NaOH Electrolyte Research Articles

Synthesis, physical and electrochemical properties of the spinel CoFe2O4: Application to the photocatalytic hydrogen production

This research is achieved for the preparation of CoFe 2 O 4 with a high purity and crystanillity by nitrate route followed by a calcination at 850 °C. The material exhibits a single phase with a cubic symmetry. The electrochemistry performed in Na 2 SO 4 solution shows a stable semiconductor with a small exchange current density (112 μA cm −2 ). The capacitance-potential measurement indicates p -type behavior, typically related to the metal insertion in octahedral sites. The narrow band gap semiconductor with a direct optical transition of 1.27 eV is due to the lifting of degeneracy of Fe 3+ : 3d orbital in 6-fold coordination, making it attractive for the photo-electrochemical (PEC) conversion. Moreover, its cathodic comportment evidenced from the negative conduction band compared to the potential of the water reduction makes it an ideal candidate for the hydrogen production. The experimental data shows a great activity for the evolution of hydrogen with an average rate of 74 μmol min −1 g cat −1 and a quantum efficiency of 0.34% under visible illumination (23 mW cm −2 ). The use of C 2 O 4 2− as reducing agent increased substantially the performances by a factor of 57%. • The spinel CoFe 2 O 4 prepared by nitrate route is a narrow band gap semiconductor with a crystallite size of 27 nm. • CoFe 2 O 4 with an optical band gap of 1.27 eV is sensitive over the whole visible region. • The oxalate C 2 O 4 2− acting as sacrificial agent enhances the H 2 production in NaOH electrolyte. • The conduction band (−0.5 V SCE ) derived from Fe 3+ : e g orbital, is more cathodic than the H 2 O/H 2 level (∼-0.4 V SCE ). • H 2 evolution rate of 74 μmol min −1 (g catalyst) −1 and quantum yield of 0.34% were obtained under visible light (23 mW cm −2 ).

Electroreforming of Glucose/Xylose Mixtures On PdAu Based Nanocatalysts

AbstractThe electroreforming of glucose/xylose mixtures has been evaluated at Pd1‐xAux/C anodes in 0.10 mol L−1 NaOH electrolyte. The catalysts synthesized by a wet chemistry route are comprehensively characterized by physicochemical and electrochemical techniques. From linear scan voltammetry and in situ Fourier transform infrared spectroscopy measurements, it was shown that the Pd0.3Au0.7/C material led to the best electrocatalytic behavior towards the electrooxidation of glucose/xylose mixtures in terms of activity (higher current densities at lower potentials) and selectivity (lower dissociative adsorption). Six‐hour chronoamperometry measurements were performed at 293 K in a 25 cm2 electrolysis cell at +0.4 V and +0.6 V and the reaction products were analyzed by high performance liquid chromatography. The main products were gluconate and xylonate, but the contributions of xylose to all formed products was always lower in percentages than the initial xylose ratios in solutions, showing that glucose was more electro‐reactive than xylose at Pd0.3Au0.7 surface.

Green synthesis of cobalt oxide thin films as an electrode material for electrochemical capacitor application

In this study, we report on the fabrication and characterization of cobalt oxide (Co3O4) thin film that is potentially important for electrochemical capacitor applications. For that purpose, the precursor powder of Co3O4 was prepared using the cost-effective sol-gel synthesis route and heat treatment at a relatively low temperature. A thin film of Co3O4 was prepared on a fluorine-doped tin oxide (FTO) substrate using a simple doctor-blade method. X-ray diffraction and Raman spectroscopy confirmed the formation of pure Co3O4 thin film on FTO, and scanning and transmission electron microscopy confirmed the nanoscale nature of the particles in the film. The electrochemical studies revealed a specific capacitance of 237 ​F ​g-1 for the Co3O4 electrode, with a remarkable cycling stability in 1 ​M NaOH electrolyte, and 77% capacity retention after 2000 cycles at 5 ​mA ​cm-2 current density (833 ​mA ​g-1); this demonstrates that Co3O4 is a promising material for electrochemical devices. Further, the electrochemical impedance measurements revealed an internal (solution) of 10 ​Ω, whereas the charge transfer resistance between the electrode and the electrolyte was roughly 40 ​Ω.

