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To improve the complexity and low catalytic performance and reduce the high cost of the traditional electrode preparation process for the sodium borohydride electro-oxidation reaction (BOR), in this work, a self-supported and efficient electrode material grown on nickel foam (CoNi/Co3O4/NF) was successfully designed using a simple hydrothermal synthesis method accompanied by the electrodeposition process. Benefiting from the three-dimensional nanoarray structure of CoNi/Co3O4/NF and the uniform distribution of Co and Ni modulating active sites by electrodeposition, the catalytic activity towards NaBH4 exhibits high efficiency. CoNi/Co3O4 exhibits excellent catalytic performance (up to 2157 mA cm−2 in 2 mol L−1 NaOH and 0.3 mol L−1 NaBH4), a high electrochemically active surface area (62.5 cm−2), and a low activation energy (15.56 kJ mol−1). The CoNi/Co3O4/NF electrode was further investigated on a direct sodium borohydride–hydrogen peroxide fuel cell (DBHPFC), which exhibited a maximum power density of 108.5 mW cm−2 and excellent stability. The excellent performance is mainly due to its unique nanoarray structure and electrodeposition distribution of Co and Ni active sites, which increases the electrochemical surface area and enhances the contact between the electrode and the electrolyte. [ABSTRACT FROM AUTHOR]

A novel and binder free Co@graphite/paper electrode is prepared by electrodeposition Co nano-sheet on the surface of a graphite layer modified paper substrate. The morphology and phase structure of the Co@graphite/paper electrode are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer, transmission electron microscope and X-ray diffractometer. The catalytic activity of the Co@graphite/paper electrode for H 2 O 2 electrooxidation is investigated by means of cyclic voltammetry and chronoamperometry. The catalyst combines tightly with the paper and exhibits a good stability. The oxidation current density reaches to 580 mA cm −2 in 2 mol dm −3 NaOH and 0.5 mol dm −3 H 2 O 2 at 0.5 V. Besides, we illustrate the reaction mechanization of the H 2 O 2 electrooxidation on the Co film. [ABSTRACT FROM AUTHOR]

Abstract: Direct carbon fuel cells are promising power sources using solid carbon directly as fuel. Their performances significantly depend on the electrooxidation activity of carbon fuel. Electrooxidation of activated carbon particulates in molten Li2CO3–K2CO3 was investigated by potentiodynamic and potentiostatic method. Results indicated that the electrooxidation performance of activated carbon was significantly enhanced by pre-soaking with Li2CO3–K2CO3 and by treatment with HF, HNO3 and NaOH, respectively. The onset potential negatively shifted by around 100 mV and the current density increased by around 50 mA cm−2 after pre-soaking. The non-oxidant acids (HF) treatments are more effective than oxidant acid (HNO3) and base (NaOH) treatments. HF treated activated carbon exhibited the highest activity among all the samples. The enhancement in electrooxidation performance can be closely correlated with the increase in surface area and porosity caused by acid and base treatments. [Copyright &y& Elsevier]

A binder-free and flexible Au electrode is prepared by spontaneous deposition of Au onto a A4 (A4-paper)-8B (8B pencil)-Ni Film substrate (ABNi) which is assembled by electrodeposition of nanoscale Ni particles on the surface of A4 paper coated by 8B pencil. The morphology and phase structure of the (A4-paper)-8B (8B pencil)-Ni Film-Au (ABNiAu) electrode are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffractometer. The catalytic activity of the ABNiAu electrode for NaBH 4 electrooxidation is investigated by means of cyclic voltammetry and chronoamperometry. The electrode exhibits a high electric conductivity and the activity substance attaches to the surface of paper substrate tightly and does not fall off at all and the nanoscale Ni and Ni Au alloy enhance the broken of the B H bond in the BH 4 − , all of which lead to a high catalytic activity for NaBH 4 electrooxidation. The oxidation current density reaches 300 mA cm −2 in 1 mol dm −3 NaOH and 0.1 mol dm −3 NaBH 4 at −0.2 V. The exchanged electrons (n) is 6.0 (8.0 in theory), which indicates that the ABNiAu electrode has much higher utilization efficiency of the fuel than our reported LaNi 5 /Pd (n = 4) electrode. [ABSTRACT FROM AUTHOR]

