Nickel-based catalysts for non-enzymatic electrochemical sensing of glucose: A review

Decomposition of ammonia by atmospheric pressure AC discharge: Catalytic effect of the electrodes

Kinetics and mechanism of glucose electrooxidation on different electrode-catalysts: Part II. Effect of the nature of the electrode and the electrooxidation mechanism

Existing energy sources based on fossil fuel is an obstacle for environmental sustainability, and there is a concern regarding the depletion of fossil fuel resources [1], [2]. Therefore, it is essential to develop new alternative energy sources. As a safe and effective method of generating power, the conversion of natural biomass to electricity in the form of direct biomass fuel cell (DBFC) has attracted significant attention due to its high efficiency and low emissions [3]. Among various DBFCs, direct urea fuel cell (DUFC) using urea in wastewater and urine as fuel has recently been validated as a clean energy device [4]. The overall power response of the DUFC mainly depends on the urea oxidation reaction (UOR), so it is vital to investigate the UOR catalysts. Ni-based catalysts, which are inexpensive and commonly used as UOR catalysts, have widely utilized for replacement of noble metals. The Ni/C electrode as an anode in the reported study achieved a power density of 1.7 mW/cm2 [5], and nanostructured Ni-based catalysts or bimetallic types of catalysts also have been implemented for better performances [6], [7]. However, the above studies proceeded in an alkaline medium, which makes it difficult to use actual wastewater or urine directly as a source for fuel cells application. Since the electrochemical features of nickel-based catalysts are based on the mechanism of electrooxidation from Ni2+ to Ni3+ in alkaline medium, the catalytic activity in neutral solutions is less well distinguished [8]. Thus, nickel-based catalysts essentially comprising Ni3+ ions will more efficiently improve the UOR performances even if a neutral atmosphere of urea solution is adopted. In this study, the catalyst with a nanostructures array based on nickel oxyhydroxide with metal (metal-NiOOH) was prepared by using the electrospinning process for DUFC. The morphology and the structure of the metal-NiOOH catalysts were observed using scanning electron microscopy, Transmission electron microscopy, and X-ray diffraction methods. The metal-NiOOH catalyst used as the DUFC anode showed excellent UOR performances and power achievements in real human urine. A comprehensive investigation on the performances of metal-NiOOH and the function of internal Ni3+ ions as a catalyst in DUFC will be presented. References Suranovic, Steven. "Fossil fuel addiction and the implications for climate change policy." Global Environmental Change 23.3 (2013): 598-608. Veziroğlu, T. Nejat, and Sümer Şahi. "21st Century’s energy: Hydrogen energy system." Energy conversion and management 49.7 (2008): 1820-1831. Zhao, Xuebing, and J. Y. Zhu. "Efficient conversion of lignin to electricity using a novel direct biomass fuel cell mediated by polyoxometalates at low temperatures." ChemSusChem 9.2 (2016): 197-207. Xu, Wei, et al. "Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell." Scientific reports 4 (2014): 5863. Lan, Rong, Shanwen Tao, and John TS Irvine. "A direct urea fuel cell–power from fertiliser and waste." Energy & Environmental Science 3.4 (2010): 438-441. Ye, Ke, et al. "Facile preparation of three-dimensional Ni (OH) 2/Ni foam anode with low cost and its application in a direct urea fuel cell." New Journal of Chemistry 40.10 (2016): 8673-8680. Guo, Fen, et al. "Preparation of nickel-cobalt nanowire arrays anode electro-catalyst and its application in direct urea/hydrogen peroxide fuel cell." Electrochimica Acta 199 (2016): 290-296. Vedharathinam, Vedasri, and Gerardine G. Botte. "Direct evidence of the mechanism for the electro-oxidation of urea on Ni (OH) 2 catalyst in alkaline medium." Electrochimica Acta 108 (2013): 660-665. Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.