Electrochemical behavior of spray deposited nickel oxide (NiO) thin film in Alkaline electrolyte

Nickel oxide (NiO) Thin film was successfully deposited on the glass substrate using an inexpensive spray pyrolysis (SP) technique. The structural, morphological, and optical properties have been studied, thus the electrochemical behavior of NiO film in Alkaline electrolytes has been investigated. The X-ray diffraction (XRD) analysis showed that NiO thin film exhibit a polycrystalline cubic rock-salt structure with a preferential orientation on the plane (111). This result was confirmed using Raman spectroscopy. The Scanning Electron Microscopy (SEM) images exhibit a smooth and dense surface without major cracks. Optical analysis shows an average transmission of about 55% in the visible light range, and the optical band gap energy was estimated by Tauc’s method and showed a value of 3,71 eV. Electrochemical properties as specific capacitance (Csp), optical density variation (ΔOD), and Coloration efficiency (CE) were studied using cyclic voltammetry in 1M KOH and 1M NaOH electrolytes. The results indicated that the behavior of the NiO layer in KOH is more effective than in NaOH electrolytes.

Entada Gigas seeds mediated synthesis of carbon for dielectric and sensing applications

In the current work, a plant-based carbon sample is synthesized successfully from monkey ladder (EntadaGigas) plant seeds by combustion technique. The prepared samples are subjected to characterizations such as Powder X-ray Diffractogram(PXRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray (EDX) Analysis. The PXRD pattern of the prepared MLC carbon sample exhibits the graphitic structure. The SEM micrograph displays the flake-like morphology; the FTIR spectrum reveals the presence of carbon-based functional groups. The dielectric property of the prepared carbon sample has been studied and confirms the good ac conductivity. The cole-cole plot of the prepared MLC carbon sample displays a single semicircle which signifies the highly resistive grain boundaries. The electrochemical study of prepared MLC Coated Ni foam electrode in 0.1 ​M NaOH electrolyte solution showed good redox potential output proposed by cyclic voltammetric and amperometric studies.The developed material exhibited a good response towards the glucose sensor with a sensitivity of 0.8 mAmM-1 and a limit of detection of 0.5 ​mM.

Magnetic assisted synthesis of ZnO nanoparticle by electrochemical discharge method

Metal oxide optoelectronics nanoparticles are widely used in industries. Many efforts were made to form uniform and pure metal oxide Nanoparticles. This paper focused on synthesizing simple step nanoflower like ZnO structure in atmospheric conditions. The Electrochemical discharge method is used to synthesize ZnO nanoparticles in NaOH electrolyte medium. The effect of electrolyte rotation on morphology was analyzed at 200 rpm resulted uniform flower shape of nanoparticles, confirmed by FESEM images. The XRD results reveal that the pure crystalline phase of nanoparticles obtained has the average crystalline size of 29 nm. The uniform voltage and current wave form was also observed at 200 rpm rotation of electrolyte. The chemical composition of the element was studied by EDS analysis to confirm the presence of zinc and oxygen element. DLS result gives the hydrodynamic diameter of nanoparticles within the range of 100 nm.

Dynamic Locking of Interfacial Side Reaction Sites Promotes Aluminum‐Air Batteries Close to Theoretical Capacity

AbstractAluminum metal has been regarded as a promising anode material for aqueous metal‐air batteries. However, the stable cycling of Al anodes is challenging due to the severe parasitic corrosion of Al metal in alkaline electrolytes. Here, a novel additive,n‐octylphosphonic acid (OPA), is introduced into the typical NaOH electrolyte system to improve the interfacial stability of Al anodes and thus promote high‐performance Al‐air batteries (AABs). Combining several experimental characterizations and theoretical calculation, it is proved that OPA molecules in an NaOH aqueous environment can modify the Al anode/electrolyte interface and alter the stacking of the discharge product. The electrolyte engineering is capable of anchoring dynamically to restrain side reactions through hydrogen bonds (H···O), homogenizing the dissolution of Al metal and avoiding precipitation agglomeration. As a proof of concept, AABs full cells with an electrolyte containing OPA achieve higher potential plateau and discharge capacity than those with a pure NaOH electrolyte. It paves a way to develop highly‐efficient and eco‐friendly electrolyte additive strategies for high‐performance AABs devices and advance the current understanding of organic additive mechanisms in AABs.

