Performance of proton exchange membrane fuel cells with microporous layer hydrophobized by polyphenylene sulfide at conventional temperature and cold start

Polyphenylene sulfide (PPS), a thermoplastic polymer with excellent chemical and thermal stability, has properties similar to those of polytetrafluoroethylene (PTFE) but is less expensive. In this study, the feasibility of using PPS to replace conventional PTFE as a hydrophobic agent for microporous layers (MPLs) in proton exchange membrane fuel cells (PEMFCs) is explored. First, PTFE-MPL and PPS-MPL with 30 wt% hydrophobic agent were prepared. The pore size, porosity, contact angle, and microstructure of the two MPL samples were measured and analyzed. Subsequently, PEMFCs with the two MPL samples were tested for their operational performance at a conventional temperature of 70 °C and cold-start capability at ?10 °C. The performances of PTFE-MPL and PPS-MPL at conventional temperatures were similar, but PPS-MPL showed obvious advantages in cold-start performance. In addition, the operating performance of PEMFC at the conventional temperature and cold-start capability at ?10 °C were investigated for PPS mass fractions of 10%, 20%, and 30% in MPL, and for PPS particle sizes of 10 and 30 μm. The results indicate that the optimal performance can be attained when the PPS particle size is 10 μm and the mass fraction is 20%.     

Valorisation of lignocellulosic biomass investigating different pyrolysis temperatures

Presently, sugarcane bagasse (SB) and oat hulls (OH) have a distinctive potential as a renewable source of biomass, due to its global availability, which is advantageous for producing liquid and gaseous fuels by thermochemical processes. Thermo-Catalytic Reforming (TCR) is a pyrolysis based technology for generating energy vectors (char, bio-oil and syngas) from biomass wastes. This work aims to study the conversion of SB and OH into fuels, using TCR in a 2 kg/h continuous pilot-scale reactor at different pyrolysis temperatures. The pyrolysis temperatures were studied at 400, 450 and 500 °C, while the subsequent reforming temperature remained constant at 500 °C. The bio-oil contained the highest calorific value of 33.4 and 33.5 MJ/kg for SB and OH, respectively at 500 °C pyrolysis temperature, which represented a notable increase compared to the raw material calorific value of SB and OH (16.4 and 16.0 MJ/kg, respectively), this was the result of deoxygenation reactions occurring. Furthermore, the increment of the pyrolysis temperature improved the water content, total acid number (TAN), viscosity and density of the bio-oil. The syngas and the biochar properties did not change significantly with the increase of the pyrolysis temperature. In order to use TCR bio-oil as an engine fuel, it is necessary to carry out some upgrading treatments; or blend it with fossil fuels if it is to be used as a transportation fuel. Overall, TCR is a promising future route for the valorisation of lignocellulosic residues to produce energy vectors.     

Review: Influence of alloy addition and spinel coatings on Cr-based metallic interconnects of solid oxide fuel cells

Solid oxide fuel cell (SOFC) is the modern eco-friendly technology of fuel cell power generation system. It generates electricity from a redox chemical reaction without producing hazardous gases. It consists of anode, cathode and electrolyte. It is operated in the form of stack connected by interconnects to boost-up power output. The recent development of low-temperature (600 °C–800 °C) brings an opportunity to use metallic interconnects over ceramics. Cr-based metallic interconnects are one of the prominent metallic interconnects. They offer chemical inertness, thermal stability, compatible coefficient of thermal expansion and highly dense structure. However, the Cr-migration towards the cathode side is the major problem in them which adversely affect the SOFCs performance. Therefore a good oxidation resistance without sacrificing electrical conductivity is required. To resolve this issue, several alloying elements and spinel coatings have experimented. These spinel coatings are the thin solid films of Mn, Co, Cu and rare earth metals. This review concluded that the Mn–Co based spinal coating showed excellent performance in reducing the Cr-migration in specially designed expensive Crofer 22 APU interconnect. However, the emerging low-cost ferritic interconnects also show their best results with Cu–Fe based spinel coating. Among them, the SUS-430 interconnect shows the equivalent performance of Crofer 22 APU interconnect after surface treatment and appropriate Cu–Fe based spinel coating. Therefore, it can replace the Crofer 22 APU interconnect on a cost basis.     

