Hydrogen production from glycerol steam reforming for low- and high-temperature PEMFCs

This paper presents a thermodynamic study of a glycerol steam reforming process, with the aim of determining the optimal hydrogen production conditions for low- and high-temperature proton exchange membrane fuel cells (LT-PEMFCs and HT-PEMFCs). The results show that for LT-PEMFCs, the optimal temperature and steam to glycerol molar ratio of the glycerol reforming process (consisting of a steam reformer and a water gas shift reactor) are 1000 K and 6, respectively; under these conditions, the maximum hydrogen yield was obtained. Increasing the steam to glycerol ratio over its optimal value insignificantly enhanced the performance of the fuel processor. For HT-PEMFCs, to keep the CO content of the reformate gas within a desired range, the steam reformer can be operated at lower temperatures; however, a high steam to glycerol ratio is required. This requirement results in an increase in the energy consumption for steam generation. To determine the optimal conditions of glycerol steam reforming for HT-PEMFC, both the hydrogen yield and energy requirements were taken into consideration. The operational boundary of the glycerol steam reformer was also explored as a basic tool to design the reforming process for HT-PEMFC.     

Thermodynamic analysis of a proton conducting SOFC integrated system fuelled by different renewable fuels

This work proposes a power generation system consisting of steam reformer and SOFC–H⁺ fuelled by different types of fuel, i.e., ethanol, glycerol and biogas. The performance analysis of integrated system is performed based on thermodynamic calculation through Aspen Plus simulator. The total of the Gibbs free energy minimization is used to determine product composition at equilibrium. The electrochemical model not only considers all voltage losses but also includes the effect of current leakage as a result from the electrolyte used. Considering the operating condition of steam reformer, it is found that the gas product contains the highest amount of hydrogen without the carbon formation when reformer is operated at 973 K with steam to carbon ratio of 1. In addition, the simulation results show that the SOFC–H⁺ operated at 973 K and 1 A/cm² can provide a suitable compromise between system performances and exhaust gas composition. The use of glycerol reformate has the highest cell and system efficiencies and fuel utilization compared to the others. In addition, the integrated system fuelled by glycerol can release low CO amount whereas there is more heat provided to the surrounding. Therefore, it can be concluded that glycerol is suitable renewable fuel for SOFC–H⁺ integrated system.     

Performance evaluation of combined solid oxide fuel cells with different electrolytes

The performance of a hybrid system of solid oxide fuel cells with different electrolytes, i.e., an oxygen-ion conducting electrolyte (SOFC-O²⁻) and a proton-conducting electrolyte (SOFC-H⁺) is evaluated in this study. Due to an internal reforming operation, SOFC-O²⁻ can produce electrical power as well as high-temperature exhaust gas containing remaining fuel, i.e., H₂ and CO that can be used for SOFC-H⁺ operation. The remaining CO can further react with H₂O via water gas-shift reaction to produce more H₂ within SOFC-H⁺ and thus, the possibility of carbon formation in SOFC-H⁺ can be eliminated and overall system efficiency can be improved. The simulation results show that the performance of the SOFC-O²⁻–SOFC-H⁺ system provides a higher efficiency (54.11%) compared with the use of a single SOFC. Further, the SOFC hybrid system performance is investigated with respect to important operating conditions, such as temperature, pressure, degree of pre-reforming, inlet fuel velocity, and cell voltage.     

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.     

Analysis of a pressurized solid oxide fuel cell–gas turbine hybrid power system with cathode gas recirculation

A pressurized solid oxide fuel cell–gas turbine hybrid system (SOFC–GT system) has been received much attention for a distributed power generation due to its high efficiency. When considering an energy management of the system, it is found that a heat input is highly required to preheat air before being fed to the SOFC stack. The recirculation of a high-temperature cathode exhaust gas is probably an interesting option to reduce the requirement of an external heat for the SOFC–GT system. This study aims to analyze the pressurized SOFC–GT hybrid system fed by ethanol with the recycle of a cathode exhaust gas via a simulation study. Effect of important operating parameters on the electrical efficiency and heat management of the system is investigated. The results indicate that an increase in the operating pressure dramatically improves the system electrical efficiency. The suitable pressure is in a range of 4–6 bar, achieving the highest system electrical efficiency and the lowest recuperation energy from the waste heat of the GT exhaust gas. In addition, it is found that the waste heat obtained from the GT is higher than the heat required for the system, leading to a possibility of the SOFC–GT system to be operated at a self-sustainable condition. Under a high pressure operation, the SOFC–GT system requires a high recirculation of the cathode exhaust gas to maintain the system without supplying the external heat; however, the increased recirculation ratio of the cathode exhaust gas reduces the system electrical efficiency.     

Thermodynamic analysis of calcium oxide assisted hydrogen production from biogas

This paper investigates calcium oxide assisted hydrogen production from biogas. Preliminary experiments were performed to compare the catalytic performance of combined carbon dioxide reforming and partial oxidation of biogas among four different adsorbent (CaO)/catalyst (Ni/SiO₂·MgO) arrangements; i.e. (i) Ni/SiO₂·MgO before CaO, (ii) CaO before Ni/SiO₂·MgO, (iii) Ni/SiO₂·MgO mixed with CaO, and (iv) Ni/SiO₂·MgO without CaO. The mixture of CaO and Ni/SiO₂·MgO was found to be the best arrangement, offering the highest hydrogen yield. Thermodynamic investigation of the integrated sorption-reaction systems for hydrogen production from biogas was performed. The system can be operated under thermal neutral condition when appropriate operating parameters are adjusted. Finally based on the thermal neutral operation, the effects of H₂O/CH₄ and CaO/CH₄ ratios on the required O₂/CH₄ ratio, hydrogen yield, hydrogen concentration and CO/H₂ ratio in product were determined. Obviously the use of CaO adsorbent can improve hydrogen production and there is an optimum H₂O/CH₄ ratio which offers the highest hydrogen production at each CaO/CH₄ ratio. Increasing H₂O/CH₄ ratio generally increases H₂/CO ratio but decreases hydrogen concentration in the product.     