Cathodic corrosion of Au in aqueous methanolic alkali metal hydroxide electrolytes: Notable role of water

AbstractCathodic corrosion is an electrochemical process that induces restructuring, roughening, and etching of metal surfaces at a highly negative surface charge density, yet, details of the reaction mechanism are not fully resolved. An in‐depth fundamental understanding of the processes and parameters underlying cathodic corrosion is crucial for tailoring the surface structure of the metal electrodes and for synthesizing shape‐ and size‐controlled nanoparticles. Here, we investigate the relevance of water and hydrogen evolution in the cathodic corrosion process. To achieve this aim, Au electrodes were polarized at ‐1.6 V versus RHE in KOH and NaOH electrolytes prepared using different water + methanol mixtures. Structural changes of the Au surfaces were studied by cyclic voltammetry and monitored by scanning electron microscopy (SEM). Most importantly, cathodic corrosion does not take place in the absence of water. There is no detectable bubble formation due to the hydrogen evolution reaction on Au in purely methanolic alkali. Furthermore, the electrochemically active surface area, facet distribution, and surface morphology of Au electrodes are significantly altered upon cathodic polarization as a function of the water concentration. Cathodic corrosion features become more and more pronounced with a further increase in water content. In addition, substantial differences in the surface structure of Au are observed as a function of the nature and concentration of alkali metal cations. Overall, this study provides a more detailed understanding of the role of water and the hydrogen evolution reaction in dominating cathodic corrosion, which might advance the understanding of this phenomenon.

Studies on Biosensing Properties of Electrodeposited Copper Oxide Films

AbstractThe copper oxide (CuO) based films have been prepared for biosensing application. Electrodeposition mode has been used for preparation of CuO films on cost effective stainless steel substrates. The structural properties of CuO material are studied by X‐ray diffraction (XRD) pattern and it shows (ī11) more intensive plane. Hierarchical multilayer nanosheets clusters have been displayed in scanning electron microscopic images. The energy dispersive X‐ray analysis (EDAX) pattern displays wt% of Cu and oxygen in CuO material and it is found to be 52.80% and 57.61%. The glucose sensing of CuO electrodes is carried out in NaOH and glucose electrolyte at different concentration of glucose and 10–50 mV s−1 scan rates. The effect of glucose sensing on CuO electrode has been studied.

Effect of NaOH on plasma electrolytic oxidation of A356 aluminium alloy in moderately concentrated aluminate electrolyte

Plasma electrolytic oxidation(PEO) of cast A356 aluminum alloy was carried out in 32 g/L NaAlO2 with the addition of different concentrations of NaOH. The stability of the aluminate solution is greatly enhanced by increasing the concentration of NaOH. However, corresponding changes in the PEO behaviour occur due to the increment of NaOH concentration. Thicker precursor coatings are required for the PEO treatment in a more concentrated NaOH electrolyte. The results show that the optimal NaOH concentration is 5 g/L, which improves the stability of storage electrolyte to about 35 days, and leads to dense coatings with high wear performance (wear rate: 4.1×10−7 mm3·N−1·m−1).

