Direct electrochemical behavior of cytochrome c on DNA modified glassy carbon electrode and its application to nitric oxide biosensor

Cytochrome c/DNA modified electrode was achieved by coating calf thymus DNA onto the surface of glassy carbon electrode firstly, then immobilizing cytochrome c on it by multi-cyclic voltammetric method and characterized by the electrochemical impedance. The electrochemical behavior of cytochrome c on DNA modified electrode was explored and showed a quasi-reversible electrochemical redox behavior with a formal potential of 0.045 ± 0.010 V (versus Ag/AgCl) in 0.10 M, pH 5.0, acetate buffer solution. The peak currents were linearly with the scan rate in the range of 20-200 mV/s. Cytochrome c/DNA modified electrode exhibited elegant catalytic activity for the electrochemical reduction of NO. The catalytic current is linear to the nitric oxide concentration in the range of 6.0 × 10⁻⁷ to 8.0 × 10⁻⁶ M and the detection limit was 1.0 × 10⁻⁷ M (three times the ratio of signal to noise, S/N = 3).     

Highly sensitive electrochemical determination of nitric oxide using fused spherical gold nanoparticles modified ITO electrode

This paper describes the highly sensitive electrochemical determination of nitric oxide (NO) using the fused spherical gold nanoparticles (FAuNPs) modified ITO electrode. The FAuNPs were self-assembled on a (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film, which was preassembled on ITO electrode. The attachment of FAuNPs on MPTS sol-gel film was confirmed by UV-vis absorption spectroscopy, atomic force microscopy (AFM) and cyclic voltammetry (CV). The AFM image shows that the AuNPs retain their fused morphology after immobilized on MPTS sol-gel film. The FAuNPs modified ITO electrode shows an excellent electrocatalytic activity towards the oxidation of NO. Using FAuNPs modified electrode, the detection of 12 nM NO was achieved for the first time by amperometry method. Further, the current response was increased linearly with increasing NO concentration in the range of 1.2 × 10⁻⁸ to 7 × 10⁻⁴ M and the detection limit was found to be 3.1 × 10⁻¹⁰ M (S/N = 3). The FAuNPs modified ITO electrode displays an excellent selectivity towards the determination of 12 nM NO even in the presence of 1000-fold excess common interfering agents.     

Electrocatalytic reduction of nitric oxide on Pt nanocrystals of different shape in sulfuric acid solutions

Pt tetrahexahedral (Pt-THH) nanocrystals enclosed with 24 {h k 0} facets, Pt nanothorns (Pt-Thorn) with a high surface density of atomic steps, and congeries of Pt nanoparticles (Pt-NP) were prepared and served as catalysts to study the electrocatalytic reduction of both adsorbed and solution nitric oxide. The structure sensitivity for the reduction of a saturated NO adlayer on the Pt nanocrystals (NCs) of different shape was studied by cyclic voltammetry (CV) and in situ FTIR spectroscopy in sulphuric acid solutions. The results revealed that two types of NO adsorbates can be reduced independently at separated potentials, i.e. the reduction of linear bonded NO (NO_L) on the Pt-NP electrode gives rise to a current peak at −0.01 V (vs. SCE), while the bridge adsorbed NO (NO_B) yields a current peak at −0.08 V. The in situ SNIFTIRS results confirmed the assignment of NO adsorbates, i.e. the NO_B species yielding a IR absorption bipolar band with its negative-going peak at 1636 cm⁻¹ and positive-going peak around 1610 cm⁻¹, and the NO_L species giving rise to a bipolar band with its negative-going peak at 1809 cm⁻¹ and positive-going peak around 1720 cm⁻¹. It has determined that the NO_L species can be preferentially formed on the Pt NCs with open surface structure, i.e. the more open the surface structure of the Pt NCs, the larger the relative quantity of NO_L versus NO_B. It has also revealed that the Pt NCs with a high surface density of atomic steps exhibit superior electrocatalytic activity for the reduction of solution NO species. The steady-state current density of NO reduction on Pt-THH NCs is 7.5-12 times as large as that on Pt-NP, and that on Pt-Thorn is 2.5-4 times of that on Pt-NP in the reduction potential region of electrochemical dynamic control.     

