energy storage: Smaller is not always better There is acritical size for nanoparticles that maximizes their electrochemical performance in energy storage devices, show a team in China. This finding goes against the conventional wisdom that smaller is better for the electrode material of such devices. Electrochemical energy storage devices such as batteries and supercapacitors are attractive power sources. One way to boost their performance has been to reduce the size of their electrode materials. Xingbin Yan and co-workers at the Lanzhou Institute of Chemical Physics prepared nine sets of Ni(OH) 2 nanoparticles having various average sizes in the range 3.3 to 12.2 nanometers. They found that the best electrochemical performance was obtained at a size of 7.9 nanometers. Below that size, the specific capacity dropped off rapidly due to the quantum confinement effect and slower charge and proton transfer. Ultra-small Ni(OH) 2 nanoparticles with different average sizes are prepared in large scale, and the best electrochemical performance is obtained at the critical size rather than the smallest size, which provides a new insight on nanosize effect on electrode materials in energy storage.

A series of porous carbon materials with wide range of specific surface areas and different heteroatom contents had been prepared using polyaniline as carbon precursor and KOH as an activating agent. Effect of surface area and heteroatom of porous carbon materials on specific capacitance was investigated thoroughly in two typical aqueous KOH and organic 1-butyl-3- methylimidazolium tetrafluoroborate/acetonitirle electrolytes. The different trends of capacitance performance were observed in these two electrolytes. Electrochemical analyses suggested that the presence of faradaic interactions on heteroatom-enriched carbon materials in organic environment is less significant than that observed in aqueous electrolytes. Thus, in aqueous electrolyte, a balance between surface area and heteroatom content of activated porous carbon would be found to develop a supercapacitor with high energy density. In organic electrolyte, the capacitance performance of porous carbon is strongly dependent on the surface area. The results may be useful for the design of porous carbon-based supercapacitor with the desired capacitive performance in aqueous and organic electrolytes.

Electrochemical double-layer capacitors (EDLCs) possess extremely high-power density and a long cycle lifespan, but they have been long constrained by a low energy density. Since the electrochemical stability of electrolytes is essential to the operating voltage of EDLCs, and thus to their energy density, the tuning of electrolyte components towards a high-voltage window has been a research focus for a long time. Organic electrolytes based on ionic liquids (ILs) are recognized as the most commercially promising owing to their moderate operating voltage and excellent conductivity. Despite impressive progress, the working voltage of IL–solvent electrolytes needs to be improved to meet the growing demand. In this review, the recent progress in the tuning of IL- based organic electrolyte components for higher-voltage EDLCs is comprehensively summarized and the advantages and limitations of these innovative components are outlined. Furthermore, future trends of IL–solvent electrolytes in this field are highlighted.

The active hydroxyl group of cellulose plays a crucial role in regulating the microstructure of cellulose-derived hard carbon, which ultimately affects its sodium storage capacity. Through small-angle X-ray scattering (SAXS) and X-ray atomic pair distribution function (PDF) analysis, we proved that modification of cellulose by esterification crosslinking can introduce more closed pores into the carbonized hard carbon, which is beneficial for promoting sodium ion storage. Our results demonstrate that by optimizing the conditions used for esterification cross-linking modification, the sodium storage capacity of cellulose-derived hard carbon could be increased from 254 to 348 mAh g−1, with an increase in plateau capacity from 140 to 230 mAh g−1. This study makes a significant contribution towards establishing industrial applications for cellulose-derived hard carbon.

The zinc anode mainly faces technical problems such as short circuits caused by the growth of dendrite, low coulomb efficiency, and a short cycle life caused by side reactions, which impedes the rapid development of aqueous zinc-ion batteries (AZIBs). Herein, a common ionic liquid, 1,1-Spirobipyrrolidinium tetrafluoroborate ([SBP]BF4), is selected as a new additive for pure ZnSO4 electrolyte. It is found that this additive could regulate the solvation sheath of hydrated Zn2+ ions, promote the ionic mobility of Zn2+, homogenize the flux of Zn2+, avoid side reactions between the electrolyte and electrode, and inhibit the production of zinc dendrites by facilitating the establishment of an inorganic solid electrolyte interphase layer. With the 1% [SBP]BF4-modified electrolyte, the Zn||Zn symmetric cell delivers an extended plating/stripping cycling life of 2000 h at 1 mA cm−2, which is much higher than that of the cell without additives (330 h). As a proof of concept, the Zn‖V2O5 battery using the [SBP]BF4 additive shows excellent cycling stability, maintaining its specific capacity at 97 mAh g−1 after 2000 cycles at 5 A g−1, which is much greater than the 46 mAh g−1 capacity of the non-additive battery. This study offers zinc anode stabilization through high-efficiency electrolyte engineering.

Hard carbon (HC), which is one of the anode materials widely used in commercial sodium-ion batteries at present, suffers from a thick and unstable solid electrolyte interface (SEI) layer formed by the self-reduction in traditional carbonate-based electrolytes on its surface. This phenomenon impacts the battery’s Coulomb efficiency, cycle stability, and rate performance. In this paper, a pyrrolidinium-type di-cation ionic liquid, butyl-1,4-di(methylpyrrolidinium) di[hexafluorophosphate] (C4di[mPy].di[PF6]), is studied as an electrolyte additive to improve the interphase stability of the HC anode. The PF6− in C4di[mPy].di[PF6] enhances the coordination number between Na+ and PF6−, and C4di[mPy]2+ is preferentially reduced, jointly participating in the construction of stable, thin, dense and NaF-rich SEI films, thus laying the foundation for improving battery performance. As a result, in the carbonate electrolyte containing 2 wt% C4di[mPy].di[PF6], the reversible capacity of the HC/Na half-cell is increased by 14.7%, and the capacity retention rate remains at 90.4% after 400 cycles. This work provides reference for future research and design of high-performance ion liquid additives.

Large Li2O2 aggregations can produce high‐capacity of lithium oxygen (Li‐O2) batteries, but the larger ones usually lead to less‐efficient contact between Li2O2 and electrode materials. Herein, a hierarchical cathode architecture based on different discharge characteristics of α‐MnO2 and Co3O4 is constructed, which can enable the embedded growth of large Li2O2 aggregations to solve this problem. Through experimental observations and first‐principle calculations, it is found that α‐MnO2 nanorod tends to form uniform Li2O2 particles due to its preferential Li+ adsorption and similar LiO2 adsorption energies of different crystal faces, whereas Co3O4 nanosheet tends to simultaneously generate Li2O2 film and Li2O2 nanosheets due to its preferential O2 adsorption and different LiO2 adsorption energies of varied crystal faces. Thus, the composite cathode architecture in which Co3O4 nanosheets are grown on α‐MnO2 nanorods can exhibit extraordinary synergetic effects, i.e., α‐MnO2 nanorods provide the initial nucleation sites for Li2O2 deposition while Co3O4 nanosheets provide dissolved LiO2 to promote the subsequent growth of Li2O2. Consequently, the composite cathode achieves the embedded growth of large Li2O2 aggregations and thus exhibits significantly improved specific capacity, rate capability, and cyclic stability compared with the single metal oxide electrode. Embedded growth of Li2O2 is realized through a scientific fabrication of α‐MnO2/Co3O4 cathode architecture, of which α‐MnO2 plays the role of initially nucleation sites for Li2O2 while Co3O4 produces plenty of dissolved LiO2, inducing the formation of large Li2O2 aggregations with embedded structure, and thus showing remarkably improved electrochemical performance of Li‐O2 battery.