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.     

Catalysts for direct ethanol fuel cells

By comparing the performance of fuel cells operating on some low molecular weight alcohols, it resulted that ethanol may replace methanol in a direct alcohol fuel cell. To improve the performance of a direct ethanol fuel cell (DEFC), it is of great importance to develop anode catalysts for ethanol electro-oxidation more active than platinum alone. This paper presents an overview of catalysts tested as anode and cathode materials for DEFCs, with particular attention on the relationship between the chemical and physical characteristics of the catalysts (catalyst composition, degree of alloying, and presence of oxides) and their activity for the ethanol oxidation reaction.     

The role of an anode microporous layer in direct ethanol fuel cells at different ethanol concentrations

Ethanol crossover and ethanol electrooxidation kinetic effects on direct ethanol fuel cell (DEFC) performance were determined at different ethanol feed concentrations for cells fabricated with and without an anode microporous layer (MPL). Several characterization techniques were used, including cell performance curves, anode polarization, electrochemical impedance spectroscopy (EIS) and ethanol crossover by the voltammetric method. It was found that the optimum ethanol feed concentration depended on the anode structure design and the cell current density operation. A microporous layer could reduce ethanol crossover but induced high mass transfer resistance, resulting in a slow ethanol electrooxidation reaction rate. However, ethanol crossover was not the dominant factor affecting DEFC performance for the ethanol feed concentration range (0.5–5.0 M) studied. The MEA without an anode MPL exhibited better performance than the one with an MPL for the entire range of ethanol concentration.     

Nickel nanorods over nickel foam as standalone anode for direct alkaline methanol and ethanol fuel cell

A highly electroactive nickel nanorod (NNR)/nickel foam (NF) electrode was fabricated for direct alcohol fuel cells (DAFCs) using a simple and cost-effective hydrothermal process. The Ni/NiO nanorods were successfully grown on the surface of an NF electrode, which strongly enhanced the anode wettability and increased surface area by 18 times (11.9 m² g⁻¹), resulting in interfacial polarization resistance reduction. The NNR/NF electrode shows high electro-catalytic activity and great stability during alcohol oxidation. The current densities obtained for NNR/NF were four (479 mA cm⁻²) and six (543 mA cm⁻²) times higher than that for pristine NF in the cases of methanol and ethanol oxidations, respectively. This high current density can be attributed to the superhydrophilic surface of the Ni/NiO nanorods and corresponding high mass transfer capability between the electrolytes and Ni/NiO nanorods embedded on the surface of the electrodes. This study presents a new approach for using the novel NNR/NF as a cheap and high performance anode in DAFCs.     

Review: Direct ethanol fuel cells

Direct ethanol fuel cells have attracted much attention recently in the search for alternative energy resources. As an emerging technology, direct ethanol fuel cells have many challenges that need to be addressed. Many improvements have been made to increase the performance of direct ethanol fuel cells, and there are great expectations for their potential. However, many improvements need to be made in order to enhance the potential of direct ethanol fuel cells in the future. This paper addresses the challenges and the developments of direct ethanol fuel cells at present. It also presents the applications of DEFC.     

Effect of water concentration in the anode catalyst layer on the performance of direct methanol fuel cells operating with neat methanol

This paper reports on a chromatography-based method for determining the water concentration in the anode catalyst layer (CL) of a direct methanol fuel cell (DMFC). By this method, the effect of the water concentration in the anode CL on the product distribution of the methanol oxidation reaction (MOR), the anode potential, and the cell internal resistance is experimentally investigated in a DMFC operating with neat methanol. Interestingly, it is found that the main product of the anode MOR is still carbon dioxide even when the water concentration in the anode CL is extremely low. The experimental data also show that an increase in the water concentration in the anode CL decreases the internal resistance, the production of by-products (methyl formate and methylal), and the anode potential. As the mole ratio of water to methanol increases beyond a critical value, however, both the internal resistance and the anode potential tend to be stabilized at the points under diluted methanol operating conditions.     

