Halogen‐Terminated Ti 3 C 2 T x MXene Electrocatalysts for Continuous Co‐Generation of Ammonia and Electricity

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

Electrocatalytic nitrate (NO3−) reduction reaction (NITRR) is an inspiring route for ammonia (NH3) synthesis at ambient condition. The metallic Cu‐based material with low cost and high activity is one of the most promising electrocatalysts for NITRR. However, due to the weaker atomic H*‐providing capacity, the produced intermediate—nitrite tends to accumulate on its surface, leading to unsatisfactory NH3 selectivity and Faradic efficiency (FE). Herein, a novel and facile O2/Ar plasma oxidation and subsequent electro‐reduction strategy is developed to synthesize a kind of metastable phase Cu. Excitingly, the metastable phase Cu demonstrates superior NITRR performance to conventional phase Cu with high NH4+ selectivity (97.8%) and FE (99.8%). Density function theory (DFT) calculations reveal that the upshift of the d‐band center to near the Fermi level in metastable phase Cu contributes to the enhanced activity, while the relatively strong adsorption of H* facilitates the conversion from NO2*/NO* to NOOH*/NOH* and thus ensures high selectivity and FE. Furthermore, when evaluated as cathode material in Zn‐NO3− battery, high power density (7.56 mW cm−2) and NH4+ yield (76 µmol h−1 cm−2) are achieved by the metastable phase Cu‐based battery.

Functionalized interfacial cover design toward pure silicon anode for high power density lithium–ion capacitor

Electrochemical storage mechanism of interstratification-assembled Ti3C2Tx MXene/NiCo-LDHs electrode in alkaline, acid and neutral electrolytes

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

With more flexible active sites and intermetal interaction, dual-atom catalysts (DACs) have emerged as a new frontier in various electrocatalytic reactions. Constructing a typical p-d orbital hybridization between p-block and d-block metal atoms may bring new avenues for manipulating the electronic properties and thus boosting the electrocatalytic activities. Herein, we report a distinctive heteronuclear dual-metal atom catalyst with asymmetrical FeSn dual atom sites embedded on a two-dimensional C2N nanosheet (FeSn-C2N), which displays excellent oxygen reduction reaction (ORR) performance with a half-wave potential of 0.914 V in an alkaline electrolyte. Theoretical calculations further unveil the powerful p-d orbital hybridization between p-block stannum and d-block ferrum in FeSn dual atom sites, which triggers electron delocalization and lowers the energy barrier of *OH protonation, consequently enhancing the ORR activity. In addition, the FeSn-C2N-based Zn-air battery provides a high maximum power density (265.5 mW cm-2) and a high specific capacity (754.6 mA h g-1). Consequently, this work validates the immense potential of p-d orbital hybridization along dual-metal atom catalysts and provides new perception into the logical design of heteronuclear DACs.

Till date, fabrication of piezoelectric nanogenerator (PNG) with highly durable, high power density, and high energy conversion efficiency is of great concern. Here a flexible, sensitive, cost effective hybrid piezoelectric nanogenerator (HPNG) developed by integrating flexible steel woven fabric electrodes into poly(vinylidene fluoride) (PVDF)/aluminum oxides decorated reduced graphene oxide (AlO‐rGO) nanocomposite film is reported where AlO‐rGO acts as nucleating agent for electroactive β‐phase formation. The HPNG exhibits reliable energy harvesting performance with high output, fast charging capability, and high durability compared with previously reported PVDF based PNGs. This HPNG is capable for harvesting energy from a variety and easy accessible biomechanical and mechanical energy sources such as, body movements (e.g., hand folding, jogging, heel pressing, and foot striking, etc.) and machine vibration. The HPNG exhibits high output power density and energy conversion efficiency, facilitating direct light on different color of several commercial light‐emitting diodes instantly and powers up many portable electronic devices like wrist watch, calculator, speaker, and mobile liquid crystal display (LCD) screen through capacitor charging. More importantly, HPNG retains its performance after long compression cycles (≈158 400), demonstrating great promise as a piezoelectric energy harvester toward practical applications in harvesting biomechanical and mechanical energy for self‐powered systems.

