Surface Acidity Dictates Proton Transport in WO3/ZrO2: Proton-Conductive Behavior and Mechanistic Insight.

Development of inorganic proton conductors that are applicable in a wide temperature range is crucial for applications such as fuel cells. Most of the reported proton conductors suffer from limited proton conductivity, especially at low temperature. In addition, the mechanism of proton conduction in the conductors is not fully understood, which limits the rational design of advanced proton conductors. In this work, we report the use of metal oxide solid acid as a promising proton conductor. WO3/ZrO2 (WZ) with different surface acidities is synthesized by controlling the content of WO3 on the surface of ZrO2. It is demonstrated that proton conductivity of WZ samples is closely related with their acidity. WZ with the strongest acidity exhibits the highest proton conduction performance at low temperatures, with a proton conductivity of 3.27 × 10-5 S cm-1 at 14 °C. The excellent performance of the WZ-type proton conductor is clarified with theoretical calculations. The results show that the enhanced water adsorption and the lowered activation barrier for breakage of the O-H bond in surface-adsorbed water are the key to the excellent proton-conductive performance of WZ. The experimental results and mechanistic insights gained in this work suggest that WZ is a promising proton conductor, and tailoring the surface acidity of metal oxides is an effective approach to regulate their proton-conductive performance.

Polyolefin-Based Separator with Interfacial Chemistry Regulation for Robust Potassium Metal Batteries.

Potassium metal batteries (KMBs) are ideal choices for high energy density storage system owing to the low electrochemical potential and low cost of K. However, the practical KMB applications suffer from intrinsically active K anode, which would bring serious safety concerns due to easier generation of dendrites. Herein, to explore a facile approach to tackle this issue, we propose to regulate K plating/stripping via interfacial chemistry engineering of commercial polyolefin-based separator using multiple functional units integrated in tailored metal organic framework. As a case study, the functional units of MIL-101(Cr) offer high elastic modulus, facilitate the dissociation of potassium salt, improve the K+ transfer number and homogenize the K+ flux at the electrode/electrolyte interface. Benefiting from these favorable features, uniform and stable K plating/stripping is realized with the regulated separator. Full battery assembled with the regulated separator showed ∼19.9 % higher discharge capacity than that with glass fiber separator at 20 mA g-1 and much better cycling stability at high rates. The generality of our approach is validated with KMBs using different cathodes and electrolytes. We envision that the strategy to suppress dendrite formation by commercial separator surface engineering using tailor-designed functional units can be extended to other metal/metal ion batteries.

Tuning the Intrinsic Activity and Electrochemical Surface Area of MoS2 via Tiny Zn Doping: Toward an Efficient Hydrogen Evolution Reaction (HER) Catalyst.

Molybdenum sulfide (MoS2 ) is considered as an alternative material for commercial platinum catalysts for electrocatalytic hydrogen evolution reaction (HER). Improving the apparent HER activity of MoS2 to a level comparable to that of Pt is an essential premise for the commercial use of MoS2 . In this work, a Zn-doping strategy is proposed to enhance the HER performance of MoS2 . It is shown that tiny Zn doping into MoS2 leads to the enhancement of the electrochemical surface area, increases in proportion of HER active 1T phase in the material and formation of catalytic sites of higher intrinsic activity. These benefits result in a high-performance HER electrocatalyst with a low overpotential of 190 mV(@10 mA cm-2 ) and a low Tafel slope of 58 mV dec-1 . The origin for the excellent electrochemical performance of the doped MoS2 is rationalized with both experimental and theoretical investigations.

A sandwich-type photoelectrochemical aptasensor using Au/BiVO4 and CdS quantum dots for carcinoembryonic antigen assay.