High performance direct ethanol fuel cell with double-layered anode catalyst layer

Double-layered anode catalyst layers with two reverse configurations, which consist of 45 wt.% Pt₃Sn/C and PtRu black catalyst layers, were fabricated to improve the performance of a direct ethanol fuel cell (DEFC). The in-house 45 wt.% Pt₃Sn/C catalyst was characterized by XRD and TEM. The cross-sectional double-layered anode catalyst layer was observed by SEM. In DEFC performance test and anode linear sweep voltammetry measurement, the anode with double-layered catalyst layer exhibited better catalytic activity for ethanol electro-oxidation than those with single-layered 45 wt.% Pt₃Sn/C and PtRu black catalyst layers. In terms of anode product distribution, the DEFC with double-layered anode catalyst layer showed a higher yield of acetic acid than that with single-layered PtRu black catalyst layer and a higher yield of CO₂ than that with single-layered 45 wt.% Pt₃Sn/C catalyst layer, respectively. These results suggest that the double-layered anode catalyst layer possessed the advantages of both Pt₃Sn/C and PtRu black catalysts for ethanol electro-oxidation, and thus showed a higher ethanol electro-oxidation efficiency and DEFC performance in the practical polarization potential region.     

A model-based parametric analysis of a direct ethanol polymer electrolyte membrane fuel cell performance

In the present work, a model-based parametric analysis of the performance of a direct ethanol polymer electrolyte membrane fuel cell (DE-PEMFC) is conducted with the purpose to investigate the effect of several parameters on the cell's operation. The analysis is based on a previously validated one-dimensional mathematical model that describes the operation of a DE-PEMFC in steady state. More precisely, the effect of several operational and structural parameters on (i) the ethanol crossover rate from the anode to the cathode side of the cell, (ii) the parasitic current generation (mixed potential formation) and (iii) the total cell performance is investigated. According to the model predictions it was found that the increase of the ethanol feed concentration leads to higher ethanol crossover rates, higher parasitic currents and higher mixed potential values resulting in the decrease of the cell's power density. However there is an optimum ethanol feed concentration (approximately 1.0 mol L⁻¹) for which the cell power density reaches its highest value. The platinum (Pt) loading of the anode and the cathode catalytic layers affects strongly the cell performance. Higher values of Pt loading of the catalytic layers increase the specific reaction surface area resulting in higher cell power densities. An increase of the anode catalyst loading compared to an equal one of the cathode catalyst loading has greater impact on the cell's power density. Another interesting finding is that increasing the diffusion layers’ porosity up to a certain extent, improves the cell power density despite the fact that the parasitic current increases. This is explained by the fact that the reactants’ concentrations over the catalysts are increased, leading to lower activation overpotential values, which are the main source of the total cell overpotentials. Moreover, the use of a thicker membrane leads to lower ethanol crossover rate, lower parasitic current and lower mixed potential values in comparison to the use of a thinner one. Finally, according to the model predictions when the cell operates at low current densities the use of a thick membrane is necessary to reduce the negative effect of the ethanol crossover. However, in the case where the cell operates at higher current densities (lower ethanol crossover rates) a thinner membrane reduces the ohmic overpotential leading to higher power density values.     

Effect of anode diffusion layer fabricated with mesoporous carbon on the performance of direct dimethyl ether fuel cell

In this study, we present the novel membrane electrode assembly (MEA) for direct dimethyl ether fuel cell (DDFC). The anode gas diffusion layer (AGDL) of the MEA is fabricated with mesoporous carbon to facilitate the anode mass transport and enhance the performance of DDFC. The major differences of mesoporous carbon AGDL (MAGDL) and XC-72 AGDL (XAGDL) are the BET surface, the pore volume, and the pore size distribution. The MAGDL provides many more passageways for mass transport than XAGDL. The MAGDL possesses hydrophilic small and hydrophobic middle pores, which benefit the liquid and gas transport simultaneously. The maximum power density of DDFC increases by 20% when using MAGDL instead of XAGDL at 60 °C. The electrochemical measurements indicate that the promotion of the anode two-phase mass transport is the main reason for the significant improvement of DDFC performance.     

Effect of addition of rhenium to Pt-based anode catalysts in electro-oxidation of ethanol in direct ethanol PEM fuel cell

