The preparation of molybdenum-modified hematite electrodes by means of chemical bath deposition and their photoelectrochemical behavior toward water oxidation are reported in this work. The addition of a molybdenum precursor to the bath solution for hematite deposition induces a remarkable change of morphology in the resulting film from (110)-oriented nanorods to polyhedral nanoparticles. Despite the resulting loss of order, by controlling the Mo/Fe molar ratio in the bath solution, a significant improvement of the water oxidation photocurrent is achieved compared to nanorod pristine hematite electrodes. Such a (photo)electrochemical enhancement is mainly explained by an effective surface state passivation in Mo-modified hematite films. FE-SEM, TEM, XRD, and XPS were employed for electrode structural and morphological characterization.
A single-step electrochemical deposition of NiS thin films incorporating various carbon nanomaterials as support is described. Advantages of this method are as follows: It is simpler and can be easily scaled up, the precursors employed are cheaper, and the deposition method is energy effective requiring no further heat treatments. Benefits of carbon nanomaterials as catalyst support are manifold including high conductivity and stability. The carbon-supported thin films exhibit high hydrogen evolution activity, low Tafel slopes, and improved double layer capacitance. A remarkable enhancement in the stability of the thin films in the acid medium has been observed. Specifically, NiS/carbon nanofibers have shown the highest activity, lowest Tafel slope, and retained more than 90% of its initial activity after the stability tests.
Graphical abstract NiS/carbon thin films were fabricated through a highly energy-efficient method as active and highly stable electrocatalysts in acid medium for hydrogen evolution reaction.
LiNi1-x-yCoxMnyO2 (NCM) with excessive lithium is known to exhibit high rate capability and charge–discharge cycling durability. However, the practical usage of NCM is difficult, because the positive electrode slurry is unstable and battery cells swell due to the alkaline residual lithium compound generated on the surface of NCM particles. To reduce the residual lithium compound, ammonium metatungstate (AMT) added to NCM is studied, and the effect is investigated by scanning electron microscopy, aberration-corrected scanning transmission electron microscopy, X-ray diffractometry, synchrotron X-ray diffractometry, and several electrochemical measurements. It is found that the AMT modification reduces the amount of alkaline residual lithium compound and improves the rate capability due to the ~1-nm-thick W-rich layer generated on the NCM surface.
Galvanic exchange involving dissolution of iron and the simultaneous growth of platinum onto 316 L stainless steel was investigated for specimens manufactured by 3D-printing, and the behavior was compared to conventional stainless steel. Novel phenomena associated with the 3D-printed steel, but not conventional steel, reacting in three distinct phases were observed: first, with low platinum loading, a bright etching pattern linked to the laser-manufacturing process is revealed at the steel surface; second, a nanostructured pore pattern with platinum nano-deposits forms; and third, a darker platinum film coating of typically 500-nm thickness forms and then peels off the steel surface with further platinum growth underneath. Unlike the conventional steel (and mainly due to residual porosity), 3D-printed steel supports well-adhered platinum films for potential application in electrocatalysis, as demonstrated for alkaline methanol oxidation.
The nucleation of Sn nanoparticles by chemical reduction was studied using three different carbonaceous substrates, to obtain Sn/C composites. When used as active materials in anodes for lithium-ion batteries, these composites displayed higher capacities than commercially used graphite, and showed a good cyclability. The differences in morphology, capacity, cyclability, and diffusion between the resulting materials are highlighted. The resulting materials were characterized by charge-discharge cycling, voltammetry, EIS, SEM, and TEM microscopy. It was found that the substrate has a determinant effect on the deposition of Sn. This effect is interpreted in terms of the relative adsorption energies of a single Sn atom obtained from DFT calculations.
Aluminum-doped ZnO thin films with pebble-like structures have been successfully deposited on glass substrates by successive ionic layer adsorption reaction method. The effect of percentage composition of the aluminum dopant on the flower-like clusters of the ZnO nanostructures on the structure, morphology, and optical properties was investigated. The ZnO thin films which were crystallized in hexagonal wurtzite structures with crystallite sizes of 44, 51, 56, and 43 nm for the intrinsic and 1, 3, and 5% Al-doped ZnO thin films, respectively. Preferred orientation of crystallites is in all cases in [001] direction perpendicular to the sample surface The Raman spectroscopy revealed decrease in the intensity of the ZnO characteristic peak due to the substitution of the Zn2+ atoms by the Al3+ and attributed to potential fluctuations of the alloy disorder. The introduction of the Al3+ dopant significantly increased the optical band gap.