A novel sandwich-type photoelectrochemical (PEC) aptasensor for the carcinoembryonic antigen (CEA) assay was fabricated using the CEA aptamer, Au/BiVO4 and CdS quantum dots (CdS QDs). In virtue of the localized surface plasmon resonance effect of Au nanoparticles, Au/BiVO4 showed an effective utilization of visible light and excellent photoactivity, and was employed as the photoanode. After CdS QDs were conjugated to Au/BiVO4 through the sandwich structure based on the hybridization of the CEA aptamer with two partially complementary single-stranded DNA molecules, the photocurrents were further enhanced by a resonance energy transfer between CdS QDs and Au nanoparticles. Meanwhile, the consumption of the photo-induced holes by ascorbic acid could also retard the combination of the electron-hole pairs and cause an increase of the photocurrents. However, the specific recognition of CEA by the CEA aptamer could destroy the sandwich structure and remarkably weaken the photocurrent response. Thus, the quantitative detection of CEA was connected with the decrease of the photocurrent. Benefitting from the above methods for signal enhancement, the PEC aptasensor showed a wide sensing range of 0.0001-10 ng mL-1 and a low detection limit of 0.047 pg mL-1 for CEA detection. The specificity, stability and recoveries of the PEC aptasensor were also excellent. Therefore, the construction of the present PEC aptasensor provides a universal and practical method for sensing other substances.

Multifunctional Polypropylene Separator via Cooperative Modification and Its Application in the Lithium-Sulfur Battery.

The continuous shuttling of dissolved polysulfides between the electrodes is the primary cause for the rapid decay of lithium-sulfur batteries. Modulation of the separator-electrolyte interface through separator modification is a promising strategy to inhibit polysulfide shuttling. In this work, we develop a graphene oxide and ferrocene comodified polypropylene separator with multifunctionality at the separator-electrolyte interface. The graphene oxide on the functionalized separator could physically adsorb the polysulfide while the ferrocene component could effectively facilitate the conversion of the adsorbed polysulfide. Due to the combination of these beneficial functionalities, the separator exhibits an excellent battery performance, with a high reversible capacity of 409 mAh g-1 after 500 cycles at 0.2 C. We anticipate that the combinatorial separator functionalization proposed herein is an effective approach for improving the performance of lithium-sulfur batteries.

The determination of trace free acid content in lithium-ion battery electrolytes by coulometric titration in non-aqueous media.

A new quantitative analysis method was proposed, aiming at resolving the difficulty encountered in accurately determining the trace content of a free acid in lithium-ion battery electrolytes in the past 30 years. The presented method overcame the three restrictive factors of lithium-ion battery electrolytes, namely, poor thermal stability, the formation of hydrofluoric acid with water and difficulty in the accurate determination of trace free acids. The free acid in lithium-ion battery electrolytes was directly titrated with ethoxide ions generated through the electrolyzation of a 0.50 mol L-1 LiCl ethanol solution. The content of free acid was obtained according to the Faraday's law, and the whole determination process could be completed in 5 minutes. The relative standard deviation was below 2.0% when the content of free acid was 2.0 µg and above. The detection limit was 1.0 µg and the recovery rate was 99.5%-102.5%. In this method, free acid determination was not affected by temperature change and the existence of a small amount of water. Thus, this study provides a simple, fast and accurate analytical method with a lower detection limit for free acid in the lithium-ion battery industry and comprehensively improves the quality of lithium-ion battery electrolytes and the performance of lithium-ion battery products.

The effects of structural properties on the lithium storage behavior of mesoporous TiO2.

Understanding the effects of structural properties on the lithium storage behavior of mesoporous TiO2 is crucial for further optimizing its performance through rational structure design. To achieve this, herein, the surface area and the grain size of the prepared mesoporous TiO2 are intentionally adjusted by controlling the calcination temperatures. It is found that the capacities of the mesoporous TiO2 contain both the lithium-ion insertion into the bulk phase (Q in) and the additional surface lithium storage (Q as). The Q in gradually increases with grain sizes to a steady level and then slightly drops. By contrast, the Q as is directly proportional to the specific surface area of the mesoporous TiO2 and is ascribed to the capacity originated from the lithium-ion insertion into the surface layer. The experimental comparison and analysis demonstrate that the fast kinetics of the Q as ensure both the better rate performance and capacity retention of mesoporous TiO2 than bulk ones. Specially, the mesoporous TiO2 calcinated at 350 °C shows the highest reversible specific capacity of 250.2 mA h g-1, the best rate capability (132.5 mA h g-1 at 2C) and good cycling stability. Our findings shed great light on the design of high-performance nanostructured TiO2 with surface lithium storage.

