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•Efficient &binder-free prickly nickel nanostructured/graphene is made for electrocatalytic HER.•Surface analysis showed that PNiNS wrapped in RGONs was pinned into Cu-Nifpl by ...prickles.•Nanocomposite exposed excellent stability & electrocatalytic activity, b=43mV/dec, η20=−57mV.•Increased activity comes partially from improved surface roughness & mainly synergetic effect.
Non-precious metal electrocatalysts with high activity towards hydrogen evolution reaction (HER) are desirable regarding renewable energy devices such as fuel cells and water electrolysis. However, fabrication of new materials for this purpose remains a main challenge. Here, a binder-free nanocomposite, prickly nickel nanostructured/reduced graphene oxide nanosheets, is constructed via electroless-deposition on cupper surface covered with a fresh prelayer of nickel (Cu-Nifpl-PNiNS/RGONs) for the first time. Then, the fabricated system is tested successfully for the HER in alkaline solutions. Structure and activity of the composite are characterized quantitatively by surface techniques and electrochemical methods. The results show that the hedgehog-like prickly nickel nanostructures wrapped in the RGONs cloth are formed, pinning the PNiNS/RGONs into the Cu-Nifpl surface, resulting in exceptional stability and activity for the Cu-Nifpl-PNiNS/RGONs system. In effect, the composite has shown excellent structural stability against disintegration by ultrasound waves; and electrocatalytic activity towards the HER as η20=−57mV, Tafel slope=−43mV dec−1 and j0=1.05mAcm−2, quite close to −22mV, −40mV dec−1 and 5.88mAcm−2, obtained in the same conditions for commercial Pt/C, respectively. The remarkable increase in electrocatalytic activity was found to be originated partially from increase in the surface roughness and mainly from synergetic chemical coupling effects between PNiNS and RGONs.
Here, a general method for fabricating active electrocatalysts is introduced for oxygen evolution reaction (OER) based on multimetallic (ternary alloy) structures formed on the N-doped nanoporous ...carbon platform without using ruthenium or iridium. Accordingly, three different sizes, small, medium, and large, of cobalt zeolitic imidazolate framework-67 (ZIF67
X
,
X: S, M, L
) are synthesized. Then, the product is carbonized via direct pyrolysis at 800 °C in an argon atmosphere to yield nitrogen-doped nanoporous carbon composited with cobalt nanoparticles (PZIF67
X
800
). To improve the activity, the most active nanoporous system for OER (PZIF67
L
800
) is further modified by electrochemical deposition of Co, Ni, and Fe (PZIF67
L
800
-CoNiFe). The electrochemical results revealed a large electrocatalytic activity for the GC-PZIF67
L
800
-CoNiFe toward the OER in alkaline media, Tafel slopes of 72 mV dec
−1
and overpotentials of 314 mV at 30 mA cm
−2
(η
30
), compared with those obtained under the same conditions on GC-RuO
2
(99 mV dec
−1
and 499 mV). The improved activity is attributed to (i) the increase in active surface area and simultaneous formation of Co nanoparticles and nitrogen-doped porous carbon, causing uniformly dispersed metal nanoparticles in the composite, and (ii) synergistic effect between the ingredients of ternary alloy nanoparticles (CoNiFe-NPs) and nitrogen-doped carbon nanoporous platform.
Graphical Abstract
University or college is a challenging reality leading to a sometimes elusive career path. By consulting social media and review websites, students have more alternatives to consider in their choice ...determination. This study develops a multifaceted model to recognize the influence of service quality and e-word of mouth on customer satisfaction and the impact of customer satisfaction on word of mouth. Data gathered from a sample of 150 university students are analyzed by SPSS and PLS-SEM. The findings indicate that service quality dimensions and e-WOM have positive impacts on customer satisfaction. Furthermore, this study reinforces that customer satisfaction has a positive influence on customers’ WOM intentions. This research recommends that university management should consider the importance of service quality factors and social media channels to meet and exceed students’ expectations in order to bolster the quality of services and boost customer satisfaction.
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Hypothesis: We hypothesize that simultaneous incorporation of ion channel peptides (in this case, potassium channel as a model) and hydrophobic magnetite Fe3O4 nanoparticles ...(hFe3O4NPs) within lipidic hexagonal mesophases, and aligning them using an external magnetic field can significantly enhance ion transport through lipid membranes.