Towards high rate and high areal capacity Zn ion hybrid supercapacitor: Fluffy graphene architecture anchored with ultrathin redox-active molecule

This study aims to quantify the synergistic effect of Ni2+ and Mn2+ ions on the capacitive performance of oxide, hydroxide and phosphate electrodes in alkaline electrolytes. Three types of phases containing both nickel and manganese in a ratio of one-to-one were selected due to their stability in alkaline media: oxides with ilmenite and spinel structures (NiMnO3 and Ni1.5Mn1.5O4); hydroxides with layered structures (β-Ni1/2Mn1/2(OH)2); and phosphates with olivine and maricite structures (LiNi1/2Mn1/2PO4 and NaNi1/2Mn1/2PO4). In the mixed hydroxides and phosphates, Ni2+ and Mn2+ ions randomly occupied one crystallographic site, whereas in the ilmenite oxide, a common face was shared by the Ni2+ and Mn4+ ions. The electrochemical parameters of the Ni–Mn compositions were evaluated in asymmetric hybrid supercapacitor cells working with alkaline electrolytes and activated carbon as a negative electrode. A comparative analysis of oxides, hydroxides and phosphates enabled us to differentiate the effects of nickel and manganese ions, structures and morphologies on their capacitive performance. Thus, the best performed electrode was predicted. The electrode composition should simultaneously contain Ni and Mn ions, and their morphologies should comprise spherical aggregates. This was an ilmenite NiMnO3, which delivers high energy and power density (i.e., 65 W h kg−1 at 3200 W kg−1) and exhibits a good cycling stability (i.e., around 96% after 5000 cycles at a current load of 240 mA g−1).

The development of efficient oxidation reactions utilizing titanosilicate/H2O2 catalytic systems holds significant importance for the green production of bulk and fine oxygenated chemicals. Precisely tailoring the microenvironment of Ti active centers in titanosilicates plays a key role in enhancing their catalytic oxidation performance. In the present study, a novel titanium active center was constructed for the first time through the high-temperature treatment of boron-containing titanosilicates under a hydrogen atmosphere. The Ti-O-B bonds in zeotype borosilicotitanate with MWW topology (Ti-B-MWW), confirmed by high-resolution time-of-flight mass spectrometry, undergo cleavage during H2 treatment, resulting in the formation of "open" Ti species surrounded by tricoordinated boron species. These unique Ti active centers promoted by boron species in the vicinity exhibited enhanced catalytic performance compared to both conventional "open" and "close" Ti active sites in selective oxidation reactions, not only due to the inherent open structure-induced lower H2O2 activation barrier but more importantly to the lower product desorption energy related to adjacent boron. This study demonstrates that the heteroatoms in proximity to Ti active sites significantly influence the catalytic behavior of titanosilicates, offering a new strategy for developing novel zeolite catalysts.

A hybrid PEMFC/supercapacitor device with high energy and power densities based on reduced graphene oxide/Nafion/Pt electrode

Boosted electron accumulation around Fe atom by asymmetry coordinated FeN3S1 for efficient oxygen reduction reaction