The electrooxidation behavior of BH4(-) on electrocatalytic Pt, hydrolytically active Ni, and noncatalytic Au electrodes were comparatively reexamined and a more generalized reaction mechanism was proposed to explain the very different anodic properties of BH4(-) on the different metal electrodes. In this mechanism, the anodic reaction behavior of BH4(-) are determined by a pair of conjugated reactions: electrochemical oxidation and chemical hydrolysis of BH4(-), the relative rates of which depend on the anodic materials, applied potentials, and chemical states of the anodic surfaces. At Pt surface, the electron number of BH4(-) oxidation increases with the increased potential polarization, while the actual electron number of BH4(-) oxidation on Ni electrode is 4 at most due to the poor electrocatalytic activity of the oxidized Ni surface and the strong catalytic activity of metallic Ni for chemical recombination of the adsorbed H intermediate. On the hydrolytic-inactive Au surface, the anodic reaction of BH4(-) can proceed predominately through direct electrochemical oxidation, delivering a near 8e discharge capacity.

Nickel-based catalysts are regarded as the most excellent urea oxidation reaction (UOR) catalysts in alkaline media. Whatever kind of nickel-based catalysts is utilized to catalyze UOR, it is widely believed that the in situ-formed Ni3+ moieties are the true active sites and the as-utilized nickel-based catalysts just serve as pre-catalysts. Digging the pre-catalyst effect on the activity of Ni3+ moieties helps to better design nickel-based catalysts. Herein, five different anions of OH-, CO32-, SiO32-, MoO42-, and WO42- were used to bond with Ni2+ to fabricate the pre-catalysts β-Ni(OH)2, Ni-CO3, Ni-SiO3, Ni-MoO4, and Ni-WO4. It is found that the true active sites of the five as-fabricated catalysts are the same in situ-formed Ni3+ moieties and the five as-fabricated catalysts demonstrate different UOR activity. Although the as-synthesized five catalysts just serve as the pre-catalysts, they determine the quantity of active sites and activity per active site, thus determining the catalytic activity of the catalysts. Among the five catalysts, the amorphous nickel tungstate exhibits the most superior activity per active site and can catalyze UOR to reach 158.10 mA·cm-2 at 1.6 V, exceeding the majority of catalysts. This work makes for a deeper understanding of the pre-catalyst effect on UOR activity and helps to better design nickel-based UOR catalysts.

In this paper, Cu nanocolumnar structure electrodes are synthetized using a clean and easy-to-scale-up direct-current magnetron sputtering (DC-MS) technique for non-enzymatic glucose sensing. The nanocolumnar structure increases the active surface area of the deposit, with the nanocolumns showing a mean size diameter of 121.0 nm ± 27.2 and a length of 2.52 µm ± 0.23. A scanning transmission electron (STEM) analysis shows the presence of Cu and a small amount of Cu2O. The behavior of the electrodes in alkaline environments and the electrochemical affinity of the Cu nanocolumns (CuNCs) towards the electro-oxidation of glucose are investigated using cyclic voltammetry (CV). After performing CV in NaOH solution, the columnar structures present corrosion products containing Cu2O, as revealed by STEM and X-ray diffraction (XRD) analyses. The amperometric responses of the CuNCs to the successive addition of glucose show a linear range up to 2 mM and a limit of detection of 5.2 µM. Furthermore, the electrodes are free from chloride poisoning, and they are insensitive to dopamine, uric acid, ascorbic acid, and acetaminophen at their physiological concentrations.

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Highly sensitive non-enzymatic glucose sensor based on carbon nanotube microelectrode set

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems. In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern. In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes. Figure 1

Integration of gasoline prereforming into autothermal reforming for hydrogen production

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems. In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern. In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes.

Three-dimensional porous Ni film electrodeposited on Ni foam: High performance and low-cost catalytic electrode for H2O2 electrooxidation in KOH solution

Kinetics and mechanism of glucose electrooxidation on different electrode-catalysts: Part I. Adsorption and oxidation on platinum

Advantages of homo- and heterogeneous catalysts are united in metallodendritic molecules where nickel-based catalysts are bound to carbosilane dendrimers. The first direct indication of a "dendritic effect" in the redox catalysis behavior is described: variation of the dendrimer support controls the proximity of the Ni(II) centers, which in turn controls catalytic activity. Catalyst deactivation, by means of Ni(III) formation, can be avoided by a larger separation of the Ni(II) centers (see picture).

The electro-oxidation of glucose on microcolumnar gold electrodes in different neutral solutions