Effect of film thickness on electrical property of microcrystalline silicon

We report dependences of electrical properties on SiH₄/H₂ dilution rate and film thickness for microcrystalline silicon films formed by a hydrogen radical-induced chemical vapor deposition (HRCVD) method. The electrical conductivity of the films at SiH₄ 18 sccm /H₂ 120 sccm was markedly increased to 10⁻³ S/cm as film thickness increased above 100 nm. Crystalline grains with (2 2 0) orientation were formed. Theoretical analysis revealed that grain boundaries among (2 2 0) grains had a low defect density of 1×10¹² cm⁻² so that the high conductivity was achieved.     

Influences of hydrogen evolution on the cell and stack performances of the direct borohydride fuel cell

To scale up power generation of the direct borohydride fuel cell (DBFC), 10-cell and 20-cell stacks have been constructed based on the single cell achievements. It has been found that the stacking loss of the DBFC is mainly caused by hydrogen evolution which leads to uneven fuel distribution in each cell of the stack. To reduce stacking loss, several efforts have been made to decrease hydrogen evolution influence on the stack performance. The anode preparation method has been modified from a dry-method to a wet-method. The influence of hydrogen evolution on stack performance can be alleviated by altering fuel supply manner. When hydrogen evolution is suppressed, an even distribution of cell voltage can be obtained and the maximum power of 10-cell stack reaches up to 229 W.     

Effect of operating parameters and anode diffusion layer on the direct ethanol fuel cell performance

A parametric study was conducted on the performance of direct ethanol fuel cells. The membrane electrode assemblies employed were composed of a Nafion^® 117 membrane, a Pt/C cathode and a PtRu/C anode. The effect of cathode backpressure, cell temperature, ethanol solution flow rate, ethanol concentration, and oxygen flow rate were evaluated by measuring the cell voltage as a function of current density for each set of conditions. The effect of the anode diffusion media was also studied. It was found that the cell performance was enhanced by increasing the cell temperature and the cathode backpressure. On the contrary, the cell performance was virtually independent of oxygen and fuel solution flow rates. Performance variations were encountered only at very low flow rates. The effect of the ethanol concentration on the performance was as expected, mass transport loses observed at low concentrations and kinetic loses at high ethanol concentration due to fuel crossover. The open circuit voltage appeared to be independent of most operating parameters and was only significantly affected by the ethanol concentration. It was also established that the anode diffusion media had an important effect on the cell performance.     

Effect of hydrogen on stability of amorphous silicon thin films

This paper presents results of the investigation of hydrogen influence on the stability of low pressure chemical vapour deposition a-Si films. We measured boron- or phosphorus-doped films post-hydrogenated by ion implantation with different hydrogen doses. The dark conductivity after fast quenching and slow cooling and the isothermal relaxation were measured at different annealing temperatures. It was found that higher hydrogen concentration causes greater metastable changes but shorter relaxation time of defects.     

A semi-empirical model considering the influence of operating parameters on performance for a direct methanol fuel cell

This research focuses on modeling the relationships between operating parameters and performance measures for a single stack direct methanol fuel cell (DMFC). Four operating parameters, including temperature, methanol concentration, and methanol and air flow rates, are considered in this work. Performance of the DMFC is described by the relationship between current density and voltage. The open circuit voltage and voltage drop in the closed circuit due to resistance, activation, and concentration polarization are influenced by the operating parameters. To consider both modeling accuracy and simplicity, a semi-empirical model is developed in this work by integrating theoretical and approximation models. Experiments were designed and conducted to collect the required data and to obtain the coefficients in the semi-empirical model. The error analysis indicates that our semi-empirical model is effective for predicating the DMFC's performance. The influence of the four operating parameters on the DMFC's performance is also analyzed based on this semi-empirical model. Possible applications of the semi-empirical model in the optimal control of fuel cell systems are also discussed.     

Enhanced polyhydroxybutyrate production through incorporation of a hydrogen fuel cell and electro-fermentation system

The integration of a hydrogen fuel cell with an electro-fermentation system represents a novel approach for improving polyhydroxybutyrate (PHB) accumulation in Ralstonia eutropha H16, using a sustainable energy source. In this study, electro-fermentation noticeably affected cell growth, biomass production, substrate consumption, and PHB accumulation. Final residual biomass concentrations and maximum specific growth rates were enhanced by supplying a 10-mA electric current. Furthermore, a remarkable enhancement in PHB content (30% higher than control) was achieved by redox-mediated electro-fermentation with a 10 mA electric current, upon the addition of a redox mediator. Two-stage cultivation limited the growth suppression caused by redox-mediated electro-fermentation, and also increased the maximum PHB productivity of the system. The additional electrons supplied upon supplementation of the redox mediator accelerated the glycolytic pathway and redox cycling of NADH/NAD⁺, led to a spontaneous boost for adenosine triphosphate (ATP) generation, and further facilitated the biosynthesis of PHB.     