Plasma-treated carbon thin films are investigated as counter electrodes for dye-sensitized solar cells. The films were grown onto fluorine-doped tin oxide (FTO) substrates by magnetron sputtering using pure graphite target and argon atmosphere and subsequently annealed at 600 °C for 30 min in vacuum. These films were then submitted to a plasma texturing process in a reactive ion etching reactor using three different gas combinations: sulfur hexafluoride/argon (SF6 + Ar), sulfur hexafluoride/hydrogen (SF6 + H2), and sulfur hexafluoride/oxygen (SF6 + O2). The morphology and structure of the obtained films were characterized by scanning electron microscopy and Raman spectroscopy. Cyclic voltammetry technique allowed accessing the improvements in their catalytic properties, while the photocurrent-voltage curves under simulated solar illumination AM 1.5G (100 mW/cm2) evaluated the performance of the respective assembled solar cells. The results show that photovoltaic performance is significantly affected by the different plasma texturing conditions used. The carbon counter electrode obtained after SF6 + O2 plasma texturing achieved the best power conversion efficiency of 2.23%, which is comparable to the 2.31% obtained using the commercial platinum counter electrode.
We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO2) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO2 thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO2 sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I2 + 0.1 M KCl) electrolyte at 40 mW cm?2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.
Cadmium selenide (CdSe) thin films were grown by electrochemical technique on fluorine-doped tin oxide (FTO)-coated conducting glass substrates in the presence of organic surfactants. The influence of organic surfactants like polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) on different physico-chemical properties and its subsequent impact on photoelectrochemical (PEC) performance of CdSe thin films have been investigated. It has observed that the organic surfactants play an important role in modifying the surface morphology of CdSe thin films. The compact grain like morphology of pure CdSe is tuned to interconnected nanofibrous network on addition of PEG and to sprouting nanorods like morphology on addition of PVP. Among these nanostructures, CdSe sprouting nanorods exhibits improved power conversion efficiency of 0.55% as compared to nanofibrous (0.24%) and granular CdSe (0.16%) nanostructures. It reveals the fourfold enhancement in the PEC performance on PVP-mediated growth which can be attributed to conversion of compact dense nanostructure to porous and relatively high surface area nanostructure. This work exemplifies the ability of organic surfactant to modulate the surface morphology of the electrodeposits and pinpoints the organic surfactant that gives rise to the suitable morphology for PEC solar cell application.
Graphical abstract TOC: The morphology of CdSe nanostructure has successfully tuned with use of surfactants to enhance the photoelectrochemical solar cell performance.
Thin films of iron-filled carbon nanotubes prepared through the liquid/liquid interfacial method were modified with a mixture of hexacyanometallates (HCMs) Prussian blue and ruthenium purple. Two different approaches were used in order to obtain both materials in the composites, based on a direct reaction starting from a mixture of both precursors or a step-by-step deposition of each compound. The modified films were characterized by cyclic voltammetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and UV-Vis spectroscopy, confirming the formation of a mixture of HCMs in both methods of synthesis. Stability studies were evaluated in different supporting electrolytes, and composites presented good performances due to carbon nanotube stabilization. Electrochromic properties were also evaluated for selected composites, showing high electrochromic efficiency and stability.
The influence of the atmosphere composition (CO, Ar, air), in which wet synthesis of Pt/C electrocatalyst was carried out, on the structural and morphological characteristics, and electrochemical behavior of electrocatalysts have been studied. For comparison, commercial Pt/C electrocatalysts with the same platinum loading were also studied. It has been shown that the adsorption of CO molecules on the surface of the growing platinum nuclei leads to the decrease in the average size of the nanoparticles and the narrowing of the size distribution in the Pt/C. Homemade electrocatalysts, with the values of electrochemically active surface area being from 94 to 139 m2 g?1 (Pt), prove to be in no way inferior to their commercial counterparts in oxygen reduction reaction mass activity. Durability of the homemade Pt/C samples in accelerated stress tests exceeds durability of the commercial ones.
