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The electrochemical water splitting to produce H 2 in high efficiency with earth-abundant-metal catalysts remains a challenge. Here, we describe a simple "cyclic voltammetry + ageing" protocol at room temperature to activate Ni electrode (AC-Ni/NF) for hydrogen evolution reaction (HER), by which Ni/Ni(OH) 2 heterostructure is formed at the surface. In situ Raman spectroscopy reveals the gradual growth of Ni/Ni(OH) 2 heterostructure during the first 30 min of the aging treatment and combined with polarization measurements, it suggests a positive relation between the Ni/Ni(OH) 2 amount and HER performance of the electrode. The obtained AC-Ni/NF catalyst, with plentiful Ni–Ni(OH) 2 interfaces, exhibits remarkable performance towards HER, with the low overpotential of only 30 mV at a H 2 -evolving current density of 10 mA/cm2 and 153 mV at 100 mA/cm2, as well as a small Tafel slope of 46.8 mV/dec in 1 M KOH electrolyte at ambient temperature. The excellent HER performance of the AC-Ni/NF could be maintained for at least 24 h without obvious decay. Ex situ experiments and in situ electrochemical-Raman spectroscopy along with density functional theory (DFT) calculations reveal that Ni/Ni(OH) 2 heterostructure, although partially reduced, can still persist during HER catalysis and it is the Ni–Ni(OH) 2 interface reducing the energy barrier of H∗ adsorption thus promoting the HER performance. [Display omitted] • The Ni/Ni(OH) 2 heterostructure is synthesized via electrochemical and ageing treatments under mild conditions. • The in situ formation of Ni/Ni(OH) 2 heterostructure is recorded by Raman spectroscopy. • The Ni/Ni(OH) 2 shows excellent HER performance with only 30 mV to reach 10 mA/cm2. • In situ Raman spectroscopy shows catalysis process during HER of Ni/Ni(OH) 2. [ABSTRACT FROM AUTHOR]

In this study, polybenzimidazole (PBI) is used as membrane material of the high-temperature membrane electrode assembly which has the features of high-performance stability and high CO tolerance. Moreover, compared to graphite bipolar plates, metallic bipolar plates have better mechanical properties and seismic capacity, as well as lighter weight. We thus use metallic bipolar plates and a PBI-based membrane electrode assembly to setup a single cell and examine its performance. The experimental results show that the cell temperature has a significant effect on the cell performance. When the temperature increases from 120 °C to 180 °C, the performance is significantly enhanced. Moreover, the CO tolerance of the fuel cell increases along with the temperature. At the same time, methane is fed in the anode stream to assess the performance of the cell under different simulated methane reformate gases. The test of various CH 4 /H 2 mixtures reveals the residual methane in the reformate gases only decreases fuel cell performance slightly due to the dilution effect. We also examined H 2 /CO/N 2 /CH 4 mixtures in this study, and these had only a small effect on the fuel cell performance at cell temperatures higher than 160 °C. As such, it is recommended that the cell temperature should be kept higher than 160 °C. [ABSTRACT FROM AUTHOR]

This study investigated the heat recovery rates of hydrogen flame modes in porous medium combustion. The porous medium was oxide-bonded silicon carbide (OB-SiC), aluminum oxide (Al 2 O 3 ) or zirconia (ZrO 2 ) with 60 or 30 PPI. The results indicated that the reaction temperature of a flame mode was controlled by the equivalence ratio (flame velocity), thermal load and solid medium thermal properties ( k and C P ). The operation region of the flame modes was controlled by the equivalence ratio and dimensionless velocity ( V ∗ ). Under ultra-lean conditions ( Φ = 0.2–0.25), the flame was blown out when the dimensionless velocity was above 4.5 for OB-SiC and Al 2 O 3 settings. In contrast no blow out occurred for the ZrO 2 setting and under a high equivalence ratio ( Φ > 0.4), and the flame mode was a conical flame when the dimensionless velocity was above unity. The heat recovery mechanism of surface and interior combustion was based on the conduction and radiation of the porous medium. The dimensionless temperature ( θ ∗ ) is defined as the ratio of the reaction temperature over the adiabatic flame temperature. When the dimensionless temperature was unity, the reaction temperature approached the adiabatic flame temperature. Under interior combustion, the maximum dimensionless temperature was 0.994 for the OB-SiC ( Φ = 0.3) setting. Furthermore, the maximum dimensionless temperature was 0.942 for Al 2 O 3 and 0.969 for ZrO 2 under operation at Φ = 0.3. The heat recovery rate of hydrogen combustion under surface and interior combustion was thus higher than that of the conical flame mode. [ABSTRACT FROM AUTHOR]