Molten salt synthesis of high-entropy alloy AlCoCrFeNiV nanoparticles for the catalytic hydrogenation of p-nitrophenol by NaBH4

High-entropy alloy (HEA) AlCoCrFeNiV nanoparticles were prepared from oxide precursors using a molten salt synthesis method without an electrical supply. The oxide precursor was directly reduced by CaH₂ reducing agent in molten LiCl at 600°C-700°C or molten LiCl–CaCl₂ at 500°C-550°C. When the reduction was conducted at 700°C, a face-centered cubic (FCC) structure produced, as identified by X-ray diffraction analysis. With lower reduction temperatures, the FCC structure was absent, replaced by a body-centered cubic (BCC) structure. With a reduction temperature of 550°C, the resulting sample was composed of highly pure HEA AlCoCrFeNiV nanoparticles with a BCC structure of 15 nm. Analyses by scanning electron microscopy/transmission electron microscopy with energy-dispersive X-ray spectroscopy confirmed the formation of homogeneous HEA AlCoCrFeNiV with a nanoscale morphology. In the hydrogenation reaction of p-nitrophenol by NaBH₄, the AlCoCrFeNiV nanoparticles (produced at 550°C) exhibited a catalytic activity with ～90% conversion and 16 kJ/mol activation energy.     

A comparison of ignition characteristics of slurry fuels prepared using coal processing waste and finely divided coal

The scientific novelty of the research is that for the first time differences in the conditions and characteristics of the ignition and burning of droplets of slurries prepared on the basis of coals and waste from their enrichment have been established. The practical significance of the research results is that they illustrate the prospects of utilization of the numerous coal enrichment wastes by combustion in the composition of aqueous slurries with the generation of a rather large amount of energy and a relatively small negative environmental impact. The most significant characteristics were compared: the limiting (minimum) temperature; the ignition delay times; the maximum combustion temperature; the concentration of the main gas anthropogenic emissions. It has been found that fuel mixtures prepared from wet waste of coal flotation are characterized by higher inertia and ignition temperatures compared to slurries with high-quality coal dust. However, the established differences considering the availability and low cost of filter cakes illustrate the prospects of waste derived fuel combustion. The combustion heat of the investigated slurries based on coal and filter cake with addition of petroleum products differs by no more than 5–30%. The average difference between the duration of ignition for fuel droplets based on dust and filter cake of coking and low-caking coals is about 20%. At that the addition of waste turbine oil (10% wt.) into the filter cake reduces the duration of ignition by 12–25% and the ignition temperature – by 10–15 °C without a significant increase in anthropogenic gas emissions. The difference between the minimum ignition temperatures of coal and waste coal based slurries was from 10 °C to 80 °C. On environmental and economic indicators, coal waste is more attractive than coal.     

A comprehensive review on the proton conductivity of proton exchange membranes (PEMs) under anhydrous conditions: Proton conductivity upper bound

The present study aims to assess the proton conductivities of the most investigated proton exchange membranes (PEMs) used in PEM fuel cells (PEMFCs). Specifically, PEMs are analyzed for their use in anhydrous fuel cells and proton conductivity upper bounds were provided for them. Considering the direct relationship between proton conductivity and temperature, an upper bound is presented. Based on the obtained upper bounds, suitable membranes for high-temperature performance are determined, and the average range of proton conductivity for each polymer group is discussed. By comparing the available proton conductivity data with upper bound, it was demonstrated that some of poly (ionic liquid)s have provided the highest proton conductivities, however aromatic polymers such as polybenzimidazole (PBI) are found more suitable choices for application at anhydrous conditions and high temperatures. The proton conductivity upper bound for anhydrous PEMs demonstrates the availability of promising polymer options for the deployment of anhydrous fuel cells.     

