Visible light-operated saccharide–O2 biofuel cell based on the photosensitization of chlorophyll derivative on TiO2 film

The visible light-operated saccharide–O₂ biofuel cell consisting of zinc chlorin-e₆ (ZnChl-e₆) adsorbed on nanocrystalline TiO₂ layer coated onto optical transparent conductive glass electrode (OTE) as an anode, platinum-coated OTE as a cathode, and the fuel solution containing sucrose as a saccharide, invertase, glucose dehydrogenase (GDH) and NAD⁺ is studied as a new type biofuel cell. The short-circuit photocurrent (I_SC) and the open-circuit photovoltage (V_OC) of this cell are 9.0 μA cm⁻² and 415 mV, respectively. The peaks in the photocurrent action spectrum of this cell are observed at 400 and 800 nm and the incident photon-to-current efficiency (IPCE) values at 400 and 800 nm are estimated to be ca. 17.3% and 10.6%. Thus, a new type of visible light-operated saccharide–O₂ biofuel cell with the visible and near IR photosensitization of ZnChl-e₆ molecules on nanocrystalline TiO₂ film electrode is accomplished.     

Preparation and characterization of a bioanode (GC/MnO2/PSS/Gph/Frt/GOx) for biofuel cell application

In this study, a bioanode (GC/MnO₂-PSS-Gph/Frt/GOx) was developed by depositing a manganese dioxide-polystyrene sulfonate-graphene (MnO₂-PSS-Gph) composite containing ferritin (Frt) as mediator and glucose oxidase (GOx) as a catalytic enzyme on a glassy carbon (GC) electrode. The GOx oxidize the glucose to gluconolactone with the release of electrons. The composite was prepared by extending the Hummers method and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FTIR) spectroscopy. The electrochemical functioning of the fabricated bioanode was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge techniques. A maximum current density of 2.7 ± 0.2 mAcm⁻² associated with the bioanode was observed at the scan rate of 100 mVs⁻¹ in a potential range from −0.2 to 0.8 V having a glucose concentration of 40 mM. The surface concentration of GOx on the prepared bioelectrode was found to be 2.3 × 10⁻¹⁰ mol cm⁻² and rate constant for the electron transfer was calculated to be 3.89 s⁻¹.     

Optimization of MnO2-Graphene/polythioaniline (MnO2-G/PTA) hybrid nanocomposite for the application of biofuel cell bioanode

This study reports the synthesis of a nanocomposite comprised of graphene (G) supported manganese dioxide (MnO₂) incorporated into the network of polythioaniline (MnO₂-G/PTA). The hybrid composite was applied as an electrode material for the development of a bioanode. The bioanode was fabricated by the electrochemical entrapment of ferritin (Frt) as mediator and glucose oxidase (GOx) enzyme in the matrix of the as-synthesized MnO₂-G/PTA deposited on glassy carbon electrode (GCE) surface. The structural features and electrochemical behaviour of the modified electrodes were investigated by Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The results unfolded that the hybrid electroactive support (MnO₂-G/PTA) employed for the immobilization of the enzyme (GOx) established an appropriate electrical cabling between the redox enzyme (GOx) and the electrode surface with the assistance provided by the biocompatible mediator (Frt) working to enhance the electrical signals. The developed GCE/MnO₂-G/PTA/Frt/GOx bioanode attained a maximum current density of 3.68 mAcm^?2 at 35 mM glucose concentration at a scan rate of 100 mVs^?1. Thus, the MnO₂-G/PTA/Frt/GOx modified electrode possesses high potential and good biocompatibility for bio-electricity production from glucose.     

