Latest ArticlesHighly active and low-cost catalytic electrodes for urea oxidation reaction (UOR) are always crucial for exploration of urea fuel cells. Herein, novel york-shell-structural Ni2P/C nanosphere hybrids (Ni2P/C-YS) are rationally constructed via a hydrothermal method and subsequent phosphidation treatment under different temperature ranging from 250 ℃ to 450 ℃ for UOR applications. In the in-situ constructed hollow york-shell structure, the coupling of conductive carbon materials and active Ni2P allows numerous interfaces facilitating the electron transfer and thereby accelerating the catalytic kinetics. The results demonstrate that Ni2P/C-YS-350 nanocomposite can boost the UOR process with a low potential of 1.366 V vs. RHE at a current density of 50 mA/cm2 in alkaline electrolyte and afford the superior durability with negligible potential decay after 23 h. This study presents that the carbon coated Ni2P hybrid with the optimized crystallinities and hollow york-shell configurations can be a promising candidate for application in urea fuel cells.
Nanocomposites comprising flexible polymers and high dielectric constant inorganic nanoparticles are considered to be one of the promising candidates for electrostatic capacitor dielectrics. However, the effect of interfacial property on electrical energy storage of dielectric polymer nanocomposites is still not clear. Herein, the role of the polarity of the interfacial region is investigated. For this purpose, three polymers with different polarity, polymethyl methacrylate (PMMA), polyglycidyl methacrylate, and polymethylsulfonyl ethyl methacrylate (PMSEMA) are attached onto BaTiO3 (BT) nanoparticle surface via surface-initiated reversible addition-fragmentation chain transfer polymerization. It is found that the polarity of shell polymers shows an apparent effect on the dielectric and energy storage of dielectric polymer nanocomposites. For example, PMSEMA@BT (shell polymer possesses the highest polarity) increases dielectric loss and decreases the breakdown strength of the nanocomposites, leading to lower energy storage capability. However, PMMA@BT (shell polymer possesses the lowest polarity) can induce higher breakdown strength of the nanocomposites. As a result, the PMMA@BT nanocomposite exhibits the highest electrical energy storage capability among the three nanocomposites. This research provides new insight into the design of core-shell nanofillers for dielectric energy storage applications.
This study was to investigate the optimal additions of the cellulose decomposition reaction to obtain the most yield of 5-HMF and other furan derivatives in various biphasic systems with FeCl3-CuCl2 mixed catalysts, and explore its depolymerization kinetics. A series of controllable reactions have been performed under mild environmentally friendly atmosphere. The experiment results showed that 49.13 wt% of 5-HMF was the maximum production along with 2.98 wt% other furan derivatives catalyzed by mixed Lewis acid FeCl3-CuCl2 under the two phases which included high concentration NaCl aqueous phase and n-butanol organic phase at 190 ℃ for 45 min. The conclusion suggested that two-phase systems benefited the yield of 5-HMF, furan derivatives via extracting the target products from reaction phase to organic phase to avoid rehydration of 5-HMF. The kinetic calculation revealed the conversion with mixed catalysts had lower reaction apparent activation energy (21.65 kJ/mol, 190-230 ℃) and the reaction rate was faster than that with acid-based catalysts. Based on experiment exploration, the probable mechanism of cellulose decomposition with FeCl3-CuCl2 was proposed.
Nowadays, Cu-based materials have attracted extensive attention as electrocatalysts, while the inherent reason of the filling of high anti-bonding state of Cu d band (3d104s1) makes it difficult to hybridize with O 2p band of oxygen intermediates during the adsorption process of oxygen evolution reaction (OER). To increase the efficiency of Cu-based electrocatalysts, efforts have been made to optimize the electronic structures and to create surface defects and hierarchical nanostructures with more exposed accessible active sites. Herein, we report a facile method for preparing CuO electrocatalysts with hierarchical nanostructures using the Cu-alanine complex as a precursor through room-temperature chemical precipitation and subsequent calcination in air. Investigations of products obtained at different calcination temperatures reveal the relationship between OER activities and the material characteristics such as specific surface areas, crystal growth orientations, and element components. The product obtained at 500 ℃ exhibits the smallest overpotential of 290 mV in 1.0 mol/L KOH for electrocatalyzing OER. Combining with various characterizations of CuO electrocatalysts after OER activities, the possible catalytic mechanism and the influence factors of their OER performance are also discussed.
The development of low-cost and highly efficient bifunctional electrocatalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of critical importance for clean energy devices such as fuel cells and metal-air batteries. Herein, a sophisticated nanostructure composed of CoS, Co and MoC nanoparticles incorporated in N and S dual-doped porous carbon nanofibers (CoS/Co/MoC-N, S-PCNFs) as a high-efficiency bifunctional electrocatalyst is designed and synthesized via an efficient multi-step strategy. The as-prepared CoS/Co/MoC-N, S-PCNFs exhibit a positive half-wave potential (E1/2) of 0.871 V for ORR and a low overpotential of 289 mV at 10 mA/cm2 for OER, outperforming the non-noble metal-based catalysts reported. Furthermore, the assembled Zn-air battery based on CoS/Co/MoC-N, S-PCNFs delivers an excellent power density (169.1 mW/cm2), a large specific capacity (819.3 mAh/g) and robust durability, demonstrating the great potential of the as-developed bifunctional electrocatalyst in practical applications. This work is expected to inspire the design of advanced bifunctional nonprecious metal-based electrocatalysts for energy storage.
