One-step Annealing Research Articles

Toward Low-Cost and Sustainable Supercapacitor Electrode Processing: Simultaneous Carbon Grafting and Coating of Mixed-Valence Metal Oxides by Fast Annealing.

There is a rapid market growth for supercapacitors and batteries based on new materials and production strategies that minimize their cost, end-of-life environmental impact, and waste management. Herein, mixed-valence iron oxide (FeOx) and manganese oxide (Mn3O4) and FeOx-carbon black (FeOx-CB) electrodes with excellent pseudocapacitive behavior in 1 M Na2SO4 are produced by a one-step thermal annealing. Due to the in situ grafted carbon black, the FeOx-CB shows a high pseudocapacitance of 408 mF cm−2 (or 128 F g−1), and Mn3O4 after activation shows high pseudocapacitance of 480 mF cm−2 (192 F g−1). The asymmetric supercapacitor based on FeOx-CB and activated-Mn3O4 shows a capacitance of 260 mF cm−2 at 100 mHz and a cycling stability of 97.4% over 800 cycles. Furthermore, due to its facile redox reactions, the supercapacitor can be voltammetrically cycled up to a high rate of 2,000 mV s−1 without a significant distortion of the voltammograms. Overall, our data indicate the feasibility of developing high-performance supercapacitors based on mixed-valence iron and manganese oxide electrodes in a single step.

Oxygen-deficient WO3via high-temperature two-step annealing for enhanced and highly stable water splitting.

When grown according to the conventional one-step annealing process at 550 °C, WO3 exhibits low photocurrent density and inferior photocurrent retention. In contrast, after a two-step annealing process at first 550 °C and second 700 °C, WO3 contains a higher concentration of oxygen deficiencies acting as shallow donors, thus leading to improved charge separation. Importantly, this results in a substantial photocurrent increase and higher material stability, two criteria that are of utmost importance for efficient photoelectrochemical water splitting.

A modified "gel-blowing" strategy toward the one-step mass production of a 3D N-doped carbon nanosheet@carbon nanotube hybrid network for supercapacitors.

In this work, we have realized the synchronous and large-scale synthesis of one-dimensional (1D) carbon nanotubes (CNTs) on two-dimensional (2D) N-doped carbon nanosheets (NCNS) by a one-step annealing of a Ni-containing gel precursor. Upon heating, the gel is "blown" into large-sized 2D NCNS with uniformly embedded Ni nanoparticles that can catalyze the in situ CNT growth, forming a three-dimensional (3D) N-doped carbon nanosheet@carbon nanotube (NCNS@CNT) hybrid. Different from our previous "gel-blowing" strategy for 2D nanosheets, the modified "gel-blowing" strategy is capable of producing 3D architecture by employing a new complexing agent and introducing ethanol as a carbon source. Importantly, this method can be easily scaled up by annealing more gel precursors with an increased amount of ethanol. The introduction of CNTs endows NCNS@CNTs with higher quality and larger specific surface area (SSA) than pure NCNS. Consequently, the electrochemical performance of 3D NCNS@CNTs is much superior to that of 2D NCNS and found to be related with the annealing temperature. The optimized NCNS@CNTs can deliver a specific capacitance of 124 F g-1 at 1 A g-1 and maintain 88% of their initial value after 10 000 cycles at 1 A g-1. Furthermore, NiO nanosheets are deposited on the NCNS@CNT framework to study its function as a conductive host. The as-fabricated hybrid electrode exhibits a high specific capacitance of 660 F g-1 at 1 A g-1 and 532 F g-1 at 20 A g-1, which is also better than its counterpart using NCNS as substrates. This method provides a simplified and low-cost way towards the mass production of NCNS@CNTs for energy application and beyond.

Formation of nickel-cobalt sulphide@graphene composites with enhanced electrochemical capacitive properties.

Here, nickel–cobalt sulphide particles embedded in graphene layers (porous Ni–Co–S@G), were successfully prepared by one-step annealing of metallocene/metal–organic framework (MOF) hybrids involving simultaneous carbonization and sulfidation. Benefiting from the porous structure, highly conductive graphene layers and large loading of super-capacitive Ni–Co–S, the obtained Ni–Co–S@G composites exhibited excellent electrochemical performance with a specific capacitance of 1463 F g−1 at a current density of 1 A g−1. A flexible solid-state asymmetric supercapacitor (ASC), assembled with Ni–Co–S@G and active carbon, demonstrated a high energy density of 51.0 W h kg−1 at a power density of 650.3 W kg−1. It is noteworthy that the ASC offered robust flexibility and excellent performance that was maintained when the devices were bent at various angles. The results indicate that the as-prepared materials could potentially be applied in high-performance electrochemical capacitors.

