An alkaline direct ethylene glycol fuel cell with an alkali-doped polybenzimidazole membrane

An alkaline direct ethylene glycol fuel cell (DEGFC) with an alkali-doped polybenzimidazole membrane (APM) is developed and tested. It is demonstrated that the use of APMs enables the present fuel cell to operate at high temperatures. The fuel cell results in the peak power densities of 80 mW cm⁻² at 60 °C and 112 mW cm⁻² at 90 °C, respectively. The power output at 60 °C is found to be 67% higher than that by DEGFCs with proton exchange membranes, which is mainly attributed to the superior electrochemical kinetics of both ethylene glycol oxidation and oxygen reduction reactions in alkaline media.     

Alkaline direct oxidation fuel cell with non-platinum catalysts capable of converting glucose to electricity at high power output

Glucose is a potential fuel for fuel cells because it is renewable, abundant, non-toxic, and easy in handle and store. Conventional glucose fuel cells that use enzymes and micro-organisms as the catalyst are limited by their extremely low power output and rather short durability. In this work, a direct glucose fuel cell that uses an anion-exchange membrane and in-house non-platinum electrocatalysts is developed. It is shown that this type of direct glucose fuel cell with a relatively cheap membrane and catalysts can result in a maximum power density as high as 38 mW cm⁻² at 60 °C. The high performance is attributed mainly to the increased kinetics of both the glucose oxidation reaction and the oxygen reduction reaction rendered by the alkaline medium with the anion-exchange membrane.     

Performance of air-breathing direct methanol fuel cell with anion-exchange membrane

This report details development of an air-breathing direct methanol alkaline fuel cell with an anion-exchange membrane. The commercially available anion-exchange membrane used in the fuel cell was first electrochemically characterized by measuring its ionic conductivity, and showed a promising result of 1.0 × 10⁻¹ S cm⁻¹ in a 5 M KOH solution. A laboratory-scale direct methanol fuel cell using the alkaline membrane was then assembled to demonstrate the feasibility of the system. A high open-circuit voltage of 700 mV was obtained for the air-breathing alkaline membrane direct methanol fuel cell (AMDMFC), a result about 100 mV higher than that obtained for the air-breathing DMFC using a proton exchange membrane. Polarization measurement revealed that the power densities for the AMDMFC are strongly dependent on the methanol concentration and reach a maximum value of 12.8 mW cm⁻² at 0.3 V with a 7 M methanol concentration. A durability test for the air-breathing AMDMFC was performed in chronoamperometry mode (0.3 V), and the decay rate was approximately 0.056 mA cm⁻² h⁻¹ over 160 h of operation. The cell area resistance for the air-breathing AMDMFC was around 1.3 Ω cm² in the open-circuit voltage (OCV) mode and then is stably supported around 0.8 Ω cm² in constant voltage (0.3 V) mode.     

Performance of alkaline electrolyte-membrane-based direct ethanol fuel cells

A single alkaline direct ethanol fuel cell (alkaline DEFC) with an anion-exchange membrane and non-platinum (non-Pt) catalysts is designed, fabricated, and tested. Particular attention is paid to investigating the effects of different operating parameters, including the cell operating temperature, concentrations of both ethanol and the added electrolyte (KOH) solution, as well as the mass flow rates of the reactants. The alkaline DEFC yields a maximum power density of 60 mW cm⁻², a limiting current density of about 550 mA cm⁻², and an open-circuit voltage of about 900 mV at 40 °C. The experimental results show that the cell performance is improved on increasing the operating temperature, but there exists an optimum ethanol concentration under which the fuel cell has the best performance. In addition, cell performance increases monotonically with increasing KOH concentration in the region of low current density, while in the region of high current density, there exists an optimum KOH concentration in terms of cell performance. The effect of flow rate of the fuel solution is negligible when the ethanol concentration is higher than 1.0 M, although the cell performance improves on increasing the oxygen flow rate.     

Performance characteristics of air-breathing anion-exchange membrane direct ethanol fuel cells

An air-breathing direct ethanol fuel cell (DEFC) with an anion-exchange membrane (AEM) and Pt-free electrodes is designed and investigated. Particular attention is paid to studying the performance characteristics of the air-breathing AEM DEFC. Experimental results reveal that this air-breathing AEM DEFC yields a peak power density as high as 38 mW cm⁻² at room temperature, which is comparable to the conventional Pt-based proton exchange membrane direct methanol fuel cells (PEM DMFCs). The overshoot/undershoot behaviors of both the cell voltage and cell temperature are avoided in the air-breathing AEM DEFC due to the use of ethanol-tolerant cathode catalyst. It is also found that the cathode water flooding behavior occurs in this air-breathing AEM DEFC, thus lowering the cell performance.     

