Urea Electro-oxidation In Alkaline Medium Research Articles

A nano-structured nickel trithiocarbonate complex supported on g-C3N4 as an efficient electrocatalyst for urea electro-oxidation

Urea electro-oxidation in alkaline medium catalysed by nickel trithiocarbonate complex and g-C3N4 composite.

Voltammetry study of electrocatalytic activity of lanthanum nickel perovskite nanoclusters-based composite catalyst for effective oxidation of urea in alkaline medium

Effective electrooxidation of urea has been the focus of research and development for energy and environmental applications. A modified glassy carbon (GC) electrode with two successive layers of conducting poly(aniline) (PANI) and lanthanum nickel oxide (LNO)-graphene oxide (GO) mixture was fabricated for urea electrooxidation in alkaline medium. Different conditions of catalyst preparation were examined for optimum electrocatalytic activity towards urea oxidation. GO improved the response and is considered advantageous support for the perovskite due to its structural and electronic differences compared to graphene (G). The highest electrocatalytic activity observed was for non-calcinated perovskite catalyst prepared by citric acid fuel and physically mixed with GO in the ratio (1:2). The use of La2NiO4 perovskite is beneficial with relatively low weight percentage of Ni (14.6 %) compared to other Ni-based catalysts for electrooxidation of urea. The perovskite catalyst is synthesized using microwave-assisted method that reduces chemicals usage and energy consumption. The non-calcinated perovskite catalyst and the (PANI/LNO-GO) composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive analysis (SEM-EDAX). The composite is applicable in temperature range (10 °C up to 50 °C), and at different urea concentrations from 0.1 M to 1.0 M in basic (KOH) electrolyte.

Lanthanum nickel oxide nano-perovskite decorated carbon nanotubes/poly(aniline) composite for effective electrochemical oxidation of urea

Here in, we introduce a modified glassy carbon (GC) electrode with two successive layers of conducting poly(aniline) (PANI) and lanthanum nickel oxide (LNO)-carbon nanotubes (CNT) mixture, (GC/PANI/LNO-CNT), for urea electrooxidation in alkaline medium. The use of La2NiO4 perovskite is advantageous with relatively low weight percentage of Ni (14.6%) compared to other Ni-based catalysts for electrooxidation of urea. The perovskite catalyst is synthesized using microwave-assisted method that reduces chemicals and energy consumption. Perovskite-based catalyst has good ionic and electronic conducting behavior, high oxygen mobility within its lattice with remarkable charge transfer rate. Carbon nanotubes increase the surface area of the electrode and act as a catalyst support to enhance the urea conversion process. Under optimized conditions, the specific current for urea electrooxidation is 1400 mA mg−1 cm−2. The perovskite catalyst and the (PANI/LNO-CNT) composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive analysis (SEM-EDAX). The composite is applicable in temperature range (10 °C to 50 °C), and at different urea concentrations (0.1 M to 1.0 M) in basic (KOH) electrolyte.

Nickel-Rhodium bimetallic dispersions supported on nickel foam as the efficient catalyst for urea electrooxidation in alkaline medium

The nickel-rhodium bimetallic dispersions supported on nickel foam (Ni–Rh/Ni foam) are prepared by the hydrogen-bubble templated electrodeposition of nickel on nickel foam (Ni/Ni foam) and the subsequent electrodeposition of rhodium on Ni/Ni foam. The physicochemical characterizations including FESEM, XRD, XPS and ICP show the Ni–Rh/Ni foam electrode owns highly porous structure and uniform unalloyed Ni–Rh dispersions, and loads minute amount of Rh (0.467 mg cm−2). By modulating the Rh electrodeposition time to 50 min, the Ni–Rh/Ni foam electrode exhibits the highest catalytic current density for urea electrooxidation and the most delayed oxygen evolution reaction. From the quadrant position of the Nyquist plots, the Rh component in Ni–Rh/Ni foam is found to exert no apparent effect on the anti-poisoning of intermediate (adsorbed CO2). Instead, Rh facilitates the formation of Ni(OH)2, which contributes to the boost in the catalytic activity of Ni–Rh/Ni foam over Ni/Ni foam. This work suggests the Ni–Rh/Ni foam electrode is a promising anode catalyst for the urea electrooxidation-assisted hydrogen production and the simultaneous urea-containing sewage disposal.

