The nickel-copper nanoalloys with tunable composition and morphology were prepared by galvanostatic deposition on copper substrate, in order to investigate the relationship between alloy composition ...and electrocatalytic activity. Both the composition and morphology of the NixCuy nanoalloys are highly dependent on the applied current density. The atomic ratio of Ni to Cu in the alloys changes from 1:9 to 3:1, with the increase of current density from 10 to 100mAcm−2. The difference in electrocatalytic activity among these nanoalloys was evaluated through the hydrogen evolution reaction (HER) in 1.0 M H2SO4 and 1.0 M KOH. The composition-dependence of the electrocatalytic activity of the alloys is more pronounced in 1.0M H2SO4 than in 1.0M KOH. By tuning the composition of NixCuy alloys, 13.5 and 5.7 times increase in exchange current density of the HER was achieved in 1.0M H2SO4 and 1.0M KOH, respectively. Meanwhile, 4.5 and 2.0 times decrease in charge transfer resistance was observed in the same two media. The best electrocatalytic activity to the HER was always achieved on the nanoalloy with a 1:1 atom ratio and a single crystal (111) plane. This favorable nanoalloy is composed of four-level dendritic nanochains. The results demonstrate that galvanostatic method can tune not only the composition but also the morphology of nanoalloys, both being important for nanoscale design of industrial electrocatalysts.
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•Both composition and morphology of NiCu nanoalloys are tunable with current density.•Electrocatalytic activity highly depends on composition and morphology.•Dendritic nanopearl chains in 1:1 atomic ratio show best electrocatalytic activity.•Difference in activity among alloys is more significant in acidic than basic media.
Coconut shell carbon (CSC) nanosheets were applied to support CdS quantum dots (≤5 nm) and Pt nanoparticles to form a composite Pt/CdS/CSC catalyst for the visible-light-driven photocatalytic H2 ...production from water. The H2 evolution rate on Pt/CdS/CSC is as high as 1679.5 μmol h−1, which is significantly enhanced as compared with that on Pt/CdS without CSC (636.2 μmol h−1). Electrocatalytic experiments indicate a highly efficient electron transfer on the CSC nanosheets, which may be due to the presence of the abundant nanopores (<4 nm) and surface oxygen-containing groups behaving as the charge capture traps. The unique electron transfer flexibility of CSC facilitates the separation of the photoinduced electron–hole pairs on CdS/Pt/CSC in the photocatalytic process. This is the main origin for the significantly enhanced photocatalytic performance of CdS/Pt/CSC. It is believed that the findings from this study will provide useful clues for designing efficient biochar-based catalysts for visible-light-driven photocatalysis.
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•Coconut shell nanocarbon (CSC) prepared for photocatalysis of H2 production.•A H2 evolution rate as high as 1679.5 μmol h−1.•Abundant nanopores and surface oxygen-containing groups on CSC.•CSC facilitating electron transfer kinetics.•CSC promoting separation of the photoinduced electron–hole pairs.
This paper describes a novel method of obtaining cyclic voltammograms (CVs) from optical signals. The obtained CVs correspond to the various specific species involved in the electrode process, which ...give more detailed information on the system under investigation than the common CV. For this purpose cyclic voltabsorptometry was used to investigate the successive oxidation processes of rutin on a graphite-wax electrode by using a long optical-path thin-layer electrochemical cell. The dynamic UV spectra of rutin showed the information on the structures of the oxidation products at different potentials. Cyclic voltabsorptiograms (CVAs) were measured in three potential ranges at the characteristic absorption wavelengths of rutin, 346, 254 and 296
nm, respectively. The CVs of three species in solution (rutin and its two products) were obtained from the derivative cyclic voltabsorptiograms (DCVAs). Based on this the redox mechanisms of rutin in different CV peaks were discussed.
