Nanoporous Pt-Pd nanoflowers supported on carbon exhibited significantly improved ORR activity and stability under acidic conditions.
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•Pt-Pd/C nanoflowers were synthesized using a ...simple wet-chemical method.•The Pd-core nanoparticles were covered with a Pt-shell layer.•The increase in the activity of the nanoflowers catalysts was attributed to the distinctive morphologies.•The catalysts developed exhibited excellent activity as well as long-term stability for ORR.
Flower-shaped Pt-Pd nanostructures supported on carbon (Pt-Pd/C) were successfully synthesized by simple wet-chemical processing by controlling the rate of reduction of a dissolved metal precursor. L-ascorbic acid (AA) was employed as a green and clean reductive agent for the coreduction of PtCl62− and PdCl42− in an aqueous solution. The electrocatalytic activity of nanoporous Pt-Pd/C on the oxygen reduction reaction (ORR) was investigated by rotating disk electrode voltammetry in a 0.1 M HClO4 solution. In particular, the Pt77-Pd23/C catalyst showed surpassing ORR activity and acceptable stability under acidic conditions compared to the commercial Pt electrocatalyst. The outstanding electrocatalytic activity was achieved by a combination of the high surface area of flower-like nanostructures and the bimetallic synergetic effect. The morphology, composition and structure of the Pt-Pd/C nanoflowers were confirmed by scanning transmission electron microscopy (STEM), TEM, X-ray photoelectron spectroscopy and X-ray diffraction. Overall, the Pt-Pd/C bimetallic nanostructures are expected to become promising cathode material in fuel cells to replace monometallic Pt ones.
Alloy ribbons of Ni50−xCoxMn50−yAly (x = 5, 6, 7, 8 and 9; y = 18 and 19) were fabricated by using melt-spinning method. By varying Co and Al concentrations, the formation of crystalline phases, ...structural transformations and magnetic phase transitions can be tuned as desired. With high Al and Co concentrations, only a ferromagnetic-paramagnetic (FM-PM) transition of the austenitic phase occurs in the range of 350–450 K. While there is an additional weak ferromagnetic- ferromagnetic (WFM-FM) transition corresponding to the martensitic-austenitic (M-A) structural transformation for the ribbons with low Al and Co concentrations. The M-A transformation temperature of the alloy ribbons can be obtained in the range of 150–360 K. An anomalous change in structure and magnetic properties was observed in the ribbon sample with Co and Al concentrations of 8 and 18 at%, respectively. The external magnetic field has a pronounced effect on the M-A transformation and tends to shift this process towards lower temperatures.
•Structure and magnetic properties of Ni50−xCoxMn50−yAly rapidly solidified alloys.•Influence of Co and Al contents on structural transformation and magnetic transition.•Coexistence of different crystalline phases in Heusler magnetic shape memory alloys.•Tuning structural transformation and magnetic transition of Ni-Co-Mn-Al alloys.•Transformation of metamagnetic phase in Ni-Co-Mn-Al rapidly solidified alloys.
The development of non-precious trimetallic electrocatalysts exhibiting high activity and stability is a promising strategy for fabricating efficient electrocatalysts for the oxygen evolution ...reaction (OER). In this study, trimetallic nitrogen-incorporated CoNiFe (N-CoNiFe) was produced to solve the low OER efficiency using a facile co-precipitation method in the presence of ethanolamine (EA) ligands. A series of CoNiFe catalysts at different EA concentrations were also investigated to determine the effects of the ligand in the co-precipitation of a trimetallic system. The introduction of an optimized EA concentration (20 mM) improved the electrocatalytic performance of N-CoNiFe dramatically, with an overpotential of 318 mV at 10 mA cm
−2
in 1.0 M KOH and a Tafel slope of 72.2 mV dec
−1
. In addition, N-CoNiFe shows high durability in the OER process with little change in the overpotential (
ca.
16.0 mV) at 10 mA cm
−2
after 2000 cycles, which was smaller than that for commercial Ir/C (38.0 mV).
