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Lithium-sulfur (Li-S) batteries are considered promising candidates for next-generation advanced energy storage systems due to their high theoretical capacity, low cost and environmental friendliness. However, the severe shuttle effect and weak redox reaction severely restrict the practical application of Li-S batteries. Herein, a functional catalytic material of tin disulfide on porous carbon spheres (SnS

An Li2B4O7 cladded carbon nanofiber membrane has been designed as an interlayer for Li–S batteries. Due to abundant electronic deficiencies [BO3] in Li2B4O7, the enhanced electrochemical performance of Li–S batteries was achieved.

The modified separator with sandwich structure can efficiently promote electrochemical reactions, block the shuttle effect, and inhibit the lithium dendrite by excellent electrical conductivity, strong physical barrier and chemical adsorption.

Highly efficient electrochemical catalysts for oxygen reduction reactions (ORRs) are urgently needed for various energy conversion and storage devices to overcome sluggish ORR kinetics. Here, N,O-codoped carbon spheres with uniform mesopores and a high specific surface area were used as supports for decorating Co3O4 nanoparticles via a facile immersion route. In addition to the benefit of ions and gas mass transfer, the abundant mesopores present in the three-dimensional (3D) carbon spheres also confine and isolate the Co3O4 nanoparticles growing in it, which help to provide rich Co3O4 active sites. The resulting hybrid material exhibits superior ORR activity in terms of even-better half-wave potential and stability than that of commercial Pt/C (40 wt%) in 0.1 M KOH electrolyte. To verify its catalytic activity, the hybrid material was employed as the cathode catalyst in a flexible solid-state zinc-air battery, which achieves a high power density of 227 mW cm−2; this power density is much higher than that of a Pt/C catalytic zinc-air battery (133 mW cm−2) under identical conditions. The improvement in catalytic activity in both aqueous and nonaqueous electrolytes can be attributed to the abundant active sites of the entangled Co3O4 nanoparticles, as well as the novel N,O-codoped carbon structure.

Lithium-sulfur (Li-S) batteries have attracted tremendous attention as promising next-generation energy-storage systems due to their high specific capacity and high specific energy. However, the shuttle of polysulfides and the growth of Li dendrites severely obstruct the practical applications of these batteries. In this work, a functional separator is designed and fabricated in which nano-calcium fluoride (CaF2) particles are embedded in reduced graphene oxide (rGO) and bladed on a PP separator. The density functional theory (DFT) calculations of the adsorption energy and bond length reveal that CaF2 has a satisfying adsorption and catalytic effect on polysulfides (Li2Sn). The factional separator could accelerate homogenous Li+ flow and retard the growth of Li dendrites. In addition, an initial specific capacity of 1504 mAh g-1 at 0.05C is achieved, and it still retains a discharge capacity of 1050 mAh g-1 over 100 cycles at 0.2C. Moreover, the capacity decay rate is only 0.06% per cycle over 420 cycles at a high current density of 0.5 C. The excellent performance could be attributed to the CaF2@rGO modified separator not only accelerating the transmission of electrons but also effectively inhibiting the shuttling of polysulfides. This work provides a better method for attaining practical applications of high-performance lithium-sulfur batteries.

α-Ni(OH)2 is an ideal candidate material for a supercapacitor except for its low conductivity and poor stability. In this work, BO2--intercalated α-NixCo(1-x)(OH)2 is synthesized by a hydrothermal method at a low cost. The Co dopant can decrease the charge-transfer resistance and enhance the cyclic stability. The special unsaturated electronic state of BO2- enhances the bonding with metal ions and attracts water molecules. Thus, the BO2- ions support the hydroxide layers as pillars and create efficient paths for proton transportation, optimizing the utilization of α-Ni(OH)2. The three-dimensional (3D) flowerlike morphology supplies an enormous number of active sites, and r-GO is added to improve the conductivity. As a result, the modified α-Ni(OH)2 exhibits the specific capacitance of 2179, 1592, and 1423 F·g-1 at 1, 20, and 40 A·g-1, respectively, showing improved rate performance. Matching with the commercial activated carbon (AC) as an anode, the asymmetric capacitor delivers an energy density of 40.66 W·h·kg-1 when its power density is 187.06 W·kg-1. Meanwhile, it retains 81.5% capacitance of the initial cycle at 5 A·g-1 after 3000 cycles. With conductivity enhanced and structure stabilized, the modified α-Ni(OH)2 confronts broader fields of application.