A high temperature proton exchange membrane fuel cell is considered a solution to improve the cell performance under CO-contained hydrogen and to simplify the gas purification process of a reformate fuel cell system. In this study, polybenzimidazole-based phosphoric acid-doped fuel cells are studied under simulated reformate gases of different H 2 , N 2 and CO concentrations. The experimental results show that the dilution effect of N 2 has a minor impact on the cell performance in absence of CO. However, the CO poisoning increases the charge transfer resistance and leads to a substantial performance drop. This work also reveals that increasing the operating temperature can effectively improve the CO tolerance by suppressing the Pt–CO binding reaction. In addition, the CO poisoning effect becomes more significant in diluted H 2 . As a result, the CO concentration should be maintained lower than a critical level to prevent a high CO coverage on the catalyst which leads to a noteworthy voltage shut-down, especially in highly diluted H 2 . [ABSTRACT FROM AUTHOR]

Abstract: In this study, the H2-rich syngas (H2 + CO) production from biomass derived gas (BDG) by dry autothermal reforming (DATR) is investigated. Methane and carbon dioxide is the major composition of biomass derived gas. DATR reaction combined benefits of partial oxidation (POX) and dry reforming (DR) reaction was carried out in this study. The reforming parameters on the conversion of methane and syngas selectivity were explored. The reforming parameters included the fuel feeding rate, CO2/CH4 and O2/CH4 molar ratios. The experimental results demonstrated that it not only supplied the energy required for self-sustained reaction, but also avoided the coke formation by dry autothermal reforming. It has a wide operation region to maintain the moderate production of the syngas. During the reforming process, the reformate gas temperature was between 650 and 900 °C, and energy loss percentage in reforming process was between 15 and 30%. Further, high CO2 concentration in the reactant had a considerable influence on the heat release of oxidation, and thereby decreased the reformate gas temperature. It caused the reduction of synthesis gas concentration and assisting/impeding combustion composition (A/I) ratio. However, it was favorable to CO selectivity because of the reverse water-gas shifting reaction. The H2/CO molar ratio between 1 and 2 was achieved by varying CO2/CH4 molar ratio. However, the syngas concentrations were affected by CO2/CH4 and O2/CH4 molar ratio. [Copyright &y& Elsevier]

This study analyzes the carbon footprint of an internal combustion engine scooter (ICE) and there are four types of electric scooters studied, namely: a hydrogen fueled scooter with on-board methanol steam reforming (on-board SMR), hydrogen scooter with methane steam reforming (SMR), plug-in electric scooter (PEV), and hybrid scooter. This paper also uses a sensitivity analysis to examine how the variations in fuel prices influence the cost-benefit of using a hydrogen scooter. The research results are as follows: (1) SMR and on-board SMR have the smallest carbon (0.0115 kg CO 2,e & 0.0117 kg CO 2,e ), PEV (0.0189 kg CO 2,e ), hybrid scooter (0.0614 kg CO 2,e ) and ICE (0.1378 kg CO 2,e ); the percentage of carbon emissions relative to ICE by each scooter are, in ascending order, 8%, 8%, 14% and 45%; (2) according to the ISO14067 standard, capital goods (fixed costs) cannot be accounted into total life cycle costs, and total life cycle costs excluding fixed costs are in descending order, SMR ($6632), ICE ($4233), on-board SMR ($3643), hybrid scooter ($3368) and PEV ($2824); (3) the variation of fuel price is the key factor of using hydrogen scooters. [ABSTRACT FROM AUTHOR]

This study investigated the control strategy for the rapid cold startup process in porous media-assisted (PM-assisted) catalyst hybrid reformers that produce syngas from the partial oxidation of methane (CH 4 ). A control strategy was established based on the axial temperature distribution and infrared thermal imaging observations of the reformer under total oxidation reaction. In this study, methane was used to explore the temperature fluctuation characteristics exhibited by various fuels (CH 4 or H 2 ) during the startup process in reformer. Methane was also used to investigate operational strategies for achieving rapid cold-startup. The experiments confirmed that the rapid flame propagation speed and small quenching distance of hydrogen can shorten the startup time, reduce chemical energy supply, and provide superior thermal stability. The experimental analyses indicated that PM-assisted cold startups can improve the thermal stability of catalyst beds, reduce the temperature fluctuations in reformed gases, and effectively increase the reactive temperature of catalyst-packed beds. [ABSTRACT FROM AUTHOR]

