Micrometer-sized electrochemical capacitors have recently attracted attention due to their possible applications in micro-electronic devices. Here, a new approach to large-scale fabrication of high-capacitance, two-dimensional MoS2 film-based micro-supercapacitors is demonstrated via simple and low-cost spray painting of MoS2 nanosheets on Si/SiO2 chip and subsequent laser patterning. The obtained micro-supercapacitors are well defined by ten interdigitated electrodes (five electrodes per polarity) with 4.5 mm length, 820 μm wide for each electrode, 200 μm spacing between two electrodes and the thickness of electrode is ∼0.45 μm. The optimum MoS2 -based micro-supercapacitor exhibits excellent electrochemical performance for energy storage with aqueous electrolytes, with a high area capacitance of 8 mF cm(-2) (volumetric capacitance of 178 F cm(-3) ) and excellent cyclic performance, superior to reported graphene-based micro-supercapacitors. This strategy could provide a good opportunity to develop various micro-/nanosized energy storage devices to satisfy the requirements of portable, flexible, and transparent micro-electronic devices.

rechargeable metal-air batteries. [1,2] This reaction demands efficient electrocatalysts that can accelerate the reaction rate, lower the overpotential, and remain stable over time. Currently, noble-metal-based compounds such as IrO 2 and RuO 2 provide good OER performance under alkaline conditions, but their large-scale application is restricted by their scarcity and high cost. [3] Accordingly, much research effort has been devoted to the development of high-performance earth-abundant OER electrocatalysts based on transition-metal elements, usually in the form of metal oxides or metal (oxy)hydroxides, that are inexpensive and stable upon prolonged exposure under oxidizing conditions. [4][5][6][7] In addition to the synergistic effects of transition metals and electrical conductivity, the intrinsic activities of these transition metal oxide or (oxy)hydroxide OER catalysts are closely connected to the number of 3d electrons of the metals; the surface transition-metal ions exhibited e g orbitals which could bond with surfaceanion adsorbates and then influence the binding of oxygenic intermediates. [8,9] The binding strength of these intermediates is thought to dictate catalytic activity. [10] Identifying the relationship between OER activity and the catalyst electronic structure can provide a simple rationale for gaining mechanistic insights and finding new design strategies for the earth-abundant OER catalysts.Among various transition metal-based OER catalysts, metal layered double hydroxides (LDHs) and oxyhydroxides have attracted much attention because of their abundance in the earth's crust and their considerable catalytic activity. [5,6,[11][12][13][14][15][16][17][18][19][20][21] NiFe LDH and more generally NiFe (oxy)hydroxides have emerged as the most active OER catalyst compared to other bimetallic earth-abundant LDHs under basic conditions, [6,15,17,22] and several studies have been directed at understanding the role of Fe in increasing the OER intrinsic activity of NiFe-containing (oxy) hydroxide materials. [23] Boettcher and co-workers demonstrated that Fe incorporation into NiOOH lattice enhances the electronic conductivity in the film and Fe exerts a partial-chargetransfer activation effect on Ni centers throughout the catalyst film, but the enhanced catalytic efficiency cannot be completely explained. [17] To better understand the role of Fe, they further studied other incorporated metal cations (Mn, Ti, Ce, Fe, and La) in NiO x H y , finding that only Fe permanently increases the OER The development of efficient and robust earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is an ongoing challenge. Here, a novel and stable trimetallic NiFeCr layered double hydroxide (LDH) electrocatalyst for improving OER kinetics is rationally designed and synthesized. Electrochemical testing of a series of trimetallic NiFeCr LDH materials at similar catalyst loading and electrochemical surface area shows that the molar ratio Ni:Fe:Cr = 6:2:1 exhibits the best intrinsic OER catalytic activity ...

Various two-dimensional (2D) materials have recently attracted great attention owing to their unique properties and wide application potential in electronics, catalysis, energy storage, and conversion. However, largescale production of ultrathin sheets and functional nanosheets remains a scientific and engineering challenge. Here we demonstrate an efficient approach for large-scale production of V 2 O 5 nanosheets having a thickness of 4 nm and utilization as building blocks for constructing 3D architectures via a freezedrying process. The resulting highly flexible V 2 O 5 structures possess a surface area of 133 m 2 g −1, ultrathin walls, and multilevel pores. Such unique features are favorable for providing easy access of the electrolyte to the structure when they are used as a supercapacitor electrode, and they also provide a large electroactive surface that advantageous in energy storage applications. As a consequence, a high specific capacitance of 451 F g −1 is achieved in a neutral aqueous Na 2 SO 4 electrolyte as the 3D architectures are utilized for energy storage. Remarkably, the capacitance retention after 4000 cycles is more than 90%, and the energy density is up to 107 W·h·kg −1 at a high power density of 9.4 kW kg −1 . KEYWORDS: 2D layers, V 2 O 5 , 3D architectures, high energy density, supercapacitor S upercapacitors, also called electrochemical capacitors or ultracapacitors, are extensively studied as they complement lithium-ion batteries due to their high power density, fast delivery rate, and long lifespan. However, the low energy density of supercapacitors largely obstructs the way of their applications as standalone devices. The energy density (E) of a supercapacitor is determined by its specific capacitance (C) and the cell voltage (V) according to the equation of E = 1/2CV 2 . 1,2Thus, improving the specific capacitance of electrode materials is an efficient way to achieve supercapacitors with a high energy density. Generally, high-capacitance electrode materials possess a high surface area and good electrical conductivity since these properties are strongly related to the electrochemical double layer capacitance or electroactive surface for redox-reactions, resulting in pseudocapacitance within an electrode. To date, a large number of high-surface-area carbonaceous materials such as activated carbon, carbon nanotubes, and graphene have been employed as electrode materials for supercapacitors.3−7 In particular, it was shown that graphene, a 2D monolayer of carbon atoms, is an excellent building block for constructing 3D architectures having improved electrochemical performance advantageous for energy storage devices. 6,8 However, these carbon-based electrochemical double-layer capacitors have a low capacitance, especially at high charge/ discharge rates. Metal oxides and hydroxides overcome these limitations of carbon and commonly exhibit high capacitance for energy storage owing to their more efficient energy storage mechanism, and they have potential to be the electrode materia...