Abstract: Acetone is the main product of 2-propanol electrooxidation in both acid and alkaline electrolytes; it always co-exists with 2-propanol in the reaction solution due to its liquid nature. Whether acetone will affect the electrooxidation of 2-propanol has not been well documented, which is a key issue that needs to be addressed for the direct 2-propanol fuel cell. In this study, the influence of acetone on the electrooxidation of 2-propanol in alkaline medium is investigated, using state-of-the-art Pd electrode, by cyclic voltammetry and chronoamperometry. The electrode is prepared using a chemical replacement method, by dipping nickel foam into acidified PdCl2 solution, and characterized by scanning electron microscopy. We found that the presence of acetone adversely affects electrooxidation performance of 2-propanol and substantially reduces the oxidation current of 2-propanol on Pd in alkaline medium. The acetone poisoning effect is interpreted by a competitive adsorption mechanism, in which acetone adsorbs onto Pd surface and occupies the active sites for 2-propanol electrooxidation, leading to a significant decrease in the number of these sites for 2-propanol electrooxidation. The results of this study point out that efficient electrocatalysts for 2-propanol electrooxidation in alkaline electrolytes must be non-adsorptive to acetone besides being highly active to 2-propanol oxidation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The unique NiCo 2 S 4 nanowire arrays directly grown on Ni foam was prepared by two-step hydrothermal routes. • The synergistic effect between Ni and Co for urea electrooxidation has been discussed. • The effects of KOH and urea concentrations for urea electrooxidation were investigated. Abstract A 3D NiCo 2 S 4 nanowire arrays directly grown on Ni foam electrode (NiCo 2 S 4 /NF) is prepared by two-step simple hydrothermal process. The morphology and phase composition of NiCo 2 S 4 /NF are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). As expected, in the following electrocatalytic measurement, the binder-free, self-made NiCo 2 S 4 /NF electrode exhibits much higher catalytic activity, lower onset potential, better stability and greater tolerance towards urea electrooxidation compared with the Ni 3 S 2 /NF electrode synthesized under the same reaction conditions. The NiCo 2 S 4 /NF electrode delivers a current density of 720 mA cm−2 at 0.18 V (vs. Ag/AgCl) in a solution containing 5 mol L−1 KOH and 0.33 mol L−1 urea. The impressive electrocatalytic activity of the NiCo 2 S 4 /NF catalyst is largely ascribed to its distinctive structure, which exposes more electrochemical active sites at the electrode–electrolyte interface. Besides, the high intrinsic electronic conductivity also largely boosts the charge transfer rates for urea electrooxidation. The results demonstrate that the NiCo 2 S 4 /NF electrode showing a beneficial application prospect in the wastewater treatment and direct urea fuel cells. [ABSTRACT FROM AUTHOR]

Novel Au@Ni nanoarrays electrode is facilely obtained by firstly template-assisted electro-deposition of Ni nanowire arrays (NAs), followed by galvanostatic deposition of Au catalysts onto the Ni NAs without any conductive agents and binders. The Au@Ni NAs electrode shows a rough surface and fringe with the diameter of ∼90 nm, which assures a high utilization of Au catalysts and provides a large specific surface area. The elemental distribution of Ni mainly exists in the inner layer of a single Au@Ni nanowire with the diameter ∼56 nm, while the elemental distribution of Au catalysts merely appears in the outer layer to form the unique core-shell nanowire structure. The Au@Ni NAs electrode reveals excellent electrochemical property and desirable stability for catalyzing NaBH 4 electro-oxidation in basic solutions. The Au@Ni NAs electrode in the 2.00 M NaOH and 0.24 M NaBH 4 solution demonstrates an oxidation current density of 2.35 A mg −1 at −0.5 V (vs. Ag/AgCl), which is much higher than that of the noble metal catalysts previously reported, indicating that this material may be hopefully used as anodic catalysts for applying in fuel cells. [ABSTRACT FROM AUTHOR]