Electrodeposition of Pt-Fe(III) nanoparticle on glassy carbon electrode for electrochemical nitric oxide sensor

An electrochemical sensor for the detection of nitric oxide (NO) was developed by electrodeposition of Pt-Fe(III) nanoparticle on a glassy carbon electrode. This sensor exhibits excellent electrocatalytic activity for the oxidation of NO. A Nafion membrane coating was used to avoid the interference of nitrite and other potential interferences which may co-exist with NO in the biological systems. The effect of scan number in the electrodeposition process and the behavior of the sensor with respect to bulk pH have been studied. The catalytic peak current is found to be linear with the NO concentration over a wider range of 8.4 × 10⁻⁸ to 7.8 × 10⁻⁴ M, with a detection limit of 1.8 × 10⁻⁸ M (s/n = 3). In addition, the sensor has also good stability and anti-interference ability.     

Superoxide Dismutase as a Novel Macromolecular Nitric Oxide Carrier: Preparation and Characterization

Nitric oxide (NO) is an important molecule that exerts multiple functions in biological systems. Because of the short-lived nature of NO, S-nitrosothiols (RSNOs) are believed to act as stable NO carriers. Recently, sulfhydryl (SH) containing macromolecules have been shown to be promising NO carriers. In the present study, we aimed to synthesize and characterize a potential NO carrier based on bovine Cu,Zn-superoxide dismutase (bSOD). To prepare S-nitrosated bSOD, the protein was incubated with S-nitrosoglutathione (GSNO) under varied experimental conditions. The results show that significant S-nitrosation of bSOD occurred only at high temperature (50 °C) for prolonged incubation time (>2 h). S-nitrosation efficiency increased with reaction time and reached a plateau at ~4 h. The maximum amount of NO loaded was determined to be about 0.6 mol SNO/mol protein (~30% loading efficiency). The enzymatic activity of bSOD, however, decreased with reaction time. Our data further indicate that NO functionality can only be measured in the presence of extremely high concentrations of Hg²⁺ or when the protein was denatured by guanidine. Moreover, mildly acidic pH was shown to favor S-nitrosation of bSOD. A model based on unfolding and refolding of bSOD during preparation was proposed to possibly explain our observation.     

Electrochemical nitric oxide microsensors based on two-dimensional cross-linked polymeric LB films of oligo(dimethylsiloxane) copolymer

Two-dimensional cross-linked polysiloxane Langmuir-Blodgett (LB) films were prepared and applied to nitric oxide (NO)-permselective membranes in order to block other electroactive interfering species. The cross-linked siloxane LB films deposited on platinum micro-disc electrodes (10 μm in diameter) offered revealing high performances as a permselective membrane for NO sensor such as high sensitivity to NO (detection limit, 40 nM) and high selectivity (e.g., the ratio of current response for acetaminophen or uric acid on the modified electrode to that on the bare electrode, less than 10⁻³). Furthermore, the permselective membrane could be easily deposited irrespective of the size and shape of electrode.     

Mechanisms of electrochemical reduction and oxidation of nitric oxide

A summary is given of recent work on the reactivity of nitric oxide on various metal electrodes. The significant differences between the reactivity of adsorbed NO and NO in solution are pointed out, both for the reduction and the oxidation reaction(s). Whereas adsorbed NO can be reduced only to hydroxylamine and/or ammonia, it takes NO in solution to produce N₂O and N₂. From the reduction of NO on a series on stepped single-crystal Pt electrodes, it is concluded that NO_ads reduction is not a structure sensitive process. The protonation of the adsorbed NO is rate-determining; neither the NO adsorption strength nor the NO bond breaking play a significant role in its reduction rate. Whereas adsorbed NO on polycrystalline Pt can only be oxidized to nitrate, in the presence of NO in solution nitrous acid HNO₂ may also be formed, in a potential region where adsorbed NO is otherwise stable. Interestingly, on Pt(1 1 1) and Pt(5 5 4) NO_ads may be oxidized to HNO₂ in a surface-bonded redox couple. Whereas surface oxides appear to catalyze the oxidation of solution NO to HNO₂, the further oxidation to nitrate seems to be inhibited by the presence of surface oxides. Both the reduction and oxidation of solution NO appear to be not very metal-dependent reactions, as they take place with approximately equal rate on all electrode metals studied, including gold. This suggests the involvement of weakly adsorbed intermediates, and the relatively unimportant role of surface-bonded NO in the bulk NO reduction and oxidation activity.     

