Zhouguang Lu

Multistimuli‐Responsive, Moldable Supramolecular Hydrogels Cross‐Linked by Ultrafast Complexation of Metal Ions and Biopolymers

A new type of multistimuli-responsive hydrogels cross-linked by metal ions and biopolymers is reported. By mixing the biopolymer chitosan (CS) with a variety of metal ions at the appropriate pH values, we obtained a series of transparent and stable hydrogels within a few seconds through supramolecular complexation. In particular, the CS-Ag hydrogel was chosen as the model and the gelation mechanism was revealed by various measurements. It was found that the facile association of Ag(+) ions with amino and hydroxy groups in CS chains promoted rapid gel-network formation. Interestingly, the CS-Ag hydrogel exhibits sharp phase transitions in response to multiple external stimuli, including pH value, chemical redox reactions, cations, anions, and neutral species. Furthermore, this soft matter showed a remarkable moldability to form shape-persistent, free-standing objects by a fast in situ gelation procedure.

Single-crystal α-MnO2 nanorods: synthesis and electrochemical properties

Single-crystal α-MnO2 nanorods were prepared by hydrothermal reaction of single KMnO4 under acidic conditions. The nanorods have a diameter of 30–70 nm and a length up to 2 µm. The formation mechanism for the α-MnO2 nanorods was investigated. Electrochemical properties of the MnO2 nanomaterials prepared for different hydrothermal times were characterized by galvanostatic charge/discharge tests and cyclic voltammetry (CV) studies. The results indicate that the MnO2 nanorods prepared for 5 and 8 h show fine capacitive behaviour with high specific capacitances of 71.1 and 70.9 F g−1, respectively.

Facile and rapid synthesis of highly porous wirelike TiO2 as anodes for lithium-ion batteries.

Highly porous wirelike TiO(2) nanostructures have been synthesized by a simple two-step process. The morphological and structural characterizations reveal that the TiO(2) wires typically have diameters from 0.4 to 2 μm, and lengths from 2 to 20 μm. The TiO(2) wires are highly porous and comprise of interconnected nanocrystals with diameters of 8 ± 2 nm resulting in a high specific surface area of 252 m(2) g(-1). The effects of experimental parameters on the structure and morphology of the porous wirelike TiO(2) have been investigated and the possible formation processes of these porous nanostructures are discussed. Galvanostatic charge/discharge tests indicate that the porous wirelike TiO(2) samples exhibit stable reversible lithium ion storage capacities of 167.1 ± 0.7, 152.1 ± 0.8, 139.7 ± 0.3, and 116.1 ± 1.1 mA h g(-1) at 0.5, 1, 2, and 5 C rates, respectively. Such improved performance could be ascribed to their unique porous and 1D nanostructures facilitating better electrolyte penetration, higher diffusion rate of electrons and lithium ion, and variation of accommodated volumes during the charge/discharge cycles.

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate.

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C− anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

Facile electrodeposition of 3D concentration-gradient Ni-Co hydroxide nanostructures on nickel foam as high performance electrodes for asymmetric supercapacitors

Novel three-dimensional (3D) concentration-gradient Ni-Co hydroxide nanostructures (3DCGNC) have been directly grown on nickel foam by a facile stepwise electrochemical deposition method and intensively investigated as binder- and conductor-free electrode for supercapacitors. Based on a three-electrode electrochemical characterization technique, the obtained 3DCGNC electrodes demonstrated a high specific capacitance of 1,760 F·g−1 and a remarkable rate capability whereby more than 62.5% capacitance was retained when the current density was raised from 1 to 100 A·g−1. More importantly, asymmetric supercapacitors were assembled by using the obtained 3DCGNC as the cathode and Ketjenblack as a conventional activated carbon anode. The fabricated asymmetric supercapacitors exhibited very promising electrochemical performances with an excellent combination of high energy density of 103.0 Wh·kg−1 at a power density of 3.0 kW·kg−1, and excellent rate capability—energy densities of about 70.4 and 26.0 Wh·kg−1 were achieved when the average power densities were increased to 26.2 and 133.4 kW·kg−1, respectively. Moreover, an extremely stable cycling life with only 2.7% capacitance loss after 20,000 cycles at a current density of 5 A·g−1 was achieved, which compares very well with the traditional doublelayer supercapacitors.

Facile preparation of PdNi/rGO and its electrocatalytic performance towards formic acid oxidation

A highly dispersed and active PdNi alloy supported on reduced graphene oxide (rGO) was successfully prepared for formic acid electro-oxidation under acidic conditions. The material was prepared by a simultaneous reduction method using NaBH4 as the reductant, followed by annealing in H2 at 500 °C. Different characterization methods verified that H2 annealing at an appropriate temperature had a significant influence on both physiochemical composition and electrocatalytic performance of the synthesized catalysts. H2 annealing at 500 °C facilitated formation of a PdNi alloy without agglomeration of the nano-sized metallic catalyst, while without H2 treatment Ni was found predominantly in the form of Ni(OH)2. Cyclic voltammetry and chromoamperometric testing demonstrated that, when compared to the sample without H2 treatment, PdNi/rGO after H2 annealing exhibited better catalytic activity and stability towards formic acid electro-oxidation. The enhanced performance can be explained by the modification of the electronic structure of Pd by Ni after alloy formation and the large specific surface area and excellent electron conductivity of the rGO support.

