The effect of halide ion concentration on capacitor performance

The effect of halide ion concentration on the capacitor performance was considered during this study. Iodide anion has been selected as the most profitable halide taking into account its electrochemical properties and environmental impact. Several concentrations of NaI were tested (from 0.25 to 5 mol L^?1 aqueous solutions) using as electrodes two commercial activated carbons and one KOH-activated carbon. Detailed electrochemical investigation by galvanostatic charging/discharging, cyclic voltammetry, and impedance spectroscopy confirmed the significant impact of iodide concentration on the supercapacitor behavior. The higher concentration of iodide affected especially the performance of positive electrode; increase of iodide concentration changed the potential range of positive electrode and its capacitance increased from 119 F g^?1 for 0.25 mol L^?1 NaI to 475 F g^?1 for 2 mol L^?1 NaI solution. The electrode capacitance measured in two-electrode system at current density of 2 A g^?1 ranged from 198 F g^?1 for 0.25 mol L^?1 NaI to 272 F g^?1 for 2 mol L^?1 NaI solution (capacitance expressed as average of the positive and negative electrode capacitances). It has been proved that 2 mol L^?1 alkali metal iodide solution is an optimal electrolyte for the capacitor based on KOH-activated carbon. High capacitance values and perfect stability (100 % retention) of such systems have been observed during long-term galvanostatic charging/discharging (15,000 cycles). In addition, satisfactory floating tests at extended voltage range (1.2 V) were performed.     

Nanoporous rice husk derived carbon for gas storage and high performance electrochemical energy storage

We report on the gas storage behaviour and electrochemical charge storage properties of high surface area activated nanoporous carbon obtained from rice husk through low temperature chemical activation approach. Rice husk derived porous carbon (RHDPC) exhibits varying porous characteristics upon activation at different temperatures and we observed high gas uptake and efficient energy storage properties for nanoporous carbon materials activated even at a moderate activation temperature of 500 °C. Various experimental techniques including Fourier transform-infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and pore size analyser are employed to characterise the samples. Detailed studies on gas adsorption behaviour of CO₂, H₂ and CH₄ on RHDPCs have been performed at different temperatures using a volumetric gas analyser. High adsorption capacities of ~9.4 mmol g^?1 (298 K, 20 bar), 1.8 wt% (77 K, 10 bar) and ~5 mmol g^?1 (298 K, 40 bar) were obtained respectively for CO₂, H₂ and CH₄, superior to many other carbon based physical adsorbents reported so far. In addition, these nanoporous carbon materials exhibit good electrochemical performance as supercapacitor electrodes and a maximum specific capacitance of 112 F g^?1 has been obtained using aqueous 1 M Na₂SO₄ as electrolyte. Our studies thus demonstrate that nanoporous carbon with high porosity and surface area, obtained through an efficient approach, can act as effective materials for gas storage and electrochemical energy storage applications.     

Electrochemical behaviour and electrowinning of rhodium in acidic chloride solution

The electrochemical behaviour and recovery of rhodium in an acidic solution were investigated using a rotating disc electrode system and a modified electrochemical cyclone cell, respectively. The electrochemical polarization data indicated that the Rh³⁺ ions were reduced to metallic Rh below ?0.1 V, and the limiting current density for rhodium deposition was observed at around ?0.3 V (vs. SCE) with a diffusion coefficient of 6.3 × 10^?6 cm² s^?1 using the Levich equation. The effects of the applied voltage and the initial concentration of rhodium were examined using the modified cyclone cell, and more than 91 % of the rhodium in solution was recovered within 2 h under the optimal conditions.     

Diamond cylindrical anodes for electrochemical treatment of persistent compounds in aqueous solution

Boron-doped diamond (BDD) films were deposited onto either silicon or niobium cylindrical substrates with areas up to 35 cm² for electrochemical applications. BDD electrodes were characterised in terms of their material and electrochemical properties by scanning electron microscopy, Raman spectroscopy and linear sweep voltammetry. These characterisation techniques indicated conductive polycrystalline BDD with low quantities of non-diamond carbon impurities. Electrochemical oxidations of pharmaceutical compounds were performed using these cylindrical electrodes and monitored by UV/Vis spectroscopy, chemical oxygen demand and total organic carbon. Mixtures of chlortetracycline, oxytetracycline and diclofenac were electrolyzed on a 9.42 cm² (? = 6 mm, h = 50 mm) cylindrical Si/BDD anode using a current density of 8.2 mA cm^?2. Ibuprofen was electrolyzed on an 18.0 cm² (? = 10 mm, h = 60 mm) cylindrical Nb/BDD anode using a current density of 25 mA cm^?2. Cylindrical-shape diamond electrodes present several advantages with respect to conventional plate-shape BDD electrodes such as handling, sealing and cell assembly. The obtained results show that BDD cylindrical anodes are promising for electrochemical wastewater treatment.     