Owing to the fast development of portable electronics and electric vehicles, the need for electrochemical energy storage has increased. Among various electrochemical energy storage devices, lithium ion batteries (LIBs) have been demonstrated as one of the most successful examples in many electric applications. Because of their distinguished features, LIBs have high energy density and good power performance. However, due to its limited resource, its price will grow high if LIBs are progressively used. In this regard, sodium ion batteries (SIBs) have been considered as a promising alternative due to its abundance source in earth crust. Due to its similar insertion chemistry, sodium can directly transform well-established electrode materials in LIBs to SIBs. Unlimited efforts have been devoted to find new anode materials for high performance SIBs, including carbonaceous materials, metal oxides and sulfides, and alloy-based materials. Recently, elemental phosphorus P has been found to be electrochemically active for sodium ion battery anode, forming sodium phosphide (Na3P). It gives a high theoretical specific capacity of 2,597 mAh/g. But, its electrochemical performance is unsatisfactory because phosphorus has a very low electrical conductivity (~10-14 S/cm) and suffer from structural pulverization problem caused by its large volume change. To overcome this problem, Sn4P3 material has been reported as a promising anode for SIBs. It has been recently reported that Sn4P3 showed a synergistic Na-storage reaction where Sn and P atoms can react with Na to form Na15Sn4 and Na3P, and that the resulting Na15Sn4 alloy acts as a conducting pathway to activate the reversible Na-storage reaction of low electrical conductive Na3P particles. Also, Sn4P3 anode material exhibits a high reversible capacity of 1,230 mAh/g. The architecture of a stable and robust protective layer on the metallic Sn anode is critically important to ensure the good electrochemical performance of SIBs. Up to now, most of SIBs anodes consisting of elemental P and Sn alloys are generally produced by ball milling, thus the morphology has not been controlled. Ball milling method have been widely used as SnxPy electrodes because their phases can be easily controlled in laboratory scale synthesis. However, ball milling method for SnxPy is usually hard to control the morphology and produce nano scale, which leads to the deterioration of an active material resulting in capacity decay by several cycles. Therefore, hydrothermal method has received significant attention because it can control the nanoscale morphology for improved electrochemical performance. Herein, we report the porous Sn4P3-C nano spheres synthesized by hydrothermal process as an anode for SIB with an ultra-long term cycle stability and a high capacity. First, SnO2 nano spheres was synthesized by hydrothermal method with glucose precursor. Glucose not only prevents the rapid precipitation of colloidal SnO2 nano spheres but also serves as a carbon precursor for SnO2-C nano spheres. Consecutively, reduction process from SnO2 to Sn was conducted. The SnO2 redox process under hydrogen atmosphere has a significant problem. The reduction of SnO2 at 600 °C generates a liquid metallic tin, which aggregates into Sn particles. To prevent this problem, we employed a thick carbon layer coating to prevent the aggregation. Finally, phosphorization process was carried out using solvothermal method. Compared with other methods, the solvothermal route is convenient, simple, mild, and the morphology can also be controlled. With suitable temperature and time, Sn nano spheres were chemically transformed into Sn4P3 nano spheres, resulting in porous Sn4P3-C nano spheres. The synthesized porous Sn4P3-C nano sphere electrode exhibited an ultra-long cycle stability (about 2,000 cycles at 2,000 mAh/g) and high reversible capacity (700 mAh/g after 100 cycles at 200 mA/g) (Fig. 1). And its original morphology is apparently retained and the characteristic sphere geometry was unchanged after cycling test. We suggest the design strategy for the next-generation SIBs, and it can be applied to other phosphorus-metal alloying composites. Figure 1

Microbial fuel cells (MFCs) can potentially be used to overcome issues with battery powered light buoys and their frequent maintenance. In this study, a phototrophic sediment microbial fuel cell (PSMFC) was chosen, as the microalgae provide oxygen to be reduced on the cathode and to release the necessary nutrients for the bacteria on the anode. To achieve this, we studied the effect of illumination, the period of the illumination, and the distance between 9-cm2 stainless steel mesh electrodes on the performance of the MFC. The illuminated cells were able to produce higher OCP (max. 205.2 mV) and higher power density (max. 0.68 mW/m2). However, the highest current was achieved during the unilluminated variation (max. 5.3 μA unilluminated and 3.3 μA illuminated). Prolonged illumination produced a higher OCP, current, and power density. A longer electrode distance produced a higher OCP, power density, and current. SEM analysis showed that biofilm formation tended to be scattered at lower electrode distance and more clumped (filling the anode area) at higher electrode distance. Through FTIR analysis, it was found that all MFC variations had the same organic matter, but a more concentrated organic content was found in the MFC at longer electrode distances.

Developing low-cost, high-performance electrocatalysts for the oxygen reduction reaction (ORR) is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m -phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative polymerization. Then iron (Fe) salt was introduced into the polymer network and transformed into ORR active Fe–N–C sites along with Fe, FeS, and FeN0.05 nanoparticles after pyrolysis, generating ORR active sandwich-like carbon nanosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential ~30 mV more positive than Pt/C in 0.1 mol L−1 KOH, while the half-wave potential of the catalyst was only ~40 mV lower than that of commercial Pt/C in 0.1 mol L−1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon nanosheets hold great potential as alternatives to precious metal-based catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.