PdCo nanotube arrays (NTAs) supported on carbon fiber cloth (CFC) (PdCo NTAs/CFC) are presented as high‐performance flexible electrocatalysts for ethanol oxidation. The fabricated flexible PdCo ...NTAs/CFC exhibits significantly improved electrocatalytic activity and durability compared with Pd NTAs/CFC and commercial Pd/C catalysts. Most importantly, the PdCo NTAs/CFC shows excellent flexibility and the high electrocatalytic performance remains almost constant under the different distorted states, such as normal, bending, and twisting states. This work shows the first example of Pd‐based alloy NTAs supported on CFC as high‐performance flexible electrocatalysts for ethanol oxidation.
PdCo nanotube arrays supported on carbon fiber cloth for use as high‐performance electrocatalysts were synthesized for ethanol electrooxidation. The system of nanotube arrays on carbon fiber cloth is highly flexible, and its high electrocatalytic performance is almost constant regardless of the distorted state, such as normal, bent, and twisted.
The oxygen reduction reaction (ORR) is the core reaction of numerous sustainable energy‐conversion technologies such as fuel cells and metal–air batteries. It is crucial to develop a cost‐effective, ...highly active, and durable electrocatalysts for ORR to overcome the sluggish kinetics of four electrons pathway. In recent years, the carbon‐based electrocatalysts derived from metal–organic frameworks (MOFs) have attracted tremendous attention and have been shown to exhibit superior catalytic activity and excellent intrinsic properties such as large surface area, large pore volume, uniform pore distribution, and tunable chemical structure. Here in this review, the development of MOF‐derived heteroatom‐doped carbon‐based electrocatalysts, including non‐metal (such as N, S, B, and P) and metal (such as Fe and Co) doped carbon materials, is summarized. It furthermore, it is demonstrated that the enhancement of ORR performance is associated with favorably well‐designed porous structure, large surface area, and high‐tensity active sites. Finally, the future perspectives of carbon‐based electrocatalysts for ORR are provided with an emphasis on the development of a clear mechanism of MOF‐derived non‐metal‐doped electrocatalysts and certain metal‐doped electrocatalysts.
Molecular organic framework‐derived heteroatom‐doped carbon‐based electrocatalysts, including nonmetal (such as N, S, B, and P) and metal (such as Fe and Co) doped carbon materials, have attracted tremendous attention and some of them exhibit superior electrocatalytic performance for oxygen reduction reaction. Significant progress has been achieved and more innovations for carbon‐based electrocatalysts will be realized in the future.
TiO2 Co nanotubes decorated with nanodots (TiO2 NDs/Co NSNTs‐CFs) are reported as high‐performance earth‐abundant electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solution. TiO2 ...NDs/Co NSNTs can promote water adsorption and optimize the free energy of hydrogen adsorption. More importantly, the absorbed water can be easily activated in the presence of the TiO2–Co hybrid structure. These advantages will significantly promote HER. TiO2 NDs/Co NSNTs‐CFs as electrocatalysts show a high catalytic performance towards HER in alkaline solution. This study will open up a new avenue for designing and fabricating low‐cost high‐performance HER catalysts.
Electrolysis of water: Carbon‐fiber‐supported nanotubes from TiO2 nanodot‐decorated Co nanosheets were fabricated for the electrocatalytic hydrogen evolution reaction (HER). The electronic interaction between TiO2 and Co can effectively activate the absorbed water molecules and optimize the free energy of H adsorption. The catalysts show an excellent electrocatalytic performance for the HER.
Highly ordered three-dimensional α-Fe2O3@PANI core–shell nanowire arrays with enhanced specific areal capacity and rate performance are fabricated by a simple and cost-effective electrodeposition ...method. The α-Fe2O3@PANI core–shell nanowire arrays provide a large reaction surface area, fast ion and electron transfer, and good structure stability, which all are beneficial for improving the electrochemical performance. Here, high-performance asymmetric supercapacitors (ASCs) are designed using α-Fe2O3@PANI core–shell nanowire arrays as anode and PANI nanorods grown on carbon cloth as cathode, and they display a high volumetric capacitance of 2.02 mF/cm3 based on the volume of device, a high energy density of 0.35 mWh/cm3 at a power density of 120.51 mW/cm3, and very good cycling stability with capacitance retention of 95.77% after 10 000 cycles. These findings will promote the application of α-Fe2O3@PANI core–shell nanowire arrays as advanced negative electrodes for ASCs.
Here we synthesize novel asymmetric all-solid-state paper supercapacitors (APSCs) based on amorphous porous Mn3O4 grown on conducting paper (NGP) (Mn3O4/NGP) negative electrode and Ni(OH)2 grown on ...NGP (Ni(OH)2/NGP) as positive electrode, and they have attracted intensive research interest owing to their outstanding properties such as being flexible, ultrathin, and lightweight. The fabricated APSCs exhibit a high areal C sp of 3.05 F/cm3 and superior cycling stability. The novel asymmetric APSCs also exhibit high energy density of 0.35 mW h/cm3, high power density of 32.5 mW/cm3, and superior cycling performance (<17% capacitance loss after 12 000 cycles at a high scan rate of 100 mV/s). This work shows the first example of amorphous porous metal oxide/NGP electrodes for the asymmetric APSCs, and these systems hold great potential for future flexible electronic devices.
