The low utilization of active sites and sluggish reaction kinetics of MoSe severely impede its commercial application as electrocatalyst for hydrogen evolution reaction (HER). To address these two issues, the first example of introducing 1T MoSe and N dopant into vertical 2H MoSe /graphene shell/core nanoflake arrays that remarkably boost their HER activity is herein described. By means of the improved conductivity, rich catalytic active sites and highly accessible surface area as a result of the introduction of 1T MoSe and N doping as well as the unique structural features, the N-doped 1T-2H MoSe /graphene (N-MoSe /VG) shell/core nanoflake arrays show substantially enhanced HER activity. Remarkably, the N-MoSe /VG nanoflakes exhibit a relatively low onset potential of 45 mV and overpotential of 98 mV (vs RHE) at 10 mA cm with excellent long-term stability (no decay after 20 000 cycles), outperforming most of the recently reported Mo-based electrocatalysts. The success of improving the electrochemical performance via the introduction of 1T phase and N dopant offers new opportunities in the development of high-performance MoSe -based electrodes for other energy-related applications.

Increasing the utilization efficiency of sulfur electrodes and suppressing the "shuttle effect" of intermediate polysulfides are the key challenge for high-performance lithium-sulfur batteries (LSBs). Herein a facile combined strategy is reported to fabricate novel porous carbon fibers/vanadium nitride arrays (PCF/VN) composite scaffold for the storage of sulfur via a facile chemical etching united solvothermal-supercritical fluid method. More active sulfur can be stored in the PCF/VN backbone and dual blocking effects associated with "physical block and chemical absorption" for polysulfides are achieved in the PCF/VN/S integrated electrode. The PCF with highly porous structure provides large space to accommodate active sulfur and possesses cross-linked maze channels to physically immobilize the polysulfide species. The VN nanobelt arrays demonstrate strong ability for chemically anchoring the polysulfides, thus retarding the shuttle effect. Due to the unique structure and dual confining effect, the designed PCF/VN/S electrode shows a high reversible capacity of 1310.8 mA h g −1 at 0.1 C, an extended cycle life (1052.5 mA h g −1 after 250 cycles) as well as enhanced rate capability, much better than other counterparts (CF/VN/S, PCF/S, and CF/S). This work opens a new door for fabricating high-performance integrated electrodes for LSBs.

Porous materials have been thriving as promising candidates for vast applications in current electrochemical energy storage field. [1][2][3] The rational design of porous architectures with hierarchical and interconnected pore networks is always strongly considered by scientific community. [4][5][6][7] In parallel with the microporous (pore size ≤ 2 nm) and mesoporous (2 nm ≤ pore size ≤ 50 nm) materials, macroporous (50 nm ≤ pore size) materials emerge and hold tremendous potentials due to their significant advantages with interconnected frameworks offering improved structural stability, as well as large channels for accelerated mass mobilization and accessibility advantageous over micro/mesoporous materials. [8] In addition, many electrochemical energy storage applications require an open cellular structure with a reasonable combination of hierarchical pore size and distribution, of which the macropores work together with mesopores and micropores to accelerate transport mass (e.g., chemicals and electrolyte), thus highlighting the necessity and importance of macropores in a porous hierarchy. [9] Porous macrocellular carbon, one member of macroporous material family, is of particularly great interest due to their excellent chemical, mechanical, and thermal stability coupled with good conductivity and high surface area. Thus, various carbonaceous porous materials (e.g., 3D rGO, [10] porous graphene, [11][12][13] carbon nanorods, [14] carbon nanotube networks, [15] microporous carbon, [16] hierarchical porous carbon, [17] biomass derived carbon, [18][19][20][21] and their hybrids) [22][23][24] are endowed with a wide range of applications in lithium ion batteries, [25] sodium ion batteries, [26] and supercapacitors. [27] Diverse techniques have been developed to fabricate macroporous carbon materials including template, [27] suspension, [28] microfluidics, [29] membrane/microchannel emulsification, [9] and seeded emulsion polymerization, [30] etc. However, such methodologies are tedious, requiring multiple synthetic steps, caustic chemical treatments, and long curing times. Therefore, it is with great interest to develop facile approaches for large-scale construction of macroporous materials.Puffing process has been extensively accepted to produce 3D edible and degradable foam from starch-based materials (e.g., (2 of 8)rice, corn, wheat, potato). [31] As a typical puffing method, the instantaneous puffing (IP) involving compression and instantaneous release processes is widely accepted for popcorn fabrication. In general, the grains are first compressed in a heated and sealed container. Then, the starch-containing feedstocks are puffed/expanded in a flash by instantaneous release of clamping force of the sealed container at a high temperature of ≈200-300 °C and a large pressure of 0.5-1.5 MPa. The bulk starch-containing feedstocks are instantaneously transformed into expanded 3D porous macrocellular materials with volume and surface area increased by dozens of times through the facile IP process. This technolog...

