Xu Liu

Bio: Xu Liu is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: X-ray photoelectron spectroscopy & Electrolyte. The author has an hindex of 26, co-authored 52 publications receiving 1844 citations. Previous affiliations of Xu Liu include Yunnan University.

Nanoparticle cluster gas sensor: Pt activated SnO2 nanoparticles for NH3 detection with ultrahigh sensitivity.

Abstract: Pt activated SnO2 nanoparticle clusters were synthesized by a simple solvothermal method. The structure, morphology, chemical state and specific surface area were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and N2-sorption studies, respectively. The SnO2 nanoparticle cluster matrix consists of tens of thousands of SnO2 nanoparticles with an ultra-small grain size estimated to be 3.0 nm. And there are abundant random-packed wormhole-like pores, caused by the inter-connection of the SnO2 nanoparticles, throughout each cluster. The platinum element is present in two forms including metal (Pt) and tetravalent metal oxide (PtO2) in the Pt activated SnO2 nanoparticle clusters. The as-synthesized pure and Pt activated SnO2 nanoparticle clusters were used to fabricate gas sensor devices. It was found that the gas response toward 500 ppm of ammonia was improved from 6.48 to 203.44 through the activation by Pt. And the results indicate that the sensor based on Pt activated SnO2 not only has ultrahigh sensitivity but also possesses good response–recovery properties, linear dependence, repeatability, selectivity and long-term stability, demonstrating the potential to use Pt activated SnO2 nanoparticle clusters as ammonia gas sensors. At the same time, the formation mechanisms of the unique nanoparticle clusters and highly enhanced sensitivity are also discussed.

Challenges and Strategies for High-Energy Aqueous Electrolyte Rechargeable Batteries.

Abstract: Aqueous rechargeable batteries are becoming increasingly important to the development of renewable energy sources, because they promise to meet cost-efficiency, energy and power demands for stationary applications. Over the past decade, efforts have been devoted to the improvement of electrode materials and their use in combination with highly concentrated aqueous electrolytes. Here the latest ground-breaking advances in using such electrolytes to construct aqueous battery systems efficiently storing electrical energy, i.e., offering improved energy density, cyclability and safety, are highlighted. This Review aims to timely provide a summary of the strategies proposed so far to overcome the still existing hurdles limiting the present aqueous batteries technologies employing concentrated electrolytes. Emphasis is placed on aqueous batteries for lithium and post-lithium chemistries, with potentially improved energy density, resulting from the unique advantages of concentrated electrolytes.

A highly sensitive VOC gas sensor using p-type mesoporous Co3O4 nanosheets prepared by a facile chemical coprecipitation method

Abstract: Mesoporous Co3O4 nanosheets were synthesized via a facile chemical coprecipitation method without using of surfactant or template. Mesoporous Co3O4 material was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) to examine the morphology and microstructure to find out the cause for the highly sensitive sensing behavior. SEM and TEM analyses reveal that the Co3O4 nanosheets consisting of nanoparticles prepared here are porous in nature, with average pore sizes of approximately 50 nm or smaller. The sensor based on porous Co3O4 nanaosheets was used for detecting the volatile organic compounds (VOCs) including ethanol, methanol, acetone, isopropanol, formaldehyde and n-butanol. The results demonstrate that the sensor shows potential for detecting VOCs. The significant improvement of sensitivity is attributed to the porous structure, good contact and relatively small crystal size. The gas sensor shows high response values, fast response and recovery times towards VOCs. So, porous Co3O4 nanosheets are considered as promising sensor material for detecting VOCs.

A high response butanol gas sensor based on ZnO hollow spheres

Abstract: ZnO hollow spheres with high crystallinity were prepared successfully via a simple template process using ZnCl 2 , carbamide and polystyrene spheres (PSS) as raw materials. The structural and morphological characterizations of the samples were carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Indirect-heating sensor using ZnO hollow spheres as sensing materials was fabricated on an alumina tube with Au electrodes and Pt wires. The gas sensing properties of the as-synthesized ZnO hollow spheres for n -butanol were investigated. It is shown that the sensor exhibited good sensing performances, characterized by high response, very short response time, and stability to n -butanol gas at operating temperature of 385 °C. These results indicate that the ZnO hollow spheres are highly promising candidates for practical detectors for n -butanol.