In this study, the characteristics of hydrogen flame stabilization in porous medium combustor were investigated. The flame was observed in a quartz tube. The porous medium was oxide-bonded silicon carbide (OB-SiC) or aluminum oxide (Al 2 O 3 ) with 60 PPI and 30 PPI pore size distributions. The results indicated that under a low equivalence operation, the flame would transform from surface combustion to interior combustion with an increased heating value. Under a high equivalence ratio, both interior combustion and flashback transition existed at the same time. The thermal conductivity of silicon carbide is higher than that of aluminum oxide. Thus, interior combustion region was more extensive under a low equivalence ratio operation with a high premixed gas velocity. Flashback was apparent for Al 2 O 3 under high an equivalence ratio with low a premixed gas velocity. Consequently, hydrogen flame stability could be controlled by the pore size distribution and thermal conductivity of the porous media, input heating value and input equivalence ratio. [ABSTRACT FROM AUTHOR]

Abstract: A porous medium-catalyst hybrid reformer for CO2 conversion by dry auto-thermal reforming (DATR) was investigated in this study, and its operating range was discovered. The hybrid design was used to enhance the oxidative heat release by internal heat recirculation during exothermic reaction conditions, thereby increasing the CO2 conversion efficiency. The experimental results show that the CO2 conversion could be enhanced with higher catalyst inlet temperatures. The examination of the operating range of DATR showed that the CO2 conversion efficiency increased at higher reaction temperatures and CO2/CH4 ratios (≧1). Moreover, DATR in high temperature conditions must be carried out with high O2/CH4 ratios. Under these conditions of high oxygen content, CO2 generation and reduction reactions occur simultaneously. Overall, optimal CO2 conversion can be obtained with an O2/CO2 ratio of approximately 0.5. At these conditions, CO2 conversion efficiency can reach approximately 13% without external heat addition. [Copyright &y& Elsevier]

Abstract: A porous medium-catalyst hybrid reformer for hydrogen-rich syngas production by dry autothermal reforming (DATR) was investigated in this study. In the reforming process, the reaction under excess enthalpy was explored by visualization in packed-bed catalyst reactor. The hybrid design was arranged with a porous medium (PM) in the upstream of the catalyst packed-bed. In the arrangement, the reactants were preheated by internal heat recirculation and the selectivity of H2-rich syngas was enhanced by the catalyst surface reaction. Controlled parameters included CO2/CH4 and O2/CH4 ratios, gas hourly space velocity (GHSV) with or without porous medium. The experimental results demonstrated that the reforming reaction with the hybrid reformer could achieve excess enthalpy under the tested parameters. The excess enthalpy ratio was between 0.15 and 0.55. The temperature measurement along the axial position and image observation of the catalyst packed-bed indicated that the flame was stably held at the interface of the PM and the catalyst bed, and this enhanced fuel conversion and reforming efficiencies, especially in the low methane conversion condition. In the dry autothermal reforming process, part of the chemical energy released from the reaction supplies the energy required for a self-sustaining reaction. Therefore, the selection of the parameters was determined to achieve high reforming efficiency and low energy loss percentage. The results showed that the energy loss percentage was between 12.7 and 24.6% and reforming efficiency was between 64.4 and 79.5% with the best reforming parameter settings (O2/CH4 = 0.7–0.9 and CO2/CH4 = 0.0–2.0). [Copyright &y& Elsevier]

This paper investigated the design of a porous medium–catalyst hybrid reformer for CO 2 conversion by dry auto-thermal reforming, with emphasis on the reaction temperature distribution. In the reforming process, the reaction under excess enthalpy was explored by interface temperature measurement and infrared thermograph observation in a porous medium assisted packed-bed catalyst reactor. The hybrid design was arranged with the catalytic packed-bed in the downstream of the porous medium. In the arrangement, the reactants were preheated by internal heat recirculation and the conversion of CO 2 was enhanced by the catalyst surface reaction. The temperature measurement at the axial position and infrared thermograph observation on the catalyst packed-bed indicated that the peak temperature could be stabilized and held at the interface of the PM and catalyst bed, which significantly improved the propagation and stability of the flame. This was helpful to the improvement of both thermal wave transfer and internal heat recirculation. [ABSTRACT FROM AUTHOR]