Recently, direct borohydride fuel cell (DBFC) has been considering as a promising energy conversion devices. During the development of DBFC, reducing the use of noble metals and increasing the anode performance are the hot topic in recent researches. In this article, reduced graphene oxide nanosheets deposit on C@TiC coaxial nanowire array (rGO-C@TiC) by means of a combine method of chemical vapor deposition and electrodeposition is chosen as 3D current collector for Pd nanoparticles deposition. The morphology and crystal structure of the as-obtained 3D electrode is checked with FESEM, TEM, EDS, and XRD. Results claim that the as-prepared 3D electrode exhibits a mushroom-like structure with the mean diameter size of Pd is 5.32 nm. Their catalytic ability for NaBH 4 electro-oxidation is evaluated in a three electrode system by using the method of cycle voltammetry and chronoamperometry, proving that the 3D Pd-rGO-C@TiC electrode has a higher catalytic performance. The oxidation current density of 1.35 A cm −2 mg −1 Pd is achieved at −0.6 V. Furthermore, a direct borohydride-hydrogen peroxide fuel cell (DBHPFC) is assembled by using the as-prepared Pd-rGO-C@TiC electrode and a Pd/CFC electrode as anode and cathode catalyst, respectively, and a maximum power density of 68.5 mW cm −2 is obtained. In addition, the assembled DBHPFC shows excellent higher performance based on the mass activity basis (1427.1 W g −1 ) among those reported literatures, indicating that our Pd-rGO-C@TiC could be acted as a promising cost-effective and ponderable alternative catalyst for NaBH 4 electrooxidation. [ABSTRACT FROM AUTHOR]

Urea electro-oxidation reaction in alkaline medium is systematically analyzed by electrochemical impedance spectroscopy (EIS). The effects of polarization potential and KOH concentration on the impedance appearance are investigated. In the presence of urea, it is found that Nyquist plots exhibit two depressed semicircles, with one at higher frequencies stably locating in the first quadrant while the other’s location at lower frequencies varying between the first and second quadrant as the polarization potential changes. Results show both indirect and direct pathways proceed in urea electro-oxidation reaction. A mathematical model indicates the reverse loop in the Nyquist plots is attributed to CO 2 poisoning on the catalyst, which is also validated by the followed chronoamperometric method. Moreover, the rate determining steps of urea electro-oxidation reaction is dependent on KOH concentration. The EIS technique gives a new sight to interpret the poor stability of urea electro-oxidation on nickel catalyst, and thus helps to explore a CO 2 -insensitive catalyst. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) reduced graphene networks (RGN) were successfully fabricated on Ni foam without any conductive agents and polymer binders by dipping commercial Ni foam into graphene oxide (GO) suspension and subsequent a electroreduction process in a buffer solution. Au nanoparticles were then deposited on the RGN through an electrodeposition process to form a novel reduced graphene networks-Au (RGNA) electrode. The morphology and phase structure of the RGNA electrode are characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction spectrometer. The NaBH 4 electrooxidation performance on the RGNA electrode is investigated by means of cyclic voltammetry and chronoamperometry. The RGNA electrode owns special hierarchical porous structure, rapid electron and ion transport, and large electroactive surface area due to the intrinsic electronic conductivity, mesoporous nature of graphene. The RGNA electrode exhibits a good stability during the electrochemical process and the oxidation current density at RGNA electrode reached 500 mA cm −2 at 0 V in the solution containing 0.1 mol dm −3 NaBH 4 and 2 mol dm −3 NaOH, which is higher than that at bare Au–Ni foam without graphene. The excellent structural stability and high catalytic performance for NaBH 4 electrooxidation make the RGNA a promising material for future energy systems. [ABSTRACT FROM AUTHOR]