High areal capacitance of FeOOH-carbon nanotube negative electrodes for asymmetric supercapacitors

The relatively low capacitance of negative electrodes, as compared to the capacitance of advanced positive electrodes, poses a serious problem, since this limits the development of asymmetric supercapacitor (SC) devices with a large voltage window and enhanced power-energy characteristics. We fabricate negative SC electrodes with a high capacitance that match the capacitance of advanced positive electrodes at similar active mass loadings, as high as 37?mg?cm^?2. Cyclic voltammetry, impedance spectroscopy, galvanostatic charge-discharge data and the power-energy characteristics of the asymmetric SC device exhibit good electrochemical performance for a voltage window of 1.6?V. Our approach involves the development and application of particle extraction through liquid-liquid interface (PELLI) methods, new extraction mechanisms and efficient extractors to synthesize α-FeOOH and β-FeOOH electrode materials. The use of PELLI allows agglomerate-free processing of powders, which facilitates their efficient mixing with multiwalled carbon nanotubes (MWCNT) and allows improved electrolyte access to the particle surface. Experiments to determine the properties of FeOOH-MWCNT composites provided insight into the influence of the electrode material and the structure of extractor molecules on the composite properties. The highest capacitance of 5.86?F?cm^?2 for negative electrodes and low impedance were achieved using α-FeOOH-MWCNT composites and a 16-phosphonohexadecanoic acid (PHDA) extractor. This extractor allows adsorption on particles, not only at the liquid-liquid interface, but also in the bulk aqueous phase and can potentially be used as a capping agent for particle synthesis and as an extractor in the PELLI method.     

Novel one-step synthesis for 3-D four-pointed micro-star of quaternary metal (Mo–V–Mn–Ag) oxide electrode for asymmetric supercapacitor

An intention of the present work is to synthesize a quaternary metal oxide by a simple and cost-effective method. MoVMnAg-oxide@Ni-foam is synthesised by one-step hydrothermal method. The as-deposited MoVMnAg-oxide sample is systematically examined through XRD, FESEM, EDS-mapping, and TEM analysis. The electrochemical performance of an MoVMnAg@Ni-foam electrode is tested using CV, GCD, and EIS techniques. MoVMnAg-oxide@Ni-foam has a considerable high areal capacitance of 651 mFcm^?2 with 0.13 mWhcm^?2 energy at 1.8 mWcm^?2 power density in 1 M KOH electrolyte calculated from GCD curves. Also, the electrode shows a diffusion coefficient of 1.52 × 10^?7 cm²s^?1 along with 91 % of diffusive-controlled contribution and a b-value of 0.51, which depicts faradaic charge storage mechanism. An assembled asymmetric supercapacitor device (MoVMnAg@Ni-foam//AC) delivers an areal capacitance of 312 mFcm^?2 with 0.37 mWcm^?2 power density at 1 mAcm^?2 current density within 0 – 1.5 V voltage window. The asymmetric device showed cyclability and coulombic efficiency of 80.3% and 95% respectively measured up to 10,000 GCD cycles. These results demonstrate the deposition of quaternary metal oxide directly on Ni-foam showing highly competitive electrochemical performance so that they can be utilized in energy storage applications.     

