Hierarchical carbon scaffold (HCS) with multi-porous structures, favoring hydrogen diffusion and physisorption is doped with 2–10 wt % Ni for storing hydrogen at ambient temperature. Due to N- and O-rich structure of melamine-formaldehyde resin used as carbon precursor, homogeneous distribution of heteroatoms (N and O) in HCS is achieved. 2 wt % Ni-doped HCS shows the highest hydrogen capacity up to 2.40 wt % H2 (T = 298 K and p (H2) = 100 bar) as well as excellent reversibility of 18.25 g H2/L and 1.25 wt % H2 (T = 298 K and p (H2) = 50 bar) and electrical production from PEMFC stack up to 0.7 Wh upon eight cycles. Computations and experiments confirm strong interactions between Ni and heteroatoms, leading to uniform distribution small particles of Ni. This results in enhancing reactive surface area for hydrogen adsorption and preventing agglomeration of Ni nanoparticles upon cycling. Ni K-edge XANES spectra simulated from the optimized structure of Ni-doped N/O-rich carbon using DFT calculations are consistent with the experimental spectra and suggest electron transfer from Ni to hydrogen to form Ni–H bond upon adsorption. Considering low desorption temperature (323 K), not only chemisorbed hydrogen is involved in adsorption mechanisms but also physisorption and spillover of hydrogen. 相似文献
CaCu3-xZnxTi4O12 ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu3Ti4O12 (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn2+ doping ions at Cu2+ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu3-xZnxTi4O12 decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu3-xZnxTi4O12 ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn2+ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu+/Cu2+ and Ti3+/Ti4+, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model. 相似文献
Various strategies to improve the dielectric properties of ACu3Ti4O12 (A = Sr, Ca, Ba, Cd, and Na1/2Bi1/2) ceramics have widely been investigated. However, the reduction in the loss tangent (tanδ) is usually accompanied by the decreased dielectric permittivity (ε′), or vice versa. Herein, we report a route to considerably increase ε′ with a simultaneous reduction in tanδ in Ta5+–doped Na1/2Y1/2Cu3Ti4O12 (NYCTO) ceramics. Dense microstructures with segregation of Cu– and Ta–rich phases along the grain boundaries (GBs) and slightly increased mean grain size were observed. The samples prepared via solid-state reaction displayed an increase in ε′ by more than a factor of 3, whereas tanδ was significantly reduced by an order of magnitude. The GB–conduction activation energy and resistance raised due to the segregation of Cu/Ta–rich phases along the GBs, resulting in a decreased tanδ. Concurrently, the grain–conduction activation energy and grain resistance of the NYCTO ceramics were reduced by Ta5+ doping ions owing to the increased Cu+/Cu2+, Cu3+/Cu2+, and Ti3+/Ti4+ ratios, resulting in enhanced interfacial polarization and ε′. The effects of Ta5+ dopant on the giant dielectric response and electrical properties of the grain and GBs were described based on the Maxwell–Wagner polarization at the insulating GB interface, following the internal barrier layer capacitor model. 相似文献
Various CeCoOx mixed-oxide catalysts with different Ce/Co ratios were prepared by surfactant-assisted template precipitation of CeO2 and Ce3O4. The obtained catalysts were characterized by X-ray diffraction, X-ray photoelectron spectra, hydrogen temperature-programmed reduction, nitrogen physisorption, and transmission electron microscopy. In general, the mixed-oxide CeCoOx catalysts showed well-dispersed CeO2 and Co3O4 and good catalytic characteristics including a high specific surface area and porous structure. The effectiveness of the prepared catalysts on the hydrogen (H2) production from steam reforming of fusel oil was studied in a packed-bed reactor. Co played an important role in C–C scission to break down the large C2–5 molecules into smaller species resulting in H2 formation. Ce could provide supplementary active oxygen to prevent coke formation on Co, resulting in a more stable activity of the mixed-oxide catalyst throughout the reaction course. 相似文献
Activated carbon (AC) from sugarcane bagasse was prepared using a simple two-step method of carbonization and chemical activation with four different activating agents (HNO3, H2SO4, NaOH, and KOH). Amorphous carbon structure as identified by X-ray diffraction was observed in all samples. Scanning electron microscopy revealed that the AC had more porosity than the non-activated carbon (non-AC). Specific capacitance of the non-AC electrode was 32.58 F g?1 at the current density of 0.5 A g?1, whereas the AC supercapacitor provided superior specific capacitances of 50.25, 69.59, 109.99, and 138.61 F g?1 for the HNO3 (AC-HNO3), H2SO4 (AC-H2SO4), NaOH (AC-NaOH), and KOH (AC-KOH) activated carbon electrodes, respectively. The AC-KOH electrode delivered the highest specific capacitance (about 4 times of the non-AC electrode) because of its good surface wettability, the largest specific surface area (1058.53 m2 g?1), and the highest total specific pore volume (0.474 cm3 g?1). The AC-KOH electrode also had a great capacitance retention of almost 100% after 1000 GCD cycles. These results demonstrate that our AC developed from sugarcane bagasse has a strong potential to be used as high stability supercapacitor electrode material.
