Electrocatalytic nitrogen reduction reaction (NRR) is a promising strategy for ammonia (NH3) production under ambient conditions. However, it is severely impeded by the challenging activation of the ...NN bond and the competing hydrogen evolution reaction (HER), which makes it crucial to design electrocatalysts rationally for efficient NRR. Herein, the rational design of bismuth (Bi) nanoparticles with different oxidation states embedded in carbon nanosheets (Bi@C) as efficient NRR electrocatalysts is reported. The NRR performance of Bi@C improves with the increase of Bi0/Bi3+ atomic ratios, indicating that the oxidation state of Bi plays a significant role in electrochemical ammonia synthesis. As a result, the Bi@C nanosheets annealed at 900 °C with the optimal oxidation state of Bi demonstrate the best NRR performance with a high NH3 yield rate and remarkable Faradaic efficiency of 15.10 ± 0.43% at −0.4 V versus RHE. Density functional theory calculations reveal that the effective modulation of the oxidation state of Bi can tune the p‐filling of active Bi sites and strengthen adsorption of *NNH, which boost the potential‐determining step and facilitate the electrocatalytic NRR under ambient conditions. This work may offer valuable insights into the rational material design by modulating oxidation states for efficient electrocatalysis.
An oxidation state modulation strategy is proposed to boost nitrogen reduction to ammonia. As a proof‐of‐concept, the surface oxidation of Bi species is tuned with the less occupied p orbital, which leads to stronger adsorption of *NNH and lower ΔG of the potential‐determining step. By optimizing Bi surface oxidation, superior nitrogen reduction reaction performance of Faradaic efficiency of 15.10 ± 0.43% is achieved.
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A macroscopic 3D porous graphitic carbon nitride (g‐CN) monolith is prepared by the one‐step thermal polymerization of urea inside the framework of a commercial melamine sponge and exhibits improved ...photocatalytic water‐splitting performance for hydrogen evolution compared to g‐CN powder due to the 3D porous interconnected network, larger specific surface area, better visible light capture, and superior charge‐separation efficiency.
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2D graphitic carbon nitride (GCN) nanosheets have attracted tremendous attention in photocatalysis due to their many intriguing properties. However, the photocatalytic performance of GCN nanosheets ...is still restricted by the limited active sites and the serious aggregation during the photocatalytic process. Herein, a simple approach to produce holey GCN (HGCN) nanosheets with abundant in‐plane holes by thermally treating bulk GCN (BGCN) under an NH3 atmosphere is reported. These formed in‐plane holes not only endow GCN nanosheets with more exposed active edges and cross‐plane diffusion channels that greatly speed up mass and photogenerated charge transfer, but also provide numerous boundaries and thus decrease the aggregation. Compared to BGCN, the resultant HGCN has a much higher specific surface area of 196 m2 g−1, together with an enlarged bandgap of 2.95 eV. In addition, the HGCN is demonstrated to be self‐modified with carbon vacancies that make HGCN show much broader light absorption extending to the near‐infrared region, a higher donor density, and remarkably longer lifetime of charge carriers. As such, HGCN has a much higher photocatalytic hydrogen production rate of nearly 20 times the rate of BGCN.
An efficient etching process, thermal treatment of bulk graphitic carbon nitride under NH3 atmosphere, has been developed to synthesize holey graphitic carbon nitride (HGCN) nanosheets. The resultant HGCN exhibits significantly improved photocatalytic hydrogen production performance under visible light.
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Developing electrochemical energy storage devices with high energy–power densities, long cycling life, as well as low cost is of great significance. Sodium‐ion capacitors (NICs), with Na+ as ...carriers, are composed of a high capacity battery‐type electrode and a high rate capacitive electrode. However, unlike their lithium‐ion analogues, the research on NICs is still in its infancy. Rational material designs still need to be developed to meet the increasing requirements for NICs with superior energy–power performance and low cost. In the past few years, various materials have been explored to develop NICs with the merits of superior electrochemical performance, low cost, good stability, and environmental friendliness. Here, the material design strategies for sodium‐ion capacitors are summarized, with focus on cathode materials, anode materials, and electrolytes. The challenges and opportunities ahead for the future research on materials for NICs are also proposed.