power sources for electric vehicles and electronics. [4][5][6][7] In such a context, nextgeneration LIBs era with Li metal anode is spring up including Li-S, Li-O 2 , and solidstate Li batteries, which require high gravimetric capacity anodes and cathodes. [8][9][10][11][12][13] The maximum gravimetric capacity of cells would be significantly increased if Li is deposited on the anode directly as pure Li metal rather than stored in intercalation compounds such as graphite in LIBs during the charge/discharge processes. The theoretical capacity based on lithiated graphite is about 372 mA h g −1 , while pure Li metal theoretically delivers 3860 mA h g −1 . Therefore, Li metal anode is strongly considered recently. [14][15][16][17] In spite of the huge potential for highenergy-density device, the practical application of Li metal to a rechargeable anode is bumpy and has many challenges. [18,19] The most tough one is that Li metal problematically forms dendrites and related unstable structures during repeated plating/stripping. The fresh metallic deposit acts as an active site inducing reductive decomposition of electrolyte components. Part of the irregular deposition may become electrically isolated, and shedding may also occur. [20] Therefore, the disordered Li deposit gives rise to a poor Coulombic efficiency and a short cycle life. The metallic Li dendrites may easily penetrate into the separator and eventually induce internal short circuit, resulting in severe safety problem. [21,22] To circumvent these issues, great efforts are devoted to exploring dendrite-free Li metal anodes. Many emerging strategies have been investigated to enhance the electrochemical performance of Li metal anode: (1) Electrolyte additive is introduced into the electrolyte to form stable solid electrolyte interphase (SEI) film and reaction interface. [23][24][25][26][27][28] (2) Buffer layer or ion transfer layer is fabricated on the surface of Li metal by physical, chemical, or electrochemical methods and ensures homogeneous deposition of Li during cycling. [29][30][31][32] (3) Solidstate electrolyte is established on the surface of Li and proven to inhibit the dendrite growth. [33][34][35] (4) Highly porous conductive matrix is applied to guide the uniform deposition of Li metal in a working cell. [36][37][38][39][40] If the Li metal can be well protected by stable SEI, extra space is therefore required for the volume expansion/shrink of Li metal. Therefore, design/fabrication of novel porous conductive matrix is particularly important Construction of stable dendrite-free Li metal anode is crucial for the development of advanced Li-S and Li-air batteries. Herein, self-supported TiC/C core/shell nanowire arrays as skeletons and confined hosts of molten Li forming integrated trilayer TiC/C/Li anode are described. The TiC/C core/ shell nanowires with diameters of 400-500 nm exhibit merits of good lithiophilicity, high electrical conductivity, and abundant porosity. The as-prepared TiC/C/Li anode exhibits prominent electrochemical performance...

Tailoring molybdenum selenide electrocatalysts with tunable phase and morphology is of great importance for advancement of hydrogen evolution reaction (HER). In this work, phase- and morphology-modulated N-doped MoSe /TiC-C shell/core arrays through a facile hydrothermal and postannealing treatment strategy are reported. Highly conductive TiC-C nanorod arrays serve as the backbone for MoSe nanosheets to form high-quality MoSe /TiC-C shell/core arrays. Impressively, continuous phase modulation of MoSe is realized on the MoSe /TiC-C arrays. Except for the pure 1T-MoSe and 2H-MoSe , mixed (1T-2H)-MoSe nanosheets are achieved in the N-MoSe by N doping and demonstrated by spherical aberration electron microscope. Plausible mechanism of phase transformation and different doping sites of N atom are proposed via theoretical calculation. The much smaller energy barrier, longer HSe bond length, and diminished bandgap endow N-MoSe /TiC-C arrays with substantially superior HER performance compared to 1T and 2H phase counterparts. Impressively, the designed N-MoSe /TiC-C arrays exhibit a low overpotential of 137 mV at a large current density of 100 mA cm , and a small Tafel slope of 32 mV dec . Our results pave the way to unravel the enhancement mechanism of HER on 2D transition metal dichalcogenides by N doping.