CaCu3Ti4O12 ceramics have been extensively studied for their potential applications as capacitors in recent years; however, these materials exhibit very large dielectric losses. A novel approach to reducing the dielectric loss tangent in two steps, while increasing the dielectric permittivity, is presented herein. Doping CaCu3Ti4O12 with a Zn dopant reduces the loss tangent of the ceramic material from 0.227 to 0.074, which is due to the increase in grain boundary (GB) resistance by an order of magnitude (from 6.3× 103 to 3.93 × 104 Ω cm). Zn-doping slightly changes the microstructure and dielectric permittivity of the CaCu3Ti4O12 ceramic, which reveals that the primary role of the Zn dopant is to tune the intrinsic properties of the GBs. Surprisingly, the addition of the Ge4+ dopant into the Zn2+-doped CaCu3Ti4O12 ceramic sample led to a further decrease in the loss tangent from 0.074 to 0.014, due to enhanced GB resistance (3.1 × 105 Ω cm). The grain size increased remarkably from 2–3 μm to 85–90 μm, corresponding to a significant increase in the dielectric permittivity (~1–4 × 104). The large increase in GB resistance is due to the intrinsic potential barrier height at the GBs and the segregation of the Cu-rich phase in the GB region. First-principles calculations revealed that Zn and Ge are preferentially located at the Cu sites in the CaCu3Ti4O12 structure. The substitution of the Ge dopant does not hinder the role of the Zn dopant in terms of improving the electrical properties at the GBs. These phenomena are effectively explained by the internal barrier layer capacitor model. This study provides a way of improving the dielectric properties of ceramics for their practical use as capacitors. 相似文献
Journal of Materials Science: Materials in Electronics - CH3NH3PbI3 perovskite films were prepared via a hot-casting method using six different CH3NH3I, PbI2 and Pb(SCN)2 solutions. Surface... 相似文献
Giant dielectric behavior and electrical properties of monovalent cation/anion (Li+, F−) co-doped CaCu3Ti4O12 ceramics prepared by a solid-state reaction route were systematically investigated. Substitution of Li+ and F− led to a significantly enlarged mean grain size. A reduced loss tangent (tanδ ~0.06) with the retainment of an ultra-high dielectric permittivity (ε′ ~7.7-8.8 × 104) was achieved in the co-doped ceramics, while the breakdown electric field and nonlinear coefficient of CaCu3Ti4O12 ceramics were increased by co-doping with (Li+, F−). The variations in nonlinear electrical properties and giant dielectric response, as well as the dielectric relaxation, were well explained by the Maxwell-Wagner polarization model for an electrically heterogeneous microstructure, in which a Schottky barrier height at the grain boundaries (GBs) was formed. ε′ was closely correlated to the GB capacitance. Significantly decreased tanδ value and enhanced nonlinear properties were related to a significant increase in the GB resistance, which was attributed to the significantly increased potential barrier height and conduction activation energy at the GBs. The semiconducting nature of the grains was also studied using X-ray photoelectron spectroscopy and found to originate from the presence of Cu+ and Ti3+ ions. 相似文献
The Mn1-xNixCo2O4 (0.00?≤?x?≤?0.20) nanoparticles were synthesized by a simple PAN-solution route. XRD, TEM, SAED, FESEM, XANES, XPS, and BET techniques were used to investigate the structural and morphology of Ni-doped MnCo2O4 nanoparticles. The effect of Ni ions substitution in MnCo2O4 nanoparticles on the electrochemical properties was examined on three-electrode systems. The results show that the substitution of Mn with Ni ions can improve the electrochemical properties of MnCo2O4 nanoparticles. The Mn1-xNixCo2O4 electrode with x?=?0.15 exhibits the highest specific capacitance of 378 F g?1 at the current density of 1 A g?1. After 1000 charge-discharges times, this electrode has good capacity retention of 85%. The good capacitance characteristics and cyclic stability indicate that these Mn1-0.85Ni0.15Co2O4 nanoparticles could be applied as active materials for energy storage devices.