Phase-pure τ-MnAlC produced by mechanical alloying and a one-step annealing route

Phase-pure τ-MnAlC powder has been synthesized using mechanical alloying followed by a single annealing step. Mechanical alloying from the elemental constituents resulted in 100 wt.% nanocrystalline β-Mn(Al) phase. Complete β-Mn(Al) to τ-MnAlC phase transformation – via the high-temperature ε-phase – was obtained through annealing and quenching of the as-milled powder. The influence of the quenching rate (3.5–100 °C/s) is discussed in detail. Powder synchrotron X-ray and neutron diffraction data was used to confirm phase-purity, and to determine the magnetic moments of Mn. A coercivity of 0.15 T was obtained for the as-synthesized τ-MnAlC, significantly higher than previously reported values for τ-MnAlC synthesized with a one-step route. A systematic study utilizing cryomilling was attempted to further increase the coercivity.

Mixed-phase Mesoporous TiO2 Film for High Efficiency Perovskite Solar Cells

Mesoporous scaffold structures have played great roles in halide perovskite solar cells(PSCs), due to the excellent photovoltaic performance and commercial perspective of mesoporous PSCs. Here, we reported a mixed-phase TiO2 mesoporous film as an efficient electron transport layer(ETL) for mesoporous perovskite solar cells. Due to the improved crystal phase, film thickness and nanoparticle size of TiO2 layer, which were controlled by varying the one-step hydrothermal reaction time and annealing time, the PSCs exhibited an outstanding short circuit photocurrent density of 25.27 mA/cm2, and a maximum power conversion efficiency(PCE) of 19.87%. It is found that the ultra-high Jsc attributes to the excellent film quality, light capturing and excellent electron transport ability of mixed-phase TiO2 mesoporous film. The results indicate that mix-phase mesoporous metal oxide films could be a promising candidate for producing effective ETLs and high efficiency PSCs.

Unique influence of heating rate on the magnetic softness of Fe81.5Si0.5B4.5P11Cu0.5C2 nanocrystalline alloy

• A finely uniform nano-crystalline structure with α-Fe phase can be obtained after slow annealing. • Small α-Fe crystals precipitated from amorphous matrix by annealing contributes to a low coercivity of 4.8 A/m. • The nano-crystallized mechanism during slow-heating-annealing process is unusual and different with NANOMET. • The simplification of the crystallization process in industry by a one-step annealing. Fe 81.5 Si 0.5 B 4.5 P 11 Cu 0.5 C 2 nanocrystalline alloy with high Fe concentration possesses a finely uniform nanocrystalline structure and numerous α-Fe crystals with a mean grain size of ∼17 nm based on XRD patterns. Such crystals precipitated from the amorphous matrix. Favorable soft magnetic properties, small value of coercivity ( H c ) of ∼4.8 A/m, and high magnetic flux density ( B s ) of ∼1.53 T can be achieved by slow heat treatment (heating rate of ∼10 °C/min). In this case, one-step annealing at a low heating rate is truly antipodal to Fe–Si–B–P–Cu alloy. We analyzed the nanocrystallized mechanism during annealing with various heating rates in Fe 81.5 Si 0.5 B 4.5 P 11 Cu 0.5 C 2 alloy, which inevitably simplified the industrial crystallization process by one-step annealing at a low heating rate.

Effect of Homogenization Treatment on Superplastic Properties of Aluminum Based Alloy with Minor Zr and Sc Additions

Effect of one-step and two-step homogenization treatment on precipitation of Al3(Sc,Zr) dispersoids, grain structure after annealing of cold rolled sheets and superplastic behaviour of a novel Al-Mg based alloy were studied. Heterogeneous nucleation of Al3(Sc,Zr) phase on dislocations and subboundaries dominated at one-step annealing and both homogeneous and heterogeneous nucleation of Al3(Sc,Zr) were observed at two-step annealing modes. It was shown that two-step treatment mode provides high density of Al3(Sc,Zr) precipitates and 650 % of elongation at the constant strain rate of 10-2 s-1 in the studied alloy.

Assembling Ultrasmall Copper-Doped Ruthenium Oxide Nanocrystals into Hollow Porous Polyhedra: Highly Robust Electrocatalysts for Oxygen Evolution in Acidic Media.