Fabrication of FeF3 nanocrystals dispersed into a porous carbon matrix as a high performance cathode material for lithium ion batteries

FeF3/C nanocomposites, where FeF3 nanocrystals had been dispersed into a porous carbon matrix, were successfully fabricated by a novel vapour–solid method in a tailored autoclave. Phase evolution of the reaction between the precursor and HF solution vapour under air and argon gas atmospheres were investigated. The results showed that the air in the autoclave played an important role in driving the reaction to form FeF3. The as-prepared FeF3/C delivered 134.3, 103.2 and 71.0 mA h g−1 of charge capacity at a current density of 104, 520, and 1040 mA g−1 in turn, exhibiting superior rate capability to the bare FeF3. Moreover, it displayed stable cycling performance, with a charge capacity of 196.3 mA h g−1 at 20.8 mA g−1. EIS and BET investigations indicated that the good electrochemical performance can be attributed to the good electrical conductivity and high specific surface area that result from the porous carbon matrix.

Facile Synthesis of Nitrogen and Sulfur Codoped Carbon from Ionic Liquid as Metal-Free Catalyst for Oxygen Reduction Reaction

Developing metal-free catalysts for oxygen reduction reaction (ORR) is a great challenge in the development of fuel cells. Nitrogen and sulfur codoped carbon with remarkably high nitrogen content up to 13.00 at % was successfully fabricated by pyrolysis of homogeneous mixture of exfoliated graphitic flakes and ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bimi][Tf2N]). The exfoliated graphite flakes served as a structure-directing substance as well as additional carbon source in the fabrication. It was demonstrated that the use of graphite flakes increased the nitrogen doping level, optimized the composition of active nitrogen configurations, and enlarged the specific surface area of the catalysts. Electrochemical characterizations revealed that the N and S codoped carbon fabricated by this method exhibited superior catalytic activities toward ORR under both acidic and alkaline conditions. Particularly in alkaline solution, the current catalyst compared favorably to the conventional 20 wt % Pt/C catalyst via four-electron transfer pathway with better ORR selectivity. The excellent catalytic activity was mainly ascribed to high nitrogen doping content, appropriate constitution of active nitrogen configurations, large specific surface area, and synergistic effect of N and S codoping.

Bimetallic organic frameworks derived CuNi/carbon nanocomposites as efficient electrocatalysts for oxygen reduction reaction

Catalysts of oxygen reduction reaction (ORR) play key roles in renewable energy technologies such as metal-air batteries and fuel cells. Despite tremendous efforts, highly active catalysts with low cost remain elusive. This work used metal-organic frameworks to synthesize non-precious bimetallic carbon nanocomposites as efficient ORR catalysts. Although carbon-based Cu and Ni are good candidates, the hybrid nanocomposites take advantage of both metals to improve catalytic activity. The resulting molar ratio of Cu/Ni in the nanocomposites can be finely controlled by tuning the recipe of the precursors. Nanocomposites with a series of molar ratios were produced, and they exhibited much better ORR catalytic performance than their monometallic counterparts in terms of limited current density, onset potential and half-wave potential. In addition, their extraordinary stability in alkaline is superior to that of commercially-available Pt-based materials, which adds to the appeal of the bimetallic carbon nanocomposites as ORR catalysts. Their improved performance can be attributed to the synergetic effects of Cu and Ni, and the enhancement of the carbon matrix.摘要氧还原催化剂在金属空气电池和燃料电池的可再生能源技术中起至关重要的作用. 尽管该方面研究已有很多, 高活性低成本的催化剂的开发仍然十分困难. 本文以金属有机骨架为前驱体, 成功合成出非贵金属铜镍双金属碳基纳米复合物并作为高效的氧还原催化剂. 单金属复合物Cu/C和Ni/C皆具有较好的氧还原催化作用, 铜镍双金属复合物进一步综合了二者优点从而提升了催化性能. 本文所合成的铜镍双金属复合物中的金属比例可通过调整前驱体中的原料配比来准确控制, 所得的一系列金属比例的铜镍双金属碳基纳米复合物在极限电流密度、起始电位和半波电位三个方面都超过了单金属复合物. 此外, 铜镍双金属碳基纳米复合物在碱性环境中具有良好的稳定性且超过了目前最好的氧还原催化材料铂, 大大加强了其作为氧还原催化剂的优势. 铜镍双金属碳基纳米复合物优越的电化学催化性能归功于金属铜和镍以及碳材料基底的协同作用.

Fabrication of LiF/Fe/Graphene nanocomposites as cathode material for lithium-ion batteries.

Homogeneous LiF/Fe/Graphene nanocomposites as cathode material for lithium ion batteries have been synthesized for the first time by a facile two-step strategy, which not only avoids the use of highly corrosive reagents and expensive precursors but also fully takes advantage of the excellent electronic conductivity of graphene. The capacity remains higher than 150 mA h g(-1) after 180 cylces, indicating high reversible capacity and stable cyclability. The ex situ XRD and HRTEM investigations on the cycled LiF/Fe/G nanocomposites confirm the formation of FeF(x) and the coexistence of LiF and FeF(x) at the charged state. Therefore, the heterostructure nanocomposites of LiF/Fe/Graphene with nano-LiF and ultrafine Fe homogeneously anchored on graphene sheets could open up a novel avenue for the application of iron fluorides as high-performance cathode materials for lithium-ion batteries.