As novel “post lithium‐ion batteries,” sodium‐ion batteries/potassium‐ion batteries (SIBs/PIBs) are emerging and show bright prospect in large‐scale energy storage applications due to abundant Na/K ...resources. Further benefits of this technology include, its low cost, chemical inertness and safety. Extensive research findings have demonstrated that carbon‐based materials are promising candidates for both SIBs and PIBs. Although the two alkali‐ion batteries have similar internal components and electrochemical reaction mechanisms, in carbon‐based materials the storage/release behaviors of Na+ and K+ are not exactly the same. Therefore, a comprehensive comparison of Na+/K+ storage behaviors in carbon anode materials is lacking. It is absolutely imperative to understand these mechanisms more clearly to achieve ideal performance. Herein, three potential Na+/K+ storage/release behaviors are discussed, which are i) intercalation/deintercalation mechanism, ii) adsorption/desorption mechanism, and iii) pore‐filling mechanism. This review not only attempts to summarize the development status of carbon anode materials (graphite, graphene, hard carbon and soft carbon), but also provides a comprehensive comparison (mechanism, capacity, rate capability, diffusion coefficient, cyclability, potassiation/sodiation potential) between SIBs and PIBs. Finally, critical issues and perspectives are discussed to demonstrate possible development directions for carbon anode materials for SIBs and PIBs.
This perspective attempts to summarize the development status of four carbon anode materials (graphite, graphene, hard carbon and soft carbon) of sodium‐ion/potassium‐ion batteries (SIBs/PIBs), and comprehensively demonstrates the similarities and differences of Na+ and K+ storage behaviors in carbon anode materials, which provides good guidance to select and optimize ideal carbon anode materials for high‐performance SIBs/PIBs.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
As one of the most effective synthesis tools, layer-by-layer (LbL) self-assembly technology can provide a strong non-covalent integration and accurate assembly between homo- or hetero-phase compounds ...or oppositely charged polyelectrolytes, resulting in highly-ordered nanoscale structures or patterns with excellent functionalities and activities. It has been widely used in the developments of novel materials and nanostructures or patterns from nanotechnologies to medical fields. However, the application of LbL self-assembly in the development of highly efficient electrocatalysts, specific functionalized membranes for proton exchange membrane fuel cells (PEMFCs) and electrode materials for supercapacitors is a relatively new phenomenon. In this review, the application of LbL self-assembly in the development and synthesis of key materials of PEMFCs including polyelectrolyte multilayered proton-exchange membranes, methanol-blocking Nafion membranes, highly uniform and efficient Pt-based electrocatalysts, self-assembled polyelectrolyte functionalized carbon nanotubes (CNTs) and graphenes will be reviewed. The application of LbL self-assembly for the development of multilayer nanostructured materials for use in electrochemical supercapacitors will also be reviewed and discussed (250 references).
This critical review highlights the simplicity and versatility of layer-by-layer self-assembly technique within the application of fuel cells and supercapacitors.
In recent decades, fuel cell technology has been undergoing revolutionary developments, with fundamental progress being the replacement of electrolyte solutions with polymer electrolytes, making the ...device more compact in size and higher in power density. Nowadays, acidic polymer electrolytes, typically Nafion, are widely used. Despite great success, fuel cells based on acidic polyelectrolyte still depend heavily on noble metal catalysts, predominantly platinum (Pt), thus increasing the cost and hampering the widespread application of fuel cells. Here, we report a type of polymer electrolyte fuel cells (PEFC) employing a hydroxide ion-conductive polymer, quaternary ammonium polysulphone, as alkaline electrolyte and nonprecious metals, chromium-decorated nickel and silver, as the catalyst for the negative and positive electrodes, respectively. In addition to the development of a high-performance alkaline polymer electrolyte particularly suitable for fuel cells, key progress has been achieved in catalyst tailoring: The surface electronic structure of nickel has been tuned to suppress selectively the surface oxidative passivation with retained activity toward hydrogen oxidation. This report of a H₂-O₂ PEFC completely free from noble metal catalysts in both the positive and negative electrodes represents an important advancement in the research and development of fuel cells.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Ionic conductivity and alkaline stability are the key properties that limited the widespread application of anion-exchange membranes (AEM) in electrochemical energy conversion/storage systems. In ...recent years, quaternary ammonium functionalized poly (ether ether ketone) (PEEK) membranes serve as a promising solution due to the good mechanical and chemical properties. Varied ionic conductivity and alkaline stability could be obtained when the membrane contains different functionalized side chains. However, it's still a challenge to understand the mechanism from the experimental study because various parameters could affect the electro-chemical performance of the membranes. In this work, we conduct coarse-grained molecular dynamics simulations to investigate two PEEK-based membranes, in which the side chains contain one (SQ) or two (GQ) quaternary ammonium groups. The simulation results indicate the self-diffusion coefficients in SQ and GQ are quite similar which should not be the main reason for the improved ionic conductivity of GQ, while the obviously increased ion-exchange capacity of GQ should result in the improved ionic conductivity. Furthermore, the simulation reveals that more water molecules wrap around the OH− in GQ, which could lead to the improved alkaline stability in comparison to that of SQ. This work provides a deeper understanding for the design of grafted copolymer based AEM with QA functional side chains.