Here, a facile and novel strategy for the preparation of Cu-doped RuO2 hollow porous polyhedra composed of ultrasmall nanocrystals through one-step annealing of a Ru-exchanged Cu-BTC derivative is reported. Owing to the optimized surface configuration and altered electronic structure, the prepared catalyst displays a remarkable oxygen evolution reaction (OER) performance with low overpotential of 188 mV at 10 mA cm-2 in acidic electrolyte, an ultralow Tafel slope of 43.96 mV dec-1 , and excellent stability in durability testing for 10 000 cycles, and continuous testing of 8 h at a current density of 10 mA cm-2 . Density functional theory calculations reveal that the highly unsaturated Ru sites on the high-index facets can be oxidized gradually and reduce the energy barrier of rate-determining steps. On the other hand, the Cu dopants can alter the electronic structures so as to further improve the intrinsic OER activity.

Unravelling the Correlation between Charge Mobility and Cocrystallization in Rod-Rod Block Copolymers for High-Performance Field-Effect Transistors.

Cocrystallization involving two or more components aggregating into cocrystals allows the preparation of materials with markedly improved charge mobility. This approach however, is little explored in all-conjugated block copolymers (BCPs). Herein, we report the first investigation into the correlation between cocrystals and charge mobility in a series of new all-conjugated BCPs: poly(3-butylthiophene)-b-poly(3-hexylselenophene) (P3BT-b-P3HS) for high-performance field-effect transistors. These rationally synthesized rod-rod BCPs self-assemble into cocrystals with high charge mobilities. Upon one-step thermal annealing, their charge mobilities decrease slightly despite their increased crystallinities. After two-step thermal annealing, P3BT-b-P3HS (P3BT/P3HS=2:1) and (1:1) cocrystals disappear and phase separation occurs, leading to greatly decreased charge mobilities. In contrast, P3BT-b-P3HS (1:2) retains its cocrystalline structure and its charge mobility.

An all-in-one material with excellent electrical double-layer capacitance and pseudocapacitance performances for supercapacitor

3D porous nitrogen-doped graphene nanosheets (PNGs) are facilely prepared via a simple one-step segmented thermal annealing method, using graphene oxide (GO) as carbon source, urea as nitrogen source and pore generator. During the pyrolysis process at 300 °C, urea and oxygenous groups on GO sheets can release large amounts of gas such as NH3, HCNO and H2O, which act as pore generators to tear and strike GO nanosheets to form 3D porous nanostructured material. When the temperature is increased up to 800 °C, a large amount of nitrogen-containing gas can react with the functional groups on GO. Consequently, the pore forming and nitrogen doping processes of GO are successfully realized and 3D PNGs are prepared. The research results show that the PNGs with an optimal N-doping content of 6.9% display a high surface area of 490.2 m2 g−1 and excellent electrochemical capacitive performance. The outstanding electrical double-layer capacitance and the increasing pseudocapacitance are attributed to the large specific surface area and the high nitrogen content, respectively. In 1 M H2SO4 electrolyte, the PNGs exhibit a specific capacitance of 337.0 F g−1 and a low capacitance loss of 2.4% after 5000 cycles. Moreover, a symmetric supercapacitor with a cell voltage of 1.3 V is assembled, which displays both high energy density and high power density of 19.9 W h kg−1 and 650 W kg−1, respectively. The all-in-one material with excellent electrical double-layer capacitance and pseudocapacitance is promising in supercapacitor.

Sulfur-doped reduced graphene oxide/MoS2 composite with exposed active sites as efficient Pt-free counter electrode for dye-sensitized solar cell

Low-cost catalysts possessing merits of high conductivity and plenty of active sites are highly desirable for the developing of Pt-free counter electrode (CE) in dye-sensitized solar cells (DSCs). In this study, porous sulfur-doped reduced graphene oxide/MoS2 (S-rGO/MoS2) composites were successfully synthesized via a simple one-step annealing strategy employing CS2 as sulfur source. Electrochemical measurements revealed that the as-prepared composite presented a superior catalytic activity on the triiodide reduction process, comparable with Pt electrode. Under optimized conditions, a power conversion efficiency of 6.96% was achieved for the N719-sensitized solar cell with a S-rGO/MoS2 CE, which is very close to that for the device containing a thermally deposited Pt CE (7.35%). The outstanding electro-catalytic activity of composite was attributed to the exposed numerous edges providing much more active sites, and good conductivity resulting from two-dimensional conductive networks of both S-rGO and MoS2. This work demonstrated S-rGO/MoS2 composite as a promising alternative for noble metal Pt in triiodide reduction process and a simple approach of employing two-dimensional nanomaterials as multifunctional materials in photovoltaic for mass application.