Ni–Co sulfide nanowires synthesized by a two-step hydrothermal method show good performance when used as the positive electrode for asymmetric supercapacitors.

demonstrated to be effective in enhancing the capacitance of carbon-based materials. For example, N, [4,6] O [7,8] and S [9,10] are the most well studied dopants for carbon-based materials. The functions of these dopants depend on their chemical environments in the carbon host structure and they can improve the capacitive performance of carbon-based materials in different manners. It has been reported that the negatively charged pyridinic N and pyrrolic N can serve as faradaic reaction sites and contribute pseudocapacitance, whereas the positively charged quaternary N can facilitate electron transport in carbon lattice. [7,11] The introduction of O and S doping can increase pseudocapacitance and improve the electrode surface wettability. [12,13] Recently, dual and multi ple heteroatom doping carbon materials have been developed and achieved excellent capacitive performance. [14][15][16] Pore engineering is another effective approach to enhance the capacitive performance of carbonbased materials. [17] First, the introduction of pores, especially micropores, can significantly increase the surface area of carbon materials. Second, the pores function as electrolyte reservoirs that can shorten ion diffusion length. Third, the rational construction of an interconnected network consisting of multiple scale pores can facilitate mass transport of ions. The combination of large surface area and efficient ion diffusion will increase the effective ion accessible surface area and therefore, the specific capacitance. This is particular important for ultrafast supercapacitors electrodes that aim to be operated at high charging/discharging rates. Despite that the pore engineering and elemental doping have been demonstrated separately on different carbon materials, the combination of these approaches has rarely been reported. Herein, we demonstrate a new porous carbon electrode with high level of structural complexity for ultrafast supercapacitors through the integration of tri-doping and pore engineering method in preparation of carbon-based electrodes. Results and DiscussionThe preparation of the N,O,S tri-doped hierarchical porous carbon foam is illustrated in Scheme 1. The precursors including graphene oxide (GO) nanosheets, Poloxamer 407 Carbonaceous materials are attractive supercapacitor electrode materials due to their high electronic conductivity, large specific surface area, and low cost. Here, a unique hierarchical porous N,O,S-enriched carbon foam (KNOSC) with high level of structural complexity for supercapacitors is reported. It is fabricated via a combination of a soft-template method, freeze-drying, and chemical etching. The carbon foam is a macroporous structure containing a network of mesoporous channels filled with micropores. It has an extremely large specific surface area of 2685 m 2 g −1 . The pore engineered carbon structure is also uniformly doped with N, O, and S. The KNOSC electrode achieves an outstanding capacitance of 402.5 F g −1 at 1 A g −1 and superior rate capability of 308.5 F g −1 at 100 A g −1...

We report a quantitative understanding of the reduction kinetics responsible for the formation of Pd-Pt bimetallic nanocrystals with two distinctive structures. The syntheses involve the use of KBr to manipulate the reaction kinetics by influencing the redox potentials of metal precursor ions via ligand exchange. In the absence of KBr, the ratio between the initial reduction rates of PdCl4(2-) and PtCl4(2-) was about 10.0, leading to the formation of Pd@Pt octahedra with a core-shell structure. In the presence of 63 mM KBr, the products became Pd-Pt alloy nanocrystals. In this case, the ratio between the initial reduction rates of the two precursors dropped to 2.4 because of ligand exchange and, thus, the formation of PdBr4(2-) and PtBr4(2-). The alloy nanocrystals took a cubic shape owing to the selective capping effect of Br(-) ions toward the {100} facets. Relative to the alloy nanocubes, the Pd@Pt core-shell octahedra showed substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). Specifically, the specific (1.51 mA cm(-2)) and mass (1.05 A mg(-1) Pt) activities of the core-shell octahedra were enhanced by about four- and three-fold relative to the alloy nanocubes (0.39 mA cm(-2) and 0.34 A mg(-1) Pt, respectively). Even after 20000 cycles of accelerated durability test, the core-shell octahedra still exhibited a mass activity of 0.68 A mg(-1) Pt, twice that of a pristine commercial Pt/C catalyst.

No abstract

Thin films of two copper-based metal vanadates (CuV2O6 and Cu2V2O7) were synthesized by a facile drop-casting method. The primary photoelectrochemical (PEC) and physical properties of these two materials including photocurrent response, band gap, flat band potential, incident photon to current conversion efficiency, chemical stability, and oxygen evolution faradaic efficiency were researched. The photocurrent density of CuV2O6 and Cu2V2O7 films at 1.23 V vs RHE in 0.1 M sodium borate buffer solution was about 25 and 35 μA/cm2, respectively. At 1.58 V vs RHE, however, the photocurrent density reached approximately 220 and 120 μA/cm2, respectively. Although the photocurrents observed for these two materials at 1.23 V vs RHE were relatively low, the photocurrents were much higher when tested with sodium sulfite as a hole scavenger. Suitable oxygen evolution catalysts are therefore expected to improve the PEC performance of these materials.