Ternary CdxZn1−xSe deposited on Ag (1 1 1) by ECALE: Electrochemical and EXAFS characterization

This paper reports the characterization of ternary II-VI semiconductor nanocrystals, deposited by the electrochemical atomic layer epitaxy (ECALE) technique.In particular, morphological and structural properties of the ternary compounds of formula Cd_xZn_1−xSe deposited on Ag (1 1 1) have been characterized as a function of composition. The number of the attainable x values is limited by the necessity of using well-defined ZnSe/CdSe deposition sequences. However, the quantitative analysis carried out on the basis of both electrochemical and extended X-ray absorption fine structure (EXAFS) experiments indicates that the ECALE method is a successful way of controlling the composition of Cd_xZn_1−xSe. In addition, the electrochemical measurements show that the amount of deposition is minimum in correspondence to the compound with x = 0.5, thus corroborating the hypothesis of a higher degree of disorder suggested both by morphological and structural investigation. The morphology was studied by atomic force microscopy (AFM). The structure of the films is estimated by EXAFS which is a powerful technique for the analysis of the local structure around chosen atoms.     

Design and electrochemical study of SnO2-based mixed oxide electrodes

For the electrochemical treatment of wastewater, it is critical to develop electrodes with a high activity for the oxidation of pollutants, long lifetimes, and low cost. In the present study, we have fabricated four different SnO₂-based electrodes (Ti/SnO₂-Sb₂O₅, Ti/SnO₂-Sb₂O₅-PtO_x, Ti/SnO₂-Sb₂O₅-RuO₂ and Ti/SnO₂-Sb₂O₅-IrO₂) using the thermal decomposition method and, for the first time, systemically studied their stability and electrocatalytic activity towards the degradation of 2-nitrophenol (2-NPh), 3-nitrophenol (3-NPh) and 4-nitrophenol (4-NPh). Scanning electron microscope (SEM) and X-ray energy dispersive spectrometry (EDS) were used to characterize the morphology and composition of the four different SnO₂-based electrocatalysts. Lifetime tests show that doping IrO₂ or RuO₂ greatly improves the stability of the SnO₂-based electrodes. The electrochemical activities of the prepared SnO₂-based electrodes were characterized using the degradation of 2-NPh, 3-NPh and 4-NPh. In situ UV/vis spectroscopy was used to monitor the concentration changes of the nitrophenols with time showing that the rate constants for the electrochemical oxidation of the nitrophenols decrease in the order of: 2-NPh > 4-NPh > 3-NPh. The effect of the applied current densities and initial concentrations of nitrophenols have also been investigated. Our study has shown that the fabricated Ti/SnO₂-Sb₂O₅-IrO₂ electrodes are very promising for the electrochemical treatment of wastewater.     

Investigation of the surface properties and the hydrogen evolution reaction, HER, at thermal rhodium oxide electrodes

A systematic investigation was conducted of the surface properties and the HER at electrodes of nominal composition Ti/Rh_xTi_(1−x)O_y prepared by thermal decomposition (T_cal: 500 °C; t_cal: 2 h; O₂ flux: 5 dm³ min⁻¹) from salt precursor solutions dissolved in 6.0 mol dm⁻³ HNO₃. Films were characterized ex situ by SEM, EDX, XPS and XRD and in situ by open circuit potential measurements and CV. The electrochemical behaviour was investigated by CV as function of the anodic, E_λ,a, and cathodic, E_λ,c, switching potentials showing the Rh surface oxidation states strongly depend on these experimental variables. Surface Rh-sites are reduced to metallic rhodium in the cathodic potential region while higher oxidation states (I-III) are formed at more positive potentials (E ≥ 0.5 V/RHE). Hydrogen adsorption and desorption peaks as well as a short double layer charging region are observed at intermediate potential values. The HER was investigated by Tafel coefficients and reaction order with respect to H⁺ as function of nominal Rh-content.     

