Electrochemical activation tactic can be adopted to boost electrochemical performance of electrodes by adjusting the composition and microstructure. Herein, venus flytrap-like CoP nanostructures and ...corresponding Co3O4 precursor are synthesized on nickel foam (NF) framework, and the electrochemical activation mechanisms of CoP and Co3O4 are investigated in KOH electrolyte. When endured for 100 CV cycles, the activated CoP exhibits a 3D framework structure consisted of thin nanosheets, and the discharge capacity enhances to 1536 C g−1 at 1 A g−1 from initial capacity of 663 C g−1. The enhanced performance is due to the composition transition from upper CoP and beneath NiP to NiCo-hydroxides and NiCoOOH, and the microstructure transition from nanoneedles to 3D framework structure stacked by thin nanosheets. Different from the transition mechanism of NF/CoP, seldom microstructure transitions are occurred for the Co3O4 precursor, only involving the change of nanoneedle diameter. The activation of Co3O4 induces a limited capacity enhancement from 242 to 623 C g−1, due to a simple transition from oxides to oxyhydroxides. The application performance of NF/CoP is investigated by assembling asymmetric supercapacitor with NF/AC. The device releases a discharge capacitance of 137 F g−1 at 1 A g−1, and the capacitance retention is 77.4% when cycling for 5000 cycles. The energy density is 48.7 W h kg−1 at 804.4 W kg−1. Compared with existing Co-based phosphides, activated NF/CoP electrode exhibits an obvious performance advantage in supercapacitors.
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•Phase transition of NF/CoP and corresponding Co3O4 precursor are disclosed in KOH.•CV activation induces significant structure and composition transitions of NF/CoP.•Activated NF/CoP presents the highest capacitance of 3072 F g−1 at 1 A g−1.•Seldom microstructure transitions of NF/Co3O4 induces a limited performance enhancement.
•System performance model was established considering working fluid charge.•High-speed closed-cycle turbo-refrigerator for −120 °C deep freezing was tested.•Characteristics of speed control and ...variable working fluid charge were studied.•Increasing speed while reducing working fluid charge enhances performance.
Compared to open-cycle turbo-refrigerators that have been extensively studied, very limited research has been done on the operating characteristics of closed-cycle turbo-refrigerators for deep freezing. Particularly, working fluid charge, as a critical operating condition, has not been considered in existing studies, and therefore a more comprehensive study on the operating characteristics of the closed-cycle turbo-refrigerator is needed. In this work, a system performance model was developed for the first time considering the working fluid charge in turbo-refrigerators, providing a great advantage in fully characterizing the system off-design operations, and a newly designed prototype for deep freezing at −120 °C was tested for model validation. Furthermore, a novel optimized operating strategy combining variable speed and working fluid charge was proposed to improve system performance. The tests demonstrated the prototype’s adaptability to a refrigeration temperature range from −125.8 °C to −62.9 °C and showed a system efficiency of 0.079 corresponding to the design point. Test data also validated the proposed model well with deviations below 15 % throughout the operating range. Further analysis shows that active speed control significantly expands the system operating range, while system efficiency penalties are imposed when dealing with reduced cooling capacities (i.e., partial-load demands) at given refrigeration temperatures by lowering the speed. Reducing the working fluid charge was found to increase system efficiency, and reason for the system efficiency improvement was revealed to be an increase in recuperator effectiveness. Combined increasing speed with reducing working fluid charge is suggested as an optimized operational strategy, especially for partial-load applications with reduced cooling capacity. By using the optimized strategy, a 30.5 % increase in system efficiency can be achieved for 15 %-reduced cooling at −120 °C.
Pursuing cost-effective water-splitting catalysts is still a significant scientific challenge to produce renewable fuels and chemicals from various renewable feedstocks. The construction of ...controllable binder-free nanostructures with self-standing holey and ultrathin nanosheets is one of the promising approaches. Herein, by employing a combination of the potentiodynamic mode of electrodeposition and low-temperature phosphidation, three-dimensional (3D) holey CoP ultrathin nanosheets are fabricated on a carbon cloth (PD-CoP UNSs/CC) as bifunctional catalysts. Electrochemical tests show that the PD-CoP UNSs/CC exhibits outstanding hydrogen evolution reaction performance at all pH values with overpotentials of 47, 90, and 51 mV to approach 10 mA cm–2 in acidic, neutral, and alkaline media, respectively. Meanwhile, only a low overpotential of 268 mV is required to drive 20 mA cm–2 for the oxygen evolution reaction in alkaline media. Cyclic voltammetry and impedance studies suggest the enhanced performance is mainly attributed to the unique 3D holey ultrathin nanosheets, which could increase the electrochemically active area, facilitate the release of gas bubbles from electrode surfaces, and improve effective electrolyte diffusion. This work suggests an efficient path to design and fabricate non-noble bifunctional electrocatalysts for water splitting at a large scale.