Integration of supercapacitors with enzymatic biobatteries toward more effective pulse-powered use in small-scale energy harvesting devices

Effective integration of electrochemical devices consisting of enzyme-based biobatteries together with high power double-layer type capacitors is discussed here. An ultimate goal is to overcome a typical drawback of enzymatic power sources (biofuel cells and biobatteries): although their energy is potentially high enough to fulfill the needs of small electronic devices, their power is often too low. It is demonstrated that properly selected capacitor can support operation of such a low power device simply by supplying appropriate power pulses with fast dynamic response that is required for many applications involving fluctuating loads. Our model integrated system is obtained by coupling a series of double-layer capacitors with well-behaved zinc/oxygen biobattery. The biobattery utilizes a stable cathodic material composed of covalently phenylated single-walled carbon nanotubes and the oxygen reduction enzyme, laccase, together with the hopeite-covered zinc rod acting as the anode. The enzymatic power source was characterized by the maximum power density of 1.8 mW cm^?2, the open circuit voltage of 1.6 V. Nevertheless, under the 50 Ω loading, the voltage of biobattery (electrode surface areas of ca. 0.3 cm²) drops to 0 V after 2 s. The practical performance (power stability) of a biobattery has significantly improved by its parallel connection to electrochemical capacitor. The importance of such capacitor’s parameters as low resistance (not more than a few hundred of milliohms), proper capacitance, and leakage current (not higher than a few microamperes) is emphasized here. The potential utility of the optimized biobattery/supercapacitor system is discussed in terms of use as a source of power to operate a digital watch.     

Electrochemical reduction of CO2 to formate at high current density using gas diffusion electrodes

The electrochemical reduction of carbon dioxide into formate was studied using gas diffusion electrodes (GDE) with Sn as electrocatalyst in order to overcome mass transport limitations and to achieve high current densities. For this purpose, a dry pressing method was developed for GDE preparation and optimized with respect to mechanical stability and the performance in the reduction of CO₂. Using this approach, GDEs can be obtained with a high reproducibility in a very simple, fast, and straightforward manner. The influence of the metal loading on current density and product distribution was investigated. Furthermore, the effect of changing the electrolyte pH was evaluated. Under optimized conditions, the GDE allowed current densities up to 200 mA cm^?2 to be achieved with a Faradaic efficiency of around 90 % toward formate and a substantial suppression of hydrogen production (<3 %) at ambient pressure. At higher current densities mass transport issues come into effect and hydrogen is increasingly produced. The corresponding cathode potential was found to be 1.57 V vs. SHE.     

Preparation and capacitance performance of polyaniline/titanium nitride nanotube hybrid

A polyaniline/titanium nitride (PANI/TiN) nanotube hybrid was prepared and used for an electrochemical supercapacitor application. Firstly, the well-aligned TiN nanotube array was prepared by anodization of titanium foil and subsequent nitridation through ammonia annealing. Then, PANI was deposited into TiN nanotube through the electrochemical polymerization process. The obtained PANI/TiN nanotube hybrid had an ordered porous structure. A high specific capacitance of 1,066 F g^?1 was obtained at the charge–discharge current density of 1 A g^?1 when only the mass of PANI was considered. The specific capacitance can even achieve 864 F g^?1 at 10 A g^?1 and still keep 93 % of the initial capacity after 200 cycles. An aqueous supercapacitor, consisting of two symmetric PANI/TiN nanotube hybrid electrodes and 1.0 M H₂SO₄ electrolyte solution, showed the specific capacitance of 194.8 F g^?1, energy density of 9.74 Wh kg^?1, and power density of 0.3 kW kg^?1.     

Electrochemical Regeneration of Zn-Saturated Granular Activated Carbon from Electroplating Wastewater Plant

An electrically assisted regeneration (EAR) process was used to assess the effectiveness of regenerating exhausted granular activated carbon (GAC) preloaded with electroplating wastewater containing hyper Zn concentration at a concentration of 950.5 mg L ^?1  (1.45 × 10 ^?2  mol L ^?1 ). The electrochemical rege-neration process supplied with direct current was controlled at a constant voltage of 5.0 V. Two regeneration methods were tested and compared: first, acid washing (pH 1.0) and, second, electrically assisted acid washing. Results showed that the Zn adsorption capacity of GAC regenerated by EAR was significantly higher than that of GAC regenerated by acid washing. The effectiveness of the Zn desorbing efficiency from GAC was enhanced by electric current in the electrochemical regeneration process. Using the EAR method, a regeneration efficiency of 88.3% was observed for GAC, whereas using acid regeneration, the efficiency was only 25.3%. These observations reveal that EAR could be a potential alternative to acid washing for the regeneration of GAC saturated with Zn.     