Effect of manifold injection of hydrogen gas in producer gas and neem biodiesel fueled CRDI dual fuel engine

The high flammability of hydrogen gas gives it a steady flow without throttling in engines while operating. Such engines also include different induction/injection methods. Hydrogen fuels are encouraging fuel for applications of diesel engines in dual fuel mode operation. Engines operating with dual fuel can replace pilot injection of liquid fuel with gaseous fuels, significantly being eco-friendly. Lower particulate matter (PM) and nitrogen oxides (NO_x) emissions are the significant advantages of operating with dual fuel.Consequently, fuels used in the present work are renewable and can generate power for different applications. Hydrogen being gaseous fuel acts as an alternative and shows fascinating use along with diesel to operate the engines with lower emissions. Such engines can also be operated either by injection or induction on compression of gaseous fuels for combustion by initiating with the pilot amount of biodiesel. Present work highlights the experimental investigation conducted on dual fuel mode operation of diesel engine using Neem Oil Methyl Ester (NeOME) and producer gas with enriched hydrogen gas combination. Experiments were performed at four different manifold hydrogen gas injection timings of TDC, 5°aTDC, 10°aTDC and 15°aTDC and three injection durations of 30°CA, 60°CA, and 90°CA. Compared to baseline operation, improvement in engine performance was evaluated in combustion and its emission characteristics. Current experimental investigations revealed that the 10°aTDC hydrogen manifold injection with 60°CA injection duration showed better performance. The BTE of diesel + PG and NeOME + PG operation was found to be 28% and 23%, respectively, and the emissions level were reduced to 25.4%, 14.6%, 54.6%, and 26.8% for CO, HC, smoke, and NO_x, respectively.     

Evaluation of a BCC alloy as metal hydride compressor via 100 MPa-class high-pressure hydrogen apparatus

In the study presented here, an apparatus that correctly measured pressure–composition isotherms (PCi) at high pressures (up to 100 MPa) and temperatures (up to 200 °C) was developed. The PCi characteristics of a vanadium–titanium–chromium alloy at high pressure and temperature were examined with the apparatus to develop a metal hydride (MH) compressor. It was revealed that it is possible to use a 40 V20Ti40Cr (at%) alloy with a heat source below 200 °C for hydrogen compression in the approximate range of 2.1–30.0 MPa. The compressed content reached approximately 1.8 wt%, which is almost the same as the reversible hydrogen capacity at 20 °C.     

A comprehensive review on water management strategies and developments in anion exchange membrane fuel cells

In spite of significant achievements in alkaline exchange membrane fuel cells (AEMFCs) in recent years, they are still lagging behind proton exchange membrane fuel cells (PEMFCs) due to performance instability. Among the relevant operational parameters of AEMFC, the researchers have found that poor water management within the cell was the main reason for failure of the system. In the past five years, numerous modeling and experimental works were reported proposing different strategies to improve water management of AEMFC. With proper water management, the achievable power output in AEMFCs is comparable with that of PEMFCs or even more. Efforts have to be continued, but AEMFCs can become a strong competitor in the market place. This review paper discusses the strategies and developments impacting water management of AEMFCs providing knowledge source for upcoming studies.     