Hydrogen effect on the optical and electrical properties of metal oxide and nitride thin films

Effect of hydrogen introduction into some metal oxide and nitride thin films was examined. Modification of electrical and optical properties by hydrogen introduction was examined on SnO₂${}_2$, Sn–GeO₂${}_2$, Ge–CdO₂${}_2$, ZnO. Electrical resistance could be reduced in some films without loosing their transparence to the visible light. Hydrogen introduction to Cu₃${}_3$N changed the film an electrical conductor. Films of AlN and TiN were rather insensitive to the hydrogen introduction; the hydrogen effect was only observed when the nitrides contain some imperfection in the compounds.     

Performance of an alkaline direct ethanol fuel cell with hydrogen peroxide as oxidant

An alkaline direct ethanol fuel cell (DEFC) with hydrogen peroxide as the oxidant is developed and tested. The present fuel cell consists of a non-platinum anode, an anion exchange membrane, and a non-platinum cathode. It is demonstrated that the peak power density of the fuel cell is 130 mW cm⁻² at 60 °C (160 mW cm⁻² at 80 °C), which is 44% higher than that of the same fuel cell setup but with oxygen as the oxidant. The improved performance as compared with the fuel cell with oxygen as the oxidant is mainly attributed to the superior electrochemical kinetics of the hydrogen peroxide reduction reaction and the reduced ohmic loss associated with the liquid oxidant.     

Predictive mathematical modeling and computer simulation of direct ethanol fuel cell

The challenges of finding a better substitute of energy as well as the shortcomings identified with direct ethanol fuel cell, includes high anode over potential and crossover necessitate the need to investigate the influence operating parameters on the performance of fuel through computer simulation. This study focus on the development of a predictive mathematical modeling for direct ethanol fuel cell for the purpose of investigating the influence pressure, temperature cathode, and reactants concentration on the performance, efficiency, and heat generated by the cell. Results obtained indicate that an increase in operating temperature led to a decrement in output voltage and cell efficiency, while the same condition of increasing the temperature positively favors the heat generated from the cell. Simulated results also show that cell performance is improved with an increase in concentration of the fuel (ethanol) and oxidant (oxygen). It can be inferred from this study that the cell performance of DEFC can be theoretically predicted with the developed model.     

Influence of hydrogen fuel cell temperature safety on bus driving characteristics and stack heating mode

Hydrogen fuel cells have developed rapidly in bus because of their cleanliness. The driving parameters of hydrogen fuel cell bus and the internal temperature distribution of hydrogen fuel stack are investigated in this study. The 1-D model of hydrogen fuel cell bus and the 2-D model of hydrogen fuel cell stack are established based on AMESim. In the cooling process, for the existing typical thermal management system, the influence of ambient temperature on the fuel cell bus driving parameters is analyzed by the 1-D model. In the heating process, the internal temperature distribution of the stack is analyzed under three heating modes by the 2-D model. As the ambient temperature increases, to ensure the safe operating temperature of the fuel cells, the bus top speed should be reduced, and the acceleration time should be extended. When the stack needs to be heated, the gas-liquid heating mode can supply a more uniform temperature distribution inside the stack.     

Carbon nanofibers as electrocatalyst support for fuel cells: Effect of hydrogen on their properties in CH4 decomposition

The influence of low partial pressure of hydrogen on carbon nanofibers (CNFs) properties has been studied in the synthesis by methane catalytic decomposition, with the purpose of using them in polymer electrolyte fuel cells as electrocatalyst support. Using CNFs in this kind of application presents a good perspective to improve the fuel cell overall performance. CNF growth in the catalytic decomposition of methane and the characteristics which are typically required in a carbonaceous support, are influenced by hydrogen concentration, which has been studied at different temperatures. The textural, morphological and structural characteristics of the obtained CNFs have been determined by nitrogen physisorption, X-ray diffraction, electron microscopy and thermogravimetry. Electrical conductivity of CNFs has been measured compressing the powder and using a two-probe method. It was observed that low values of partial pressure of hydrogen in methane influence positively structural ordering of CNFs, and in turn improve electrical conductivity, with a slight influence on textural properties leading to highly mesoporous carbon.     