Technical and economic study of integrated system of solid oxide fuel cell,palladium membrane reactor,and CO2 sorption enhancement unit

This paper deals with the integrated system of solid oxide fuel cell (SOFC), palladium membrane reactor (PMR), and CO₂ sorption enhancement (SE) unit. Three configurations of the SOFC systems fed by biogas are considered, i.e., PMR–SOFC, SE–PMR–SOFC, and SE–PMR–SOFC with a retentate gas recycling (SER–PMR–SOFC). The SOFC system equipped with a conventional reformer (CON–SOFC) is considered as a base case. The simulation results show that the capture of CO₂ in biogas before being fed to PMR (SE–PMR–SOFC) can improve H₂ recovery. The performance of SE–PMR–SOFC can be further enhanced by recycling retentate gas from PMR to CO₂ sorption enhancement unit (SER–PMR–SOFC). Compared to CON–SOFC, both SE–PMR–SOFC and SER–PMR–SOFC give higher power density and thus require smaller stack size (the stack size reduction of 1.55% and 8.27% are observed for SE–PMR–SOFC and SER–PMR–SOFC, respectively). The economic analysis is performed to identify the potential benefits of each SOFC configuration. The results indicate that SE–PMR–SOFC and SER–PMR–SOFC are not cost-effective systems compared with CON–SOFC; however, the capture of CO₂ in these SOFC systems offers an environmental benefit. High %total CO₂ capture and low cost of CO₂ capture are achieved under these SOFC systems.     

Analysis of a proton-conducting SOFC with direct internal reforming

This paper presents a performance analysis of a planar SOFC (solid oxide fuel cell) with proton-conducting electrolyte (SOFC-H⁺). The SOFC-H⁺ is fueled by methane and operated under direct internal reforming and isothermal conditions. A one-dimensional steady-state model coupled with a detailed electrochemical model is employed to investigate the distribution of gas composition within fuel and air channels and all the electrochemical-related variables. The current–voltage characteristics of SOFC-H⁺ are analyzed and the result shows that the operation of SOFC-H⁺ at 0.7 V gives a good compromise on power density and fuel utilization. However, high CO content at fuel channel is observed at this condition and this may hinder the SOFC-H⁺ performance by reducing catalyst activity. The effect of key cell operating parameters, i.e., steam to carbon ratio, temperature, pressure, and water content in oxidant, on the performance of SOFC-H⁺ and the content of CO is also presented in this study.     

Light-assisted synthesis of Pt-Zn porphyrin nanocomposites and their use for electrochemical detection of organohalides

Pt-Zn porphyrin nanocomposites have been synthesized using zinc porphyrin and dihydrogen hexachloroplatinate in the presence of light and ascorbic acid. TEM and AFM imaging revealed that Pt nanoparticles with an average diameter of approximately 3.5 nm were embedded within the Zn porphyrin matrix. The glassy carbon electrode was modified with Nafion-stabilized Pt-Zn porphyrin nanocomposites and used for dehalogenation of carbon tetrachloride, chloroform, pentachlorophenol, chlorobenzene, and hexachlorobenzene as five test models. The Pt-Zn porphyrin nanocomposite-modified electrode exhibited catalytic activity for the reduction of organohalides at -1.0 V versus Ag/AgCl. Raman signatures confirmed the dehalogenation of chlorobenzene by the nanocomposite-modified electrode. The above two aliphatic and three aromatic organohalides had detection limits of 0.5 microM with linearity up to 8 microM. The modified electrode was good for at least 80 repeated measurements of 4 microM chlorobenzene with a storage stability of 1 month at room temperature. The deactivation of the electrode activity was associated with the loss of platinum nanoparticles from the nanocomposite structure.     

Voltammetric sensor for general purpose organohalide detection at picogram per liter concentrations based on a simple collector-generator method

With the aim of producing a general purpose sensor for environmental analysis, we describe a simple and sensitive method for organohalide detection, based on an electrochemical collector-generator process. The sensor consists of four coplanar electrodes contacting a solution volume of 300 microL, containing organohalide. At the first working electrode (a Zn/PTFE composite), the analyte is electrolyzed to liberate halide ions. At the second working electrode (Ag), the halide ions are detected by cathodic stripping voltammetry. Using a preconcentration time of 600 s, with differential pulse voltammetry for stripping, the responses to 1-chloropropane, chloroform, carbon tetrachloride, iodoethane, and bromoethane can be plotted on a common calibration curve, with a detection limit of 0.1 nM (1.3 pg L(-1) or less depending on the organohalide). To the best of our knowledge, this is the lowest reported organohalide detection limit by an electrochemical method and is so far the only general purpose electrochemical method sensitive enough for regulatory requirements. The sensor response was invariant for approximately 40 measurements. Analysis of tap water, spiked with chloroform or carbon tetrachloride, gave recoveries within 1.0-2.6% of the recoveries by the standard GC method.