Ternary graphene@polyaniline-TiO2 composite for glucose biofuel cell anode application

In this work p-toluenesulfonic acid (p-TSA) doped highly conductive ternary graphene @polyaniline-TiO₂ (GN@Pani-TiO₂) was synthesized chemically. The conducting polymers incorporated with metal oxide have good electrical conductivity and large pseudo capacitance which have been utilized as a potential electrode material for biofuel cell electrode preparation. The redox mediator ferritin (Frt) and enzyme glucose oxidase (GOx) was immobilized successfully. The oxidation of glucose by the prepared bioanode was increased with the increase in glucose concentration in the range of 4–24 mM. The electrochemical performance of the bioanode was satisfactory at 20 mM glucose in a phosphate buffer solution (PBS) of pH 7.0 analyzed by cyclic voltammetry (CV) in 20 mM of glucose at different scan rates (20–100 mVs⁻¹), linear sweep voltammetry (LSV) and chronoamperometry. A saturation current density of 6.77 ± 0.2 mAcm⁻² was achieved at a 100 mVs⁻¹ scan rate for 20 mM of glucose oxidation.     

Effect of ZrO2 addition on Ni/Al2O3 catalyst to produce H2 from glycerol

In this work, ZrO₂ was employed as support and as Al₂O₃ modifier of Ni based catalysts due to its special interesting characteristics. The catalytic activity of these systems was studied in steam reforming of glycerol to produce H₂. As the activity results at 773 K and 873 K showed, the NiZ catalyst allowed low glycerol conversion and H₂ production when compared to the NiγA catalyst. Moreover, the NiZ catalyst was not able to reform intermediate liquid products into gaseous products.     

Hydrogen production from glycerol on Ni/Al2O3 catalyst

The growing demand of hydrogen needs renewable sources of raw materials to produce it. Glycerol, by-product of biodiesel synthesis, could be a bio-renewable substrate to obtain hydrogen. A Ni(5.8%)-alumina catalyst was evaluated in the steam reforming of glycerol at 600–700 °C, atmospheric pressure, 16:1 water:glycerol molar ratio, and 3.4–10.0 h⁻¹ WHSV. A glycerol aqueous solution was fed, while a nitrogen stream was co-fed. After 4 h-on-stream, conversion was 96.8% at 600 °C increasing to 99.4% at 700 °C, reaching the largest hydrogen selectivity (99.7%) at 650 °C. After 8 h, conversion decreases more significantly at 600 °C, while the hydrogen selectivity does not significantly change with temperature and increases by decreasing WHSV. After 4 h, the main by-product was methane (76–97%), increasing at higher temperature, followed by ethene, ethane, propene, and propane. At 700 °C and 10.0 h⁻¹ WHSV, the main by-products were ethene (47%) and methane (37%); it could be associated to catalyst deactivation.     

Electrochemical performance of a glucose/oxygen microfluidic biofuel cell

A microfluidic glucose/O₂ biofuel cell, delivering electrical power, is developed based on both laminar flow and biological enzyme strategies. The device consists of a Y-shaped microfluidic channel in which fuel and oxidant streams flow laminarly in parallel at gold electrode surfaces without convective mixing. At the anode, the glucose is oxidized by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from interfering parasite reaction of O₂ at the anode and works with different streams of oxidant and fuel for optimal operation of the enzymes. The dependence of the flow rate on the current is evaluated in order to determine the optimum flow that would provide little to no mixing while yielding high current densities. The maximum power density delivered by the assembled biofuel cell reaches 110 μW cm⁻² at 0.3 V with 10 mM glucose at 23 °C. This research demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O₂ biofuel cell device.     

Photoelectrochemical performance of graphene-modified TiO2 photoanodes in the presence of glycerol as a hole scavenger

Graphene-modified TiO₂ (G-TiO₂) photoanode films were successfully prepared by a simple, versatile, and low-cost spray pyrolysis deposition method. The effects of graphene incorporation on the relevant properties of TiO₂ films were investigated by means of XRD, SEM, UV–vis absorbance spectroscopy, and photoelectrochemistry-related measurements. Bias-dependant efficiency calculated from linear-sweep voltammograms shows that the presence of graphene within the film networks, despite its low content, could promote a substantial improvement in maximum photoconversion efficiency from 0.39% (at −0.27 V vs HgO|Hg) to 0.65% (at −0.35 V vs HgO|Hg). This improvement is attributable to the enhancement of the electron-transferring ability upon the insertion of graphene, as confirmed by transient photocurrent analysis and Electrochemical Impedance Spectroscopy (EIS). The effectiveness of the photoelectrochemical cell employing G-TiO₂ as an excellent photoanode was further examined by running it in the presence of glycerol as a hole scavenger. Glycerol plays an important role as an effective sink for the photogenerated holes so that the surface charge recombination can be significantly suppressed and, subsequently, the photocurrent is enhanced. The additional photocurrent due to glycerol introduction into the cell depends upon the initial concentration of glycerol according to a model resembling a Langmuir–Hinshelwood isotherm. Based upon the results of the present study, further improvements in terms of graphene content, surface morphology modification or the use of other organic wastes as hole scavengers may be important for future investigation.     