Supramolecular assembly of porphyrin bound DNA and its catalytic behavior for nitric oxide reduction

A stable Fe(4-TMPyP)-DNA-PADDA (FePyDP) film was prepared on pyrolytic graphite electrode (PGE) through the supramolecular interaction between water-soluble iron(III) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(4-TMPyP)) and DNA template, where PADDA (poly(acrylamide-co-diallyldimethylammonium chloride)) is employed as a co-immobilizing polymer. Electronic absorption spectral and quartz crystal microbalance measurements revealed that Fe(4-TMPyP) interacted with DNA to generate a species with the molar ratio of 1:5 for Fe(4-TMPyP):DNA phosphate. Cyclic voltammetry of FePyDP film showed a pair of stable and reversible peaks corresponding to Fe^III/Fe^II redox potential of −0.13 V versus Ag|AgCl in pH 7.4 PBS. The electron transfer was expected across the double-strand of DNA by an “electron tunneling” mechanism. The modified electrode displayed an excellent catalytic activity for NO reduction at −0.61 V versus Ag|AgCl. The catalytic current was enhanced at lower pH. Chronoamperometric experiments demonstrated a rapid response to the reduction of NO with a linear range from 0.1 to 90 μM. The detection limit was 30 nM at a signal-to-noise ratio of 3.     

Cobalt oxide nanoparticles on mesoporous MCM-41 and Al-MCM-41 by supercritical CO2 deposition

CoO and Co₃O₄ nanoparticles were uniformly dispersed inside mesoporous MCM-41 and Al-MCM-41 supports using supercritical CO₂ reactive deposition. This method represents a one-pot reproducible procedure that allows the dissolution of the organocobalt precursor and supports impregnation in supercritical CO₂ at 70 °C and 110 bar, followed by the precursor thermal decomposition into cobalt species at 200 °C and 160 bar. By the relative concentration of the cobalt precursor [cobalt (II) bis (η⁵-ciclopentadienil)], the load of cobalt nanoparticles was controlled and then determined by Inductively Coupled Plasma (ICP-OES). The synthesis of CoO and Co₃O₄ species inside the MCM-41 and Al-MCM-41 substrates was confirmed by X-ray Photoelectron (XPS) and Laser Raman Spectroscopies (LRS). By N₂ adsorption and Small Angle X-ray Scattering (SAXS), it was determined that the hexagonal arrangement as well as the surface area and pore size of the substrates changed after the addition of cobalt. By means of X-ray mapping from SEM images, a homogeneous distribution of cobalt nanoparticles was observed inside the mesopores when the cobalt loading was 1 wt.%. In addition, spherical cobalt nanoparticles of average diameter close to 20 nm were detected on the outer surface of MCM-41 and Al-MCM-41 supports when the cobalt content was higher. On the other hand, by Transmission Electron Microscopy (TEM), it was possible to measure the interplanar distance of the crystalline plane of the outer nanoparticles, which was later compared with the theoretical distance values which allowed identifying the CoO and Co₃O₄ phases.     

A numerical and experimental study of counterflow syngas flames at different pressures

Synthesis gas or “Syngas” is being recognized as a viable energy source worldwide, particularly for stationary power generation due to its wide availability as a product of bio and fossil fuel gasification. There are, however, gaps in the fundamental understanding of syngas combustion and emissions characteristics, especially at elevated pressures that are relevant to practical combustors. This paper presents a numerical and experimental investigation of the combustion and NO_x characteristics of syngas fuel with varying composition, pressure and strain rate. Experiments were performed at atmospheric conditions, while the simulations considered different pressures. Both experiments and simulations indicate that stable non-premixed and partially premixed counterflow flames (PPFs) can be established for a wide range of syngas compositions and strain rates. Three chemical kinetic models, GRI 3.0, Davis et al., and Mueller et al. are examined. The Davis et al. mechanism is found to agree best with the experimental data, and hence used to simulate the PPF structure at different pressure and fuel composition. For the pressure range investigated, results indicate a typical double flame structure with a rich premixed reaction zone (RPZ) on the fuel side and a non-premixed reaction zone (NPZ) on the oxidizer side, with RPZ characterized by H₂ oxidation, and NPZ by both H₂ and CO oxidation. While thermal NO is found to be the dominant route for NO production, a reburn route, which consumes NO through NO + O + M→ NO₂ + M and H + NO + M → HNO + M reactions, becomes increasingly important at high pressures. The amount of NO formed in syngas PPFs first increases rapidly with pressure, but then levels off at higher pressures. At a given pressure, the peak NO mole fraction exhibits a non-monotonic variation with syngas composition, first decreasing to a minimum value, and then increasing as the amount of CO in syngas is increased. This implies the existence of an optimum syngas composition that yields the lowest amount of NO production in syngas PPFs, and can be attributed to the combined effects of thermal and reburn mechanisms.     