Porous Ni2P nanoflower supported on nickel foam as an efficient three-dimensional electrode for urea electro-oxidation in alkaline medium

Porous Ni2P nanoflower supported on nickel foam (Ni2P@Ni foam) electrodes are synthesized via a simple hydrothermal growth strategy accompanied with further phosphating treatment. The prepared electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Electro-catalytic performances towards urea electro-oxidation are tested by cyclic voltammetry (CV), chronoamperometry (CA) coupled with electrochemical impedance spectroscopy (EIS). By phosphating Ni(OH)2 precursor, the final obtained Ni2P@Ni foam electrode presents a porous Ni2P nanoflower structure within abundant porosity, and so exposes a large amount of electro-catalytic active sites and electronic transmission channels to accelerate the interfacial reaction. Compared with Ni(OH)2@Ni foam precursor, the Ni2P@Ni foam catalyst exhibits more excellent electro-catalytic activity as well as lower onset oxidation potential. Remarkably, the Ni2P@Ni foam catalyst reaches a peak current density of 750 mA cm−2 with an onset oxidation potential of 0.24 V (vs. Ag/AgCl) accompanied by an excellent stability in 0.60 M urea with 5.00 M KOH solutions. Benefiting from the unique porous nanosheet structure, the as-synthesized Ni2P@Ni foam catalyst performs a highly enhanced catalytic behavior for alkaline urea electro-oxidation, indicating that the material can be hopefully applied in direct urea fuel cells.

Conducting Polymer-Mixed Oxide Composite Electrocatalyst for Enhanced Urea Oxidation

Considerable interest in urea electrooxidation reaction has developed recently because of possible generation of hydrogen and in direct urea fuel cell applications. Nickel and nickel-containing catalysts are the preferred electrode materials because of their efficient activity for this reaction. This work investigates a novel platform composed of a conducting poly(aniline) modified with lanthanum-nickel-based oxides/reduced graphene oxide as an electrocatalyst for urea electrooxidation in alkaline medium. The catalyst was prepared using a one-step and energy-saving procedure with graphene oxide as a substrate. The glassy carbon electrode modified with this catalyst exhibits an exceptional high specific current activity of 342 mA mg−1 cm−2 in 0.33 M urea/1.0 M KOH and reaches 615 mA mg−1 cm−2 in 0.33 M urea/3.0 M KOH. The catalyst was studied using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy showing long term stability and resistance against fouling. The structure and morphology of the resulting material was characterized with XRD, SEM and EDAX analyses.

NiO nanoparticles on graphene nanosheets at different calcination temperatures as effective electrocatalysts for urea electro-oxidation in alkaline medium

NiO nanoparticles were supported on graphene nanosheets (NiO/Gr) through coprecipitation step of Ni(OH)2 species, followed by calcination at different temperature values. The formed nanocomposites were characterized by employing X-ray diffraction (XRD) and transmission electron microscopy (TEM) to investigate their crystalline structure and morphology. The effect of varying the calcination temperature during the preparation of NiO/Gr electrocatalyst on some kinetic parameters in 0.5M NaOH solution was studied. The electrocatalytic activity of synthesized electrocatalysts was examined for urea electro-oxidation reaction in alkaline solution using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Among the fabricated NiO/Gr electrocatalysts, the one that was heated at 200°C exhibited the highest urea oxidation current density value with most stable performance for long time.

Mesoporous Ni-P nanocatalysts for alkaline urea electrooxidation

Mesoporous nickel phosphide (Ni-P) nanocatalysts have been synthesized via a facile solvothermal strategy and used for urea electrooxidation in alkaline medium. The physicochemical properties and electrocatalytic performances have been investigated. Due to the structural effect and electronic effect, the Ni-P nanocatalysts achieve a lower overpotential, higher activity and better stability compared with the Ni nanocatalysts. Therefore, an onset oxidation potential of 1.37V (vs. RHE), a peak current density of 70mAcm−2 and a good current retention of 58% for 1000s at 1.52V have been achieved by the Ni-P nanocatalysts, which show enhanced performance compared to the Ni nanocatalysts (1.42V, 62mAcm−2, 39% retention), indicating a promising application of the mesoporous Ni-P nanocatalysts towards alkaline urea electrooxidation.