Optimization of Porous Structures of Carbon Matrices for Loading Red Phosphorus to Achieve High-Capacity and Long-Life Anodes for All-Solid-State Lithium-Ion Batteries.

All-solid-state lithium-ion batteries (ASSLIBs) using sulfide electrolytes and high-capacity alloy-type anodes have attracted sizable interest due to their potential excellent safety and high energy density. Encapsulating insulating red phosphorus (P) inside nanopores of a carbon matrix can adequately activate its electrochemical alloying reaction with lithium. Therefore, the porosity of the carbon matrix plays a crucial role in the electrochemical performance of the resulting red P/carbon composites. Here, we use zeolite-templated carbon (ZTC) with monodisperse micropores and mesoporous carbon (CMK-3) with uniform mesopores as the model hosts of red P. Our results reveal that micropores enable more effective pore utilization for the red P loading, and the P@ZTC material can achieve a record-high content (65.0 wt %) of red P confined within pores. When used as an anode of ASSLIBs, the P@ZTC electrode delivers an ultrahigh capacity of 1823 mA h g-1 and a high initial Coulombic efficiency of 87.44%. After 400 deep discharge-charge cycles (running over 250 days) at 0.2 A g-1, the P@ZTC electrode still holds a reversible capacity of 1260 mA h g-1 (99.92% capacity retention per cycle). Moreover, a P@ZTC||LiNi0.8Co0.1Mn0.1O2 full cell can deliver a reversible areal capacity of over 3 mA h cm-2 at 0.1C after 100 cycles.

Potassium-Hydrogen Hybrid Ion Alkaline Battery: A New Rechargeable Aqueous Battery Combined a K+ Storage Cathode and an Electrochemical Hydrogen Storage Anode.

A rechargeable aqueous hybrid ion alkaline battery, using a proton and a potassium ion as charge carriers for the anode and cathode, respectively, is proposed in this study by using well-developed potassium nickel hexacyanoferrate as the cathode material and mesoporous carbon sheets as the anode material, respectively. The constructed battery operates in a concentrated KOH solution, in which the energy storage mechanism for potassium nickel hexacyanoferrate involves the redox reaction of Fe2+/Fe3+ associated with potassium ion insertion/extraction and the redox reaction of Ni(OH)2/NiOOH. The mechanism for the carbon anode is electrochemical hydrogen storage. The cathode made of potassium nickel hexacyanoferrate exhibits both an ultrahigh capacity of 232.7 mAh g-1 under 100 mA g-1 and a consistent performance of 214 mAh g-1 at 2000 mA g-1 (with a capacity retention of 92.8% after 200 cycles). The mesoporous carbon sheet anode exhibits a capacity of 87.6 mAh·g-1 at 100 mA g-1 with a good rate and cyclic performance. The full cell provides an operational voltage of 1.55 V, a capacity of 93.6 mAh g-1 at 100 mA g-1, and 82.4% capacity retention after 1000 cycles at 2000 mA g-1 along with a low self-discharge rate. The investigation and discussion about the energy storage mechanisms for both electrode materials are also provided.

Boosting Interfacial Ion Transfer in Potassium-Ion Batteries via Synergy Between Nanostructured Bi@NC Bulk Anode and Electrolyte.