Effects of methane processing strategy on fuel composition,electrical and thermal efficiency of solid oxide fuel cell

Natural gas is a cheap and abundant fuel for solid oxide fuel cell (SOFC), generally integrating the SOFC system with methane pre-treating system for improving the stability of SOFC. In this paper, the accurate effects of methane processing strategy on fuel composition, electrical efficiency and thermal efficiency of SOFC are investigated based on the thermodynamic equilibrium. Steam reforming of methane is an endothermic process and can produce 3 mol of H₂ and 1 mol of CO from 1 mol of methane, and thus the electrical efficiency of SOFC is high at the same O/C ratio and equivalent fuel utilization, whereas the thermal efficiency is low. On the contrary, partial oxidation of methane is an exothermal process and only produces 2 mol of H₂ and 1 mol of CO from 1 mol of methane, and thus the electrical efficiency of SOFC is low at the same O/C ratio and equivalent fuel utilization, whereas the thermal efficiency is high. When the O/C ratio is 1.5, the electrical efficiency of SOFC is 55.3% for steam reforming of methane, while 32.7% for partial oxidation of methane. High electrical efficiency of SOFC can be achieved and carbon deposition can be depressed by selecting suitable O/C ratio from methane pretreatment according to the accurate calculation and analysis of effects of different methane processing strategies on the electrical efficiency and thermal efficiency of SOFC.     

Effect of design and operating parameters on dynamic response of a micro direct methanol fuel cell

Dynamic response of the micro direct methanol fuel cell (μDMFC) is of significant importance, and has to be considered during cell design as well as operation. In order to explore the effect of design parameter and operating conditions on dynamic behavior, a μDMFC with stainless steel current collectors as well as stainless steel mesh was fabricated. Different load conditions were applied to the cell to test the effect of stainless steel mesh, cell orientation, methanol concentration and methanol flow rate on transient performance of the cell. A variety of physical and electrochemical processes in the cell are coupled and interactive, which determine that factors affecting transient behavior are complex. But experimental results indicate that methanol crossover through proton exchange membrane (PEM), methanol transportation in anode, removal of CO₂ bubbles and heat loss brought away by methanol solution are four crucial causes influencing dynamic behavior of the cell.     

Numerical study of hydrogen dispersion in a fuel cell vehicle under the effect of ambient wind

In the rescue of hydrogen-fueled vehicle accidents, once accidental leakage occurs and hydrogen enters the cabin, the relatively closed environment of the vehicle is prone to hydrogen accumulation. Excessive hydrogen concentration inside the vehicle cabin may cause suffocation death of injured passengers and rescue crews, or explosion risk. Based on hydrogen fuel cell vehicle (HFCV) with hydrogen storage pressure 70 MPa, four different scenarios (i. with opened sunroof, ii. opened door windows, iii. opened sunroof and door windows and iv. opened sunroof, door windows and rear windshield) under the condition of accidental leakage were simulated using computational fluid dynamics (CFD) tools. The hydrogen concentration inside the vehicle and the distribution of flammable area (>4% hydrogen mole fraction) were analyzed, considering the effect of ambient wind. The results show that in the case of convection between interior and exterior of the vehicle via the sunroof, door windows or rear windshield, the distribution of hydrogen inside the vehicle is strongly affected by the ambient wind speed. In the least risk case, ambient wind can reduce the hydrogen mole fraction in the front of the vehicle to less than 4%, however the rear of the vehicle is always within flammable risk.     

Cathode electrocatalyst selection and deposition for a direct borohydride/hydrogen peroxide fuel cell

Catalyst selection, deposition method and substrate material selection are essential aspects for the design of efficient electrodes for fuel cells. Research is described to identify a potential catalyst for hydrogen peroxide reduction, an effective catalyst deposition method, and supporting material for a direct borohydride/hydrogen peroxide fuel cell. Several conclusions are reached. Using Pourbaix diagrams to guide experimental testing, gold is identified as an effective catalyst which minimizes gas evolution of hydrogen peroxide while providing high power density. Activated carbon cloth which features high surface area and high microporosity is found to be well suited for the supporting material for catalyst deposition. Electrodeposition and plasma sputtering deposition methods are compared to conventional techniques for depositing gold on diffusion layers. Both methods provide much higher power densities than the conventional method. The sputtering method however allows a much lower catalyst loading and well-dispersed deposits of nanoscale particles. Using these techniques, a peak power density of 680 mW cm⁻² is achieved at 60 °C with a direct borohydride/hydrogen peroxide fuel cell which employs palladium as the anode catalyst and gold as the cathode catalyst.     