Experiments: In this study, we successfully characterized the incorporation of gramicidin membrane ion channels and hFe3O4NPs in the lipidic hexagonal structure using SAXS and cryo-TEM methods. Additionally, we thoroughly investigated the conductive characteristics of freestanding films of lipidic hexagonal mesophases, both with and without gramicidin potassium channels, utilizing a range of electrochemical techniques, including impedance spectroscopy, normal pulse voltammetry, and chronoamperometry.
Findings: Our research reveals a state-of-the-art breakthrough in enhancing ion transport in lyotropic liquid crystals as matrices for integral proteins and peptides. We demonstrate the remarkable efficacy of membranes composed of hexagonal lipid mesophases embedded with K+ transporting peptides. This enhancement is achieved through doping with hFe3O4NPs and exposure to a magnetic field. We investigate the intricate interplay between the conductive properties of the lipidic hexagonal structure, hFe3O4NPs, gramicidin incorporation, and the influence of Ca2+ on K+ channels. Furthermore, our study unveils a new direction in ion channel studies and biomimetic membrane investigations, presenting a versatile model for biomimetic membranes with unprecedented ion transport capabilities under an appropriately oriented magnetic field. These findings hold promise for advancing membrane technology and various biotechnological and biomedical applications of membrane proteins.
•The designed model of lipid rafts serves as a platform hosting a transmembrane protein.•Activity of immobilized HMG-CoA reductase was confirmed by the electroreduction of NADP generated in the ...process.•Inhibition of HMG-CoA reductase by statin is demonstrated on the example of fluvastatin.
Electrochemical methods are used to characterize transport phenomena in the presence of membrane proteins to monitor changes in their catalytic properties or activity in the presence of activators or inhibitors. Because membrane proteins are fully active in their natural environment, the lipid membrane, electrochemical investigations of enzymes should be carried out when they are present in an appropriate lipid bilayer deposited on an electrode surface. Here, HMG-CoA reductase (HMGR), the membrane protein responsible for cholesterol synthesis, and its related coenzyme (HMG-CoA) were incorporated into a lipid bilayer obtained by spreading proteoliposomes on the surface of a gold electrode modified with a thioglucose. Nicotinamide adenine dinucleotide phosphate, NADPH was oxidized to NADP+ during the enzymatic reaction when HMG-CoA was reduced to the product, mevalonate, which is further transformed into cholesterol. The reconstitution of HMG-CoA reductase and its mechanism were investigated by following the NADP+ reduction on the electrode using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The activity of HMGR was studied over time and in the presence of fluvastatin, an exemplary HMGR reductase inhibitor commonly used to treat hypercholesterolemia. The inhibitory effect of the statin was electrochemically evaluated by monitoring the decrease of NADP+ reduction current and changes in the impedance parameters of the HMGR-proteoliposome-derived bilayer.
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This paper presents the nickel–cobalt nanoprickly particles (PNi
2
Co
3
) composited with graphene nanosheets (GNs) and carbon nanotubes (CNT), prepared via the one-pot hydrothermal method (PNi
2
Co
...3
/GNs/CNT), as an efficacious nonprecious metal bifunctional electrocatalyst for both oxygen evolution and reduction reactions (OER/ORR). The study employs a comprehensive methodology, incorporating cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) analysis to characterize and assess the materials and electrochemical properties investigated in the article. The primary objective was to successfully prepare a bifunctional electrocatalyst, and the PNi
2
Co
3
/GNs/CNT material achieved this goal. It exhibited superior OER activity, durability, and resistance to crossover effects, by an overpotential (
η
) of 480 mV and a Tafel slope of 61 mV dec
−1
, significantly higher than those obtained for RuO
2
nanoparticles (
η
= 970 mV, Tafel slope = 85 mV dec
−1
). A similar trend was observed for ORR, where the PNi
2
Co
3
/GNs/CNT displayed high activity with an
n
= 3.93, close to the activity of a Pt/C (20 wt%), commercial catalyst with
n
= 4. Careful analysis of the EIS results via suitable models, in conjunction with Tafel data, revealed that the enhanced activity originates mainly from two factors: (a) the large surface area of the Ni–Co nanoprickly alloy and graphene sheets, where the CNTs (as a spacer) helped graphene nanosheets to avoid restacking and decreasing the surface area, and (b) the synergistic effect between Ni–Co nanoprickly and carbon components (GNs and CNT) of the composite.