In fossil energy utilization processes, only about one-third of fuels is used effectively upon conversion, while the rest becomes waste heat. Therefore, making full use of waste heat is an effective way to save energy. Nowadays, the moderate-high temperature heat utilization systems continue to mature and develop. However, existing heat-to-electricity energy conversion technologies are not very efficient for utilization of low-grade waste heat. Herein, based on our previous finding in H+-ion concentration power generator, we design a cell stack structure in series to optimize and improve its thermal-to-electric performance with temperatures ranging from 50 °C to 170 °C. This experiment reveals that the thermal-to-electric conversion efficiency of 3-cell stack can reach up to 17.86%, which is more than twice as likely to a single-cell (8.39%). The electrochemical kinetic analysis and temperature distribution thermoanalysis results convince us that this tandem device is beneficial to the development for low-level heat recovery.

A H2/CO2 fuel cell is a promising device that can convert CO2 into hydrocarbon fuel with electricity generation. Herein, a facile electrospinning method has been used to synthesize the embedded Ru-CNF catalyst in which Ru nanoparticles are dispersed homogeneously within N-doped carbon nanofibers. This catalyst exhibits a high CH4 production rate of 308.46 μmol gcat-1 h-1 at 170 °C, which is superior to that of the Ru/CNF (242.53 μmol gcat-1 h-1) and Ru/CNT (194.24 μmol gcat-1 h-1). The enhanced CO2RR performance of Ru-CNF is ascribed to the well-distributed Ru nanoparticles within the CNF matrix and synergistic effect of Ru sites with N species, which results in forming the increased CO2RR active sites, hence improving the catalytic activity. Simultaneously, it can achieve a peak power density of 1.8 W m-2 on the strength of anodic (H2 oxidation) and cathodic (CO2 reduction and H2 evolution) reactions with remarkable stability. Such findings give a theoretical basis of CO2RR in the H2/CO2 fuel cell system, which could hold great value to further develop the high-efficiency catalysts for CO2 reduction.

H2/CO2 fuel cells are important devices that convert CO2 into CH4 while generating electricity at mild temperatures. Anhydrous ruthenium oxide (RuO2) on carbon nanotubes (CNT) as a cathode catalyst causes CO2 methanation, but the methane production rate needs to be improved. In this paper, a core–shell structure of CNT@hydrous RuO2 was fabricated by a simple sol–gel method. Unlike anhydrous RuO2, which is a single electronic conductor, CNT@hydrous RuO2 is a proton–electron mixed conductive material. Therefore, protons transfer not only in thepolybenzimidazole (PBI) film but also in the catalyst layer with the assistance of crystalline water in hydrous RuO2. CO2 methanation involving a reaction of multiple protons and electrons can be accelerated. The methane generation rate of CNT@hydrous RuO2 reached 331.2 μmol gcat−1 h−1 at 190 °C which is 3 times higher than that of anhydrous RuO2. This research result provides an effective strategy for the catalytic reaction of multiple proton–electron transfers.

H+-ion concentration cell, which can harvest thermal energy to generate electricity by hydrogen concentration difference principle with a fuel cell structure, is an innovative thermoelectric conversion device. In this system, phosphoric acid-doped polybenzimidazole (PA-doped PBI) membrane is a key component influencing the power generation performance of the cell. Herein, 30, 45, 60, 75, and 90 μm thick PBI membranes are successfully synthesized and doped with phosphoric acid. To achieve a good compromise between the proton conductivity and durability, the properties of PA-doped PBI membranes are experimentally evaluated to clarify the effect of the acid doping time and membrane thickness on cell performance. The results indicate that the higher the acid doping level, the worse the dimensional stability of the membrane. Also the thinner the PBI membrane, the smaller the membrane resistance to ions motion, while the poorer the stability. Upon reaction at 170 °C, this cell can boast a power density from 3.0 to 8.0 W m−2, which results in a thermoelectric conversion efficiency of 5.97–14.32%. This study potentially boosts the practical application of thermal-to-electrical conversion technology.

Lithium-rich layered oxides exhibit one of the highest reversible discharge capacities among cathode materials for lithium-ion batteries. However, their voltage decay and poor cycle stability severely restrict their use as a commercial cathode material. In this work, a novel approach of that combines Cr doping and a Li3PO4 coating was designed to address the problems associated with lithium-rich Li1.2Mn0.54Ni0.13Co0.13O2 materials. The synergistic method not only increases the discharge capacity and cycle stability but also decreases the voltage decay. The 1.0 wt% Li3PO4 coating and 0.08 Cr doping on Li1.2Mn0.54Ni0.13Co0.13O2 cathode shows a capacity retention of 76.5% compared to the 59.0% capacity retention for the pristine electrode after 200 cycles. The initial discharge capacity is also increased from 255.8 mAh·g−1 to 265.2 mAh·g−1. In addition, the discharge voltage decay decreases from 0.84 V to 0.39 V after 200 cycles as a result of the Cr doping and Li3PO4 coating. These enhanced electrochemical properties are attributed to the fact that the Cr doping stabilized the layered structure and inhibited its phase transformation to the spinel phase, and the Li3PO4 coating confined the interfacial side reactions between the electrode and electrolyte. This work may provide a new method to solve the subsistent problems of lithium-rich cathode materials.

