Latest ArticlesHierarchical porous carbon (HPC) from bituminous coal was designed and synthesized through pyrolysis foaming and KOH activation. The obtained HPC (NCF-KOH) were characterized by a high specific surface area (SBET) of 3472.41 m2/g, appropriate mesopores with Vmes/Vtotal of 57%, and a proper amount of surface oxygen content (10.03%). This NCF-KOH exhibited a high specific capacitance of 487 F/g at 1.0 A/g and a rate capability of 400 F/g at 50 A/g based on the three-electrode configuration. As an electrode for a symmetric capacitor, a specific capacitance of 299 F/g at 0.5 A/g was exhibited, and the specific capacitance retained 96% of the initial capacity at 5 A/g after 10,000 cycles. Furthermore, under the power density of 249.6 W/kg in 6 mol/L KOH, a high energy density of 10.34 Wh/kg was obtained. The excellent charge storage capability benefited from its interconnected hierarchical pore structure with high accessible surface area and the suitable amount of oxygen-containing functional groups. Thus, an effective strategy to synthesize HPC for high-performance supercapacitors serves as a promising way of converting coal into advanced carbon materials.
Surfactants with polyoxometalates (POMs) as polar head groups have shown fascinating self-assembly behaviors and various functional applications. However, self-assembly them into reverse micelles is still challenging owing to the large molecular size and intermolecular strong electrostatic repulsions of POM heads. In this work, a zwitterionic POM-based surfactant was synthesized by covalently grafting two cationic long alkyl tails onto the lacunary site of [PW11O39]7−. With decreased electrostatic repulsions and increased hydrophobic effect, the POM-based reverse micelles with an average diameter of 5 nm were obtained. Interestingly, when these reverse micelles were applied for catalyzing the oxidation of styrene, an unprecedented β-hydroxyl peroxide compound of 2-hydroxyl-2-phenylethan-1-tert-butylperoxide was produced in high selectivity of 95.2%. In comparison, the cetyltrimethylammonium electrostatically encapsulated POMs mainly generated the epoxides or 1, 2-diols. A free radical mechanism was proposed for the oxidation reaction catalyzed by the zwitterionic POM surfactants.
Amphiphilic molecules adsorbed at the interface could control the orientation of liquid crystals (LCs) while LCs in turn could influence the distributions of amphiphilic molecules. The studies on the interactions between liquid crystals and amphiphilic molecules at the interface are important for the development of molecular sensors. In this paper, we demonstrate that the development of smectic LC ordering from isotropic at the LC/water interface could induce local high-density distributions of amphiphilic phospholipids. Mixtures of liquid crystals and phospholipids in chloroform are first emulsified in water. By fluorescently labeling the phospholipids adsorbed at the interface, their distributions are visualized under fluorescent confocal microscope. Interestingly, local high-density distributions of phospholipids showing a high fluorescent intensity are observed on the surface of LC droplets. Investigations on the correlation between phospholipid density, surface tension and smectic LC ordering suggest that when domains of smectic LC layers nucleate and grow from isotropic at the LC/water interface as chloroform slowly evaporates at room temperature, phospholipids transition from liquid-expanded to liquid-condensed phases in response to the smectic ordering, which induces a higher surface tension at the interface. The results will provide an important insight into the interactions between liquid crystals and amphiphilic molecules at the interface.
Organic room temperature phosphorescent (ORTP) materials provide an exciting research direction for phosphorescent oxygen (O2) sensors due to their high sensitivity and rapid response to O2. However, most pure ORTP materials are tightly-packed aromatic compound crystals in a face-to-face manner, which largely prohibits effective O2 diffusion for sensing. Thus, how to solve this contradiction still faces huge challenges. Here, the use of organic phosphorescent indicator carbon dots (CDs), inorganic matrix layered double hydroxides (LDHs) and polymers (PVA) successfully prepared an ultra-long RTP composite film whose phosphorescence decay intensity is linearly related to O2 concentration. More importantly, the use of the abundant O2 defects (Vo) on the surface of the inorganic matrix LDHs to adsorb O2, which further accelerates the phosphorescence quenching of the thin film and improves the O2 response. This strategy will provide the possibility to develop high-sensitivity phosphorescent O2 sensors from a new perspective.
It is of great importance to directionally construct advanced carbon host to achieve high-performance carbon/sulfur cathodes for lithium sulfur batteries (LSBs). Herein, we report a unique hollow pumpkin-like carbon with notable rich-wrinkle microstructure and intrinsically dual doping with N & P elements via a facile annealing process of Aspergillus niger spore. Furthermore, highly conductive polar absorbents, TiC nanoparticles, are in situ implanted into the above Aspergillus niger spore carbon (ANSC) by carbothermal reaction, accordingly forming high-performance ANSC/TiC composite host for sulfur. Impressively, TiC nanoparticles play dual roles of not only pore formation in ANSC matrix but also enhancement of chemical absorption with polysulfides. With the positive synergistic effect between N & P co-doped ANSC matrix and TiC polar absorbent, the designed ANSC/TiC-S cathodes show unique advantages including larger accommodation space for sulfur, higher surface area, enhanced conductivity and better chemical absorption with soluble polysulfide intermediates. Consequently, the ANSC/TiC-S cathodes are endowed with good rate performance (496 mAh/g at 0.5 C) and enhanced long-term cycling stability (736 mAh/g with a capacity retention of 78.8% at 0.1 C after 100 cycles). Our research opens a new door to controllably design advanced composite cathodes from microorganisms for application in lithium sulfur batteries.