Using high-capacity alloy-type anodes can greatly advance potassium-ion batteries (PIBs). However, the primary limits are unstable solid electrolyte interphase (SEI) and tough interfacial ion transfer associated with large-size K+ during electrochemical (de)alloy reactions. Here, we achieve excellent energy storage performance of PIBs via the synergy between a nanostructured Bi@N-doped carbon (Bi@NC) bulk anode and a KPF6-dimethoxyethane (DME) electrolyte. The Bi@NC material with a high tap density of 3.81 g cm-3 is prepared by simply pyrolyzing a commercial Bi salt yet affords a favorable nano/microstructure consisting of Bi nanograins confined in 3D ultrathin N-doped carbon shells, facilitating electron/ion transport and structural integrity. Detailed impedance spectroscopy investigation unveils that K+ transport through SEI at the Bi@NC anode, rather than the desolvation of K+, dominates the interfacial K+ transfer. More importantly, spectroscopic and microscopic characterizations provide clear evidence that the interplay between Bi@NC anode and optimized KPF6-DME electrolyte can produce a unique SEI layer containing Bi3+-solvent complex that enables the activation energy of interfacial K+ transfer as low as 25.9 kJ mol-1, thereby ultrafast charge transfer at Bi@NC. Consequently, the Bi@NC anode in half cells achieves exceptional rate capability (206 mAh g-1 or 784 mAh cm-3 at 120C) accompanied by high specific capacity (331 mAh g-1 or 1261 mAh cm-3) and long cycle life (running 1400 cycles at 15C with a tiny capacity fading rate of 0.013% per cycle). Moreover, the Bi@NC anode and KPF6-DME electrolyte are also compatible with a potassium Prussian blue cathode and assembled full PIBs achieve stable cyclability (87.3% capacity retention after 100 cycles at 2.5C) and excellent rate performance (65.1% capacity retention upon increasing rates from 1 to 20C).

In-situ polymerized composite polymer electrolyte with cesium-ion additive enables dual-interfacial compatibility in all-solid-state lithium-metal batteries.

Solid composite polymer electrolytes (CPEs) that combine the advantages of inorganic and organic electrolytes are regarded as the most appealing candidates for all-solid-state lithium-metal batteries (ASSLMBs). Nonetheless, the interfacial incompatibility issues resulting from poor cathode/electrolyte contact and uncontrolled dendrite growth on Li anode are fundamentally challenging for the development of ASSLMBs. Herein, we design a solid CPE with dual-interface compatibility based on in-situ thermal polymerization of a precursor solution containing polymer monomer, cesium-ion (Cs+), and inorganic Li+ conductor. The resultant Cs+ containing CPE creates intimate interface contact with the cathode while achieving high interfacial stability with the Li-metal anode. Accordingly, this solid electrolyte can perform reversible Li plating/stripping over 750 h at 0.3 mA cm-2 and a critical current density (CCD) of 0.8 mA cm-2, in sharp contrast with its Cs+-free counterpart (failure after 11 h and a CCD of 0.5 mA cm-2). Furthermore, the full ASSLMBs (Li|LiFePO4) enable decent capacity retention of 90% over 100 cycles at 0.5C and high Coulombic efficiency of nearly 100%. Therefore, constructing solid-state electrolytes with dual-interfacial compatibility may be an effective avenue to achieve high-performance ASSLMBs.

Ultrasensitive electrochemical sensor for mercury ion detection based on molybdenum selenide and Au nanoparticles via thymine-Hg2+-thymine coordination.

An ultrasensitive and specific-selection electrochemical sensor was constructed for Hg2+ detection based on Au nanoparticles and molybdenum selenide (Au NPs@MoSe2) as well as the thymine-Hg2+-thymine (T-Hg2+-T) coordination. Herein, Au NPs@MoSe2 not only could improve the sensitivity due to the large surface area and good electrical conductivity but also offered more sites to immobilize thiol-labeled T-rich hairpin DNA probes (P-1), which has a specific recognition for Hg2+ and methylene blue-labeled T-rich DNA probes (MB-P). When Hg2+ and MB-P exist, P-1 and MB-P can form a stable T-Hg2+-T complex. Then, methylene blue can be close to the electrode and detectable via differential pulse voltammetry (DPV). Benefiting from the specific recognition of T-Hg2+-T and the merits of Au NPs and MoSe2, the fabricated biosensor presented an ultrasensitive and highly selective performance. The DPV responses had a positive linear relationship with Hg2+ concentrations over ten orders of magnitude from 1.0 × 10-16 to 1.0 × 10-7 mol L-1. The detection limit was down to 1.1 × 10-17 mol L-1. Moreover, the developed sensor exhibited a promising application for trace Hg2+determination in water samples.