MOG-derived porous FeCo/C nanocomposites as a potential platform for enhanced catalytic activity and lithium-ion batteries performance

The transition metal alloy nanoparticles (NPs) have received significant attention because of their unique physicochemical properties as well as low cost. Herein, we report a facile and clean synthetic route to prepare porous FeCo/C bimetallic alloy nanocomposites by using metal-organic gels (MOGs) as precursors. The bimetallic MOGs based on iron and cobalt bridged by tri-carboxylate organic ligands were first synthesized by a general and fast solvothermal method. The desired FeCo/C nanocomposites were then obtained by a one-step annealing process in which MOGs served as both the precursor and the self-sacrificing template. Significantly, the as-synthesized FeCo/C nanocomposites exhibit excellent catalytic activity and lithium-ion batteries performance. This fast and clean synthetic strategy is extended to synthesis diversity and range of potential applications of porous carbon-coated transition-metal alloy nanocomposites.

On the construction of hollow nanofibers of ZnO-SnO2 heterojunctions to enhance the NO2 sensing properties

One dimensional ZnO-SnO2 hollow nanofibers were synthesized via a one-step electrospinning method and annealing treatment. The morphology and structure of the nanofibers have been characterized by various analysis methods, and the sensing properties to 0.5–5 ppm NO2 have also been examined. The results reveal that the 20 atm%Zn composite not only exhibits the highest response that is 9 and 5.2 times higher than that of pristine ZnO and SnO2 respectively, but also exhibits rapid response, excellent selectivity and stability at low operating temperature of 90 °C. So, herein synthesized composite is a promising sensing material for detection of NO2. The enhancing sensing mechanism is discussed in detail, which is attributed to the unique one-dimensional hollow nanostructures and the formation of heterojunctions at interface between both metal oxides.

MOF-Derived Hierarchical MnO-Doped Fe3O4@C Composite Nanospheres with Enhanced Lithium Storage.

Hierarchically nanostructured binary/multiple transition-metal oxides with electrically conductive coatings are very attractive for lithium-ion batteries owing to their excellent electrochemical properties induced by their unique compositions and microstructures. Herein, hierarchical MnO-doped Fe3O4@C composite nanospheres are prepared by a simple one-step annealing in Ar atmosphere, using Mn-doped Fe-based metal-organic frameworks (Mn-doped MIL-53(Fe)) as precursor. The MnO-doped Fe3O4@C composite particles have a uniform nanosphere structure with a diameter of ∼100 nm, and each nanosphere is composed of clustered primary nanoparticles with an amorphous carbon shell, forming a unique hierarchical nanoarchitecture. The as-prepared hierarchical MnO-doped Fe3O4@C composite nanospheres exhibit markedly enhanced lithium-storage performance, with a large capacity of 1297.5 mAh g-1 after 200 cycles at 200 mA g-1. The cycling performance is clarified through analyzing the galvanostatic discharge/charge voltage profiles and electrochemical impedance spectra at different cycles. The unique microstructures and Mn element doping of the hierarchical MnO-doped Fe3O4@C composite nanospheres lead to their enhanced lithium-storage performance.

Precipitation behavior of L12 Al3Zr phase in Al-Mg-Zr alloy

Increasing the recrystallization resistance and the mechanical properties of aluminum-based alloys is possible due to the formation of a nanoscale L12-structured Al3Zr phase. Treatment conditions and alloys composition affect the size and density of dispersoids and their final properties. In this work we analyze the decomposition of the supersaturated solid solution in the as-cast Al-3%Mg-0.25%Zr alloy for different annealing modes to understand the precipitation kinetics of the Al3Zr phase in the presence of Mg. We found that both discontinuous and continuous precipitation mechanisms of the Al3Zr phase are possible in the studied low-alloyed material. One-step annealing leads to the formation of coarse (17 nm) spherical precipitates of a coherent L12-structured Al3Zr phase and discontinuously formed fan-shaped aggregations of the same phase. Two-step annealing provided for the maximum precipitation hardening with the formation of high-density nanoscale (7 nm) dispersoids of the Al3Zr phase. This study highlights the importance of the annealing mode of the as-cast material for achieving a high density of the fine L12 structured Al3Zr phase and the maximum hardening effect.