Green hydrogen production and CO2 fixation have been identified as the fundamental techniques for sustainable economy. The open challenge is to develop high performance catalysts for hydrogen evolution reaction (HER) and CO2 electroreduction (CO2ER) to valuable chemicals. Under such context, this work reported computational efforts to design promising electrocatalyst for HER and CO2ER based on the swarm-intelligence algorithm. Among the family of transition-metal phosphides (TMPs), Pt2P3 monolayer has been identified as excellent bifunctional catalysts due to high stability, excellent conductivity and superior catalytic performance. Different from typical d-block catalysts, p-band center presented by P atoms within Pt2P3 monolayer plays the essential role for its reactivity towards HER and CO2ER, underlining the key value of p-electrons in advanced catalyst design and thus providing a promising strategy to further develop novel catalysts made of p-block elements for various energy applications.
The unveiling of MOF growth mechanism is hampered by the lack of fundamental knowledge about the very early stage of nucleation, especially the form and ratio of molecular species in the solution for crystal growth. Herein, we report the detection of growth species for a series of MOFs with mono-linker, Cu-MOF-2-BDC and Cu-MOF-2-NDC, and two linkers, MTV-MOF-2-(C4H4), by high resolution ESI-MS, where a large variety of Cu-containing species are identified unambiguously. The solvent molecules such as H2O, methanol and DMF participate in the formation of these species, other than ethanol. Furthermore, in the growth solution of MTV-MOF-2-(C4H4), growth species containing two different organic linkers are observed. The feeding ratio is not the only factor controlling the distribution of growth species for MTV-MOFs, but also the solvent involves in coordination, an aspect usually overlooked previously.
Constructing molecule@support composites is an attractive strategy to realize heterogeneous molecular electrocatalysis. Herein, we synthesized metal-organic framework (MOF)-supported molecular catalysts for hydrogen evolution and oxygen reduction reaction (HER/ORR). Ligand exchange strategy was used to prepare molecule@support hybrids due to the same functional group. A series of hybrids were obtained using Co porphyrin (1) and different MOFs including MIL-88(Fe), MOF-5(NiCo) and UIO-66(Zr). The 1@MOF-5(NiCo) had the best HER and ORR activity compared with 1@MIL-88(Fe) and 1@MOF-5(NiCo). These hybrids also exhibited tunable selectivity for ORR with four-electron process, which can be attributed to the synergistic effect of porphyrin molecules and MOFs. This work provides a possibility for molecular catalysts to improve activity of HER and tune selectivity of ORR.
Developing efficient and inexpensive OER electrocatalysts is a challenge for overall water splitting. Herein, the heterostructured FeCo LDH@NiCoP/NF nanowire arrays with high performance were rationally designed and prepared using an interface engineering strategy. Benefitting from the special heterostructure between FeCo LDH and NiCoP, the as-synthesized FeCo LDH@NiCoP/NF electrocatalyst exhibits outstanding OER performance with an exceptionally low overpotential of 206 mV to achieve 20 mA/cm2 current density in an alkaline electrolyte. Importantly, a cell constructed using the FeCo LDH@NiCoP/NF electrocatalyst as cathode and anode just needs a voltage of 1.48 V at 10 mA/cm2, and shows excellent stability over 80 h. Experimental and theoretical results verified that the introduction of NiCoP efficiently regulates the electronic structure of FeCo LDH, which tremendously boosts the conductivity and intrinsic catalytic activity of FeCo LDH@NiCoP/NF electrocatalyst. The present work provides guidance for the preparation of other efficient and cheap electrocatalytic materials.
The large overpotential for conventional Li-O2 batteries is an enormous challenge, which impedes their practical application. Here, we prepare a defective TiO2 (Ov-TiO2) hollow nanosphere as photo-electrocatalyst for photo-assisted Li-O2 batteries to reduce the overpotential. Under illumination, the oxygen vacancies as a charge separation center contribute to the separation of electrons and holes. The generated electrons could promote reducing O2 to Li2O2 during oxygen reduction reaction (ORR) process, while the generated holes are beneficial to Li2O2 decomposition during oxygen evolution reaction (OER) process. Additionally, the proper concentration of oxygen vacancies will decrease the recombination rate between electrons and holes. The photo-assisted Li-O2 batteries with Ov-TiO2-650 exhibit advanced performances, such as the low overpotential (0.70 V), the fine rate capability, and the considerable reversibility accompanied with the formation/decomposition of Li2O2. We expect that these results could open a new mind to design of highly efficient photo-electrocatalysts for photo-assisted Li-O2 battery.
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