Cellulose-based material in lithium-sulfur batteries: A review.

Lithium-sulfur (Li-S) battery is considered to be a promising energy storage system due to its high energy density and low cost. However, the commercialization of Li-S battery is hindered by several problems such as the insulating nature of active materials, notorious "shuttle effect" and damage of lithium dendrites. Cellulose-based materials have attracted widespread attention in the development of Li-S battery on account of their environmentally friendly nature, unique network structure, and possibility for chemical functionalization. This review summarizes the application of cellulose-based materials in Li-S batteries mainly as either the separator, the carbon material for binder assisted modification of separator or as carbon hosts for sulfur cathode and discusses the challenges that utilization of the cellulose-based materials could potentially encountered in Li-S battery. Perspectives regarding the future development of cellulose-based materials for Li-S battery are also discussed.

Activating the hydrogen evolution activity of Pt electrode via synergistic interaction with NiS2.

Electrocatalytic hydrogen evolution reaction (HER) is a green approach to produce high-quality hydrogen fuel. Developing efficient electrocatalyst is the key to realize cost-effective HER. Pt is the state-of-the-art HER catalyst so far. However, the use of Pt for HER is limited by its high cost. Thus, it is essential to lower down the usage of Pt in the electrocatalyst by improving the intrinsic activity of Pt. In this work, we propose to achieve this goal by introducing synergistic interaction between Pt and substrate material (NiS2). The favorable synergy interaction can modify the d band structure of Pt (111) facet and modulate the hydrogen adsorption on Pt (111), which enhances the intrinsic electrocatalytic activity of Pt. The effectiveness of this strategy is demonstrated with both experimental and theoretical investigations.

3D Coral-like LLZO/PVDF Composite Electrolytes with Enhanced Ionic Conductivity and Mechanical Flexibility for Solid-State Lithium Batteries.

Composite polymer electrolytes (CPEs) are very promising for high-energy lithium-metal batteries as they combine the advantages of polymeric and ceramic electrolytes. The dimensions and morphologies of active ceramic fillers play critical roles in determining the electrochemical and mechanical performances of CPEs. Herein, a coral-like LLZO (Li6.4La3Zr2Al0.2O12) is designed and used as a 3D active nanofiller in a poly(vinylidene difluoride) polymer matrix. Building 3D interconnected frameworks endows the as-made CPE membranes with an enhanced ionic conductivity (1.51 × 10-4 S cm-1) at room temperature and an enlarged tensile strength up to 5.9 MPa. As a consequence, the flexible 3D-architectured CPE enables a steady lithium plating/stripping cycling over 200 h without a short circuit. Moreover, the assembled solid-state Li|LiFePO4 cells using the electrolyte exhibit decent cycling performance (95.2% capacity retention after 200 cycles at 1 C) and excellent rate capability (120 mA h g-1 at 3 C). These results demonstrate the superiority of 3D interconnected garnet frameworks in developing CPEs with excellent electrochemical and mechanical properties.

Self-assembled N-doped carbon with a tube-in-tube nanostructure for lithium-sulfur batteries.