Graphical abstract
Supercapacitive performance and electrocatalytic activity of the nickel@nickel oxide core@shells (Ni@NiO), formed with different composition, structure, and morphology via electroless deposition on ...the surface of carbon black/reduced graphene oxide nanosheets (CB/RGONs) in the presence of citrate ion are reported here. The conditions are controlled and the synthesis is carried out systematically via three different routes: (a) in the absence of CB and citrate ion, (b) just in the presence of CB, and (c) in the presence of both CB and citrate ion. Then, the synthesized composites were transferred onto the GC electrodes, leading to (a) GC-RGONs-PNi@NiO(Particles), (b) GC-RGONs-HENi@NiO(Hedgehog), and (c) GC-CB/RGONs-NPNi@NiO(Nanoprickly) systems, respectively. The synthesis process is followed by several surfaces and electrochemical techniques, from which the physicochemical behaviors of the prepared composites and electrode systems were determined, and the systems were characterized. Then, their activities for capacitive charge storage and electrooxidation of methanol were quantitatively studied. The composite fabricated under optimized conditions, Nanoprickly system, exhibited (i) the most efficient charge storage behavior with specific capacitance (Cs) of 2398 F g−1; and (ii) a large electrocatalytic activity for electrooxidation of methanol with peak current density of 154 A g−1 at 10 mV s−1, compared with values of 1451 & 1049 F g−1 and 72 & 58 A g−1 obtained for the composite ancestors, Hedgehog and Particle systems, respectively. The increase in the Cs and improvement in the electrocatalytic activity of the nanocomposite are attributed to the (i) crucial role of CB nanospacer, preventing graphene layers from restacking, (ii) role of RGONs, dispersing and stabilizing of Ni@NiO nanoprickly particles, and (iii) synergetic chemical coupling effect between NPNi@NiO and CB/RGONs.
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•The Nanoprickly Ni@NiO core/shells were constructed on CB/RGONs.•The CB nanospacer prevents RGONs from restacking to disperse & stabilize Nanoprickly Ni@NiO.•Particle & Hedgehog forms of Ni@NiO were also prepared on RGONs & studied for comparison.•The constructed systems were successfully tested for charge storage &electrooxidation of MeOH.•Excellent activity is observed (charge storage, Cs ~ 2398 F g−1) & (MeOH oxidation, Ip ~ 154 A g−1).
Porous graphene nanoribbons are synthesized via an effective and template-free method based on introducing of carbon black (CB) into the graphene oxide (GO) layers, and then, thermal exfoliation ...under hydrogen plasma (H2) stream (PGNRs/CB). The nanocomposites are transferred onto the glassy carbon electrode surface (GCE) and tested directly for charge storage intentions or further modified with Pt-Ru alloy nanoclusters and examined for electrooxidation of methanol. The physicochemical characteristics and electrochemical activities of composites are studied by several surface techniques and electrochemical methods. A remarkable specific capacitance (223.0 F g−1 at 1.0 A g−1) is achieved for PGNRs/CB electrode, compared with 137.2 and 67.6 F g−1 values obtained for porous graphene nanoribbons (PGNRs) and graphene nanosheets (GNs-Ar) formed in the presence of H2 plasma and pure argon streams, respectively. The capacitance retention remained at more than 91% even after 5000 cycles. The supercapacitive behavior and excellent durability achieved for PGNRs/CB materials are attributed to the (i) large surface area of PGNRs obtained by annealing in H2 plasma, and thus, the increased ion accessibility of graphene system, and (ii) stability against the restacking of the PGNRs achieved in the presence of CB. In addition, the GCE-PGNRs/CB was successfully used as a favorable support and further modified with Pt-Ru alloy nanoclusters via electrodeposition. The GCE-PGNRs/CB/Pt-Ru showed an excellent electrocatalytic activity, high resistance against poisoning effect of CO and good stability toward oxidation of methanol. The experimental results are presented and discussed, regarding charge storage and electrocatalytic oxidation of methanol.
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•Porous graphene nanoribbons/carbon black, 1062 m2g–1, thermally fabricated in H2-plasma.•The PGNRs/CB electrode showed a large specific capacitance, 223.0 F g−1 at 1.0 A g−1.•GC-PGNRs/CB was successfully modified with Pt-Ru metal alloy nanocluster.•GC-PGNRs/CB/Pt-Ru electrode showed excellent activity & stability for CH3OH oxidation.
