Size effect investigation on battery performance: Comparison between micro- and nano-particles of β-Ni(OH)2 as nickel battery cathode material

In this work we report on the comparison between nano- and micro-particles of β-Ni(OH)₂ as cathode material of Ni battery. The synthesis of nano- and micro-particles of nickel hydroxide is done by two different procedures: sonication process and stirrer. Nano-particles of β-Ni(OH)₂ are synthesized by chemical precipitation from a solution containing NiCl₂·6H₂O and surfactant under ultrasonic irradiation. Micro-particles of β-Ni(OH)₂ are synthesized by a similar procedure while applying magnetic stirring instead of ultrasonic. The products are characterized by scanning electron microscopy and X-ray powder diffraction. Under the optimized conditions nickel hydroxide nano-particles, with an average particle size of 18 nm, are obtained. Cyclic voltammetric (CV) studies show a pair of well-defined peaks for Ni(OH)₂/NiOOH redox reaction, along with faster proton diffusion coefficient and higher oxygen evolution potential for nano-particles of nickel hydroxide compared to that of micro-particles. Electrochemical impedance spectroscopy (EIS) studies of Ni(OH)₂ electrodes show that the reaction occurring at the nickel hydroxide is controlled by charge transfer and Warburg diffusion. The β-Ni(OH)₂ nano-particles are found to exhibit a superior cycling reversibility and improved capacity when they are used as positive electrode materials of alkaline rechargeable batteries.     

Effects of addition of different carbon materials on the electrochemical performance of nickel hydroxide electrode

Nickel hydroxide is used as an active material in positive electrodes of rechargeable alkaline batteries. The capacity of nickel-metal hydride (Ni-MH) batteries depends on the specific capacity of the positive electrode and utilization of the active material because of the Ni(OH)₂/NiOOH electrode capacity limitation. The practical capacity of the positive nickel electrode depends on the efficiency of the conductive network connecting the Ni(OH)₂ particle with the current collector. As β-Ni(OH)₂ is a kind of semiconductor, the additives are necessary to improve the conductivity between the active material and the current collector. In this study the effect of adding different carbon materials (flake graphite, multi-walled carbon nanotubes (MWNT)) on the electrochemical performance of pasted nickel-foam electrode was established. A method of production of MWNT special type of catalysts had an influence on the performance of the nickel electrodes. The electrochemical tests showed that the electrode with added MWNT (110-170 nm diameter) exhibited better electrochemical properties in the chargeability, specific discharge capacity, active material utilization, discharge voltage and cycling stability. The nickel electrodes with MWNT addition (110-170 nm diameter) have exhibited a specific capacity close to 280 mAh g⁻¹ of Ni(OH)₂, and the degree of active material utilization was ∼96%.     

Comparative structural and electrochemical study of high density spherical and non-spherical Ni(OH)2 as cathode materials for Ni-metal hydride batteries

In this paper we compare the behavior of non-spherical and spherical β-Ni(OH)₂ as cathode materials for Ni-MH batteries in an attempt to explore the effect of microstructure and surface properties of β-Ni(OH)₂ on their electrochemical performances. Non-spherical β-Ni(OH)₂ powders with a high-density are synthesized using a simple polyacrylamide (PAM) assisted two-step drying method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG-DTA), Brunauer-Emmett-Teller (BET) testing, laser particle size analysis, and tap-density testing are used to characterize the physical properties of the synthesized products. Electrochemical characterization, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge/discharge test, is also performed. The results show that the non-spherical β-Ni(OH)₂ materials exhibit an irregular tabular shape and a dense solid structure, which contains many overlapped sheet nano crystalline grains, and have a high density of structural disorder and a large specific surface area. Compared with the spherical β-Ni(OH)₂, the non-spherical β-Ni(OH)₂ materials have an enhanced discharge capacity, higher discharge potential plateau and superior cycle stability. This performance improvement can be attributable to a higher proton diffusion coefficient (4.26 × 10⁻⁹ cm² s⁻¹), better reaction reversibility, and lower electrochemical impedance of the synthesized material.     