A highly conductive sulfur cathode is crucial for improving the kinetic performance of a Li–S battery. The encapsulation of sulfur in porous nanocarbons is expected to benefit the Li+ migration, yet ...the e– conduction is still to be improved due to a low graphitization degree of a conventional carbon substrate, especially that pyrolyzed from carbohydrates or polymers. Aiming at facilitating the e– conduction in the cathode, here we propose to use ketjen black, a highly graphitized nanocarbon building block to form a conductive network for electrons in a biomass-derived, hierarchically porous carbon sponge by a easily scaled-up approach at a low cost. The specifically designed carbon host ensures a high loading and good retention of active sulfur, while also provides a faster electron transmission to benefit the lithiation/delithiation kinetics of sulfur. The sulfur cathode prepared from the carbon network shows excellent cycling and rate performance in a Li–S battery, rendering its practicality for emerging energy storage opportunities such as grids or automobiles.
An industrially attractive electrocatalyst needs to meet a series of criteria such as simple and scalable preparation, robust stability, as well as highly efficient catalytic activity. In this study, ...we demonstrate that a defect network present within high pure polycrystalline graphite can work as a wonderful matrix of electrocatalysts. The electrodes were prepared simply by drop-casting binder-free catalyst precursor solutions on the graphite surface. The precursor ions can infiltrate into the defect channels up to about 3.6 mm deep. Excellent electrocatalytic activity and robust stability were verified using hydrogen and oxygen evolution reactions with different electrocatalysts. The depth-dependent catalytic activities were measured and the depth-profile analyses were performed. The rigid defect network structure significantly improves structural integrity and robust stability and minimizes the electron transfer barrier. Such sustainable electrocatalysts fixed in a rigid defect network have the potential to provide all the features necessary for industrial applications.
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•Graphite defect network as an unexploited but promising electrocatalyst matrix.•Depth-dependent catalytic activity and depth-profile analysis.•Ultralow catalyst loading and simple preparation.•Excellent electrocatalytic activity and robust stability.
Bipolar electrochemistry is an unconventional but powerful technique in the fields of materials science and analytical chemistry. We report here the one-step cathodic deposition of NixCu1–x alloys ...with a composition gradient and a morphology evolution on a copper substrate, based on an in-plane potential gradient over the interface of a bipolar electrode (BPE) and an electrolytic solution. The alloy gradient was characterized using scanning and transmission electron microscopy techniques. As a result, the deposited alloy layer exhibits a composition gradient from 0 to ca. 89% Ni atoms corresponding to an abundant morphology evolution from pyramids to dendrites and to nano/microballs along the surface of the BPE. Electrochemical screenings were performed for the dissected alloy specimens as the electrocatalyst of hydrogen evolution reaction. The present work shows that bipolar electrochemistry can give access to the fabrication of alloys with abundant architectures as high throughput screening candidates.
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•A bipolar electrochemistry approach for a gentle and wide surface gradient•Abundant surface morphologies from pyramids to dendrites and to nano/microballs alongside the bipolar electrode•Efficient preparation of a series of alloy specimens in a single-step electrodeposition•Sampling-position-dependent electrocatalytic performance revealed by three electrochemical methods
•Cyclic voltabsorptometry peaks assigned to redox of Cu–glycine complexes.•Nanofoil electrode adaptable for use in cyclic voltabsorptometry of metals.•High electrochemical stability of Cu(I)–glycine ...complex.•Difficult formation of Cu(II)–glycine complex due to kinetic hindrance.
Real time detection of the electrode products as a function of potential during the electrolysis is desirable for fundamental analyses of the electrode processes. In the present work, cyclic voltabsorptometry was used to investigate the electrochemical behavior of copper in glycine solutions at acidic, neutral and alkaline pH levels. A long-optical-path thin-layer cell was used for the spectroelectrochemical measurements. Electro-oxidation of the deposited copper nanofoil leads to formation of Cu(I)–glycine complex with high electrochemical stability. At a high concentration of glycine, all the deposited copper can be directly converted into soluble Cu(I)–glycine complex in the KCl-containing solutions without accumulation of the intermediate CuClads. The Cu(I)–glycine complex is also evidenced to be an intermediate in the cupric complex reduction to copper. This Cu(I) complex can be destroyed at relatively positive potentials where the evolution of chlorine occurs, especially in acidic and neutral solutions. This work proves that cyclic voltabsorptometry is adaptable for the analysis of the potential-dependent formation and conversion of the light-absorbing metal complexes.