Preparation and electrochemical properties of poly‐2,5‐dihydroxyaniline/activated carbon composite electrode in organic electrolyte

Poly‐2,5‐dimethoxyaniline coating has been fabricated on active carbon (AC) substrates by cyclic voltammetry (CV) in organic system. The resulted coating is hydrolyzed to produce poly‐2,5‐dihydroxyaniline (PDHA) to enhance the capacitance of the composite electrode. Scanning electron microscope, Fourier transform infrared spectroscopy, X‐ray diffraction, Raman spectra, CV, electrochemical impedance spectroscopy, and galvanostatic charge/discharge test are used to investigate the properties of these electrodes. In organic electrolyte, due to the introduced hydroquinone units, high value of capacitance up to 975 F g^?1 of the PDHA/AC has been obtained at a current density of 0.37 A g^?1 at a potential window of 0–1.5 V. An asymmetric capacitor has been assembled with the PDHA/AC positive and pure AC negative electrodes, which is able to obtain a specific energy as high as 178 Whkg^?1 in the potential range of 0–2.0 V at a current density of 0.93 A g^?1. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrochemical determination of malachite green at graphene quantum dots–gold nanoparticles multilayers–modified glassy carbon electrode

A graphene quantum dots–gold nanoparticles–modified glassy carbon electrode was used to investigate the electrochemical behaviors of malachite green (MG). Cyclic voltammetry curves of MG at the modified electrode exhibited a pair of quasi-reversible adsorption-controlled redox peaks at 0.502 V (E _pa) and 0.446 V (E _pc) in a 0.05 mol L^?1 H₂SO₄ solution. Under the optimal conditions, by using differential pulse voltammetry as the detection method, a linear relationship was obtained between the oxidation peak current and the MG concentration in the range of 4.0 × 10^?7 to 1.0 × 10^?5 mol L^?1 with the detection limit as 1.0 × 10^?7 mol L^?1 (signal-to-noise ratio of 3). The modified electrode was applied in the determination of MG in fish samples, and the results were satisfactory with recoveries from 96.25 to 98.00 %. Furthermore, the modified electrode showed very good reproducibility and stability.     

Construction and Performance Characteristics of Modified Screen Printed and Modified Carbon Paste Sensors for Selective Determination of Cu(II) Ion in Different Polluted Water Samples

Four new ion-selective electrodes (ISEs), based on N,N′-bis(salicylaldehyde)-p-phenylene diamine (SPD) as ionophore, are constructed for the determination of copper(II) ion. The modified carbon paste (MCPEs; electrodes I and II) and modified screen-printed sensors (MSPEs; electrodes III and IV) exhibit good potentiometric response for Cu(II) over a wide concentration range of 1.0 × 10^?6 – 1.0 × 10^?2 mol L^?1 for electrodes (I and II) and 4.8 × 10^?7–1.0 × 10^?2 mol L^?1 for electrodes (III and IV) with a detection limit of 1.0 × 10^?6 mol L^?1 for electrodes (I and II) and 4.8 × 10^?7 mol L^?1 for electrodes (III and IV), respectively. The slopes of the calibration graphs are 29.62 ± 0.9 and 30.12 ± 0.7 mV decade^?1 for electrode (I) (tricresylphosphate (TCP) plasticizer) and electrode (II) (o-nitrophenyloctylether o-NPOE plasticizer), respectively. Also, the MSPEs showed good potentiometric slopes of 29.91 ± 0.5 and 30.70 ± 0.3 mV decade^?1 for electrode (III) (TCP plasticizer) and electrode (IV) (o-NPOE plasticizer), respectively. The electrodes showed stable and reproducible potentials over a period of 60, 88, 120, and 145 days at the pH range from 3 to 7 for electrodes (II), (III), and (IV) and pH range from 3 to 6 for electrode (I). This method was successfully applied for potentiometric determination of Cu(II) in tap water, river, and formation water samples in addition to pharmaceutical preparation. The results obtained agree with those obtained with the atomic absorption spectrometry (AAS).     