Electrochemical properties of enzyme electrode covalently immobilized on a graphite oxide/cobalt hydroxide/chitosan composite mediator for biofuel cells

A critical factor for the performance of a biofuel cell is an immobilization of the redox enzyme for continuous catalytic reaction and efficient electron transfer. However, the main obstacle associated with enzyme electrode is the reduced surface area for the accommodation of enzymes, leading to poor power output. This study aimed to optimize the efficient electrical communication for glucose oxidase (GOx) on the surface of a graphite oxide/cobalt hydroxide/chitosan composite as mediator, thereby enhancing the generation of power output. Immobilization efficiency was affected by the different concentrations of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC)/N-hydroxysuccinimide (NHS). Also, the surface of enzyme electrode was observed by XPS, Raman, and AFM, respectively. The electrochemical characterization showed that the immobilized GOx possesses the highest activity at EDC:NHS(40:80 mM) concentration. The power output under the optimal condition was found to be 2.24 mWcm^?2 of power density using the three-electrode cell in 0.1 M PBS solution at room temperature.     

Production of CO-rich hydrogen gas from glycerol dry reforming over La-promoted Ni/Al2O3 catalyst

Dry reforming of glycerol has been carried out over alumina-supported Ni catalyst promoted with lanthanum. The catalysts were characterized using EDX, liquid N₂ adsorption, XRD technique as well as temperature-programmed reduction. Significantly, catalytic glycerol dry reforming under atmospheric pressure and at reaction temperature of 1023 K employing 3 wt%La–Ni/Al₂O₃ catalyst yielded H₂, CO and CH₄ as main gaseous products with H₂:CO < 2.0. Post-reaction, XRD analysis of used catalysts showed carbon deposition during glycerol dry reforming. Consequently, BET surface area measurement for used catalysts yielded 10–21% area reduction. Temperature-programmed gasification studies with O₂ as a gasification agent has revealed that La promotion managed to reduce carbon laydown (up to 20% improvement). In comparison, the unpromoted Ni/Al₂O₃ catalyst exhibited the highest carbon deposition (circa 33.0 wt%).     

Explosion behavior of CH4/O2/N2/CO2 and H2/O2/N2/CO2 mixtures

In this work, the explosion behavior of stoichiometric CH₄/O₂/N₂/CO₂ and H₂/O₂/N₂/CO₂ mixtures has been studied both experimentally and theoretically at different CO₂ contents and oxygen air enrichment factors. Peak pressure, maximum rate of pressure rise and laminar burning velocity were measured from pressure time records of explosions occurring in a closed cylindrical vessel. The laminar burning velocity was also computed through CHEMKIN–PREMIX simulations.     

Bioreactor for glycerol conversion into H2 by bacterium Enterobacter aerogenes

Glycerol was used as a substrate for H₂ production by bacterium Enterobacter aerogenes in the test tubes and bioreactor. A BioFlo/CelliGen 115 bioreactor (10 L working volume) was utilized to conduct the experiments for conversion of glycerol into H₂ by E. aerogenes cells. The highest H₂ production rate was observed under 2% glycerol in the culture medium. The glycerol uptake efficiency by bacteria in the bioreactor was found to be 65% during the 6 day period, matching glycerol uptake efficiency observed in the test tubes experiment (65%).Hydrogen production from glycerol (2% glycerol, v/v) by E. aerogenes in the bioreactor and test tubes was measured over the 6 days, showing the maximal H₂ rate at 650 mL g⁻¹ dry weight h⁻¹. The yield of H₂ production from glycerol at 0.89 mol/mol in the bioreactor was high, corresponding to the theoretical yield of 1 mol of H₂ per 1 mol of glycerol.     