Study on water transport in PEM of a direct methanol fuel cell

Water transport phenomenon in PEM and the mechanism of occurrence and development of a two-phase countercurrent flow with corresponding transport phenomenon in the PEM are analyzed. A one-dimensional steady state model of heat and mass transfer in porous media system with internal volumetric ohmic heating is developed and simulated numerically. The results show that two dimensionless parameters D and N, which reflect the liquid water flow rate and inner heat source in the PEM, respectively, are the most important factors for the water fraction and thermal balance in the PEM. The saturation profiles within the two-phase region at various operating modes are obtained. Smaller mass flow rate of liquid water and high current density are the major contributions to the membrane dehydration.     

Effect of support materials on the performance of direct ethanol fuel cell anode catalyst

Pt–Ru catalysts supported on mesoporous carbon nitride (MCN), multiwall carbon nano tubes (MWCNTs), treated MWCNTs (t-MWCNTS) and Vulcan-XC were prepared using co-impregnation reduction method for the oxidation of ethanol in direct ethanol fuel cell (DEFC) to study the effect of support material. The MCN support was prepared using SBA-15 as template and t-MWCNTs were prepared by refluxing in HNO₃ and H₂SO₄ mixture (1:3) using MWCNTs. XRD shows the formation of Pt–Ru bi-metallic catalyst with size ranges from 7 to 17 nm using different supports. The catalyst and its supports were characterized by physically and electrochemically. Linear sweep voltammetry, cyclic voltammetry and chrono amperometry studies of the above systems reveal that MCN supported Pt–Ru catalyst shows higher electro-catalytic activity towards ethanol oxidation compared to Pt–Ru in treated t-MWCNTs, MWCNts and Vulcan-XC supports. The performance of DEFC based on maximum power density is found to be in the order Pt–Ru/MCN > Pt–Ru/t-MWCNTs > Pt–Ru/MWCNTs > Pt–Ru/Vulcan-XC. The Pt–Ru/MCN shows highest power density of 61.1 mW cm⁻² at 100 °C, 1 bar pressure with catalyst loading of 2 mg cm⁻² using 2 M ethanol feed.     

Dynamic simulation and lifecycle assessment of hydrogen fuel cell electric vehicles considering various hydrogen production methods

In this research study, a real model of a hydrogen fuel cell vehicle is simulated using Simcenter Amesim software. The software used for vehicle simulation enabled dynamic simulation, resulting in more precise simulation. Furthermore, considering that fuel cell degradation is one of the significant challenges confronting fuel cell vehicle manufacturers, we examined the impact of fuel cell degradation on the performance of hydrogen vehicles. According to the findings, a hydrogen vehicle with a degraded fuel cell consumes 14.3% more fuel than a fresh fuel cell hydrogen vehicle. A comprehensive life cycle assessment (LCA) is also performed for the designed hydrogen vehicle. The results of the hydrogen vehicle life cycle assessment are compared with a gasoline vehicle to fully understand the effect of hydrogen vehicles in reducing air emissions. The methods considered for hydrogen production included natural gas reforming, electrolysis, and thermochemical water splitting method. Furthermore, because the source of electricity used for electrolysis has a significant impact on the life cycle emission of a hydrogen vehicle, three different power sources were considered in this assessment. Finally, while a hydrogen vehicle with a degraded fuel cell emits lower carbon dioxide (CO₂) than a gasoline vehicle, the emitted CO₂ from this vehicle using hydrogen from electrolysis is approximately 25% higher than that of a new hydrogen vehicle.     

Influence of the electrode systems parameters on the electricity generation and the possibility of hydrogen production in a plant-microbial fuel cell

The work is devoted to the creation of plant-microbial fuel cell (PMFC). A design of а PMFC has been developed, which makes it possible to study the effect of the configuration and material of electrode systems on the values of bioelectric potentials (BEP) generated in the system of root environment-plant. The possibility of using the developed technology for measuring BEP to create long-term plant-microbial fuel cells based on the use of plants electrical activity as an electromotive force is shown. The electrodes were made of various carbon materials and stainless steel. The created experimental PMFCs are capable of generating voltages at the level of 230 mV in soil systems and 150 mV in hydroponic ones. The output power was about 50 mW/m² at a load of 10 kΩ, which did not cause significant deviations in the state of the plants. The calculated possible yield of hydrogen per m³ of the root environment was 0.2 mmol/day. Thus, PMFC can become a promising source of green energy that can be combined with significant production processes for obtaining plant products or hydrogen.