Electrochemical remediation of BPA in a soil matrix by Pd/Ti and RuO2/Ti electrodes

This study aimed to investigate the bisphenol A (BPA) degradation performance of an electrokinetic process coupled with Pd/Ti (PT) and RuO₂/Ti (RT) binary metallic oxidation electrodes under a potential gradient of 2 Vcm^?1 for 5 days. Fifteen experiments conducted with five processing fluids, namely deionized water (DW), Na₂SO₄, citric acid (CA), NaOH and NaCl, and two binary metallic oxidation electrodes, Pd/Ti and RT, were investigated in this study. Electroosmosis permeability of 3.2 × 10^?6–4.7 × 10^?6, 4.0 × 10^?6–4.9 × 10^?6, and 3.7 × 10^?6–6.8 × 10^?6 cm² V^?1 s^?1 were observed in the electrokinetic system with Ti, PT, and RT electrodes, respectively. A significant detachment of the coated metals was observed in BMOEEK–PT system with Na₂SO₄, CA, and NaOH processing fluids. A higher BPA treatment efficiency of 52.2–67.3 % was found in the BMOEEK–RT system, which was 1.4–1.8 times greater than in the EK–Ti system with DW as the processing fluid. The best treatment efficiency was found in the system with NaCl as the processing fluid, which may mostly result from less detachment of the coated metal from electrode and increased hypochlorite (OCl^?) generation in the anode reservoir. The primary treatment mechanism in the BMOEEK system with NaCl procession fluid was degradation by anodic oxidation. It was concluded that both the binary metallic electrode and processing fluid played key roles in enhancing the electrochemical degradation of BPA. The electrode characteristics (progressive cyclic voltammogram and SEM micrograph with EDAX), electrokinetic behavior (specimen pH and current density), and treatment mechanism were also discussed in this study.     

Facile synthesis of reduced graphene oxide/MWNTs nanocomposite supercapacitor materials tested as electrophoretically deposited films on glassy carbon electrodes

This paper reports on a facile synthesis method for reduced graphene oxide (rGO)/multi-walled carbon nanotubes (MWNTs) nanocomposites. The initial step involves the use of graphene oxide to disperse the MWNTs, with subsequent reduction of the resultant graphene oxide/MWNTs composites using l-ascorbic acid (LAA) as a mild reductant. Reduction by LAA preserves the interaction between the rGO sheets and MWNTs. The dispersion-containing rGO/MWNTs composites was characterized and electrophoretically deposited anodically onto glassy carbon electrodes to form high surface area films for capacitance testing. Pseudo capacitance peaks were observed in the rGO/MWNTs composite electrodes, resulting in superior performance with capacitance values up to 134.3 F g^?1 recorded. This capacitance value is higher than those observed for LAA-reduced GO (LAA-rGO) (63.5 F g^?1), electrochemically reduced GO (EC-rGO) (27.6 F g^?1), or electrochemically reduced GO/MWNTs (EC-rGO/MWNTs) (98.4 F g^?1)-based electrodes.     

The influence of the acidic scouring treatment on the wastewater treatment of TiO<Subscript>2</Subscript> loaded activated carbon electrode

Activated carbon (AC) electrodes were loaded with TiO₂ by using sol–gel method after a pretreatment process, the effect of the acidic pretreatment of the TiO₂ loaded electrode on its deionization efficiency of the wastewater containing NaCl solutions was studied; the physical, chemical and electrochemical properties of the electrode were characterized. The physical and chemical properties of the activated carbon before and after loaded with TiO₂ nanoparticles are characterized by using scanning electron microscopy, energy dispersion spectrum analyzer, Brunauer–Emmett–Teller gas adsorption method, thermal gravimetric analysis, Fourier transform infrared spectroscopy respectively. Electrochemical properties were characterized by employing electrochemical workstation and electrical adsorption deionization test. It was found that both the specific capacitance and the ions removal efficiency of the activated carbon loaded with TiO₂ had an increase of 16.4 and 49.8 % respectively in comparison with original activated carbon electrode. It was believed that this is due to the presence of crystal anatase TiO₂ nanoparticles (the mass content of titanium element in the TiO₂/AC complex is about 24.91 %) on the surface and pores in the activated carbon; while Ti–O–C bonds was found on the surface of the activated carbon, its surface wetting properties was significantly improved. However, it was also noticed that and the specific surface area of the activated carbon was decreased from 680.5 to 523.35 m² g^?1. This might lead to the decrease of the physical adsorption properties of the activated carbon electrodes, but its Electrical double-layer capacitance increases, electrical adsorption efficiency was improved.     