Thermodynamic analysis of hydrogen production via glycerol steam reforming with CO2 adsorption

Thermodynamic equilibrium for glycerol steam reforming to hydrogen with carbon dioxide capture was investigated using Gibbs free energy minimization method. Potential advantage of using CaO as CO₂ adsorbent is to generate hydrogen-rich gas without a water gas shift (WGS) reactor for proton exchange membrane fuel cell (PEMFC) application. The optimal operation conditions are at 900 K, the water-to-glycerol molar ratio of 4, the CaO-to-glycerol molar ratio of 10 and atmospheric pressure. Under the optimal conditions, complete glycerol conversion and 96.80% H₂ and 0.73% CO concentration could be achieved with no coke. In addition, reaction conditions for coke-free and coke-formed regions are also discussed in glycerol steam reforming with or without CO₂ separation. Glycerol steam reforming with CO₂ adsorption has the higher energy efficiency than that without adsorption under the same reaction conditions.     

Development of a ternerry condunting composite (PPy/Au/CNT@Fe3O4) immobilized FRT/GOD bioanode for glucose/oxygen biofuel cell applications

Enzymatic biofuel cells (EBFCs) are considered as a promising technology to sustain the requirements of miniaturized portable energy sources. Electrode materials being one of the substantial aspects of EBFCs have stimulated immense interest in research. A new platform made of nanocomposite, involving magnetic particles of iron oxide (Fe₃O₄), carbon nanotubes (CNT), gold nanoparticles (Au) and a conducting polymer polypyrrole (PPy), was used as the electrode support for the immobilization of glucose oxidase (GOD) which improves the bioelectrocatalysis of the enzyme towards oxidation of glucose. The structural and electrochemical characterization of the modified bioanode GCE/PPy/Au/CNT@Fe₃O₄/FRT/GOD was performed using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). The performance of the bioanode was evaluated with promising results showing the maximum current density of 6.01 mA cm^?2 (0.22 V vs. Ag/AgCl) in 40 mM of glucose concentration at 0.38 V open circuit potential (OCV). The results suggested that PPy/Au/CNT@Fe₃O₄ nanocomposite significantly improve the surface area of the electrode and served as a suitable environment for enzyme immobilization, and established good electrical communication by facilitating electron transfer between enzymes and electrode surface. The as-synthesized composite has been inferred as a promising platform for improved bioelectrocatalysis owing to the excellent combination of superparamagnetism of Fe₃O₄ with good electrocatalytic properties of CNT, PPy, and Au nanoparticles. Thus PPy/Au/CNT@Fe₃O₄ nanocomposite can be considered as a prospective electrode material for developing better electrochemical biosensors and biofuel cell anode.     

Hydrogen and power generation from supercritical water reforming of glycerol and pressurized SOFC integrated system: Use of different CO2 adsorption process

The performance analysis of an integrated system of glycerol supercritical water reforming and pressurized SOFC was presented. The use of different CO₂ adsorption processes that include in situ and ex situ processes was compared to determine the suitable process for hydrogen and power generations. The influence of operating condition, e.g., temperature and pressure of reformer, supercritical water to glycerol (S/G) molar ratio, and calcium oxide to glycerol (CaO/G) molar ratio was examined. Then, the electrical performance of each integrated process was considered with respect to the SOFC conditions comprising temperature, pressure, and current density. The simulation results revealed that both processes have same favourable conditions for temperature and pressure operated at 800 °C and 240 atm, respectively. The suitable S/G and CaO/G molar ratios for in situ process are 10 and 2 whereas those for ex situ process are 20 and 1. Under these conditions, maximum hydrogen can be achieved as 87% and 75% for in situ and ex situ processes, respectively. When both integrated processes are operated at the optimal SOFC conditions as 900 °C, 4 atm, and current density of 10,000 A/m², the SOFC efficiency of 71.56% and 62.12% can provide for in situ and ex situ processes, respectively.     