Sodium‐ion capacitors (NICs) have attracted increasing attention due to their merits in combining the high energy densities of batteries, high power densities of supercapacitors, as well as the earth‐abundant reserves of sodium. Recent progresses on advanced materials for NICs are summarized. The challenges and opportunities ahead are also proposed.
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5.
Carbon electrodes for capacitive deionization Huang, Zheng-Hong; Yang, Zhiyu; Kang, Feiyu ...
Journal of materials chemistry. A, Materials for energy and sustainability,
2017, Volume:
5, Issue:
2
Journal Article
Peer reviewed
Carbon materials for electrodes of capacitive deionization (CDI) process are reviewed. Electrochemical cells are briefly explained by classifying into conventional, membrane and flow-electrode CDI ...cells. CDI performance of carbon materials, porous carbons, including activated carbons (ACs), activated carbon fibers (ACFs), templated nanoporous carbons, carbon aerogels, carbon nanotubes (CNTs), carbon nanofibers (CNFs) and graphenes, have been reviewed in detail. The feasibility of CDI techniques is then discussed on the basis of the experimental results reported.
Carbon materials for electrodes of capacitive deionization (CDI) process are reviewed.
An asymmetric supercapacitor with high energy and power densities has been fabricated using MnO2/carbon nanofiber composites as positive electrode and activated carbon nanofibers as negative ...electrode in Na2SO4 aqueous electrolyte. Both electrode materials are freestanding in nature without any conductive additives or binders and exhibit outstanding electrochemical performances. The as-assembled asymmetric supercapacitor with optimal mass ratio can be operated reversibly over a wide voltage range of 0–2.0V, and presents a maximum energy density of 30.6Whkg−1, which is much higher than those of symmetric supercapacitors. Moreover, the supercapacitor exhibits excellent rate capability (high power density of 20.8kWkg−1 at 8.7Whkg−1) and long-term cycling stability with only 6% loss of its initial capacitance after 5000 cycles. These attractive results make these freestanding materials promising for applications in aqueous electrolyte-based asymmetric supercapacitors with high energy and power densities delivery.
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Single atomic metal (SAM) doping is reported as an effective strategy to promote the electrochemical property of carbon‐based anode materials for high‐power sodium‐ion batteries (SIBs). However, the ...effects of SAM with different configurations on solid electrolyte interphase (SEI) and energy storage mechanism of Na+ are not revealed. Herein, Cr single atoms (CrSAs) are reported with controllable configurations (Cr–N4 or Cr–N2) implanted on the N, P co‐doped carbon (NPC) anode materials (denoted as CrN4SAs/NPC or CrN2SAs/NPC). The CrN4SAs/NPC anode displays a high specific capacity (318.2 mAh g−1 at 0.05 A g−1) and outstanding rate performance (145.1 mAh g−1 at 5 A g−1), better than those of CrN2SAs/NPC and NPC. The superiority is originated from the difference of SEI and the energy storage mechanism of sodium ions during electrochemical process, which are unveiled through ex situ characterization and theoretical calculation. The full cell assembled with CrN4SAs/NPC anode and Na3V2(PO4)2F3@C cathode displays a high energy density at a high power density.
Cr single atoms can influence the components of solid electrolyte interphase, and the Cr–N4 configuration can promote the adsorption of Na+ and the electron transfer. Hence, the CrN4SAs/NPC anode displays superior capacity and outstanding rate performance, and the full cell demonstrates high power characteristics (127.5 Wh kg−1 at 1133 W kg−1).