Characterization of honeycomb-like “β-Ni(OH)2” thin films synthesized by chemical bath deposition method and their supercapacitor application

Nanostructured nickel hydroxide thin films are synthesized via a simple chemical bath deposition (CBD) method using nickel nitrate Ni(NO₃)₂ as the starting material. The deposition process is based on the thermal decomposition of ammonia-complexed nickel ions at 333 K. The structural, surface morphological, optical, electrical and electrochemical properties of the films are examined. The nanocrystalline “β” phase of Ni(OH)₂ is confirmed by the X-ray diffraction analysis. Scanning electron microscopy reveals a macroporous and interconnected honeycomb-like morphology. Optical absorption studies show that “β-Ni(OH)₂” has a wide optical band-gap of 3.95 eV. The negative temperature coefficient of the electrical resistance of “β-Ni(OH)₂”, is attributed to the semiconducting nature of the material. The electrochemical properties of “β-Ni(OH)₂” in KOH electrolyte are examined by cyclic voltammetric (CV) measurements. The scan-rate dependent voltammograms demonstrate pseudocapacitive behaviour when “β-Ni(OH)₂” is employed as a working electrode in a three-electrode electrochemical cell containing 2 M KOH electrolyte with a platinum counter electrode and a saturated calomel reference electrodes. A specific capacitance of ∼398 × 10³ F kg⁻¹ is obtained.     

Regulation of the discharge reservoir of negative electrodes in Ni-MH batteries by using Ni(OH)x (x = 2.10) and γ-CoOOH

In this paper, a novel strategy to regulate the discharge reservoir of negative electrodes in Ni-MH batteries is introduced by using Ni(OH)_x (x = 2.10) and γ-CoOOH. The electrochemical measurements of these batteries demonstrate that the use of Ni(OH)_x (x = 2.10) and γ-CoOOH can not only successfully regulate the discharge reservoir of negative electrodes in Ni-MH batteries to an adequate quantity, but also effectively improve the electrochemical performance of the batteries. Compared with normal batteries, the in-house prepared batteries with a lower discharge reservoir exhibit an enhanced discharge capacity, improved high-rate discharge ability, higher discharge potential plateau and superior cycle stability. The effect of Ni(OH)_x (x = 2.10) and γ-CoOOH on the electrochemical performance of nickel electrode is also investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results suggest that the new method is simple and effective for cost reduction of Ni-MH batteries with improved electrochemical performance.     

Oxidation of methanol on perovskite-type La2-xSrxNiO4 (0 ≤ x ≤ 1) film electrodes modified by dispersed nickel in 1 M KOH

Finely-dispersed nickel particles are electrodeposited on high surface-area perovskite-type La_2-xSr_xNiO₄ (0 ≤ x ≤ 1) electrodes for possible use in a direct methanol fuel cell (DMFC). The study is conducted by cyclic voltammetry, chronoamperometry, impedance spectroscopy and anodic Tafel polarization techniques. The results show that the apparent electrocatalytic activities of the modified oxide electrodes are much higher than those of unmodified electrodes under similar experimental conditions; the observed activity is the greatest with the modified La_1.5Sr_0.5NiO₄ electrode. At 0.550 V (vs. Hg|HgO) in 1 M KOH + 1 M CH₃OH at 25 °C, the latter electrode delivers a current density of over 200 mA cm⁻², whereas other electrodes of the series produce relatively low values (65–117 mA cm⁻²). To our knowledge, such high methanol oxidation current densities have not been reported on any other non-platinum electrode in alkaline solution. Further, the modified electrodes are not poisoned by methanol oxidation intermediates/products.     

Evaluation of the effects of oxygen evolution on the capacity and cycle life of nickel hydroxide electrode materials

The effect of charge–discharge cycling on the capacity of surface-adhered nickel hydroxide (Ni(OH)₂) micro-particles is investigated in aqueous KOH by cyclic voltammetry, and compared with that for pasted nickel hydroxide electrodes. Cyclic voltammetry on adhered Ni(OH)₂ micro-particles enables rapid screening of four types of commercially available, battery-grade, nickel hydroxide samples and allows the separation of the oxidation process from the oxygen evolution reaction. With large pasted electrodes, due to their high uncompensated resistance (R_u), these processes are poorly resolved. Pasted β-nickel hydroxide electrodes with a specific capacity of between 190 and 210 mAh g⁻¹ are charged and discharged at constant currents greater than 15 C (18 mA cm⁻²). With no voltage limit in the charging profile, excess oxygen evolution occurs and capacity fading is observed within the first 50 cycles. Loss of capacity is attributed to the degradation of the electrode due to excess oxygen evolution at switching potentials greater than 0.55 V versus Hg/HgO (1 M KOH). X-ray diffraction (XRD) measurements confirm the formation of γ-NiOOH in these electrodes. Limiting the cell voltage to 1.5 V, and thereby minimizing oxygen evolution, results in no observed capacity loss within 100 cycles, and only β-Ni(OH)₂ can be detected by XRD phase analysis.     