Fast pyrolysis of date palm biomass using Py-GCMS

Pyrolysis of Date Palm Petiole (DPP) and Date Palm Seed (DPS) biomass was conducted by fast pyrolysis and on-line analysis of the outlet stream by gas chromatography connected to mass spectrometry (Py-GCMS) at different temperatures (450, 500 and 600 °C) in order to study the effect of this variable on the product distribution. The concentration of the components in the volatile stream (bio-oil and non-condensable gases) was greatly influenced by temperature and, to a minor extent, by the content of the biomass components (cellulose, hemicellulose and lignin). The most abundant compound families quantified are acids, anhydrosugars, ketones, furans and phenols. The most abundant compound identified was levoglucosan, which is mainly derived from the degradation of cellulose, with its relative content being as high as 18.3% for DPS pyrolysis at 450 °C and considerably lower for DPP pyrolysis (12.2%). The relative content of acetic acid was as higher as 10.2% at 450 °C for DPP pyrolysis. The knowledge of product composition is crucial for the development of large scale fast pyrolysis units for the valorization of these Tunisian agricultural wastes.     

Studies on 10kg alloy mass metal hydride based reactor for hydrogen storage

A 10 kg alloy mass metal hydride reactor, with LaNi₅ alloy was designed. Heat transfer enhacement in the reactor was achieved by including embedded cooling tubes and an external water jacket. Detailed parametric study has been carried to understand the performance of the system. The effect of both geometrical and operational parameters was studied in simulations. The optimized geometrical parameters were used for fabricating the reactor. Experimental studies were carried on the fabricated reactor. Absorption studies were carried out for different supply pressure and different cooling fluid temperatures. Storage capacity of 1.13 wt% was found in 1620 s at a supply pressure of 25 bar and with a flow rate of 20 LPM. Similarily, desorption studies were carried out for varying heat transfer fluid temperatures. Complete and fastest desorption was observed at 80 °C with the reaction completion time of 2700 s.     

Comparative study on the electrochemical performance of coals and coal chars in a molten carbonate direct carbon fuel cell with a novel anode structure

Molten carbonate direct carbon fuel cells (MC-DCFCs) allow the efficient and clean use of coal. In this study, a novel anode structure is designed, and the performances of six coal-based fuels are investigated in MC-DCFC. The mechanisms of performance differences are investigated, as well as the effect of operating temperature on performance. The results reveal the fuel cell performance in the following order: meagre coal (109.8) ≈ bituminous coal (108.7) > bituminous coal char (98.1) > lignite coal (83.7) > lignite coal char (71.3) > meagre coal char (53.2) in mW cm^?2. Coal performs better because of its high carbon content, high volatile content, rich oxygen-containing functional groups, larger specific surface area, stronger thermal reactivity, and other factors. The electrochemical reactivity of coal fuel increased with higher reaction temperatures and varied throughout the temperature ranges. This study implies that using coal fuel to commercialize MC-DCFC could be a realistic alternative.     

Effect of introducing manganese as additive on microstructure,hydrogen storage properties and rate limiting step of Ti–Cr alloy

TiCr₂ with adding different amount of Mn (0, 2, 4 and 8 wt.%) alloys have been investigated. All alloys have C14-type main phase (gray color in SEM) and Ti minor phase (dark gray color in SEM). Rietveld fitting results proved that the lattice parameter a and cell volume of C14-type phase decreased with increasing Mn content. The first hydrogenation measurement manifest that all alloys have best activation properties and could be activated without any prior heat treatment and hydrogen exposure. However, introducing Mn led to the decrease of the first hydrogen absorption rate of TiCr₂ alloy, which may be due to the decrease of cell volume of C14-type main phase. The first hydrogenation properties at low temperature and effect of air exposure of the alloy were discussed. The results showed that the maximum hydrogen absorption capacity at 0 °C was obviously higher than that at room temperature. In addition, TiCr₂ alloy doped with minor amounts of Mn after long-time air exposure showed better hydrogenation performance. This may be due to the Mn additive acting as a deoxidizer. Finally, the first hydrogenation kinetic mechanisms of all alloys at different temperature were also studied by using the rate limiting step.     