Nonaqueous synthesis of Ag-functionalized In2O3/ZnO nanocomposites for highly sensitive formaldehyde sensor

Abstract: In this work, Ag-functionalized In 2 O 3 /ZnO (IZO) nanocomposites with various contents were successfully fabricated by a nonaqueous route. The ZnO and In 2 O 3 showed separated phases and different sizes deriving from the faster growth of ZnO than In 2 O 3 using benzyl alcohol as the oxygen supplying agent. To demonstrate the usage of such Ag-functionalized IZO, the gas sensors have been fabricated and investigated for formaldehyde (HCHO) detection. The results reveal that the as-synthesized 3 wt% Ag-functionalized IZO samples exhibit high response of about 842.9 towards 2000 ppm HCHO at operating temperature of 300 °C. All sensors show rapid response and recovery. The highly sensing properties are attributed to the synergistic effects arising from the presence of these multiple functional materials, i.e. the special structure of IZO nanocomposites, the formation of the heterojunctions, the influence of Ag nanoparticles, and the mutual doping effect.

Issues and opportunities facing aqueous zinc-ion batteries

Abstract: Zinc-ion batteries built on water-based electrolytes featuring compelling price-points, competitive performance, and enhanced safety represent advanced energy storage chemistry as a promising alternative to current lithium-ion battery systems. Attempts to develop rechargeable aqueous zinc-ion batteries (ZIBs) can be traced to as early as the 1980s; however, since 2015, the research activity in this field has surged throughout the world. Despite the achievements made in exploring electrode materials so far, significant challenges remain at the material level and even on the whole aqueous ZIBs system, leading to the failure of ZIBs to meet commercial requirements. This review aims to discuss how to pave the way for developing aqueous ZIBs. The current research efforts related to aqueous ZIBs electrode materials and electrolytes are summarized, including an analysis of the problems encountered in both cathode/anode materials and electrolyte optimization. Some concerns and feasible solutions for achieving practical aqueous ZIBs are discussed in detail. We would like to point out that merely improving the electrode materials is not enough; synergistic optimization strategies toward the whole battery system are also deeply needed. Finally, some perspectives are provided on the subsequent optimization design for further research efforts in the aqueous ZIB field.

Active Materials for Aqueous Zinc Ion Batteries: Synthesis, Crystal Structure, Morphology, and Electrochemistry

Abstract: Aqueous zinc ion batteries (ZIBs) are truly promising contenders for the future large-scale electrical energy storage applications due to their cost-effectiveness, environmental friendliness, intri...

Superconcentrated Electrolytes for a High-Voltage Lithium-Ion Battery

Abstract: Finding a viable electrolyte for next-generation 5 V-class lithium-ion batteries is of primary importance. A long-standing obstacle has been metal-ion dissolution at high voltages. The LiPF6 salt in conventional electrolytes is chemically unstable, which accelerates transition metal dissolution of the electrode material, yet beneficially suppresses oxidative dissolution of the aluminium current collector; replacing LiPF6 with more stable lithium salts may diminish transition metal dissolution but unfortunately encounters severe aluminium oxidation. Here we report an electrolyte design that can solve this dilemma. By mixing a stable lithium salt LiN(SO2F)2 with dimethyl carbonate solvent at extremely high concentrations, we obtain an unusual liquid showing a three-dimensional network of anions and solvent molecules that coordinate strongly to Li(+) ions. This simple formulation of superconcentrated LiN(SO2F)2/dimethyl carbonate electrolyte inhibits the dissolution of both aluminium and transition metal at around 5 V, and realizes a high-voltage LiNi0.5Mn1.5O4/graphite battery that exhibits excellent cycling durability, high rate capability and enhanced safety.

Design Strategies for Vanadium-based Aqueous Zinc-Ion Batteries

Abstract: Aqueous zinc-ion batteries (ZIBs) are considered promising energy storage devices for large-scale energy storage systems as a consequence of their safety benefits and low cost. In recent years, various vanadium-based compounds have been widely developed to serve as the cathodes of aqueous ZIBs because of their low cost and high theoretical capacity. Furthermore, different energy storage mechanisms are observed in ZIBs based on vanadium-based cathodes. In this Minireview, we present a comprehensive overview of the energy storage mechanisms and structural features of various vanadium-based cathodes in ZIBs. Furthermore, we discuss strategies for improving the electrochemical performance of vanadium-based cathodes; including, insertion of metal ions, adjustment of structural water, selection of conductive additives, and optimization of electrolytes. Finally, this Minireview offers insight into potential future directions in the design of innovative vanadium-based electrode materials.