Lithium-sulfur batteries hold broad prospects as the low-cost and high-energy storage system. However, the practical application is limited by the intrinsic insulating nature of sulfur and severe shuttle effect of soluble polysulfide intermediates. Herein, we demonstrate a convenient self-assembly strategy for encapsulating carbon nanotubes in nitrogen-doped hollow carbon shells, to construct a nitrogen-doped tube-in-tube carbon nanostructure (NTTC) as a host material of sulfur. In this peculiar structure, the highly conductive carbon nanotube cores facilitate the electron transfer while the hollow porous structure is capable of accommodating high sulfur content of 70 wt% in the composites. Moreover, the nitrogen doping helps to alleviate the shuttle effect owing to enhanced chemisorption towards polysulfides. Benefiting from these merits, the NTTC/S composite with the high areal mass loading of ~2.5 mg cm-2 presents a high reversible capacity (1346.9 mAh g-1 at 0.05 C) and excellent rate capability (533.5 mAh g-1 at 3C). More impressively, NTTC/S electrode exhibits good cycling stability at a high rate of 2 C corresponding to slight capacity decay of 0.055% per cycle over 500 discharge/charge cycles.

Chemical Prelithiation of Negative Electrodes in Ambient Air for Advanced Lithium-Ion Batteries.

This study reports an ambient-air-tolerant approach for negative electrode prelithiation by using 1 M lithium-biphenyl (Li-Bp)/tetrahydrofuran (THF) solution as the prelithiation reagent. Key to this strategy are the relatively stable nature of 1 M Li-Bp/THF in ambient air and the unique electrochemical behavior of Bp in ether and carbonate solvents. With its low redox potential of 0.41 V vs Li/Li+, Li-Bp can prelithiate various active materials with high efficacy. The successful prelithiation of a phosphrous/carbon composite electrode and the notable improvement in its initial Coulombic efficiency (CE) demonstrates the practicality of this strategy.

Confining nano-sized platinum in nitrogen doped ordered mesoporous carbon: An effective approach toward efficient and robust hydrogen evolution electrocatalyst.

Despite recent progress in the development of earth abundant electrochemical catalyst for hydrogen evolution reaction (HER), Pt based materials still stand as the state of the art HER catalyst. Due to the high cost of Pt, it is desirable to increase the utilization efficiency of Pt in practical HER process to a realize cost effective hydrogen production. Herein, we repot a novel nitrogen doped ordered mesoporous carbon supported Pt (Pt@NOMC-A) catalyst with a low Pt loading of 7.2 wt% and show that the synergy between Pt nanoparticles and carbon support, as well as the physical confinement offered by the carbon support enhance the electrochemical performance of the novel catalyst. Pt@NOMC-A exhibits a low HER overpotential comparable with commercial 20 wt% Pt/C catalyst under acidic, neutral and alkaline condition. Furthermore, Pt@NOMC-A shows a superior electrochemical stability under working conditions suppressing that of commercial Pt/C catalyst.

Electrochemical Hydrogen Storage in Facile Synthesized Co@N-Doped Carbon Nanoparticle Composites.

A Co@nitrogen-doped carbon nanoparticle composite was synthesized via a facile molecular self-assembling procedure. The material was used as the host for the electrochemical storage of hydrogen. The hydrogen storage capacity of the material was over 300 mAh g-1 at a rate of 100 mAg-1. It also exhibited superior stability for storage of hydrogen, high rate capability, and good cyclic life. Hybridizing metallic cobalt nanoparticle with nitrogen-doped mesoporous carbon is found to be a good approach for the electrochemical storage of hydrogen.

Self-assembly synthesis of a unique stable cocoon-like hematite @C nanoparticle and its application in lithium ion batteries.

A novel cocoon-like Fe2O3@C nanoparticle was fabricated via a facile hydrothermally molecular self-assembly procedure. Compared to bare Fe2O3 nanoparticles, the carbon coated Fe2O3 nanoparticles exhibit higher specific capacity, excellent rate capacity and cyclic stability as the anode in lithium ion batteries. These cocoon-like Fe2O3@C nanoparticles carry enhanced lithium storage properties with a reversible capacity of 358mAhg-1 after 150 cycles under the current density of 1000mAg-1, while the carbon-free bare Fe2O3 can only deliver a much lower capacity of 127.6mAhg-1 with a continuously decreasing trend. The excellent performance of Fe2O3@C is attributed to the coated carbon layers, which not only enhance the electronic conductivity but also reduce the stress upon the Fe2O3 nanoparticles caused by the volume change during the charge/discharge process.