High-rate discharge properties of nickel hydroxide/carbon composite as positive electrode for Ni/MH batteries

A chemical co-precipitation method was attempted to synthesize nickel hydroxide/carbon composite material for high-power Ni/MH batteries. The XRD analysis showed that there were a large amount of defects among the crystal lattice of the Ni(OH)₂/C composite, and the SEM investigation revealed that the as-synthesized spherical particles were composed of hundreds of nanometer crystals with a unique three-dimensional petal shape. Compared with pure Ni(OH)₂, the Ni(OH)₂/C composite showed improved electrochemical properties such as superior cycling stability, higher discharge capacity and higher mean voltage of discharge under high-rate discharge conditions, the discharge capacity and the mean discharge voltage of the Ni(OH)₂/C composite were about 281 mAh g⁻¹ and 0.303 V (vs. Hg/HgO) at 1 C-rate, 273 mAh g⁻¹ and 0.296 V at 5 C-rate, 250 mAh g⁻¹ and 0.292 V at 10 C-rate, respectively. The cyclic voltammetry (CV) tests showed that the Ni(OH)₂/C composite exhibited good electrochemical reversibility and the formation of γ-NiOOH during the charge–discharge processes was prevented. The existence of carbon in the Ni(OH)₂/C composite contributed great effect on the improvement of high-rate discharge performance.     

Effects of different Ni(OH)2 precursors on the structure and electrochemical properties of NiOOH

Nickel oxyhydroxide (NiOOH), an active material for alkaline Zn-NiOOH batteries, was synthesized by electrolysis oxidation of different Ni(OH)₂ precursors, which were prepared by three methods: polyacrylamide (PAM) assisted two-step drying (PTSD), conventional co-precipitation (CCP), and “controlled crystallization” (CC). The NiOOH samples were characterized and tested using X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) testing, laser particle size analysis, tap-density testing, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a discharge test. The results demonstrate that the physical and electrochemical properties of NiOOH are strongly dependent on the properties of the Ni(OH)₂ precursor, such as its morphology, microstructure, tap density, and specific surface area. The results of the electrochemical studies also show that the sample prepared by the PTSD method is superior to the others in electrochemical performance. The as-prepared, high-density, non-spherical NiOOH is a promising active material for the positive electrode in Zn-NiOOH batteries.     

Fabrication and electrochemical activity of Ni-attached carbon nanotube electrodes for hydrogen storage in alkali electrolyte

The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with Ni nanoparticles was investigated. A surface modification technique enabled different Ni particle densities to coat onto the CNT surface, which was chemically oxidized by nitric acid. It was found that each nickel nanoparticle has an average size of 30–50  nm, and the Ni-attached CNTs still possessed a similar pore size distribution. Cyclic voltammetry measurements in 6  M KOH showed that the electrochemical adsorption and desorption amount of hydrogen is a linearly increasing function of the Ni loading. This enhancement of electrochemical activity was ascribed to a fact that Ni particle acts as a redox site for hydrogen storage, thus leading to a greater specific peak current. According to our calculation, the electrochemical capacitance of nickel nanocatalyst in KOH electrolyte was estimated to be the value of 217  F/g. Charge/discharge cycling demonstrated that the Ni-attached CNT electrode maintains fairly good cycleability during 50 cycles.     

Pseudocapacitive properties of electrochemically prepared nickel oxides on 3-dimensional carbon nanotube film substrates