Facile preparation of disposable immunosensor for Shigella flexneri based on multi-wall carbon nanotubes/chitosan composite

Based on multi-wall carbon nanotubes (MWCNT)/chitosan/horseradish peroxidase labeled antibodies to Shigella flexneri (HRP-anti-S. flexneri) biocomposite film on a screen-printed electrode (SPE) surface, a disposable immunosensor has been developed for the rapid detection of S. flexneri. The HRP-anti-S. flexneri can be entrapped into MWCNT/chitosan composite matrix without other cross-linking agent. Thionine and H₂O₂ were used as the mediator and substrate, respectively. The surface morphologies of modified films were characterized by atomic force microscope (AFM). Cyclic voltammery (CV) was carried out to characterize the electrochemical properties of the immobilization of materials on the electrode surface and quantified S. flexneri. Due to the strong electrocatalytic properties of MWCNT and HRP toward H₂O₂, the response signal was significantly amplified. S. flexneri could be detected by the decrease of the reduction peak current before and after immunoreaction. Under optimal conditions, S. flexneri could be detected in the range of 10⁴ to 10¹⁰ cfu mL⁻¹, with a detection limit of 2.3 × 10³ cfu mL⁻¹ (S/N = 3). Furthermore, the proposed immunosensor exhibited a satisfactory specificity, reproducibility, stability and accuracy, indicating that the proposed immunosensor has potential application for a facile, rapid and harmless immunoassay.     

Evolution of the local structure and electrochemical properties of spinel LiNixMn2−xO4 (0 ≤ x ≤ 0.5)

A series of Ni substituted spinel LiNi_xMn_2−xO₄ (0 ≤ x ≤ 0.5) have been synthesized to study the evolution of the local structure and their electrochemical properties. X-ray diffraction showed a few Ni cations moved to the 8a sites in heavily substituted LiNi_xMn_2−xO₄ (x ≥ 0.3). X-ray photoelectron spectroscopy confirmed Ni²⁺ cations were partially oxidized to Ni³⁺. The local structures of LiNi_xMn_2−xO₄ were studied by analyzing the and A_1g Raman bands. The most compact [Mn(Ni)O₆] octahedron with the highest bond energy of Mn(Ni)O was found for LiNi_0.2Mn_1.8O₄, which showed a Mn(Ni)O average bond length of 1.790 Å, and a force constant of 2.966 N cm⁻¹. Electrolyte decomposition during the electrochemical charging processes increased with Ni substitution. The discharge capacities at the 4.1 and 4.7 V plateaus obeyed the linear relationships with respect to the Ni substitution with the slopes of −1.9 and +1.9, which were smaller than the theoretical values of −2 and +2, respectively. The smaller slopes could be attributed to the electrochemical hysteresis and the presence of Ni³⁺ in the materials.     

Preparation and characterization of thiocyanate-selective electrodes based on new complexes of copper(II) as neutral carriers

The complexes of hydroxycitronellal (o-aminobenzoic acid) copper(II) (Cu(II)-HXAB) and salicylaldehyde (o-aminobenzoic acid) copper(II) (Cu(II)-SHAB) were used as neutral carriers in PVC-based membrane ion-selective electrodes. The electrode based on Cu(II)-HXAB exhibited near-Nernstian potential response to thiocyanate (SCN⁻) in a linear range of 1.0 × 10^− 6 to 1.0 × 10^− 1 M with a detection limit of 8.5 × 10^− 7 M and a slope of − 57.3 mV/decade in 0.01 M phosphate buffer solution (pH 5.0). The electrode exhibited high selectivity to SCN⁻ over other tested anions with an anti-Hofmeister selectivity sequence. The selectivity behavior might be discussed in terms of UV-Vis spectrum and infrared spectrum. The transfer process of thiocyanate across the membrane interface was investigated by making use of the AC impedance technique. The electrode containing Cu(II)-HXAB could be applied to thiocyanate analysis in waste water with satisfactory results.     