Modeling of single coal particle combustion in O2/N2 and O2/CO2 atmospheres under fluidized bed condition

A one-dimensional transient single coal particle combustion model was proposed to investigate the characteristics of single coal particle combustion in both O₂/N₂ and O₂/CO₂ atmospheres under the fluidized bed combustion condition. The model accounted for the fuel devolatilization, moisture evaporation, heterogeneous reaction as well as homogeneous reactions integrated with the heat and mass transfer from the fluidized bed environment to the coal particle. This model was validated by comparing the model prediction with the experimental results in the literature, and a satisfactory agreement between modeling and experiments proved the reliability of the model. The modeling results demonstrated that the carbon conversion rate of a single coal particle (diameter 6 to 8 mm) under fluidized bed conditions (bed temperature 1088 K) in an O₂/CO₂ (30:70) atmosphere was promoted by the gasification reaction, which was considerably greater than that in the O₂/N₂ (30:70) atmosphere. In addition, the surface and center temperatures of the particle evolved similarly, no matter it is under the O₂/N₂ condition or the O₂/CO₂ condition. A further analysis indicated that similar trends of the temperature evolution under different atmospheres were caused by the fact that the strong heat transfer under the fluidized bed condition overwhelmingly dominated the temperature evolution rather than the heat release of the chemical reaction.     

Mechanism of O2 evolution on TiO2 photoanodes

The mechanism of O₂ evolution over titanium oxide photoanodes has been studied by relating structural properties, derived from XRD and XPS, and electrochemical properties currents, (cyclic voltammetry and flatband potentials) to the performance in PEC cells of five specimens of lowest and highest photoelectrochemical efficiency.     

Laminar burning velocities and transition to unstable flames in H2/O2/N2 and C3H8/O2/N2 mixtures

Effects of positive flame stretch on laminar burning velocities, and conditions for transition to unstable flames, were studied experimentally for freely propagating spherical flames at both stable and unstable preferential-diffusion conditions. The data base involved new measurements for H₂/O₂/N₂ mixtures at values of flame stretch up to 7600 s⁻¹, and existing measurements for C₃H₈/O₂/N₂ mixtures at values of flame stretch up to 900 s⁻¹. Laminar burning velocities varied linearly with increasing Karlovitz numbers—either decreasing or increasing at stable or unstable preferential-diffusion conditions—yielding Markstein numbers that primarily varied with the fuel-equivalence ratio. Neutral preferential-diffusion conditions, however, were shifted toward the unstable side of the maximum laminar burning velocity condition that the simplest preferential-diffusion theories associate with neutral stability. All flames exhibited transition to unstable flames: unstable preferential-diffusion coditions yielded early transition to irregular flame surfaces, and stable preferential-diffusion conditions yielded delayed transition to cellular flames by hydrodynamic instability. Conditions for hydrodynamic instability transitions for H₂/O₂/N₂ mixtures were consistent with an earlier correlation due to Groff for propane/air flames, based on the predictions of Istratov and Librovich.     

Experimental and numerical investigation of low-pressure laminar premixed synthetic natural gas/O2/N2 and natural gas/H2/O2/N2 flames

The oxidation of laminar premixed natural gas flames has been studied experimentally and computationally with variable mole fractions of hydrogen (0, 20, and 60%) present in the fuel mixture. All flames were operated at low pressure (0.079 atm) and at variable overall equivalence ratios (0.74<?<1.0) with constant cold gas velocity. At the same global equivalence ratio, there is no significant effect of the replacement of natural gas by 20% of H₂. The small differences recorded for the intermediate species and combustion products are directly due to the decrease of the amount of initial carbon. However, in 60% H₂ flame, the reduction of hydrocarbon species is due both to kinetic effects and to the decrease of initial carbon mole fraction. The investigation of natural gas and natural gas/hydrogen flames at similar C/O enabled identification of the real effects of hydrogen. It was shown that the presence of hydrogen under lean conditions activated the H-abstraction reactions with H atoms rather than OH and O, as is customary in rich flames of neat hydrocarbons. It was also demonstrated that the presence of H₂ favors CO formation.