Nickel oxides on carbon nanotube electrodes (NiO_x/CNT electrodes) are prepared by depositing Ni(OH)₂ electrochemically onto carbon nanotube (CNT) film substrates with subsequent heating to 300 °C. Compared with the as deposited Ni(OH)₂ on CNT film substrates (Ni(OH)₂/CNT electrodes), the 300 °C heat treated electrode shows much high rate capability, which makes it suitable as an electrode in supercapacitor applications. X-ray photoelectron spectroscopy shows that the pseudocapacitance of the NiO_x/CNT electrodes in a 1 M KOH solution originates from redox reactions of NiO_x/NiO_xOH and Ni(OH)₂/NiOOH. The 8.9 wt.% NiO_x in the NiO_x/CNT electrode shows a NiO_x-normalized specific capacitance of 1701 F g⁻¹ with excellent high rate capability due to the 3-dimensional nanoporous network structure with an extremely thin NiO_x layer on the CNT film substrate. On the other hand, the 36.6 wt.% NiO_x/CNT electrode has a maximum geometric and volumetric capacitance of 127 mF cm⁻² and 254 F cc⁻¹, respectively, with a specific capacitance of 671 F g⁻¹, which is much lower than that of the 8.9% NiO_x electrode. This decrease in specific capacitance of the high wt.% NiO_x/CNT electrodes can be attributed to the dead volume of the oxides, high equivalent series resistance for a heavier deposit, and the ineffective ionic transportation caused by the destruction of the 3-dimensional network structure. Deconvolution analysis of the cyclic voltammograms reveals that the rate capability of the NiO_x/CNT electrodes is adversely affected by the redox reaction of Ni(OH)₂, while the adverse effects from the reaction of NiO_x is insignificant.     

High-temperature electrochemical performance of Al-α-nickel hydroxides modified by metallic cobalt or Y(OH)3

Al-α-Ni(OH)₂ microspheres are modified with metallic Co and Y(OH)₃, respectively, in order to improve the high-temperature electrochemical performance. The microstructure, morphology, and surface chemical state of the as-prepared and the modified Al-α-Ni(OH)₂ microspheres are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Metallic cobalt nanoparticles are distributed on the nanosheets of the microsphere edges. The existence of metallic Co and Y(OH)₃ can be further verified from ICP and XPS results. The effect of metallic Co or Y(OH)₃ on high-temperature performance of the Al-α-Ni(OH)₂ microspheres is measured by galvanostatic charge–discharge experiments and cyclic voltammetric (CV) measurements. The discharge capacities of the Al-α-Ni(OH)₂ microspheres, with optimized 5 wt% Co and 1 wt% Y(OH)₃, are 283.5 mAh g⁻¹ and 315 mAh g⁻¹, respectively, much higher than that of the as-prepared Al-α-Ni(OH)₂ (226.8 mAh g⁻¹) at 0.2 C and 60 °C. Furthermore, the high-rate discharge capability at high temperature can be also improved for both the modified samples.     

Improved pseudocapacitive performance and cycle life of cobalt hydroxide on an electrochemically derived nano-porous Ni framework

The pseudocapacitance and morphology of an electrodeposited cobalt hydroxide (Co(OH)₂) significantly depends on the architecture of the electrode substrate. The nano-porous Ni framework, derived from the selective dissolution of Cu from a Ni-Cu alloy, effectively promotes the electrochemical utilization of deposited Co(OH)₂ even at a high loading amount condition. The great electronic and ionic conduction within the nano-structured electrode improves the energy storage performance of Co(OH)₂ as compared to that for a conventional flat Ni substrate. In this work, the Co(OH)₂ mass specific capacitance, evaluated using cyclic voltammetry (CV), only slightly decreases from 2650 to 2470 F g⁻¹ when the potential sweep rate is substantially increased from 5 to 200 mV s⁻¹. The developed Ni(OH)₂/NiOOH (from the nano-porous framework) incorporates with the deposited Co(OH)₂ upon CV cycling; the mixed hydroxide shows a noticeably synergistic capacitance. Furthermore, the dissolution of Co(OH)₂ in KOH electrolyte is greatly suppressed due to the incorporation of Ni(OH)₂/NiOOH, consequently prolonging the electrode cycle life.     

Boosting discharge capability of α-Ni(OH)2 by cobalt doping based on robust spherical structure