The present work has studied electrochemical and optical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film electrodes drop-casted from commercial PEDOT:PSS aqueous dispersion with preliminary addition and without addition of LiClO4 electrolyte (further denoted as PEDOT:PSS/LiClO4 and PEDOT:PSS). Cyclic voltammetry measurements showed the significant increase in capacitance of PEDOT:PSS/LiClO4 film electrodes in comparison to PEDOT:PSS. Furthermore, the improved charge transport in PEDOT:PSS/LiClO4 films was demonstrated by electrochemical impedance spectra. In situ spectroelectrochemical measurements revealed that preliminary addition of LiClO4 into PEDOT:PSS aqueous dispersion allows to increase amount of free charge carriers (polaron and bipolaron states) in the resulting film during electrochemical oxidation in LiClO4 propylene carbonate solution. This increase was attributed to ion-induced charge screening between positively charged PEDOT and negatively charged PSS in polyelectrolyte structure, which was supported by structural investigations of both types of film electrodes by using FTIR, SEM, and XPS measurements. Charge screening results from a more open structure that allows conformational relaxation of PEDOT molecules during charge transport, which leads to partial separation of oppositely charged PSS and PEDOT molecules and facilitating the increase of electrochemical activity.
A biodegradable composite polymer membrane is fabricated by synthesizing polyvinylpyrrolidone (PVP) on the matrix of lignin, and then the corresponding gel polymer electrolyte (LP-GPE) is further prepared by absorbing the liquid electrolyte. The morphology, mechanical property, and thermal stability of the composite lignin-PVP membrane and the electrochemical properties of LP-GPE are investigated. The results of the investigation present that the mechanical property of the membrane is remarkable improved (670%) and the composite membrane exhibits a better thermal security. For electrochemical properties, a high ionic conductivity of 2.52 × 10?3 S cm?1 at room temperature, excellent lithium-ion transference number of 0.56, and outstanding electrochemical stability of LP-GPE are confirmed. Moreover, the C-rate performance and capacity retention based on Li/LP-GPE/LiFePO4 cell are superior to that of the commercial Celgard 2730 cell. Consequently, all these results demonstrate that LP-GPE can be applied as a novel electrolyte for lithium ion battery with high-performance, low-cost, and environment-friendly properties.
A gold bare template modified with self-assembled layers (SAMs) composed of gold nanoparticles and organic S-containing compound: cysteamine and dihydrolipoic acid were prepared. The electrode with SAMs endowed with gold nanoparticles gave a high catalytic effect for dopamine electrooxidation alone and in the presence of biogenic interfering compounds: ascorbic acid and uric acid in solution at pH 7. For this novel sensor, a linear relationship between the current response of dopamine at the potential of peak maximum (jp) and the concentration of this compound in solution (cDA) was found over the range 0.1 μM to 0.85 mM with the detection limit of 0.023 μM.
A series of PANI-CNTs/TiO2 nanotubes/Ti electrodes were fabricated via pulse current co-electrodeposition of polyaniline and functionalized carbon nanotubes onto TiO2 nanotubes/Ti electrodes. FT-IR spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy were applied in order to characterize the modified TiO2 nanotubes/Ti electrodes. The morphology studies showed that the PANI-CNTs/TiO2 nanotubes/Ti nanocomposite electrode has many interlaced PANI-CNTs nanorods on the surface of TiO2 nanotubes. The electrochemical measurements of the modified electrodes confirmed that the CNTs in the composite can significantly improve the capacitive behavior as well which have been compared with that of PANI/TiO2 nanotubes/Ti electrodes. The modified electrode exhibited much higher specific capacitance (190 mF cm?2 with 90% retention after 1000 cycles) compared to the PANI/TiO2 nanotubes/Ti (70 mF cm?2 with 77% retention after 1000 cycles) at a current density of 0.85 mA cm?2, indicating its great potential for supercapacitor applications.