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A cost-effective approach to obtain electrode materials with excellent electrochemical performance is critical to the development of supercapacitors (SCs). Here we report the preparation of a ...three-dimensional (3D) honeycomb-like porous carbon (HLPC) by the simple carbonization of pomelo peel followed by KOH activation. Structural characterization indicates that the as-prepared HLPC with a high specific surface area (SSA) up to 2725 m(2) g(-1) is made up of interconnected microporous carbon walls. Chemical analysis shows that the HLPC is doped with nitrogen and also has oxygen-containing groups. Electrochemical measurements show that the HLPC not only exhibits a high specific capacitance of 342 F g(-1) and 171 F cm(-3) at 0.2 A g(-1) but also shows considerable rate capability with a retention of 62% at 20 A g(-1) as well as good cycling performance with 98% retention over 1000 cycles at 10 A g(-1) in 6 M KOH. Furthermore, an as-fabricated HLPC-based symmetric SC device delivers a maximum energy density of ∼9.4 Wh kg(-1) in the KOH electrolyte. Moreover, the outstanding cycling stability (only 2% capacitance decay over 1000 cycles at 5 A g(-1)) of the SC device makes it promising for use in a high-performance electrochemical energy system.
Surface‐enhanced Raman scattering (SERS) is a sensitive, fast, and nondestructive technology to detect trace amounts of molecules. The development of ultrasensitive and environmentally stable ...noble‐metal‐free SERS substrates is crucial for practical applications but still very challenging. In this contribution, an in situ substitutional doping strategy to synthesize Re‐doped WSe2 (Re‐WSe2) with different doping levels is reported. By increasing the Re content to ≈50 at%, the Re‐WSe2 alloy inherits the 1T″ phase of the ReSe2 lattice. Furthermore, Nb atoms are doped into the 1T″ Re‐WSe2 alloy to further modulate its electronic structure. The as synthesized 1T″ Nb, Re‐WSe2 demonstrates a femtomolar‐level molecular sensing capability with a detectable concentration of 5 × 10–15 m and the corresponding enhancement factor is 2.0 × 109, which is superior to that of most non‐noble‐metal SERS substrates and comparable or even superior to that of noble‐metal substrates to the best of the authors’ knowledge. More importantly, the as‐synthesized 1T″ Nb, Re‐WSe2 exhibits excellent air‐stability over a long term (≈6 months) and selective detection capability in the mixed molecular solution, which are essential for their practical applications. The work provides a new strategy for the rational design of noble‐metal‐free SERS substrates to achieve ultrasensitive molecular sensing.
The synthesis of a Nb, Re dual‐doped monolayer WSe2 with the phase modulation is reported. The as‐synthesized Nb, Re‐WSe2 demonstrates an ultrasensitive molecular sensing performance with a record low concentration of 5 × 10–15 m, which is superior to that of most state‐of‐the‐art non‐noble metal substrates, and exhibits excellent environmental stability (≈6 months) and selective detection.
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Electrospun carbon nanotubes-embedded carbon nanofibers (CNF) fabric is employed as freestanding substrates for in-situ coating MnO2 nanostructures. Birnessite-type MnO2 nanoflakes are observed to ...grow vertically on individual CNF, thus building hierarchical coaxial architecture. This work presents an extensive study of the effect of temperature on the pseudo-capacitive behavior of the as-prepared freestanding MnO2@CNF composites electrodes in mild Na2SO4 electrolyte. The results show that the MnO2@CNF composites exhibit excellent pseudo-capacitive behaviors at different temperatures between 0 °C and 75 °C. The specific capacitance at 1 A g−1 increases from 365 F g−1 at 0 °C to 546 F g−1 at 75 °C, whereas the coulombic efficiency decreases with the increasing temperature, especially at lower charging rate. The cycling stability of the composites strongly depends on the temperature, i.e., 95.3% at 25 °C and 82.4% at 75 °C. This study provides a fundamental understanding of the temperature-dependent capacitive properties of MnO2 in mild electrolyte, which gives an insight into the supercapacitor design for industrial applications.
► Hierarchical δ-MnO2 nanoflakes @carbon nanofibers composites are prepared. ► Effect of temperature on pseudo-capacitive behaviors is extensively studied. ► The composites show good electrochemical performance in range of 0–75 °C ► The δ-MnO2 is found to evolve to γ-MnO2 nanorods during cycling test at 75 °C.
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