α-Ni(OH)₂ is a promising candidate of the currently commercialized β-Ni(OH)₂ due to its higher theoretical discharge capacity in alkaline solution; however, its instability and poor conductivity plague the practical application. Herein, we propose α-Ni(OH)₂ with Co doping and spherical structure to strengthen the stability and enhance the conductivity and use it as the cathode for nickel-metal hydride batteries. Studies show that proper Co doping promotes the electrochemical reaction between the active materials and the electrolyte due to the spherical α-Ni(OH)₂ with enlarged interlayer distance and abundant hole channels, as well as high conductivity of Co, therefore, the obtained spherical α-Ni(OH)₂ with 7 mol% Co doping delivers significantly improved discharge capability, which is 384.6 mAh g^?1 at 70 mA g^?1 (0.2 C), increased by 54.3 mAh g^?1 compared with pure α-Ni(OH)₂, and at a high current of 5 C, it still gives 269.4 mAh g^?1, in contrast 218.5 mA g^?1 for the pure α-Ni(OH)₂. Besides, the cycling stability of the α-Ni(OH)₂ with 7 mol% Co doping maintains 340 cycles at a capacity retention of 80% (1C), which is extended 110 cycles in contrast to the pure α-Ni(OH)₂. These results provide the underpinning platform of α-Ni(OH)₂ for battery applications with high discharge ability and cycle life.     

Synthesis, characterization, and electrochemical properties of ultrafine β-Ni(OH)2 nanoparticles

Nickel hydroxide was deposited via cathodic electrodeposition from low-temperature 0.005 M NiCl₂ bath without using any surfactant or template. The cathodic current density was 1 mA cm⁻² and stainless steel was used as the cathode. The XRD pattern confirmed that the prepared sample has a pure brucite crystal phase of β-Ni(OH)₂ and the broadening of diffraction peaks showed that the particles size of the prepared β-Ni(OH)₂ is extremely small. Thermal behavior and composition of the prepared β-Ni(OH)₂ were investigated by DSC-TG and FT-IR analyses. Morphological characterization by SEM and TEM revealed that β-Ni(OH)₂ is composed of well dispersed ultrafine particles with size of about 5 nm. The electrochemical properties of the prepared nanoparticles were studied by means of cyclic voltammetry (CV) and galvanostatic charge-discharge tests in 1 M KOH. The prepared β-Ni(OH)₂ nanoparticles showed excellent capacitance behavior of 740 F g⁻¹ in the potential window of 0-0.55 V vs. Ag/AgCl. These results make the β-Ni(OH)₂ nanoparticles as a promising candidate for the supercapacitor electrodes.     

Development of NiMH-based Fuel Cell/Battery (FCB) system: Characterization of Ni(OH)2/MnO2 positive electrode for FCB

The performance of the positive electrode composed of a mixture of nickel hydroxide (Ni(OH)₂) and a small amount of manganese dioxide (MnO₂) was investigated for the positive electrode of Fuel Cell/Battery (FCB) system. It was found that the positive electrode can function not only as an active material of secondary batteries when it is charged but also as a catalyst of fuel cells when oxygen is supplied, which was confirmed by the following characterization: electrochemical characterization was performed with cyclic voltammetry (CV) and galvanostatic discharge curve in oxygen and oxygen-free atmosphere. CV of Ni(OH)₂/MnO₂ positive electrode exhibited the redox reaction of Ni(OH)₂ as well as oxygen reduction reaction. It was observed that the discharge curves of positive electrode had two working potentials in half cell test when the electrode was charged and oxygen was supplied: one from the reactions of nickel oxyhydroxide (NiOOH); the other from the fuel cell reactions of manganese dioxide (MnO₂). It was also observed that the discharge curves had two working voltages in full cell test when the cell was fully charged and oxygen was supplied: one at 1.2 V from the battery reactions of NiOOH; the other at 0.8 V from the fuel cell reactions of MnO₂. In particular, the discharge capacity of overcharged cell was improved approximately 2 times compared with a battery of the same electrode quantity due to the additional function of this system as a fuel cell by using oxygen generated by water electrolysis. XRD analysis showed that there was no crystal structure change before and after (over)charge–discharge cycles. In summary, these experimental results showed that the novel bi-functional FCB system could provide an improved overall energy density per weight compared with conventional secondary batteries.     