Lithium-rich layered oxides are considered as promising cathode materials for lithium-ion batteries due to its high capacity, but the rapid decay of capacity and operating voltage are great challenges to achieve its commercial application. In this work, the nonstoichiometry of Li-rich layered oxide Li1.2Mn0.6Ni0.2O2 was designed by directly declining the Mn amounts in the form of Li1.2MnxNi0.2O2 (x = 0.59, 0.57, 0.55). The nonstoichiometric sample Li1.2Mn0.55Ni0.2O2 exhibits a capacity of 170.73 mAh g−1 at 0.5 C, a little lower than 187.29 mAh g−1 of Li1.2Mn0.6Ni0.2O2, however, better cycling stability of operating voltage and capacity is attained with the reduction of Mn amounts, compared to that of Li1.2Mn0.6Ni0.2O2. The capacity retention of Li1.2Mn0.55Ni0.2O2 is enhanced to 88.7% via 74.7% of Li1.2Mn0.6Ni0.2O2 after 100 cycles at 0.5 C. The declining value of operating voltage for Li1.2Mn0.55Ni0.2O2 is 0.200 V as compared to 0.559 V for Li1.2Mn0.6Ni0.2O2. X-ray photoelectron spectra (XPS) was employed to confirm the existence of Ni3+ in the nonstoichiometric samples, and the amounts of Ni3+ increase along the Mn contents decrease. The improvement of electrochemical properties for nonstoichiometric samples is attributed to the presence of Ni3+ due to Ni3+ can defer the transition of layered-to-spinel structure through decreasing the Li/Ni mixing.

Metal-free carbon materials are currently of considerable interest to researchers because they have been proven to have a good ability to catalyze many electrochemical processes. Making such materi...

Although the lithium–sulfur battery has been developed for many years, how to restrain the intrinsic polysulfide shuttle is still a hot topic. Recently, it has been found that adding a multifunctio...

The effect of prior austenite grain size on martensitic transformation has been studied in a high‑carbon steel with the composition of 1.0C-1.5Cr-0.3Mn-0.3Si-Fe (wt%). Powder metallurgy was used to obtain different grain-sized samples given its high performance to resist grain growth during austenitization. It is found that transformation twin is suppressed and replaced by dislocation martensite when the prior austenite grain size (PAGS) is reduced to about 3 μm. Furthermore, besides film-like retained austenite, blocky retained austenite is also observed with a total volume fraction of more than 30% when PAGS reaches 0.54 μm.

Although Li-rich layered materials are some of the best potential cathode materials owing to their high capacity (>250 mA h g−1), low cost and reduced pollution, they still faces some problems, including low initial coulombic efficiency, poor cycling performance, and bad rate capability. In this work, Li-rich spinel Li4Mn5O12 and MgF2 are constructed on the surface of a Li-rich layered material by simple liquid-phase erosion and liquid-phase deposition methods, respectively. The Li-rich spinel Li4Mn5O12 layer provides 3D Li-ion channels and it restrains the growth of SEI film and oxygen release. The outermost amorphous MgF2 layer of coating also favors Li-ion migration and further protects Li4Mn5O12 from HF corrosion. It is found that the double surface modifications induce a phase transformation from a layered structure to an Li4Mn5O12-type spinel during cycling, which is different from the traditional structural transformation from a layered structure to a LiMn2O4 spinel-like structure, and it exhibits a slower structural transformation. Benefiting from these collaborative contributions from Li4Mn5O12 and MgF2, the material shows superior electrochemical properties, including a high initial coulombic efficiency of 96.4%, excellent capacity retention of 80% after 300 cycles, a small voltage decay rate of 1.5 mV per cycle, and a remarkable rate capability.

Electrocatalytic conversion of CO2 into hydrocarbons is one of the most promising approaches to reduce the concentration of CO2 in the atmosphere as well as to produce various valuable chemical products from this most prevalent greenhouse gas. However, this process is still many steps away from finding practical application because of its high energy demand. Herein we report an innovative CO2/H2 fuel cell that can convert CO2 into a synthetic fuel (CH4) while generating electricity instead of consuming it. This is unlike conventional electrochemical CO2 reduction cells, which typically consume electricity to reduce CO2. In the new cell, H2 is oxidized to H+ ions (and electrons) at the anode, and the H+ ions then pass through a proton exchange membrane to reduce CO2 to CH4 at the cathode. While doing so, the cell can generate a current density of 94.1 A m−2, a peak power density of 3.9 W m−2 and CH4 at a rate of 75.29 μmol gcat−1 h−1 at 170 °C, a temperature that can be derived from waste heat from various processes. Density functional theory is applied to determine the reaction mechanism on the catalyst in the cell.