Concurrent Deposition and Exfoliation of Nickel Hydroxide Nanoflakes Using Liquid Crystal Template and Their Activity for Urea Electrooxidation in Alkaline Medium

Nickel hydroxide nanoflakes (Ni(OH)2-NF) were prepared by chemical deposition and in situ exfoliation of nickel hydroxide layers confined in the aqueous domain of the liquid crystalline hexagonal template of Brij®78 surfactant. Using excess of sodium borohydride as a reducing agent generates concurrent excessive dynamic hydrogen bubbles which exfoliated and fragmented the nickel hydroxide layers precipitated within the soft hexagonal template. The physicochemical characterizations of Ni(OH)2-NF by using surface area analyser, X-ray diffraction (XRD), XPS and transmission electron microscope (TEM) showed the formation of α-Ni(OH)2 nanoflakes with thickness of 2–3 nm and have about 450 m2 g−1 surface area which is 20 times higher than that for bare nickel (bare-Ni) deposited without surfactant template. The electrocatalytic activity of the Ni(OH)2-NF catalyst for urea electrolysis was studied by cyclic voltammetry and chronoamperometry techniques. The Ni(OH)2-NF has shown a superior activity for the electrochemical oxidation of urea in alkaline solution and exhibits more than tenfold increase in activity in comparison with the bare-Ni deposit. The enhancement of urea electrooxidation activity was related to the superficial enhancement in the electroactive surface area of Ni(OH)2-NF. This new approach of deposition and in situ exfoliation by using liquid crystal template and hydrogen bubbles offers a new platform to nanostructuring wide range of catalysts with better catalytic performance.

Template-assisted synthesis of Ni–Co bimetallic nanowires for urea electrocatalytic oxidation

Nickel–cobalt bimetallic nanowire electrocatalyts (NCNE), synthesized through anodic aluminium oxide templates, were evaluated for urea electro-oxidation in alkaline medium for their applications in wastewater remediation, hydrogen production, and fuel cells. Compared to bulk nickel film electrocatalysts (NFE), the NCNE resulted in a ca. 110 mV decrease in the overpotential of urea electro-oxidation. In addition, the NCNE exhibited higher oxidation current density and current efficiency for urea electrolysis than those of NFE and nickel–cobalt bimetallic film electrocatalysts (NCFE). The maximum current efficiency for urea electro-oxidation on the NCNE reached up to 81 %, which is ~25 % higher than those of the NFE and NCFE.

Highly porous nickel@carbon sponge as a novel type of three-dimensional anode with low cost for high catalytic performance of urea electro-oxidation in alkaline medium

Highly porous nickel@carbon sponge electrode with low cost is synthesized via a facile sponge carbonization method coupled with a direct electrodeposition of Ni. The obtained electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The catalytic performances of urea electro-oxidation in alkaline medium are investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The Ni@carbon sponge electrode exhibits three-dimensional open network structures with a large surface area. Remarkably, the Ni@carbon sponge electrode shows much higher electrocatalytic activity and lower onset oxidation potential towards urea electro-oxidation compared to a Ni/Ti flat electrode synthesized by the same procedure. The Ni@carbon sponge electrode achieves an onset oxidation potential of 0.24 V (vs. Ag/AgCl) and a peak current density of 290 mA cm−2 in 5 mol L−1 NaOH and 0.10 mol L−1 urea solutions accompanied with a desirable stability. The impressive electrocatalytic activity is largely attributed to the high intrinsic electronic conductivity, superior porous network structures and rich surface Ni active species, which can largely boost the interfacial electroactive sites and charge transfer rates for urea electro-oxidation in alkaline medium, indicating promising applications in fuel cells.

Preparation of nickel nanowire arrays electrode for urea electro-oxidation in alkaline medium

Fully metallic nickel nanowire arrays (NWAs) electrode is prepared by electrodepositing nickel within the pores and over-plating on the surface of polycarbonate template (PCT) with subsequent dissolution of the template in dichloromethane. The as-prepared electrode is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Urea electro-oxidation reaction in KOH solution on the nickel NWAs electrode is investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The results show that the nickel NWAs electrode achieves an onset oxidation potential of 0.25 V (vs. Ag/AgCl) and a peak current density of 160 mA cm−2 in 5 mol L−1 KOH and 0.33 mol L−1 urea accompanied with considerable stability.