A trimetallic nitrogen-incorporated CoNiFe exhibited good catalytic properties toward the oxygen evolution reaction,
e.g.
, high stability and low overpotential (318 mV at 10 mA cm
−2
).
This paper reports the facile and scalable synthesis of hybrid N-doped carbon quantum dots/multi-walled carbon nanotube (CD/CNT) composites, which are efficient alternative catalysts for the oxygen ...reduction reaction (ORR) in fuel cells. The N-doped CDs for large-scale production were obtained within 5 minutes
via
a one-step polyol process using ethylenediamine (ED) in the presence of hydrogen peroxide as an oxidizing agent. For comparison, different CDs were also prepared using ethylene glycol (EG) and ethanolamine (EA) in the same manner. Physicochemical characterization suggested the successful formation of a CD(ED)/CNT hybrid without individual CD(ED)s and CNTs. The N-doped CD(ED)/CNT catalyst exhibited excellent electrocatalytic activity in an alkaline solution compared to other composites (CD(EG)/CNT and CD(EA)/CNT). The Tafel slope (−60.9 mV dec
−1
) and durability (∼9.1% decay over 10 h) for CD(ED)/CNT were superior to high-performance Pt/C catalysts. The electrochemical double-layer capacitance on the CD(ED)/CNT hybrid showed apparent improvement of the active surface area because of N-doping and highly decorated CDs on the CNT wall. These results provide an innovative approach for the potential application of all carbon hybrid structures in electrocatalysis.
The ORR measurements showed that the CD(ED)/CNT catalyst was superior to CD(EG)/CNT and CD(EA)/CNT. They even surpassed the activity of commercial Pt/C in terms of durability, Tafel slope, and MeOH tolerance.
This paper introduces a facile one-step process to synthesize highly interconnected nanoporous Ir-Pd alloys supported on carbon that exhibit excellent bifunctional electrocatalytic activities for ...both the oxygen reduction and oxygen evolution reactions with reasonable stability in alkaline electrolytes. Nanoporous Pd networks with crystalline {111} faces were shown experimentally to serve mainly as active sites for the oxygen reduction reaction, whereas the Ir nanoparticles incorporated in the Pd nanoframe networks, where the optimized Ir:Pd ratio was 0.23:0.77 (n = 10), were responsible for the oxygen evolution reaction. Such three-dimensional architectures provide a high density of active sites for the oxygen electrochemical reaction and facilitate electron transport. More importantly, the nanoporous Ir-Pd alloy nanocomposites exhibited similar stability for the oxygen reduction reaction but superior catalytic activity to the commercial Pd catalyst in alkaline solutions. In addition, the materials were also highly active for the oxygen evolution reaction, e.g., a small overpotential at 10 mA cm−2 (1.628 V vs. reversible hydrogen electrode), making it a high-performance bifunctional catalyst for both the oxygen electrochemical reaction. Rotating ring-disk electrode measurements showed that the oxygen reduction and oxygen evolution reactions on the Ir-Pd catalysts proceeded predominantly through the desired 4-electron pathway.
A highly active bifunctional electrocatalyst for the oxygen reduction and evolution reactions was developed based on a highly interconnected nanoporous Ir-Pd bimetallic alloy network. Display omitted
•Facile one-step synthesis of a nanoporous Ir-Pd bimetallic alloy network.•The composites exhibited bifunctional ORR/OER performance compared to Pd/C and Ir/C.•Ir23Pd77/C exhibited the highest activity with good durability and overpotential.•The properties of Ir23Pd77/C were due to its high surface area and high porosity.