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•Coarse-grained molecular dynamics simulations of the SQ and GQ AEMs were conducted.•The ions diffusion has little contribution to the improved ionic conductivity of GQ.•The improved ionic conductivity should attribute to the obvious promotion of IECs.•More H2O molecules wrap around OH− in GQ, leading to the better alkaline stability.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Phosphoric acid (PA)-doped high temperature polymer electrolyte membranes (HT-PEMs) are crucial materials for HT-PEM fuel cells (HT-PEMFCs). However, the development of HT-PEMs suffers from the ...trade-off between proton conductivity and mechanical strength. High proton conductivity requires a high doping level of PA, and PA acts as a plasticizer that reduces the mechanical properties. Here, a new strategy is employed to address the unresolved challenges; the strategy is to graft poly(1-vinylimidazole) as PA doping sites on the polysulfone backbone. This is achieved via atom transfer radical polymerization. High proton conductivity is achieved because of the formation of micro-phase separated structures, and the mechanical properties are retained because of the reduced plasticizing effect, which is caused by the separation of PA adsorption sites and the polymer backbone. The prepared PA-doped membranes have excellent proton conductivity of 127 mS cm−1 at 160 °C and outstanding tensile strength of 7.94 MPa. Meanwhile, single H2-O2 cell performance with the optimized membrane is impressive, reaching a peak power density of 559 mW cm−2 at 160 °C. More importantly, this work provides new insight into solving the trade-off between proton transport and mechanical strength for PA-doped HT-PEMs.
•Poly(1-vinylimidazole) grafted on polysulfone membranes were synthesized.•Phosphoric acid doped membranes possess micro-phase separation structure.•The membranes display enhanced conductivity with increasing length of side chains.•The tensile strength of phosphoric acid doped membranes still remains 7.94 MPa.•The single cell with membranes shows a peak power density of 559 mW cm−2 at 160 °C.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Although the proton exchange membrane fuel cell (PEMFC) has made great progress in recent decades, its commercialization has been hindered by a number of factors, among which is the total dependence ...on Pt‐based catalysts. Alkaline polymer electrolyte fuel cells (APEFCs) have been increasingly recognized as a solution to overcome the dependence on noble metal catalysts. In principle, APEFCs combine the advantages of and alkaline fuel cell (AFC) and a PEMFC: there is no need for noble metal catalysts and they are free of carbonate precipitates that would break the waterproofing in the AFC cathode. However, the performance of most alkaline polyelectrolytes can still not fulfill the requirement of fuel cell operations. In the present work, detailed information about the synthesis and physicochemical properties of the quaternary ammonia polysulfone (QAPS), a high‐performance alkaline polymer electrolyte that has been successfully applied in the authors' previous work to demonstrate an APEFC completely free from noble metal catalysts (S. Lu, J. Pan, A. Huang, L. Zhuang, J. Lu, Proc. Natl. Acad. Sci. USA 2008, 105, 20611), is reported. Monitored by NMR analysis, the synthetic process of QAPS is seen to be simple and efficient. The chemical and thermal stability, as well as the mechanical strength of the synthetic QAPS membrane, are outstanding in comparison to commercial anion‐exchange membranes. The ionic conductivity of QAPS at room temperature is measured to be on the order of 10−2 S cm−1. Such good mechanical and conducting performances can be attributed to the superior microstructure of the polyelectrolyte, which features interconnected ionic channels in tens of nanometers diameter, as revealed by HRTEM observations. The electrochemical behavior at the Pt/QAPS interface reveals the strong alkaline nature of this polyelectrolyte, and the preliminary fuel cell test verifies the feasibility of QAPS for fuel cell applications.