Liquid metal enabled continuous flow reactor: A proof-of-concept

Liquid metal enabled continuous flow reactor: A proof-of-concept

Synergistic interaction between magnesium and iron layered hydroxide with enhanced supercapacitor performance

The utility of multivalent metal ions with aqueous electrolyte increases the electrochemical performances of supercapacitors. These compounds are non- toxic, low cost and provide accessible ionic potential towards the application’s scenario. Herein, we report a facile and effective combination of magnesium and iron layered double hydroxides (L-MFH) synthesized by industrially applicable electrodeposition technique. As of now, the bulky compositions between the metals, poor ionic conductivity and deteriorated nanostructure limits the innovation in supercapacitors. Interestingly, L-MFH dendritic structure delivers high specific capacity, 610 Cg−1 at 10 mV/s in 1 M NaOH electrolyte. The derived material retains 80% specific capacity over 3000 cycles, further the asymmetric device through the combination of L-MFH//ACC (activated carbon cloth) delivered a high energy and power densities of 39.86 Whkg−1 and 1206.03 Wkg−1, respectively. Our prescribed methodology encourages the reliability of electrode preparations, which promotes high performances of many hybrid devices.

Fabrication of efficient electrochemical capacitors rooted in sol-gel derived NiMn2O4 nanoparticles

NiMn 2 O 4 (NMO) nanoparticles are prepared by the sol–gel method. The electrode fabricated by drop casting the NMO nanoparticles onto Ni-foam showed specific capacitance of 658 Fg −1 in 1 M NaOH electrolyte. • NiMn 2 O 4 (NMO) nanoparticles are synthesized by sol–gel method. • Electrochemical properties of NMO-Ni foam are investigated in NaOH, KOH, and Na 2 SO 4 . • NMO-Ni foam exhibit specific capacitance of 658 Fg −1 in 1 M NaOH. • NMO-Ni foam showed 96.4 % cyclic stability for 1000 cycles in 1 M NaOH. NiMn 2 O 4 (NMO) nanoparticles (NPs) with a cubic spinel structure have been synthesized via the sol–gel method. The surface morphology study explored the porous nature of the NMO NPs. The compositional analysis displayed the constituent elements Ni, Mn, and O in NMO NPs. Electrochemical properties of the electrodes prepared from NMO NPs are investigated in 1 M KOH, 1 M NaOH, and 1 M Na 2 SO 4 electrolytes. At a scan rate of 5 mVs −1 , a specific capacitance of 658 Fg −1 is obtained for the NMO-Ni foam electrodes in 1 M NaOH electrolyte. At a current density of 0.5 mAcm −2 , the determined values of specific energy and specific power for the NMO-Ni foam electrodes are 13.4 Whkg −1 and 523.8 Wkg −1 , respectively, in 1 M NaOH electrolyte. The NMO-Ni foam electrodes showed 96.4 % capacitance retention in 1 M NaOH for 1000 cycles.

Electrochemical mechanisms of activated carbon, α-MnO2 and composited activated carbon-α-MnO2 films in supercapacitor applications

Pure α-MnO2 and activated carbon-MnO2 (AC-MnO2) films coated on Ni foam by electrophoretic deposition were applied as a supercapacitor electrode. The specific capacitance of AC-MnO2 films (155.03 F g−1) surpasses those of the pure AC (110.62 F g−1) and pure MnO2 film in the 1 M NaOH electrolyte. EDX and XPS detect an increase in the Na content and the reduction of Mn4+ to Mn3+ on the discharged MnO2 electrode (at 0.0 V), whereas a decrease in the Na content and the oxidation of Mn3+ to Mn4+ were obtained on the charged MnO2 electrode (at 0.45 V). Computational simulation of the Na inserted α-MnO2 structure displays the connection of Na to O atoms and the increasing electron density on Mn atoms. EDX of the charged AC-MnO2 (at −1.0 V) film detects a rise in the Na and a fall in the O contents, but the discharged AC-MnO2 film (at 0.0 V) shows a decrease in Na and increase in O contents. The AC-MnO2 film could retain 82.29% of the initial specific capacity after 10,000 cycles. Four series-supercapacitor coin cell assembled from the AC-MnO2 anode and MnO2 cathode delivers a power density of 2.79 kW kg−1 and an energy density of 168.8 Wh kg−1.