In order to advance the commercialization of rechargeable Li-air batteries, it is of importance to explore cathode catalyst with efficient catalytic activity. Transition metal oxides have poor ...electrical conductivity, while cobalt phosphide has excellent electrical conductivity and large specific surface area. Nevertheless, its application in organic Li-air batteries has been much less studied, and the electrocatalytic activity desires to be further elevated. Here, CoP/Co2P heterojunction composite with higher polarity was fabricated. The discharge product of high-polarity CoP/Co2P had a new porous box-like morphology, which was easy to be decomposed and exposed more active sites. The highly polar CoP/Co2P heterostructure composite had homogeneous pores, the synergistic effect existed between CoP and Co2P, and the discharge product was porous box mixed with Li2O2 and LiOH, which made CoP/Co2P achieve high specific capacity of 14632 mAh/g and cycle stably 161 times when used as air electrode cathode catalyst. This work furnished a thought for the construction of cathode catalysts with efficient catalytic activity for Li-air batteries.
Construction of highly polar CoP/Co2P heterojunction materials: improving performance by turning the composition and morphology of discharge products. Display omitted
The nanoparticles of CoPx anchoring to honeycomb-like P,N co-doped 3D reticular porous carbon framework was designed and fabricated by using PAN as nitrogen-containing carbon source and hypophosphite ...as P source. This electrocatalyst shows excellent sensing performance for nitrite, originating from the unique multi-level porosity and hierarchical connectivity of P,N co-doped carbon network, and superb electrocatalytic activity of uniformly dispersed CoPx NPs.
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•Novel nanocomposite of CoPx embedded into 3D P,N doped carbon framework was proposed.•Encapsulating CoPx into porous carbon framework enhance electrocatalytic activity.•The nanocomposite has both unique 3D porous structure and hierarchical connectivity.•Well structural virtues and synergistic effect endow high nitrite sensing property.•Acceptable recovery in real sample indicated its real application value.
An assembly and self-template strategy is presented for the synthesis of cobalt phosphide nanoparticles (CoPx, x = 1, 2) embedded into 3D phosphorus/nitrogen co-doped reticular porous carbon frameworks (denoted as CoPx@P,N–RPCs) utilizing polyacrylonitrile (PAN) as the in situ nitrogen doping carbon source and hypophosphite as phosphorus source via hydrothermal method and subsequent phosphorization. The obtained CoPx@P,N–RPCs nanocomposite possesses the inherent features of both unique 3D porous structure and hierarchical connectivity, providing highly efficient pathways for electron, ion, and mass transport. The unique P,N co-doped carbon network confines nanostructural CoPx into the microstructural carbon network, which prevents them from aggregating, improves the conductivity of CoPx, meanwhile alleviates large volume expansion/contraction effect, thus results in high electrochemical performance and cycling durability. Benefiting from its unique structural advantages, the CoPx@P,N–RPCs nanocomposite exhibits excellent electrochemical performance for nitrite (NO2–) detection with a wide linear range of 10 nM to 1.184 mM, a low detection limit of 5 nM, and a very high stability, which is better than most nitrite sensors reported previously. Importantly, the nitrite level can be determined by the resulting sensor in food and drinking water with excellent recoveries, implying its feasibility for realistic application.
Secretory proteins traffic from the ER to the Golgi via COPII-coated transport vesicles. The five core COPII proteins (Sar1p, Sec23/24p, and Sec13/31p) act in concert to capture cargo proteins and ...sculpt the ER membrane into vesicles of defined geometry. The molecular details of how the coat proteins deform the lipid bilayer into vesicles are not known. Here we show that the small GTPase Sar1p directly initiates membrane curvature during vesicle biogenesis. Upon GTP binding by Sar1p, membrane insertion of the N-terminal amphipathic α helix deforms synthetic liposomes into narrow tubules. Replacement of bulky hydrophobic residues in the α helix with alanine yields Sar1p mutants that are unable to generate highly curved membranes and are defective in vesicle formation from native ER membranes despite normal recruitment of coat and cargo proteins. Thus, the initiation of vesicle budding by Sar1p couples the generation of membrane curvature with coat-protein assembly and cargo capture.