The development of nanocomposites with high activity and stability to generate hydrogen as a green fuel is an interesting challenge for several industrial requirements. Here, ternary alloy ...nanoparticles of NiCoMo are fabricated electrochemically on graphene nanosheets (GNs) as new nanocomposites using a glassy carbon electrode (GC) base, and then the prepared electrode systems are decorated with ruthenium nanoparticles (Ru NPs). The electrodes are characterized by several surface analysis techniques. The electrocatalytic activity of the electrodes is monitored toward the hydrogen evolution reaction (HER) in alkaline solutions, and the fabrication conditions are optimized systematically based on advanced optimization methods such as central composite design (CCD) and simplex-lattice mixture design (SLMD). Initially, the electrodeposition bath parameters are investigated and optimized by CCD. Then, the SLMD analysis is utilized to obtain the optimal mole ratio of metal ions using HER kinetic data. The results revealed an optimized mole ratio of 33:27:40 for metal ions of Ni/Co/Mo in the electrodeposition bath leading to a GC-GNs-Ni0.20Co0.36Mo0.44 electrode structure. A Tafel slope of −45 mV dec–1, j 0 of 1.26 mA cm–2, and η50 of −82 mV are obtained at the optimized structure, which are close to −42 mV dec–1, 5.93 mA cm–2, and −48 mV obtained under the same conditions on the GC electrode modified with commercial Pt/C (GC-Pt/C). The electrode is further decorated with Ru NPs through electrodeposition to form GC-GNs-Ni0.15Co0.31Mo0.38/Ru0.16. The results obtained on this electrode showed high physical and electrochemical stabilities and excellent kinetic performance for the HER, Tafel slope of −38 mV dec–1, j 0 of 6.31 mA cm–2, and η50 of −49 mV, which are similar or even better than the results obtained on the GC-Pt/C electrode.
Owing to the growing significance of hydrogen as a non-polluting fuel, design and construction of low-cost, efficient and highly stable electrocatalysts are required for its production by means of ...water electrolysis. Herein, a general strategy is introduced to fabricate a new type of electrocatalysts based on bimetallic core@shell structure formed on nitrogen-doped nanoporous carbon for electrocatalytic hydrogen evolution reaction (HER). Accordingly, a nickel metal organic framework, Ni‒MOF, synthesized by using benzene-1,3,5-tricarboxylic acid (H3BTC) as the carbon source and 2-methyl-imidazole as the carbon and nitrogen source, is employed, and the nickel/nitrogen−doped nanoporous carbon composite, Ni/NNPC system, is synthesized by the direct carbonization of Ni‒MOF system, i.e. annealing the system in argon atmosphere without using any carbon precursor additive. Then, the outer layers of nickel in Ni/NNPC system are replaced by Pt via galvanic reaction to synthesize the nanostructured system, Ni metal core@Pt thin layer shell, Ni@Pt/NNPC. The step-by-step synthesis of the system and formation of core@shell was supported by several surface analysis techniques. The fabricated materials were transferred onto a glassy carbon (GC) electrode and studied for the HER. The electrochemical results revealed a large electrocatalytic activity for the GCE/Ni@Pt/NNPC system toward the HER in both alkaline and acidic media, compared with GCE, GCE/Ni−MOF and GCE/Ni/NNPC. Tafel slopes of 43.78 and 46.73 mV dec−1, and overpotentials of −33.80 and −76.32 mV (vs RHE) at 20 mA cm−2 (η20) were observed on GCE/Ni@Pt/NNPC electrode in the alkaline and acidic media, under the same conditions, respectively. The observed activity is attributed to (i) the increased electrochemically active surface area, (ii) the cooperative action or synergistic effect between the Pt thin layer shell and the Ni metal core as well as between the Ni@Pt nanoparticles and the NNPC platform, and (iii) effective pore structures of the Ni@Pt/NNPC system.
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•Nickel/nitrogen-doped nanoporous carbon (Ni/NNPC) fabricated by the carbonization of Ni-MOF.•The Ni(core)@Pt(shell) structures formed on Ni/NNPC via galvanic replacement of Ni by Pt.•Based on the ICP analysis, the amount of Pt in the system was 7%, compared with 20% in Pt/C.•The system exposed excellent electrocatalytic activity for HER in both acidic and alkaline media.•The activities originate from synergistic effects, improved EASA, and pore structures.
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