Breaking of C–C bond at low temperature to completely oxidize ethanol in direct ethanol fuel cell (DEFC) is the limiting factor for the development of DEFC as alternative source of power in portable electronic equipment. Binary and ternary Pt based catalysts with addition of Re, Pt–Re/C (20:20), Pt–Sn/C (20:20), Pt–Re–Sn/C (20:10:10) and Pt–Re–Sn/C (20:5:15) catalysts were prepared from their precursors by co-impregnation reduction method to study electro-oxidation of ethanol in DEFC. The electrocatalysts characterized by transmission electron microscope, scanning electron microscope, energy dispersive X-ray, and X-ray diffraction shows the formation of above mentioned bi- and tri-metallic catalyst with size ranges from 6 to 16 nm. Electrochemical analyses by cyclic voltammetry, linear sweep voltammetry and chronoamperometry show that Pt–Re–Sn/C (20:5:15) gives higher current density compared to that of Pt–Re/C (20:20) and Pt–Sn/C (20:20). The addition of Re to Pt–Sn/C is conducive to electro-oxidation of ethanol in DEFC. The power density obtained using Pt–Re–Sn/C(20% Pt, 5% Re, 15% Sn by wt) (30.5 mW/cm²) as anode catalyst in DEFC is higher than that for Pt–Re–Sn/C(20% Pt, 10% Re, 10% Sn by wt) (19.8 mW/cm²), Pt–Sn/C (20% Pt, 20% Sn by wt) (22.4 mW/cm²) and Pt–Re/C (20% Pt, 20% Re by wt) (9.8 mW/cm²) at 100 °C, 1 bar, with catalyst loading of 2 mg/cm² and 5 M ethanol as anode feed.     

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.     

Performance of an alkaline-acid direct ethanol fuel cell

This paper reports on the performance of an alkaline-acid direct ethanol fuel cell (AA-DEFC) that is composed of an alkaline anode, a membrane and an acid cathode. The effects of membrane thickness and the concentrations of various species at both the anode and cathode on the cell performance are investigated. It has been demonstrated that the peak power density of this AA-DEFC that employs a 25-μm thick membrane is as high as 360 mW cm⁻² at 60 °C, which is about 6 times higher than the performance of conventional DEFCs reported in the literature.     

Synthesis of NiPt alloy nanoparticles by galvanic replacement method for direct ethanol fuel cell

The alloy of NiPt nanoparticles was successfully synthesized by galvanic replacement method in which Ni nanoparticles used as the templates and H₂PtCl₆ solution as additional reagent. The preparation conditions of Ni nanoparticle were optimized. The effect of platinum contents on the structure, morphology, magnetic and electrocatalyst of NiPt was investigated. The phase analysis by XRD showed the presence of Ni and Pt crystalline phases on the alloy. The TEM images indicated that the NiPt nanoparticles had porous crystalline structure with grain size in the range of 25 nm–30 nm. Besides, composition analysis by EDX showed that the ratios of Ni and Pt were changed with a change of the amount of H₂PtCl₆ using for the galvanic reaction. The magnetic properties of NiPt nanoparticles change significantly with a change of Pt composition. The NiPt nanoparticles exhibit ferromagnetic behavior depending on the amount of Pt composition. In particular, saturation magnetization decreases from 6.5 emu/g to 4.0 emu/g with the decrease of Ni:Pt ratio from 57.0:3.6 to 57.0:8.1 respectively. With lower Ni:Pt ratio (57.0:18.0), the NiPt nanoparticles exhibits superparamagnetic properties. The magnetic properties were attributed to the formation of NiPt alloy in which the electrons transfer from Pt atoms to d band of Ni. The cyclic voltammetry measurement showed that NiPt nanoparticles exhibit better ethanol oxidation in alkali medium comparing with pure Platinum.     

Effect of polymer binders in anode catalyst layer on performance of alkaline direct ethanol fuel cells

In preparing low-temperature fuel cell electrodes, a polymer binder is essential to bind discrete catalyst particles to form a porous catalyst layer that simultaneously facilitates the transfer of ions, electrons, and reactants/products. For two types of polymer binder, namely, an A3-an anion conducting ionomer and a PTFE-a neutral polymer, an investigation is made of the effect of the content of each binder in the anode catalyst layer on the performance of an alkaline direct ethanol fuel cell (DEFC) with an anion-exchange membrane and non-platinum (non-Pt) catalysts. Experiments are performed by feeding either ethanol (C₂H₅OH) solution or ethanol–potassium hydroxide (C₂H₅OH–KOH) solution. The experimental results for the case of feeding C₂H₅OH solution without added KOH indicate that the cell performance varies with the A3 ionomer content in the anode catalyst layer, and a content of 10 wt.% exhibits the best performance. When feeding C₂H₅OH–KOH solution, the results show that: (i) in the region of low current density, the best performance is achieved for a membrane electrode assembly without any binder in the anode catalyst layer; (ii) in the region of high current density, the performance is improved with incorporation of PTFE binder in the anode catalyst layer; (iii) the PTFE binder yields better performance than does the A3 binder.     

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.     