Functional electrode materials play an increasingly important role in the advancement of energy conversion and storage technologies used in batteries, electrolyzers, supercapacitors, fuel cells, and other electrochemical devices. To address the problems related to accelerating demand for the so-called renewable energy, which are simultaneously coupled with environmental concerns, new generations of materials, engineering methodologies, and innovative techniques are necessary. Among many synthetic methods, microwave-assisted synthesis becomes nowadays a very popular approach to efficiently control both the composition and morphology of solids. In this review, we focus on its applications to create new advanced energy electrode materials.
The electron transport layer (ETL) plays a crucial role in the rapidly developed perovskite solar cells (PSCs). SnO2 has become one of the most promising alternatives to the TiO2 ETL due to its superior characteristics, such as the wider bandgap and hysteresis-free. However, at this stage, a lot of preparation methods of SnO2 ETL exist in high temperature and long time, those undoubtedly increase the cost and time of preparation. Herein, we report a low-temperature solution-processed SnO2 ETL without high annealing temperature, and a special bromine salt is used to modify SnO2, which leads to a higher transmittance and improved carrier transport ability. Due to the excellent optical and electrical properties, the photoelectric conversion efficiency of the prepared PSC reaches up to 18.8%. Moreover, it can be fabricated using facile solution processing at low temperature, making it particularly attractive for flexible development and low-cost commercialization.
This paper reports the voltammetric determination of 17β-estradiol in urine and buttermilk samples using a simple detector based on a carbon paste electrode (CPE) modified with copper(II) oxide (CuO). The CuO was obtained by the Pechini method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive (EDS), Fourier transform infrared (FTIR), and Raman spectroscopies. Cyclic voltammetry (CV) and square-wave voltammetry (SWV) demonstrated that the CuO-modified carbon paste electrode (CuO/CPE detector) displayed much higher electrocatalytic activity in the 17β-estradiol oxidation reaction than the CPE without modification, exhibiting a low detection limit of 21.0 nmol L?1 with a wide linear range from 60.0 to 800.0 nmol L?1 (R = 0.998). Satisfactory results were obtained for the determination of 17β-estradiol in human urine and buttermilk samples. The proposed electrochemical detector offers high repeatability, stability, fast response, low cost, and potential for practical application in the quantification of this hormone.
A novel polyhedral oligomeric silsesquioxane (POSS) composite polyacrylonitrile (PAN)-based porous structure gel polymer electrolyte (GPE) is prepared by phase inversion method. The POSS additive filler is firstly obtained in the dehydration condensation reaction of vinyltrimethoxysilane (VTMS) and 3-methacryloxypropyltrimethoxysilane (MPTMS). The composition and structure of synthetic POSS and the prepared POSS composite PAN-based GPEs are investigated. It is found that compared with pure PAN-based GPE, the POSS composite PAN-based GPE with 8 wt.% POSS presents the homogeneous pore distribution and abundant electrolyte uptake (540.4 wt.%), which endows GPE-8% with the excellent comprehensive performances: the highest ionic conductivity of 2.62?×?10?3 S cm?1 at room temperature, the higher lithium ion transference number of 0.38, the good compatibility with lithium anode, and the higher electrochemical stability window of 5.7 V (vs. Li/Li+). At 0.2 C, the GPE-8%-based lithium ion battery produces a satisfactory discharge capacity of 140 mAh g?1.
Novel potential type electrochemical chiral biosensing system with unique capability of distinguishing and quantitating of tyrosine (Tyr) enantiomers by L-cysteic acid and left-handed chiral carbonaceous nanotubes (L-CCNT) modified glassy carbon electrode (L-Cys/L-CCNT/GCE) was first developed. The effect of sweep cycles of L-Cys and the kinds of L-CCNT on electrochemical chiral biosensing performance of L-Cys/L-CCNT/GCE were investigated. The electrochemical identification and quantitative determination of L- and D-tyrosine in their mixed solution were successfully achieved based on the different oxidation potential signals. The chiral structure of L-CCNT, the aromatic ring of Tyr, and also the intermolecular hydrogen bond between cysteic acid (CyA) and Tyr could possibly produce the difference in the free energy, which reflects as potential difference of L- and D-tyrosine. A good linear relationship between the potential, current, and different concentration ratios of L- and D-Tyr was obtained. Our present work realizes the simultaneous detection of Tyr enantiomers in their mixed solution based on the different potential signals, and it is of far-reaching significance in real electrochemical chiral biosensor study.