Cellulose paper (CP)‐based asymmetrical thin film supercapacitors (ATFSCs) have been considered to be a novel platform for inexpensive and portable devices as the CP is low‐cost, lightweight, and can ...be rolled or folded into 3D configurations. However, the low energy density and poor cycle stability are serious bottlenecks for the development of CP‐based ATFSCs. Here, sandwich‐structured graphite/Ni/Co2NiO4‐CP is developed as positive electrode and the graphite/Ni/AC‐CP as negative electrode for flexible and high‐performance ATFSCs. The fabricated graphite/Ni/Co2NiO4‐CP positive electrode shows a superior areal capacitance (734 mF/cm2 at 5 mV/s) and excellent cycling performance with ≈97.6% Csp retention after 15 000 cycles. The fabricated graphite/Ni/AC‐CP negative electrode also exhibits large areal capacitance (180 mF/cm2 at 5 mV/s) and excellent cycling performance with ≈98% Csp retention after 15 000 cycles. The assembled ATFSCs based on the sandwich‐structured graphite/Ni/Co2NiO4‐CP as positive electrode and graphite/Ni/AC‐CP as negative electrode exhibit large volumetric Csp (7.6 F/cm3 at 5 mV/s), high volumetric energy density (2.48 mWh/cm3, 80 Wh/kg), high volumetric power density (0.79 W/cm3, 25.6 kW/kg) and excellent cycle stability (less 4% Csp loss after 20 000 cycles). This study shows an important breakthrough in the design and fabrication of high‐performance and flexible CP‐based electrodes and ATFSCs.
Cellulose paper (CP)‐based asymmetrical thin film supercapacitors are assembed by using sandwich‐structured graphite/Ni/Co2NiO4‐CP as positive electrode and graphite/Ni/AC‐CP as negative electrode. The assembed devices exhibit large Csp (7.6 F/cm3 at 5 mV/s), high volumetric energy density (2.48 mWh/cm3, 80 Wh/kg), high volumetric power density (0.79 W/cm3, 25.6 kW/kg), and excellent cycle stability (less 4% Csp loss after 20 000 cycles).
Helical hierarchical porous Na
MnO
/CC and MoO
/CC, which are assembled from nanosheets and nanoparticles, respectively, are fabricated using a simple electrodeposition method. These unique helical ...porous structures enable electrodes to have a high capacitance and an outstanding cycling performance. Based on the helical Na
MnO
/CC as the positive electrodes and helical MoO
/CC as the negative electrodes, high performance Na
MnO
/CC//MoO
/CC asymmetric supercapacitors (ASCs) are successfully assembled, and they achieve a maximum volume
of 2.04 F cm
and a maximum energy density of 0.92 mW h cm
for the whole device and an excellent cycling stability with 97.22%
retention after 6000 cycles.
The novel carbon (C)/MnO2 double-walled nanotube arrays (DNTAs) are designed and fabricated via template-assisted electrodeposition. The unique DNTA architectures of C/MnO2 composites with high ...weight fraction of MnO2 allow high electrode utilization ratio and facilitate electron and ion transmission. In the half-cell test, the hybrid C/MnO2 DNTAs as electrodes show a large specific capacitance (C sp) of 793 F/g at the scan rate of 5 mV/s, high energy/power densities, and much enhanced long-term cycle stability. After 5,000 cycles, the C sp retention of C/MnO2 DNTAs keeps ∼97%, which is much larger than 69% of the MnO2 nanotube arrays (NTAs). The symmetrical supercapacitors (SSCs) composed of C/MnO2 DNTAs also show the predominant performance, such as large C sp of 161 F/g and high energy density of ∼35 Wh/kg, indicating that the C/MnO2 DNTAs is a potential electrode for supercapacitors. The high order pore passages, double-walled structures, hollow structures, and high conductivity are responsible for the superior performance of C/MnO2 DNTAs. Such hybrid C/MnO2 DNTAs may bring new opportunities for the development of supercapacitors with superior performance.
The RWL model for the phonon confinement effect in nanocrystals (NCs) had been found to result in deviations and limitations for crystals exhibiting obvious anisotropic phonon dispersions and ...modified models have been proposed to overcome these deficiencies. Here, we examine this issue in black phosphorus (BP), a typical anisotropic two-dimensional crystal exhibiting pronounced anisotropy in phonon dispersions. A detailed study is performed on the Raman spectra of BP NCs prepared by the ion implantation technique. With decreasing NC size, the peak positions of the three characteristic Raman modes, Ag1, B2g and Ag2 modes, remain almost unchanged, while the Ag1 and Ag2 modes show significant asymmetrical broadening tails towards higher- and lower-frequency sides, respectively. It is found that the RWL model based on one-dimensional phonon dispersion along Γ-Y and Γ-X axes in the Brillouin zone (BZ) cannot interpret the unusual frequency invariance and inhomogeneous line shape broadening of these three modes. However, after considering the contribution of two-dimensional anisotropic phonon dispersions from the whole BZ, the frequency and asymmetrical broadening of the Ag1 and Ag2 modes can be well reproduced. This study demonstrates that the RWL model can be applicable for crystals with anisotropic phonon dispersions once the phonons in the whole two-dimensional or three-dimensional BZ are properly taken into account, and provides a physically sound route into understanding the phonon confinement effect for anisotropic systems.
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