Assessment of ammonia as energy carrier in the use with reversible solid oxide cells

Ammonia represents one of the most promising potential solutions as energy vector and hydrogen carrier, having a higher potential to transport energy than hydrogen itself in a pressurized form. Furthermore, solid oxide fuel cells (SOFCs) can directly be fed with ammonia, thus allowing for immediate electrical power and heat generation. This paper deals with the analysis of the dynamic behavior of commercial SOFCs when fueled with ammonia. Several measurements at different temperatures have been performed and performances are compared with hydrogen and a stoichiometrically equivalent mixture of H₂ and N₂ (3:1 M ratio). Higher temperature led to smaller drops in voltage for both fuels, thus providing higher efficiencies. Ammonia resulted slightly more performant (48% at 760 °C) than hydrogen (45% at 760 °C), in short stack tests. Moreover, different ammonia-to-air ratios have been investigated and the stack area-specific resistance has been studied in detail by comparing numerical modeling predictions and experimental values.     

Promising components of waste-derived slurry fuels

The paper presents the results of experimental studies of energy (calorific value, ignition delay times and threshold ignition temperatures, duration and temperature of combustion) and environmental (CO₂, NO_x and SO_x emission) characteristics of fuel slurries based on pulverized wood (sawdust), agricultural (straw), and household (cardboard) waste. Wastewater from a sewage treatment plant served as a liquid medium for fuels. Petrochemical waste and heavy oil were additives to slurries. The focus is on obtaining the maximum efficiency ratio of slurry fuel, calculated taking into account environmental, cost, energy and fire safety parameters. All slurry fuels were compared with typical coal-water slurry for all the parameters studied. A comparison was also made between slurries and traditional boiler fuels (coal, fuel oil). The relative efficiency indicator for waste-based mixtures was varied in the range of 0.93–10.92. The lowest ignition costs can be expected when burning a mixture based on straw, cardboard and oil additive (ignition temperature is about 330 °C). The volumes of potential energy generated with the active involvement of industrial waste instead of traditional coal and oil combustion are forecasted. It is predicted that with the widespread use of waste-derived slurries, about 43% of coal and oil can be saved.     

Synthesis of binary Co–Mg–O oxide system and study of its behavior in reduction/oxidation cycling

The nanoscale Co–Mg–O oxide sample (15 wt% in terms of Co₃O₄) was prepared from the corresponding xerogel synthesized by the modified sol-gel method. The hydrolysis of as-prepared Mg(OCH₃)₂ was carried out using the aqueous solution of Co(NO₃)₂ precursor. The CoO_x nanocrystallites of about 10–20 nm in size were shown to be uniformly distributed within the MgO matrix. The reduction of Co–Mg–O in H₂ flow was found to proceed in two separate stages within the temperature ranges of 200–350 °C and 350–600 °C. The prepared binary Co–Mg–O system was demonstrated to possess completely reproducible reduction behavior in the consecutive reduction/reoxidation cycles. The phase composition of the sample exposed to both the reducing and oxidative environment was followed by an in situ X-ray diffraction analysis performed at temperatures of 25, 300, 500 and 700 °C. The determined lattice parameters for MgO (a = 4.219 Å) and Co₃O₄ (a = 8.110 Å) were found to be slightly increased as compared with the values from Powder Diffraction File, so that the formation of joint non-stoichiometric (Mg_1-xCo_x)O and (Co_3-xMg_x)O₄ phases was suggested. The strong chemical interaction of cobalt oxide with MgO matrix was also evidenced by the data of a diffuse reflectance UV–vis spectroscopy.     

Simulation and optimization of hydrogen production by steam reforming of natural gas for refining and petrochemical demands in Lebanon

Steam reforming of natural gas produces the majority of the world's hydrogen (H₂) and it is considered as a cost-effective method from a product yield and energy consumption point of view. In this work, we present a simulation and an optimization study of an industrial natural gas steam reforming process by using Aspen HYSYS and MATLAB software. All the parameters were optimized to successfully run a complete process including the hydrogen production zone units (reformer reactor, high temperature gas shift reactor HTS and low temperature gas shift reactor LTS) and the purification zone units (absorber and methanator). Optimum production of hydrogen (87,404 MT/year) was obtained by fixing the temperatures in the reformer and the gas shift reactors (HTS & LTS) at 900 °C, 500 °C and 200 °C respectively while maintaining a pressure of 7 atm, and a steam to carbon ratio (S/C) of 4. Moreover, ~99% of the undesired CO₂ and CO gases were removed in the purification zone and a reduction of energy consumption of 77.5% was reached in the heating and cooling units of the process.     