Understanding the performance degradation of anion-exchange membrane direct ethanol fuel cells

It has recently been demonstrated that anion-exchange membrane direct ethanol fuel cells (AEM DEFCs) can yield a high power density. The operating stability and durability of this type of fuel cell is, however, a concern. In this work, we report the durability test of an AEM DEFC that is composed of a Pd/C anode, an A201 membrane, and a Fe-Co cathode and show that the major voltage loss occurs in the initial discharge stage, but the loss becomes smaller and more stable with the discharge time. It is also found that the irreversible degradation rate of the fuel cell is around 0.02 mV h⁻¹, which is similar to the degradation rate of conventional acid direct methanol fuel cells (DMFCs). The experimental results also reveal that the performance loss of the AEM DEFC is mainly attributed to the anode degradation, while the performance of the cathode and the membrane remains relatively stable. The TEM results indicate that the particle size of the anode catalyst increases from 2.3 to 3.5 nm after the long-term discharge, which reduces the electrochemical active surface area and hence causes a decrease in the anode performance.     

A novel direct ethanol fuel cell with high power density

A new type of direct ethanol fuel cell (DEFC) that is composed of an alkaline anode and an acid cathode separated with a charger conducting membrane is developed. Theoretically it is shown that the voltage of this novel fuel cell is 2.52 V, while, experimentally it has been demonstrated that this fuel cell can yield an open-circuit voltage (OCV) of 1.60 V and a peak power density of 240 mW cm⁻² at 60 °C, which represent the highest performance of DEFCs that has so far been reported in the open literature.     

Effect of cathode micro-porous layer on performance of anion-exchange membrane direct ethanol fuel cells

The effect of a cathode micro-porous layer that is composed of carbon powder or carbon nanotubes on cell performance is investigated. Polarization curves, together with the respective anode and cathode potentials, are measured. The results show that the cathode potential can be significantly improved with adding a hydrophobic micro-porous layer between the cathode catalyst layer and the gas-diffusion layer. The increased performance with the cathode micro-porous layer is mainly attributed to the fact that the cathode water flooding can be alleviated as a result of the reduced water crossover, which consequently facilitates the transport of oxygen to the catalyst layer. It is also found that a crack-free micro-porous layer made of carbon nanotubes gives a much higher cathode potential compared with a micro-porous layer composed of carbon powder.     

Preparation, characterization and application of Pt-Ru-Sn/C trimetallic electrocatalysts for ethanol oxidation in direct fuel cell

This work aimed to develop a method for the preparation of carbon-supported platinum nanocatalysts modified with Ruthenium and Tin, which were then evaluated for ethanol eletrooxidation in direct fuel cells. The Pechini method was employed to obtain these catalysts. This method consists in the decomposition of a polymeric precursor of metal salts. Nanocatalysts containing different Pt/Ru/Sn molar ratios were prepared by keeping the carbon/metal ratio at a constant value of 60/40%. The obtained nanoparticles were physico-chemically characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Energy Dispersive X-ray Spectroscopy (EDX). Crystallite size of around 7.0 nm and 5.8 nm were achieved for the bimetallic and trimetallic nanocatalysts, respectively. The experimental composition was close to the nominal one, but the metal particles were not evenly distributed on the carbon surface. Electrochemical characterization of the nanoparticles was accomplished by cyclic voltammetry (CV) and chronoamperometry. High Performance Liquid Chromatography (HPLC) was carried out after ethanol electrolysis for determining the products generated. Acetaldehyde was the main electrolysis product and traces of CO₂ and acetic acid were also detected. Addition of Ru and Sn to the pure Pt nanoelectrocatalyst significantly improved its performance in ethanol oxidation. The onset potential for ethanol electrooxidation was 0.2 V vs. RHE, in the case of the trimetallic nanocatalyst Pt_0.8Ru_0.1Sn_0.1/C, which was lower than that obtained for the pure Pt catalyst (0.45 V vs. RHE).     

Investigation of amorphous CoB alloy as the anode catalyst for a direct borohydride fuel cell

Co-B amorphous alloy powders have been synthesized by chemical reduction of cobalt chloride with potassium borohydride in an aqueous solution. We find that this alloy can be used as an anode catalyst for a direct borohydride fuel cell (DBFC). This catalyst exhibits excellent electrocatalytic activity. An essential power output of 220 mW cm⁻² has been achieved at 15 °C, and a life test last for 160 h with no attenuation has been observed. The amorphous structure of the CoB alloy is still stable after the life test.