A Co2 P/WC Nano-Heterojunction Covered with N-Doped Carbon as Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction.

The hydrogen evolution reaction (HER) produces clean hydrogen through an electrochemical process. However, new nonprecious-metal electrocatalysts for the HER are required to reduce the consumption of energy. Herein, we report a new Co2 P/WC nano-heterojunction that consists of Co2 P and WC composite phases coated with a few-layer N-doped graphitic carbon shells (Co2 P/WC@NC). The composite was prepared by a one-step annealing of the polyoxometalate Na9 (NH4 )5 [{(B-α-PW9 O34 )Co3 (OH)(H2 O)2 (Ale)}2 Co]⋅35 H2 O (Co7 P6 W18 ) and dicyandiamide (DCA). The preparation method consisted of the simultaneous phosphorization of Co and carbonization of W in a confined space to isolate a Co2 P/WC nano-heterojunction phase for the first time. Co2 P/WC@NC facilitated the generation of hydrogen in the electrolysis process, which had an overpotential of only 91 mV at a current density of 10 mA cm-2 in the acid solution; an excellent HER performance (2 H+ +2 e- →H2 ) and Tafel slope (40 mV dec-1 ) as well as durability over a period of 50 h were achieved. Theoretical calculations showed that the Co2 P, WC, and Npyridinic C dopants in the material synergistically promoted the HER activity rather than the individual constituents. Furthermore, Co2 P/WC@NC nano-heterojunctions showed good HER performance in the whole pH range of electrolytes and considerable durability in acidic media containing transition metal ions, which may attract more attention for the exploration and optimization of nano-heterojunction catalysts for the HER.

“Pickles Method” Inspired Tomato Derived Hierarchical Porous Carbon for High-Performance and Safer Capacitive Output

Biomass derived porous carbon have attracted more and more attention for the application of energy storage. More effective activation strategy is required for production of biomass derived porous carbon. In this work, “pickle method” inspires the incorporated strategy of the activation agent, because it can realize more effective and uniform mixture between activation agent and precursor. Based on the cell structure, the tomato pickled with ZnCl2 is transferred into natural nitrogen doped (1.2%) porous carbon materials using the one-step annealing. Porous analysis based on density functional theory (DFT) confirms that the materials possess well-defined distributions of mesopores and micropores and high specific surface area (863.6 m2 g−1). The synergetic effects of the hierarchical porous monolithic structure, natural nitrogen doping and high specific area results in the high specific capacitance (347.4 F g−1 at 0.5 A g−1). The ultimate symmetric supercapacitor exhibits ultrahigh specific energy density (142.6 Wh Kg−1) based on the active materials mass. Meanwhile, the materials exhibit less impurities (such as the oxygen of ultralow content (1.1%)), which benefits safer energy storage. Finally, drop, bending and nondestructive temperature tests demonstrate the stable and safe capacitive performance of the supercapacitors.

Metal organic framework derived CoFe@N-doped carbon/reduced graphene sheets for enhanced oxygen evolution reaction

Architectures of CoFe@N-doped carbon/wrinkled rGO sheets are synthesizedviathe one-step annealing of Prussian blue analogues and GO sheet composites. The optimized structure exhibits a low overpotential of 278 mV to drive 10 mA cm−2and has a durable stability.

Nickel foam derived nitrogen doped nickel sulfide nanowires as an efficient electrocatalyst for the hydrogen evolution reaction

Ni3S2 has been validated as an effective electrocatalyst for the oxygen evolution reaction, attributable to its suitable electronic configuration. However, pure Ni3S2 towards the hydrogen evolution reaction (HER) exhibits relatively low catalytic activity. Herein, a one-step annealing strategy is demonstrated for the synthesis of Ni3S2 nanowires on nickel foam (NF) through N doping towards vigorous HER performance both in acid and alkaline solution. The 1D N-Ni3S2 nanowires, integrated onto a 3D NF electrode, show a high catalytic current density of 10 mA cm-2 at a low overpotential of 196 mV and a small Tafel slope of 63 mV dec-1 in an acid electrolyte. In an alkaline medium, the N-Ni3S2 NWs exhibit a low overpotential of 105 mV at the current density of 10 mA cm-2, which is lower than other reported Ni3S2-based HER catalysts. The superior HER catalytic performance is attributed to its unique structural features, both the morphology and electronic structure. Our work provides profound guidance for the design and optimization of electrocatalysts for an efficient HER.