Electrochemical and ex situ XRD investigations on (1−x)LiNiO2·xLi2TiO3 (0.05≤x≤0.5)

An attempt to understand the unusual electrochemical behaviors in (1−x)LiNiO₂·xLi₂TiO₃ (0.05≤x≤0.5), an excess initial charge capacity exceeding the oxidation of transitional metal to +4 accompanying the appearance of an irreversible initial charge plateau when x reached 0.075, was performed. The decreased charge-discharge polarization after charging to 4.6 and 4.8 V and increased columbic reversibility after charging to 4.6 V typically for x=0.1 and 0.2, in contrast to charging to 4.4 V, suggested that the excess initial charge capacity possibly did not come mainly from electrolyte decomposition; while ex situ XRD results in the sample with x=0.2 confirmed that Li⁺ were really extracted at the stage of the charge plateau, ruling out the possibility that electrolyte decomposition mainly accounted for the unusual electrochemical behaviors. It was inferred that the species responsible for charge compensation for the excess charge capacity must be oxygen ions in these materials, considering that Ni⁴⁺ and Ti⁴⁺ are generally impossible to be oxidized to a higher valence. Various electrochemical cycling experiments demonstrated that the sample for x=0.05 with high resistant ability to high voltage and temperature is very promising cathode material in view of observed capacity and cycleability from a viewpoint of application.     

Electrochemical characteristics of cobalt-substituted lithium nickel oxides synthesized from lithium hydro-oxide and nickel and cobalt oxides

LiNi_1−yCo_yO₂ (y=0.1, 0.3 and 0.5) were synthesized by solid state reaction method at 800 °C and 850 °C from LiOH·H₂O, NiO and Co₃O₄ as starting materials. The electrochemical properties of the synthesized LiNi_1−yCo_yO₂ were investigated. As the content of Co decreases, particle size decreases rapidly and particle size distribution gets more homogeneous. When the particle size is compared at the same composition, the particles synthesized at 850 °C are larger than those synthesized at 800 °C. LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest intercalated and deintercalated Li quantity Δx among LiNi_1−yCo_yO₂ (y=0.1, 0.3 and 0.5). LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest first discharge capacity (178 mAh/g), followed by LiNi_0.7Co_0.3O₂ (162 mAh/g) synthesized at 800 °C. LiNi_0.7Co_0.3O₂ synthesized at 800 °C has discharge capacities of 162 and 125 mAh/g at n=1 and n=5, respectively.     

Gold nanoparticle/carbon nanotube hybrids as an enhanced material for sensitive amperometric determination of tryptophan

In this work, a highly sensitive electrochemical sensor for the determination of tryptophan (Trp) was fabricate by electrodeposition of gold nanoparticles (AuNPs) onto carbon nanotube (CNT) films pre-cast on a glassy carbon electrode (GCE), forming an AuNP-CNT composite-modified GCE (AuNP-CNT/GCE). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used for the surface analysis of the electrode. The results indicate that the hybrid nanomaterials induced a substantial decrease in the overpotential of the Trp oxidation reaction and exhibited a remarkable synergistic effect on the electrocatalytic activity toward the oxidation of Trp. In phosphate buffer solution (pH 7.4), the modified electrode showed excellent analytical performance for the amperometric determination of Trp. The peak currents possess a linear relationship with the concentration of Trp in the range of 30 nM to 2.5 μM, and the detection limit is 10 nM (S/N = 3). In addition, the modified electrode was used to determine Trp concentration in pharmaceutical samples with satisfactory results.     

A direct electrochemical route from oxide precursors to the terbium-nickel intermetallic compound TbNi5

Successful direct electrochemical reduction of mixed powders of terbium oxide (Tb₄O₇) and nickel oxide (NiO) to the intermetallic compound, TbNi₅, is demonstrated in molten CaCl₂ at 850 °C by constant voltage (2.4-3.2 V) electrolysis. The reduction mechanism was investigated by cyclic voltammetry using a molybdenum cavity electrode in conjunction with characterisations of the products from both constant voltage and potentiostatic electrolysis under different conditions by XRD, SEM and EDX. It was found that the reduction started from NiO to Ni, followed by that of Tb₂O₃ (resulting from Tb₄O₇ decomposition) on the pre-formed Ni to form the intermetallic compound. The reduction speed increased with increasing the cell voltage, but the speed gain was counterbalanced by decreased current efficiency and increased electric energy consumption. At 2.4 V, the current efficiency reached 63.2%, and the energy consumption by electrolysis was as low as 3.2 kWh/kg TbNi₅ when the oxide phase was converted fully to the metal phase (XRD) in 4 h. The oxygen level in the produced TbNi₅ could readily reach 1800 ppm by electrolysis at 3.2 V for 12 h with the energy consumption being 18.9 kWh/kg TbNi₅.