Physical properties of the delafossite CuCoO2 synthesized by co-precipitation /hydrothermal route

CuCoO2 crystallizing in the delafossite structure was prepared by co-precipitation/hydrothermal method at low temperature (~ 150 °C). It is stable in air up to ~400 °C beyond which it turns into the spinel. The oxide has a direct optical transition attributed to the crystal field splitting of Cu+, linearly coordinated. It exhibits p-type behavior due to O2− insertion in the layered lattice. Such property is corroborated by a cathodic photocurrent in the intensity-potential (J – E) plot and a negative slope of the capacitance potential (C−2– E) plot. The latter traced in NaOH (0.01 M) electrolyte, exhibits a straight line from which a flat band potential of +0.411 V and a hole density of 6.9 × 1023 m−3 were extracted. An exchange current density of 7.36 μA cm−2and a polarizarion resistance (6.69 kΩ cm2), derived from the semi-logarithmic curve (log(J) – E), indicate a good electrochemical stability with a medium hysteresis loop and a low H2-over potential. The anisotropy of the 2 D dimensional crystal structure allows reversible oxygen insertion in the (0 0 n) planes evidenced from the (J – E) profiles. The Electrochemical Impedance Spectroscopy (EIS) measurements give two well-distinguished depressive semicircles in the dark. The diameter of the semicircle at high frequencies (1.49 kΩ cm2) decreases down to (1.28 kΩ cm2) under irradiation, a behavior typical of a non-degenerate semi conductivity of CuCoO2.

Enhanced photoelectrochemical water oxidation in Hematite: Accelerated charge separation with Co doping

Hematite (α-Fe2O3) is one of the most promising candidates for a photoanode for photoelectrochemical water splitting. However, it has low efficiency because of poor conductivity in the bulk and sluggish oxygen evolution (OER) kinetics on the surface. In this study, a Co-doped α-Fe2O3 photoanode was prepared by the hydrothermal method. It had increased charge separation efficiency and accelerated surface reaction kinetics simultaneously. At the optimal Co content, the photocurrent density of the Co-doped α-Fe2O3 increased by 23 times to 0.54 mA/cm2 at 1.23 VRHE in 1 M NaOH electrolyte; this increase was attributed to the improvement in carrier density and charge transfer behavior. Moreover, the cathodic shift of onset potential for Co-doped α-Fe2O3 reached 290 mV owing to the accelerated OER kinetics. This work reveals the key roles of Co doping and provides a suitable photoanode for solar hydrogen technology.

Effect of Electrolyte pH on CH4 Adsorption and Desorption Behavior in Electrochemically Modified Lean Coal.

Practical application of the electrochemical method for enhancing coalbed methane (CBM) extraction is limited due to the insufficiency of in-depth experimental and theoretical research. Therefore, H2SO4, Na2SO4, and NaOH electrolytes with different pH values were selected to electrochemically modify lean coals and their CH4 adsorption and desorption behaviors were tested. The experimental results showed that the amount of CH4 adsorption decreased after modification using H2SO4 and Na2SO4 electrolytes, and increased after electrochemical modification using the NaOH electrolyte. The ratio of CH4 desorption increased from 83.20 to 90.10 and 87.84%, respectively, after electrochemical modification using H2SO4 and Na2SO4 electrolytes, and decreased to 81.71% after electrochemical modification using the NaOH electrolyte. The pore volume and average pore size increased, and the specific surface area decreased with the decrease of electrolyte pH. Lower pH electrolytes perform better and the mechanism was analyzed by the change of surface energy, surface groups, and pore structures. The work will provide a basis for the reasonable selection of electrolyte pH when using in situ electrochemical methods for enhancing CBM extraction.