Electrochemical dissolution of metallic platinum in ionic liquids

The electrochemical dissolution of Pt in several ionic liquids (IL’s) was studied. Different IL’s were tested assessing their potential to dissolve Pt. Dissolution rate and current efficiency were evaluated. The main focus was on Cl containing IL’s: first generation, eutectic based IL’s and second generation IL’s with discrete anions. Pt dissolution only occurred in type 1 eutectic-based IL’s with a max. dissolution rate of 192.2 g m^?2 h^?1 and a max. current efficiency of 99 % for the ZnCl₂-1-ethyl-3-methylimidazolium chloride IL, and 9.090 g m^?2 h^?1 and 96 % for the 1:1 ZnCl₂–choline chloride ionic liquid. The dissolution occurred via the formation of [PtCl _x ] ^y? complexes. To form these complexes, addition of a metal chloride was necessary. Furthermore, an IL with an electrochemical window of 1.5 V, preferably 2.0 V is required to achieve Pt dissolution. The added metal salt needed to have a higher decomposition potential than 1.5 V or should be a Pt salt.     

Graphene/Polyaniline Aerogel with Superelasticity and High Capacitance as Highly Compression-Tolerant Supercapacitor Electrode

Superelastic graphene aerogel with ultra-high compressibility shows promising potential for compression-tolerant supercapacitor electrode. However, its specific capacitance is too low to meet the practical application. Herein, we deposited polyaniline (PANI) into the superelastic graphene aerogel to improve the capacitance while maintaining the superelasticity. Graphene/PANI aerogel with optimized PANI mass content of 63 wt% shows the improved specific capacitance of 713 F g^?1 in the three-electrode system. And the graphene/PANI aerogel presents a high recoverable compressive strain of 90% due to the strong interaction between PANI and graphene. The all-solid-state supercapacitors were assembled to demonstrate the compression-tolerant ability of graphene/PANI electrodes. The gravimetric capacitance of graphene/PANI electrodes reaches 424 F g^?1 and retains 96% even at 90% compressive strain. And a volumetric capacitance of 65.5 F cm^?3 is achieved, which is much higher than that of other compressible composite electrodes. Furthermore, several compressible supercapacitors can be integrated and connected in series to enhance the overall output voltage, suggesting the potential to meet the practical application.     

Erratum to: Electrochemical dissolution of metallic platinum in ionic liquids

The electrochemical dissolution of Pt in several ionic liquids (ILs) was studied. Different ILs were tested assessing their potential to dissolve Pt. Dissolution rate and current efficiency were evaluated. The main focus was on Cl containing ILs: first generation, eutectic-based ILs and second generation ILs with discrete anions. Pt dissolution only occurred in type 1 eutectic-based ILs with a max. dissolution rate of 192.2 g m^?2 h^?1 and a max. current efficiency of 99 % for the ZnCl₂–1-ethyl-3-methylimidazolium chloride IL, and 9.090 g m^?2 h^?1 and 96 % for the 1:1 ZnCl₂–choline chloride IL. The dissolution occurred through the formation of [PtCl_x]^y? complexes. To form these complexes, addition of a metal chloride was necessary. Furthermore, an IL with an electrochemical window of 1.5 V, preferably 2.0 V was required to achieve Pt dissolution. The added metal salt needed to have a higher decomposition potential than 1.5 V or should be a Pt salt.     

Electrochemical sensing of NADH on NiO nanoparticles-modified carbon paste electrode and fabrication of ethanol dehydrogenase-based biosensor

In this work, an electrochemical β-nicotinamide adenine dinucleotide (NADH) sensor based on a carbon paste electrode modified with nickel oxide nanoparticles (NiONPs) was developed. The key highlights of this work are ease of preparation of the NiONPs-modified carbon paste electrode (NiONPs/MCPE), and its high sensitivity to NADH. The electrochemical characterization of NiONPs/MCPEs was performed via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrochemical oxidation response of NADH was investigated by differential pulse voltammetry and chronoamperometry. The results indicated that the electrocatalytic effects of NiONPs on the response current of NADH significantly facilitated the electron transfer and improved the performance of the biosensor. Compared to bare carbon paste electrode (BCPE), the oxidation potential was shifted toward more negative potentials and the oxidation current was increased remarkably. Under optimum conditions, NADH could be detected in the range from 1.0 × 10^?4 to 1.0 mmol L^?1 with lower detection limit (0.05 μmol L^?1). The proposed NADH sensor demonstrated fast and reproducible response. Furthermore, an ethanol biosensor was prepared using NiONPs and NAD⁺-dependent alcohol dehydrogenase enzyme giving linear responses over the concentration range of 1.6 and 38 mmol L^?1 of ethanol.