A conductive polymer, poly(2-amino-5-mercapto-1,3,4-thiadiazole) (PAMT), was electrodeposited on a glassy carbon substrate for electrocatalyzing hydrogen evolution reaction (HER) in H2SO4 ...electrolytes. The prepared material was characterized by scanning electron microscope and X-ray photoelectron spectroscopy. The surface of the PAMT film was uniform, crack-free, and was full of curly short filaments (<100 nm long). The free active sites of the PAMT for HER could be represented as –N, which exist in pairs meeting the dual-site requirements for H–H combination. The Tafel analysis revealed that the open circuit potential was positively shifted by 313 mV due to the PAMT catalyst, with a prominent decrease in activation energy. Both the electrochemical impedance spectroscopy and chronopotentiometry suggested that the PAMT can not only significantly reduce the charge transfer resistance of the HER, but also facilitate the desorption of the generated hydrogen from the active sites. These results indicate that the N- and S-rich conductive polymers deserve further investigation as potential electrocatalyst candidates for hydrogen energy production.
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•An N,S-rich conductive polymer PAMT prepared for electrocatalysis of H2 evolution.•Imine nitrogen atom pairs as free active sites for H+ reduction.•313 mV positive shift in open circuit potential due to PAMT catalyst.•PAMT facilitating electron transfer kinetics of H+ reduction.•PAMT facilitating desorption of hydrogen from active sites.
•Double-wavelength cyclic voltabsorptometry used for oxidation of salicylaldehyde.•Enhanced observation of trace amounts of redox couples.•Highly pH-dependent oxidative pathway of salicylaldehyde.•A ...complex parallel-consecutive mechanism proposed for oxidation of salicylaldehyde.
The advances in knowledge of the oxidation mechanism of salicylaldehyde are important in understanding its role and conversion in the involved oxidative degradation, synthesis and aerobic metabolism processes. The electrochemical oxidation of salicylaldehyde was investigated in different pH media using cyclic voltammetry, in situ UV–vis spectroscopy and cyclic voltabsorptometry based on a long optical-path thin-layer electrochemical cell. ATR-FTIR spectroscopy was used for characterization of the oxidation products deposited on the electrode surfaces. Time-derivative cyclic voltabsorptograms were obtained at the characteristic wavelengths of salicylaldehyde and the soluble oxidized salicylaldehyde, for comparative discussion with the corresponding cyclic voltammograms. Two couples of redox peaks, subsequent to the main oxidation peak of salicylaldehyde, were observed on the voltabsorptograms but nearly indistinguishable on the voltammograms. Salicylaldehyde was initially oxidized to reactive phenoxyl radicals, followed by a series of transformation steps leading to different final products. A parallel-consecutive reaction mechanism was proposed for the pH-dependent formation of a deposited polyester and two trace amounts of soluble quinoid products.
•An attempt on diffusion restriction of ions for uniform electrodeposition.•An additional 3D nucleation process in the initial deposition stage.•Constant growth rate of Pt particles due to diffusion ...restriction.•Equivalent circuit fitting for negative impedance and inductance.•High catalytic activity to methanol oxidation kinetics.
Diffusion restriction of precursor ions was applied using filter paper during platinum electrodeposition on a solid carbon paste substrate, in order to uniformize the growth of Pt catalyst particles. An additional 3D nucleation process was then observed in the initial deposition stage, and the growth rate of Pt particles kept constant over whole deposition time. The prepared particles showed a sunflower-head-like morphology with numerous nanoscale “seeds” on the surface. Both the “sunflower-heads” and the “seeds” become more uniform in size, shape and surface distribution due to diffusion restriction, leading to an increase in the electrochemical active area of Pt particles and an enhancement in methanol oxidation kinetics. The analysis of electrochemical impedance spectroscopy by equivalent circuit fitting yields potential-dependent charge-transfer resistances and inductances with the same sign (positive or negative), corresponding to the regeneration or passivation of surface active sites at different potentials. This study offers insight into the role of the diffusion-restricted electrodeposition in preparing the catalyst particles with high catalytic activity.