System optimization for effective hydrogen production via anaerobic digestion and biogas steam reforming

To construct a system for the effective hydrogen production from food waste, the conditions of anaerobic digestion and biogas reforming have been investigated and optimized. The type of agitator and reactor shape affect the performance of anaerobic digestion reactors. Reactors with a cubical shape and hydrofoil agitator exhibit high performance due to the enhanced axial flow and turbulence as confirmed by simulation of computational fluid dynamics. The stability of an optimized anaerobic digestion reactor has been tested for 60 days. As a result, 84 L of biogas is produced from 1 kg of food waste. Reaction conditions, such as reaction temperature and steam/methane ratio, affect the biogas steam reforming reaction. The reactant conversions, product yields, and hydrogen production are influenced by reaction conditions. The optimized reaction conditions include a reaction temperature of 700 °C and H₂O/CH₄ ratio of 1.0. Under these conditions, hydrogen can be produced via steam reforming of biogas generated from a two-stage anaerobic digestion reactor for 25 h without significant deactivation and fluctuation.     

Kinetics of formic acid decomposition in subcritical and supercritical water – a Raman spectroscopic study

The decomposition of formic acid is studied in a continuous sub- or supercritical water reactor at temperatures between 300 and 430 °C, a pressure of 25 MPa, residence times between 4 and 65 s, and a feedstock concentration of 3.6 wt%. In situ Raman spectroscopy is used to produce real-time data and accurately quantify decomposition product yields of H₂, CO₂, and CO. Collected spectra are used to determine global decomposition rates and kinetic rates for individual reaction pathways. First-order global Arrhenius parameters are determined as log A (s⁻¹) = 1.6 ± 0.20 and E_A = 9.5 ± 0.55 kcal/mol for subcritical decomposition, and log A (s⁻¹) = 12.56 ± 1.96 and E_A = 41.90 ± 6.08 kcal/mol for supercritical decomposition. Subcritical and supercritical Arrhenius parameters for individual pathways are proposed. The variance in rate parameters is likely due to changing thermophysical properties of water across the critical point. There is strong evidence for a surface catalyzed free-radical mechanism responsible for rapid decomposition above the critical point, facilitated by low density at supercritical conditions.     

Hydrofluoroolefin-based mixed refrigerant for enhanced performance of hydrogen liquefaction process

Hydrogen has the highest gravimetric energy density of all fuels; however, it has a low volumetric energy density, unfavorable for storage and transportation. Hydrogen is usually liquefied to meet the bulk transportation needs. The exothermic interconversion of its spin isomers is an additional activity to an already energy-intensive process. The most significant temperature drop occurs in the precooling cycle (between ?150 °C and up to ?180 °C) and consumes more than 50% of the required energy. To reduce the energy consumption and improve the exergy efficiency of the hydrogen liquefaction process, a new high-boiling component, Hydrofluoroolefin (HFO-1234yf), is added to the precooled mixed refrigerant. As a result, the specific energy consumption of precooling cycle reduces by 41.8%, from 10.15 kWh/kg_LH2 to 5.90 kWh/kg_LH2, for the overall process. The exergy efficiency of the proposed case increases by 43.7%; however, the total equipment cost is also the highest. The inflated cost is primarily due to the added ortho-to-para hydrogen conversion reactor, boosting the para-hydrogen concentration. From the perspective of bulk storage and transportation of liquid hydrogen, the simplicity of design and low energy consumption build a convincing case for considering the commercialization of the process.