Urea peroxide as a solid-state fuel instead of liquid hydrogen peroxide is electro-catalytic oxidized by nickel nanowire arrays (NWAs) electrode. Nickel NWAs electrode is prepared by galvanostatically electrodepositing nickel into the pores and over-plating on the surface of polycarbonate template (PCT) from nickel bath solution. The NWAs are obtained after dissolving PCT in methylene chloride. Results show that urea peroxide decomposes into hydrogen peroxide and urea in aqueous solutions, then is electro-oxidized via two processes: i, hydrogen peroxide electro-oxidation at lower potential region; ii, both hydrogen peroxide and urea electro-oxidation at higher potential region. The onset oxidation potential and current density of urea peroxide electro-oxidation in 6.0 mol L −1 KOH and 1.0 mol L −1 urea peroxide are ca. -0.2 V and 700 mA cm −2 at 0.6 V, respectively. The nickel NWAs electrode demonstrates excellent stability for urea peroxide electro-oxidation under different polarization potentials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Direct carbon fuel cells are promising power sources with their performance significantly depending on the electrooxidation activity of carbon fuel. The impurities in the carbon fuel may affect the anode reactions. Sulfur and some of its inorganic compounds (CaSO 4 , K 2 SO 3 , K 2 S, FeS 2 ) were added in molten carbonate and their effect on graphite electrooxidation was investigated. Cyclic voltammograms of gold electrode with addition of these sulfur compounds showed CaSO 4 was stable and other compounds were electrochemically oxidized to high valence state sulfur compounds at operating voltage range. Linear sweep voltammetry of graphite with addition of sulfur compounds exhibited enhanced current density compared to pure graphite electrooxidation. Chronoamperometry was carried out to examine steady-state test of graphite electrooxidation in presence of sulfur compounds and the results indicated the enhanced current densities were caused by improved Boudouard reaction for CaSO 4 and sulfur electrooxidation for other compounds, respectively. These inorganic sulfur compounds had no impact on electrooxidation process of graphite. [ABSTRACT FROM AUTHOR]

Abstract: Flexible and wearable cobalt electrode with a unique three-dimensional hierarchical-network structure is prepared by electrodeposition of spherical Co particles onto multiwalled carbon nanotubes (MWNTs) which are assembled on the skeleton of cosmetic cotton (CC). The morphology and phase structure of the cobalt–multiwalled carbon nanotubes–cosmetic cotton (Co–MWNTs–CC) electrode are characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction spectrometer. The NaBH4 electrooxidation performance on the Co–MWNTs–CC electrode is investigated by means of cyclic voltammetry and chronoamperometry. Results show that the Co–MWNTs–CC electrode exhibits remarkably high catalytic activity and good stability for NaBH4 electrooxidation. The oxidation current density reaches as high as 170 mA cm−2 at −0.7 V in 1.0 mol dm−3 NaOH and 0.1 mol dm−3 NaBH4, which is higher than the most-related previous results. [Copyright &y& Elsevier]

Abstract: Running of direct 2-propanol fuel cell generates liquid acetone as the main product in the anode compartment. Its concentration continuously increases during cell operation. Its effect on the electrooxidation of 2-propanol at the anode catalyst deserves to be addressed. In this study, the influence of acetone concentration and reaction temperature on the electrooxidation of 2-propanol at Pt and Au electrode in alkaline electrolyte is investigated by cyclic voltammetry and chronoamperometry. The results show that the rate of 2-propanol electrooxidation at Pt and Au electrode is remarkably diminished with the increase of acetone concentration. When the concentration of acetone reaches 0.1molL−1, the oxidation current of 2-propanol at Pt and Au electrode decreases by around 50% and 30%, respectively. The effect of acetone can be attributed to its competitive adsorption with 2-propanol on electrodes surface, leading to the poison of electrodes. Increase of reaction temperature decreases the oxidation current of 2-propanol at Au electrode. Au electrode is more tolerant to acetone than Pt electrode at low acetone concentration. Results of this study suggest that new acetone insensitive electrocatalysts are needed for 2-propanol electrooxidation in alkaline electrolytes. [Copyright &y& Elsevier]