This study aimed to investigate the neuroprotective and therapeutic effects of
Diospyros kaki
L.f. leaves (DK) on transient focal cerebral ischemic injury and underlying mechanisms using a middle ...cerebral artery occlusion (MCAO) model of mice. The animals received the MCAO operation on day 0. The daily administrations of DK (50 and 100 mg/kg, p.o) and edaravone (6 mg/kg, i.v), a reference drug with radical scavenging activity, were started 7 days before (pre-treatment) or immediately after the MCAO operation (post-treatment) and continued during the experimental period. Histochemical, biochemical, and neurological changes and cognitive performance were evaluated. MCAO caused cerebral infarction and neuronal cell loss in the cortex, striatum, and hippocampus in a manner accompanied by spatial cognitive deficits. These neurological and cognitive impairments caused by MCAO were significantly attenuated by pre- and post-ischemic treatments with DK and edaravone, suggesting that DK, like edaravone, has therapeutic potential for cerebral ischemia-induced brain damage. DK and edaravone suppressed MCAO-induced changes in biomarkers for apoptosis (TUNEL-positive cell number and cleaved caspase-3 protein expression) and oxidative stress (glutathione and malondialdehyde contents) in the brain. Interestingly, DK, but not edaravone, mitigated an increase in blood–brain permeability and down-regulation of vascular endothelial growth factor protein expression caused by MCAO. Although the exact chemical constituents implicated in the effects of DK remain to be clarified, the present results indicate that DK exerts neuroprotective and therapeutic activity against transient focal cerebral ischemia-induced injury probably by suppressing oxidative stress, apoptotic process, and mechanisms impairing blood–brain barrier integrity in the brain.
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•Mathematical model of water treatment with low-strength ammonium and organics.•A single set of oligotrophic biofilm kinetics applicable to different water sources.•Identification of ...biofilm attachment and detachment in filtration run and backwash.•Empirical equation on required oxygen to design the bioreactor.
A kinetic model of a nitrifying expanded-bed reactor for the pretreatment of drinking water was developed to analyze its behavior under different concentrations of influent dissolved oxygen, ammonium, and organic substrate. In laboratory, an up-flow expanded-bed reactor (linear velocity: 15.5 m/h, space velocity: 7.8 h−1, specific surface area: 5587 m2/m3) was initially fed with synthetic water containing 1 mg NHx-N/L to stimulate nitrifiers growth, followed by varied NHx-N loadings (1–2 mg NHx-N/L with a fixed linear velocity). From tracer tests, the hydraulic regime of the expanded-bed reactor was simulated to be 11 tanks-in-series. To model the even distribution of media in the expended-bed height, a mathematical internal recycle flow with biofilm media was made. The performances were also studied on the pilot- and full-scale reactors receiving river water in two water treatment plants in Vietnam. A single set of biological kinetic and stoichiometric parameters was elaborated that successfully reproduced the five different datasets over the lab-, pilot- and full-scale reactors. The attachment/detachment specific rates of the biofilm were estimated during filtration cycles and backwash events. The graphical guidance and empirical equation were provided to obtain the reactor treatment efficiency under variable influent and temperature.
The present work reports efficient electrochemical nanosensors for the sensitive monitoring of 4-nitrophenol (4-NP) in tomato samples using various biosynthesized silver nanoparticles (bio-AgNPs). ...Three different bio-AgNP types were synthesized using natural plant extracts, including green tea (GT) leaf, grapefruit peel (GP), and mangosteen peel (MP), aiming to investigate their effects on the formation of bio-AgNPs, as well as the analytical performance of 4-NP. Based on the obtained results, it was found that the phytochemical content in various plant extracts directly influenced the physicochemical parameters of the created bio-AgNPs, such as particle size, crystallinity, and distribution. More importantly, these parameters have decisive effects on the electrocatalytic activity, conductivity, and electrochemical sensing performance of electrodes modified with them for 4-NP detection. Among the three bio-AgNPs evaluated, the GT-AgNPs (using green tea leaf extract) with uniform shape, small size without aggregation, and high crystallinity showed the best analytical performance for 4-NP determination. The electrode-modified GT-AgNPs exhibited a good 4-NP analytical performance with an electrochemical sensitivity of 1.25 μA μM
−1
cm
−2
and a detection limit of 0.43 μM in the detection range from 0.5 to 50 μM. The practical applicability of the sensor was also studied in tomato samples, promising satisfactory results toward 4-NP detection in other real samples.
In this work, we systematically investigated and compared the electrochemical sensing performances of three electrodes modified with various bio-AgNPs toward 4-NP detection in tomato samples.
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