Lithium-sulfur battery is strongly considered as the most promising next-generation energy storage system because of the high theoretical specific capacity. The serious "shuttle effect" and sluggish reaction kinetic limited the commercial application of lithium-sulfur battery. Many heterostructures were applied to accelerate polysulfides conversion and suppress their migration in lithium-sulfur batteries. Nevertheless, the effect of the interface in heterostructure was not clear. Here, the Co2B@MXene heterostructure is synthesized through chemical reactions at room temperature and employed as the interlayer material for Li-S batteries. The theoretical calculations and experimental results indicate that the interfacial electronic interaction of Co2B@MXene induce the transfer of electrons from Co2B to MXene, enhancing the catalytic ability and favoring fast redox kinetics of the polysulfides, and the theoretical calculations also reveal the underlying mechanisms for the electron transfer is that the two materials have different Fermi energy levels. The cell with Co2B@MXene exhibits a high initial capacity of 1577 mAh/g at 0.1 C and an ultralow capacity decay of 0.0088% per cycle over 2000 cycles at 2 C. Even at 5.1 mg/cm2 of sulfur loading, the cell with Co2B@MXene delivers 5.2 mAh/cm2 at 0.2 C.
Lithium metal has a very outstanding theoretical capacity (3860 mAh/g) and is one of the most superior anode materials for high energy density batteries. However, the uncontrollable dendrite growth and the formation of "dead lithium" are the important hidden dangers of short cycle life and low safety. However, the uncontrollable dendrite growth and the formation of dead lithium leads to short cycle life and hidden danger, which hinder its practical application. Controlling the nucleation and growth process of lithium is an effective strategy to inhibit lithium dendrite. Herein, a simple in situ self-catalytic method is used to construct nitrogen doped carbon nanotube arrays on stainless steel mesh (N-CNT@SS) as a lithium composite anode. The N-doped CNTs provide a great number of N-functional groups, which enhance the lithiophilic of anode and provide a large number of uniform nucleation sites, hence it has excellent structural stability for cycles. The arrays provide neat lithium-ion transport channels to uniform lithium-ion flux and inhibits dendrite generation, revealed by the COMSOL multi-physics concentration field simulation. The N-CNT@SS composite anode sustain stable at 98.9% over 300 cycles at 1 mA/cm2. N-CNT@SS as the anode is coupled LiFePO4 (LFP) as the cathode construct a full battery, demonstrating excellent cycling stability with a capacity of 152.33 mAh/g and capacity retaining ratio of 95.4% after 100 cycles at 0.5 C.
2D halide perovskites have emerged as promising materials because of their stability and passivation effect in perovskite solar cells (PSCs). However, the introduction of bulky organic ammonium cations from 2D halide perovskites would decrease the device performance generally compared to the traditional 3D MAPbI3. Incorporation of ultrathin 2D halide perovskite nanosheets (NSs) with 3D MAPbI3 could address this issue. Herein, we report a rationally designed PSCs with dimensional graded 3D/2D MAPbI3/(PEA)2PbI4 heterojunction, in which 2D (PEA)2PbI4 NSs were synthesized and incorporated between 3D MAPbI3 and hole-transporting layer. Besides the significantly improved stability, a notable increasement in power conversion efficiency (PCE) of 20% was obtained for the 3D/2D perovskite solar cells due to the favourable band alignment among (PEA)2PbI4 NSs and the other components. The graded structure of MAPbI3/(PEA)2PbI4 would upshift the energy level continuously, which enhances the hole extraction efficiency thus reduces the interface charge recombination, leading to the increasements of VOC from 1.04 V to 1.07 V, JSC from 21.81 mA/cm2 to 23.15 mA/cm2 and the fill factor from 67.89% to 74.78%, and therefore an overall PCE of 18.53%.
The development of active, low-cost and durable bifunctional electrocatalysts toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are important for overall water splitting. Here, well-defined arrays of vanadium-iron bimetal organic frameworks (VFe-MOF) with controllable stoichiometry have been successfully prepared on nickel foam (NF). The as-fabricated VFe-MOF@NF electrode exhibits excellent electrocatalytic activity and durability for OER and HER in alkaline medium. The material's overpotentials of 10 mA/cm2 are 246 mV for OER and 147 mV for HER, respectively. The electrolyzer made from the VFe-MOF@NF electrodes as both the cathode and anode in 1 mol/L KOH needs only a voltage of 1.61 V to reach a current density of 10 mA/cm2. The superior performance of VFe-MOF@NF can be attributed to the morphological control and electronic regulation of the bimetals, that is, 1) the exposure of the active sites at electrocatalyst/electrolyte interfaces due to the array structure; 2) the synergistic effect of vanadium and iron metals on electro-catalyzing the overall water splitting.
In this paper, the process of ammonia borane (AB) hydrolysis generate H2 on the transition metal Fe@Co core-shell structure has been obtained. According to the different roles played by H2O molecules and the number of H2O molecules involved, there are three schemes of reaction paths. Route Ⅰ does not involve the dissociation of H2O molecules and all H atoms come from AB. Moreover, the H2O molecule has no effect on the breaking of the BH bond or the NH bond. The reaction absorbs more heat during the formation of the second and third H2 molecules. Route Ⅱ includes the dissociation of H2O molecules and the cleavage of BH or NH bonds, respectively, and the reaction shows a slight exotherm. Route Ⅲ started from the break of the BN bond and obtained 3H2 molecules through the participation of different numbers of H2O molecules. After multiple comparative analyses, the optimal hydrolysis reaction path has been obtained, and the reaction process can proceed spontaneously at room temperature.
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