Effects of surface coating of Y(OH)3 on the electrochemical performance of spherical Ni(OH)2

The effects of surface coating of Y(OH)₃ on the electrochemical performance of spherical Ni(OH)₂ were studied by cyclic voltammetry (CV) with soft-embedded electrode (SE-E). The coating was performed by chemical surface precipitation under different conditions. The structure, morphology, chemical composition and electrochemical properties of two different samples with surface coating of Y(OH)₃ were characterized and compared. The results show that a two-step oxidation process exists in the oxidation procedure of spherical Ni(OH)₂ corresponding to the formation of Ni(III) and Ni(IV), respectively. The conversion of Ni(III) to Ni(IV) is regarded as a side reaction in which Ni(IV) species is not stable. The presence of Y(OH)₃ on the particle surface can restrain the side reactions, especially the formation of Ni(IV). The application of coated Ni(OH)₂ to sealed Ni–MH batteries yielded a charge acceptance of about 88% at 60 °C. The results manifest that the high-temperature performance of Ni(OH)₂ electrode is related to the distribution of the adding elements in surface oxide layer of Ni(OH)₂, the sample with dense and porous coating surface, larger relative surface content and higher utilization ratio of yttrium is more effective.     

Oxygen reduction reaction via the 4-electron transfer pathway on transition metal hydroxides

Carbon-supported Co(OH)₂ and Ni(OH)₂ catalysts are prepared to examine the mechanism of oxygen reduction reaction (ORR) on hydroxide catalysts. ORR via the 4-electron transfer pathway on a hydroxide undergoes oxidation of hydroxide by O₂ to form oxyhydroxide, followed by electrochemical reaction of oxyhydroxide to regain hydroxide. β-Ni(OH)₂ has the same crystal structure and lattice parameters as β-Co(OH)₂, but it exhibits a poorer catalytic activity toward ORR than β-Co(OH)₂ at a low temperature. The poor catalytic activity of Ni(OH)₂/C can be attributed to the difficulty in Ni(OH)₂ oxidation and the slow kinetics of NiOOH electroreduction to Ni(OH)₂. The catalytic activity of the Ni(OH)₂/C catalyst is significantly improved through elevating the operation temperature because Ni(OH)₂ oxidation to NiOOH and NiOOH electroreduction are improved at a high temperature. A model of ORR via the 4-electron transfer pathway on transition metal hydroxides is suggested and discussed.     

Synthesis and characterization of nanocrystalline Zn1−xMxO (M = Ni, Cr) thin films for efficient photoelectrochemical splitting of water under UV irradiation

Nanocrystalline thin films of Zn_1−xM_xO (M = Ni, Cr) were deposited on glass substrate by sol-gel method. To a solution of zinc acetate 2-hydrate in dimethyl formamide, calculated quantities of nickel nitrate or chromium acetate were added. The clear solution, obtained after 2 h of continuous stirring, was coated on conducting glass (ITO plates). After preannealing at 250 °C to remove organic impurities, films were sintered at 400, 500 and 600 °C. XRD analysis reveals dominant evolution of hexagonal ZnO with a possible simultaneous growth of meta-stable cubic ZnO. AFM analysis indicated preferential growth of nanocrystallites along c-axis, while SEM analysis confirmed films having uniform morphology. Optical characterization led to two band gap values; one matching with the band gap of bulk ZnO and the second slightly higher, which suggest quantum confinement effect in nanocrystallites. Ni and Cr incorporation influenced the two band gap energies differently. Photoelectrochemical (PEC) splitting of water was attempted, using prepared thin films as working electrode, in conjunction with Pt counter electrode and saturated calomel reference electrode along with 150 W Xenon Arc light source and aqueous solution of NaOH (0.01 M). Results indicate Ni:ZnO films yielding improved photoresponse compared to Cr:ZnO films. Ni:ZnO (5 % at.) films sintered at 600 °C resulted in significantly enhanced photocurrent due to improved optical absorption and decrease in resistivity.     

Synthesis of ZSM-5 zeolite: Electrochemical behavior of carbon paste electrode modified with Ni (II)-zeolite and its application for electrocatalytic oxidation of methanol

In this research, we reported a novel method for synthesis of ZSM-5 zeolite. The synthesized zeolite was characterized using X-ray diffraction, scanning electronic microscopy and FT-IR techniques. The modified carbon paste electrode was prepared by incorporation of Ni (II)-zeolite in the carbon paste matrix. The electrochemical oxidation of methanol was investigated at the surface of this modified electrode in alkaline solution using cyclic voltammetry and chronoamperometry methods. It was found that methanol was oxidized by NiOOH generated with further electrochemical oxidation of nickel hydroxide on the surface of this modified electrode during the anodic potential sweep. The effect of some parameters such as scan rate of potential, concentration of methanol, amount of Ni (II)-zeolite was investigated on the oxidation of methanol at this electrode. Also, the rate constant for the catalytic reaction (k) of methanol was obtained.