Alkaline polymer electrolytes (APEs) have long been a dream of electrochemists and electrochemical engineers because they are the key, but so far commercially unavailable, material for realizing low‐cost electrochemical devices such as fuel cells, electrolyzers, and sensors. Here, the synthesis and physicochemical properties of a class of APEs, quaternary ammonia polysulfone (QAPS) are reported (see figure), which feature high ionic conductivity, high chemical and thermal stability, and good mechanical performance. Their application to fuel cells is also demonstrated.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The development of high temperature proton exchange membranes (HT-PEMs) with high proton conduction and excellent mechanical properties remains a challenge. Herein, the graphitic carbon nitride (CN) ...nanosheets were successfully introduced into poly(ether sulfones)-poly(vinyl pyrrolidone) polymer matrix to prepare composite membrane through a facile blending method. The synthesized CN nanosheets were characterized by scanning electron microscope (SEM), Transmission electron microscopy (TEM), Raman spectrum, and X-ray photoelectron spectroscopy (XPS). The proton conductivity of the composite membrane was improved up to 36% (0.104 S cm−1) after incorporating CN nanosheets at 160 °C, due to increased PA doping level and faster proton dissociation. Meanwhile, the tensile strength of the composite membrane is increased of 60% (6.0 MPa) compared to that of pristine membrane, because of the physical reinforced effect from the 2D structure of CN. Furthermore, the single cell fabricated with the optimized membrane exhibits a peak power density of 512 mW cm−2 at the temperature of 160 °C for 200 h with no obvious loss of current density.
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•Graphitic carbon nitride (CN) nanosheets were incorporated into PES-PVP membranes.•The composite membranes displayed enhanced mechanical properties.•The proton conductivity was improved with an optimized content of CN.•The HT-PEMFC with 0.5 wt% CN shows a peak power density of 512 mW cm−2 at 160 °C.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The microstructures of catalyst layers (CLs) provide the paths for phosphoric acid (PA) invasion and decide the amount and distribution of PA in CLs, which is essential to improve the performance and ...stability of high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). In this work, the CLs with different microstructures are constructed and the effects of Pt loading on the performance and degradation of HT-PEMFCs are studied. The results show the CLs with flat surface slow down the process of PA invasion and well-developed pore structures promote the redistribution of PA, which results in low mass transfer resistance. Therefore, the peak power density of HT-PEMFC based on CLs prepared by ultrasonic-spraying is 1.4 times than that by screen-printing, while the performance degradation is only 11% after accelerated stress test of 30,000 cycles with the Pt loading of 0.5 mg cm−2. Distribution of relaxation times analysis is used to assist the electrochemical impedance spectroscopy to further distinguish the different physicochemical process within cells. The result reveals that mass transfer is affected greatly by the effects of microstructures and Pt loadings, and gets deterioration gradually with the invasion of PA into CLs, which not only makes Pt particle growth but decreases kinetics of oxygen reduction reaction.
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•Understanding the impact of electrode microstructures on Pt utilization.•Distribution of relaxation times analyses were performed to identify loss processes.•Analysis of loss processes dependencies on electrode microstructures, Pt loading.•The deterioration of mass transfer leads to performance degradation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The increasing demand for efficient energy storage and water desalination requires advanced porous carbon materials from biomasses due to their sustainability and renewability. The morphologies, ...microstructures, and properties of carbon materials were determined by the biomass precurors. Here, a novel bamboolike Typha orientalis fiber was selected as a precursor to prepare porous carbon material by carbonization and activation methods. The carbon material retains the bamboolike microfiber structure of the precursor and presents high specific surface area, well-balanced pore size distribution, and high conductivity and good hydrophilic property. It also displays a specific capacitance of 351 F g−1 at current density of 1.0 A g−1 as well as good stability over 10000 cycles for a supercapacitor as well as an outstanding salt adsorption capacity of 18.5 mg g−1 at voltage of 1.6 V and 81% retention after 55 cycles for capacitive deionization.
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