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•Hollow CoP nanoparticles in CNTs are prepared in virtue of the Kirkendall effect.•Discrete active particles in CNTs alleviates the pulverization and aggregation.•CNTs improves the ...intrinsic conductivity, and stabilizes the active CoP-NPs.•1D nanotube network facilitates the rapid Na ion/electron transport.
We report a facile strategy to prepare carbon nanotubes embedded with hollow CoP nanoparticles arrays (H-CoP-NPs@CNTs) on flexible carbon cloth through hydrothermal synthesis, carbothermal reduction and phosphorization. The unique H-CoP-NPs@CNTs as free-standing sodium ion battery anodes exhibit remarkable electrochemical performances a specific capacity of 965.6 mA h g−1 for the 1st cycle and 63% retained capacity after rates test and 100 cycles at 100 mA g-1. The capacity retention rate is as high as 94.3% after different current sweeps. The excellent electrochemical performance can be attributed to the unique 1D hybrids nanoarrays structures, in which the pore inside and between hollow CoP nanoparticles provide more free spaces and active sites for favorable Na+ insertion/extraction, and the CNTs nanoarrays on flexible carbon cloth are able to improve the conductivity and maintain the structural integrity. Moreover, the 1D hybrids network also makes it favorable rapid ion/electron transport and enhanced rate performance.
Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) have been considered as two critical processes in the field of electrocatalytic water-splitting for hydrogen production and fuel ...cells. However, the sluggish reaction kinetics of HER and ORR required efficient electrocatalyst such as Pt to promote such process. Transition metal phosphides (TMPs) exhibit great potential to replace noble metal electrocatalysts to accelerate HER and ORR due to their high activity and easy availability. Herein, a highly-efficient bifunctional CoP electrocatalyst for HER and ORR, featuring a unique core-shell structure decorated on nitrogen-doped carbon matrix was designed and constructed via etching a cobalt-based zeolitic imidazolate framework (ZIF-67) with phytic acid (PA) followed by pyrolysis treatment (PA-ZIF-67–900). Experimental results revealed that the pure-phase single-crystalline CoP exhibited outstanding electrocatalytic performance in HER and ORR, superior to Co(PO3)2 in PA-ZIF-67–700, hybrid phase of Co(PO3)2 and CoP in PA-ZIF-67–800 and Co2P-doped CoP in PA-ZIF-67–1000. To reach the current density of 10 mA/cm2 the as-synthesized CoP required an overpotential of 120 mV for HER in 1 mol/L KOH and half-wave potential of 0.85 V in O2-saturated 0.1 mol/L KOH. This work present new clue for construction of efficient and bifunctional electrocatalyst in the field of energy conversion and storage
A phase-mediated cobalt phosphide with unique core-shell architecture was synthesized which could serve as efficient and bifunctional electrocatalyst for hydrogen evolution and oxygen reduction reaction. Display omitted
•Friction waste heat utilization improves Stirling water dispenser performance.•Annular water jackets are used to redirect the piston's waste heat.•COP, cooling and heating load, charging pressure, ...and speed are discussed.•Water jackets improve heating and cooling loads by about 91% and 45%.
Water dispensers are considered essential. So, water dispensers that use vapor-compression urgently need more energy-saving and environmentally friendly alternatives. Stirling water dispensers are a suitable option. However, the waste heat generated via friction between the pistons and their cylinders decreases the cooling load and power consumption. The present work uses the waste heat of both piston friction via water jackets to save energy and improve Stirling water dispenser performance. The result indicates that the heating and cooling loads of the present water dispenser are increased by about 2952 W and 834 W using the waste heat of both pistons at 1200 rpm. The increase of water flow rate within water jackets increases the heating and cooling loads due to the increased absorption of frictional heat. The comparison shows that the current water dispenser reveals an average increase in cooling load of up to 400 percent at low speeds and 61 percent at high speeds, and an increase in heating load of up to 390 percent at low speeds and 28 percent at high speeds.
Proteins synthesized within the endoplasmic reticulum (ER) are exported from ER exit sites via coat protein complex II (COPII)-coated vesicles. Although the mechanisms of COPII-vesicle formation at ...the ER exit sites are highly conserved among species, vertebrate cells secrete a wide range of materials, including collagens and chylomicrons, which form bulky structures within the ER that are too large to fit into conventional carriers. Transport ANd Golgi Organization 1 (TANGO1) was initially identified as a cargo receptor for collagens but has been recently rediscovered as an organizer of ER exit sites. We would like to review recent advances in the mechanism of large cargo secretion and organization of ER exit sites through the function of TANGO1.
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