The wide application of direct ethanol fuel cells (DEFCs) was blocked by the sluggish catalytic activity of catalysts, insufficient ionic conductivity of the polymer electrolyte membrane (PEM), and ethanol crossover issues. To overcome the problems mentioned above, a novel DEFC system with a polymer fiber membrane (PFM) and nonplatinum catalysts is proposed. In this system, the performance of the anode catalyst Pd/C is significantly promoted by homogeneous Ni-doped SnO2 nanoparticles, and the inexpensive permeable PFM is used as a substitute for the PEM. Due to the remarkable catalytic activity and the optimized resistance, the PFM-based DEFC exhibits encouraging performance, which can afford a peak power density of 47.4 mW cm−2 with a porous NiCo2O4 cathode catalyst. Moreover, it can operate continuously for 100 h with only 4.56% drop in electrical output. Therefore, this study provides a very effective strategy for optimizing DEFCs with low cost and high performance.

β-MnO2 with its stable tunnel structures can adapt to the insertion and extraction of Li-ions, and it has exhibited attractive potential as the cathode for a Li-ion battery. In our work, a type of hollow β-MnO2 bipyramid was synthesized by the hydrothermal method with an initial discharge capacity of 181.3 mA h g−1 at 20 mA g−1. Considering the poor conductivity of manganese oxide, the samples were successfully modified with N-doped carbon by in situ synthesis of polydopamine on the surface of the samples and annealing. The carbon-coated samples (β-MnO2@C) deliver a higher initial capacity of 235.5 mA h g−1, better rate performance and higher cycle stability, compared to that of the bare samples. This is mainly because the carbon layer forms conductive networks on the surface of the electrodes to enhance the electrochemical kinetics, and also suppresses the volume expansion caused by the insertion and extraction of Li-ions. In addition, the mechanisms of lithium storage were studied by ex situ XRD measurement, showing that rutile β-MnO2 irreversibly transforms to orthorhombic LixMnO2 in the initial cycle and no other phases are generated in the subsequent charge–discharge process.

High energy density and long cycle life of lithium-sulfur (Li-S) batteries suffer from the shuttle/expansion effect. Sufficient sulfur storage space, local fixation of polysulfides, and outstanding electrical conductivity are crucial for a robust cathode host. Herein, a modified template method is proposed to synthesize a highly regular and uniform nitrogen/oxygen dual-doped honeycomb-like carbon as sulfur host (N/O-HC-S). The unique structure not only offers physical entrapment for polysulfides (LiPSs) but also provides chemical adsorption and catalytic conversion sites of polysulfides. In addition, this structure offers enough space for loading sulfur, and a regular space of nanometer size can effectively prevent sulfur particles from accumulating. As expected, the as-prepared N/O-HC900-S with high areal sulfur loading (7.4 mg cm

Li-rich layered oxides are recognized as promising candidates for next-generation Li-ion batteries owing to the high capacity of250 mAh g

Platinum group metal (PGM)-free M-N-C catalysts have exhibited dramatic electrocatalytic performance and are considered the most promising candidate of the Pt catalysts in oxygen reduction reaction (ORR). However, the electrocatalytic performance of the M-N-C catalysts is still limited by their inferior intrinsic activity and finite active site density. Regulating the coordination environment and increasing the pore structure of the catalyst is an effective strategy to enhance the electrocatalytic performance of the M-N-C catalysts. In this work, the coordination environment and pore structure exquisitely regulated Fe-N-C catalyst exhibit excellent ORR activity and durability. With the enhanced intrinsic activity and increased active site density, the optimized Fe-N/S-C catalyst shows impressive ORR activity (E

Lithium-sulfur (Li-S) batteries have attracted considerable attention owing to their extremely high energy densities. However, the application of Li-S batteries has been limited by low sulfur utilization, poor cycle stability, and low rate capability. Accelerating the rapid transformation of polysulfides is an effective approach for addressing these obstacles. In this study, a defect-rich single-atom catalytic material (Fe-N4/DCS) is designed. The abundantly defective environment is favorable for the uniform dispersion and stable existence of single-atom Fe, which not only improves the utilization of single-atom Fe but also efficiently adsorbs polysulfides and catalyzes the rapid transformation of polysulfides. To fully exploit the catalytic activity, catalytic materials are used to modify the routine separator (Fe-N