GaN nanorods on V-groove textured Si (111): significant light trapping for photoelectrocatalytic water splitting

Although gallium nitride (GaN) nanostructures are auspicious for photocatalytic activity, geometrical optimization has paid much attention for a significant light trapping in photoelectrochemical applications. To minimize the optical losses, we designed a prototype V-groove textured Si (100) with (111) facets, and GaN nanorods (NRs) were grown over a prototype substrate using plasma-assisted molecular beam epitaxy. The photocurrent density of V-groove textured GaN NRs in the NaOH electrolyte is found to be 801.62 μA/cm2 at 1.14 V vs reversible hydrogen electrode, which was 2.1-fold larger than that of GaN NRs on plain Si (111). Using this prototype V-groove textured Si(100) with (111) facets, a significant light can be trapped and modulated into GaN NRs. Furthermore, the heterostructure between GaN NRs and V-groove textured Si stimulates effective charge separation and transportation. These results represent an important forward step in solar photoelectrolysis.

Anodic behaviour of Zn0.5Al doped with molybdenum in acidic, neutral and alkaline media

The paper presents the results of a potentiodynamic study of the anodic behaviour of Zn0.5Al doped with molybdenum in the acidic (0.1 M, pH = 1; 0.01 M, pH = 2; 0.001 M, pH = 3), neutral (0.03, 0.3, 3%, pH = 7) and alkaline (0.001 M, pH = 10; 0.01 M, pH = 11; 0.1 M, pH = 12) media of HCl, NaCl and NaOH electrolytes. In the potentiodynamic mode with an electrode potential sweep rate of 2 mV/s, all Zn0.5Al-Mo samples containing from 0.01 to 1.0 wt% of molybdenum demonstrated a shift in the potentials of corrosion, pitting formation and repassivation. These potentials shift towards negative values in acidic and alkaline media, while shifting to positive values in a neutral medium. It was established that an increase in the concentration of electrolytes led to a shift of all the considered potentials towards negative values in all media - acidic, neutral and alkaline. This dependence is associated with the specific features of the process of anodic dissolution of alloys during the formation of an oxide film on their surface. The significance of the dependence of the stationary potential of free corrosion of alloys on time for establishing the passivity of surfaces in acidic, neutral and alkaline media was shown. It was determined that zinc alloys doped with molybdenum are resistant to pitting corrosion in all the investigated media. This resistivity is particularly high in acidic (0.001 M), neutral (0.03%) and alkaline (0.001 M) media of HCl, NaCl and NaOH electrolytes. The favourable effect of molybdenum on both the anodic behaviour of Zn0.5Al and the overall increase in the corrosion resistance of alloys was demonstrated. In comparison with undoped Zn0.5Al alloys, the corrosion rate of alloys doped with molybdenum (0.01-1.0 wt%) is 2-2.5 times lower. The proposed compositions of Zn0.5Al-Mo alloys can be used as noncorrosive coatings for steel products.

Enhance corrosion behavior of AZ31 magnesium alloy by tailoring the anodic oxidation time followed by heat treatment in simulated body fluid

Purpose This paper aims to investigate the impact of anodizing time and heat treatment on morphology, phase and corrosion resistance of formed coating. To characterize the anodic oxide layer, X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) that was equipped with energy dispersive spectroscopy (EDS) was hired. The corrosion behavior of oxide-coated samples was estimated by electrochemical polarization test in simulated body fluid (SBF). Design/methodology/approach Anodic oxidation method is applied to reinforce the corrosion and biological properties of biomaterials in the biomedical industry. In this paper, the alkaline NaOH (1 M) electrolyte was used for AZ31 magnesium alloy anodizing accompanied by heat treatment in the air. Findings It can be concluded that the best corrosion resistance belongs to the 10 min anodic oxidized sample and among the heat-treated samples the 30 min anodized sample represented the lowest corrosion rate. Originality/value In this study, to the best of the authors’ knowledge for the first time, this paper describes the effect of anodizing process time on NaOH (1 M) electrolyte at 3 V on corrosion behavior of magnesium AZ31 alloy with an alternate method to change the phase composition of the formed oxide layer. The morphology and composition of the obtained anodic oxide layer were investigated under the results of SEM, EDS and XRD. The corrosion behavior of the oxide coatings layer fabricated on the magnesium-based substrate was studied by the potentiodynamic polarization test in the SBF solution.