As ynergistic Nd oping plus PO 4 3À intercalation strategy is used to induce high conversion (ca. 41 %) of 2H-MoS 2 into 1T-MoS 2 ,which is muchhigher than single Ndoping (ca. 28 %) or single PO 4 3À intercalation (ca. 10 %). Ascattering mechanism is proposed to illustrate the synergistic phase transformation from the 2H to the 1T phase,w hich was confirmed by synchrotron radiation and spherical aberration TEM. To further enhance reaction kinetics,t he designed (N,PO 4 3À )-MoS 2 nanosheets are combined with conductive vertical graphene (VG) skeleton forming binder-free arrays for high-efficiency hydrogen evolution reaction (HER). Owing to the decreased band gap,l ower d-band center,a nd smaller hydrogen adsorption/desorption energy,t he designed (N,PO 4 3À )-MoS 2 /VGe lectrode shows excellent HER performance with al ower Tafel slope and overpotential than N-MoS 2 /VG, PO 4 3À -MoS 2 /VGc ounterparts,a nd other Mo-base catalysts in the literature.

Pursuit of advanced batteries with high-energy density is one of the eternal goals for electrochemists. Over the past decades, lithium-sulfur batteries (LSBs) have gained world-wide popularity due to their high theoretical energy density and cost effectiveness. However, their road to the market is still full of thorns. Apart from the poor electronic conductivity of sulfur-based cathodes, LSBs involve special multielectron reaction mechanisms associated with active soluble lithium polysulfides intermediates. Accordingly, the electrode design and fabrication protocols of LSBs are different from those of traditional lithium ion batteries. This review is aimed at discussing the electrode design/fabrication protocols of LSBs, especially the current problems on various sulfur-based cathodes (such as S, Li 2 S, Li 2 S x catholyte, organopolysulfides) and corresponding solutions. Different fabrication methods of sulfur-based cathodes are introduced and their corresponding bullet points to achieve high-quality cathodes are highlighted. In addition, the challenges and solutions of sulfur-based cathodes including active material content, mass loading, conductive agent/binder, compaction density, electrolyte/sulfur ratio, and current collector are summarized and rational strategies are refined to address these issues. Finally, the future prospects on sulfur-based cathodes and LSBs are proposed.

renewable energy is imperative and of great significance for human beings. As the ideal alternatives, green energy sources including wind, solar energy, water, and tide power have been widely applied in modern industry successfully, but their intermittent and variability feature cannot support all-weather utilization. [3][4][5] Hence, developing high-efficiency energy storage and conversion technology is a powerful measure to solve the above problems. Currently, there has been great interest in developing/refining high-performance electrochemical energy storage (EES) devices such as batteries, supercapacitors, and fuel cells. Among various EES technologies, secondary rechargeable batteries (e.g., lead-acid batteries, Ni-Cd batteries, nickel-metal hydride batteries, and lithium/sodium ion batteries) have been extensively studied and play an important role in modern electronics and transportation. [6] Typically, since the successful commercialization of lithium ion batteries (LIBs) by Sony in 1991, we have entered into an era of LIBs due to their high working voltage, long cycles, low self-discharge, large energy density, and low maintenance. [7] After rapid development over the past decades, the fabrication techniques and performance of LIBs have made great progress and matured significantly to be used as main power source for sophisticated electronics, [8] hybrid electric vehicles, and pure electric vehicles. [1,9] However, the high Scrupulous design and smart hybridization of bespoke electrode materials are of great importance for the advancement of sodium ion batteries (SIBs). Graphene-based nanocomposites are regarded as one of the most promising electrode materials for SIBs due to the outstanding physicochemical properties of graphene and positive synergetic effects between graphene and the introduced active phase. In this review, the recent progress in graphene-based electrode materials for SIBs with an emphasis on the electrode design principle, different preparation methods, and mechanism, characterization, synergistic effects, and their detailed electrochemical performance is summarized. General design rules for fabrication of advanced SIB materials are also proposed. Additionally, the merits and drawbacks of different fabrication methods for graphene-based materials are briefly discussed and summarized. Furthermore, multiscale forms of graphene are evaluated to optimize electrochemical performance of SIBs, ranging from 0D graphene quantum dots, 2D vertical graphene and reduced graphene oxide sheets, to 3D graphene aerogel and graphene foam networks. To conclude, the challenges and future perspectives on the development of graphene-based materials for SIBs are also presented.