Ultra-low catalyst loading cathode electrode for anion-exchange membrane fuel cells

A new cathode architecture for anion-exchange membrane fuel cells (AEMFCs) is proposed and fabricated by direct deposition of palladium (Pd) particles onto the surface of the micro-porous layer (MPL) that is interfaced with a backing layer. The MPL is composed of carbon nanotubes while the backing layer is made of a carbon paper. The sputter-deposited electrode with a worm-like shape not only extends the electrochemical active surface area, but also facilitates the oxygen transport. This new cathode, albeit with a Pd loading as low as 0.035 mg cm⁻², enables the peak power density of an AEM direct ethanol fuel cell to be as high as 88 mW cm⁻² (at 60 °C), which is even higher than that using a conventional cathode with a 15-times higher Pd loading. The significance of the present work lies in the fact that the new sputter-deposited electrode is more suitable for fuel-electrolyte-fed fuel cells than the conventional electrode designed for proton-exchange membrane fuel cells (PEMFCs).     

A high-performance integrated electrode for anion-exchange membrane direct ethanol fuel cells

We propose a new anode electrode structure that is composed of a nickel foam layer with thin catalyst films coated onto the skeleton of the foam. This innovative design of the anode electrode enables the integration of the catalyst and diffusion layers, thereby extending the electrochemical active surface area and facilitating the transport of species. The experimental results indicate that the use of the integrated electrode in an anion-exchange membrane direct ethanol fuel cell can significantly improve the cell performance as compared with the use of the conventional electrode that has separated catalyst and diffusion layers; a peak power density of 130 mW cm⁻² and a maximum current density of 1060 mA cm⁻² are achieved at 80 °C.     

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.     

Performance of a hybrid direct ethylene glycol fuel cell

In this work, a hybrid fuel cell is developed and tested, which is composed of an alkaline anode, an acid cathode, and a cation exchange membrane. In this fuel cell, ethylene glycol and hydrogen peroxide serve as fuel and oxidant, respectively. Theoretically, this fuel cell exhibits a theoretical voltage reaching 2.47 V, whereas it is experimentally demonstrated that the hybrid fuel cell delivers an open‐circuit voltage of 1.41 V at 60°C. More impressively, this fuel cell yields a peak power density of 80.9 mW cm^?2 (115.3 mW cm^?2 at 80°C). Comparing to an open‐circuit voltage of 0.86 V and a peak power density of 67 mW cm^?2 previously achieved by a direct ethylene glycol fuel cell operating with oxygen, this hybrid direct ethylene glycol fuel cell boosts the open‐circuit voltage by 62.1% and the peak power density by 20.8%. This significant improvement is mainly attributed not only to the high‐voltage output of this hybrid system design but also to the faster kinetics rendered by the reduction reaction of hydrogen peroxide.     

Alkaline anion-exchange polymer membrane with grid-plug microstructure for hydrogen fuel cell application

Porous polysulfone membrane, prepared by a phase-inversion technique, is filled with (3-acrylamidopropyl)trimethylammonium chloride and N,N′-methylenebisacrylamide via interfacial diffusion. The impregnated membrane is then subjected to UV-irradiation for polymerizing monomers that are entrapped in pore channels of the membrane. This in-situ polymerization engenders a grid-plug microstructure, where the grid is polysulfone and the plugs are an ion (OH⁻) conducting phase. As the plugs are extensively interconnected and non-tortuous throughout the membrane matrix, the ion-conducting phase sustains a power density as high as 55 mW cm⁻² at 60 °C. Thermal analysis indicates that the pore-filling condition affects the packing density of the plugs that in turn, impacts on ion transport flux.     

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.     

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.     

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.     

Study of fuel efficiency in a direct borohydride fuel cell

In this study, direct borohydride fuel cells (DBFCs) potentialities are evaluated. These emerging systems make it possible to reach maximum powers of about 200 mW cm⁻² at room temperature and ambient air (natural convection) with high concentrated borohydride solutions. On the other hand, a part of borohydride hydrolyses during cell operating which leads to hydrogen formation and fuel loss: the practical capacity represents about only 18% of the theoretical one. In order to improve fuel efficiency, thiourea is tested as an inhibitor of the catalytic hydrolysis associated with BH₄⁻ electro-oxidation on Pt. The practical capacity is drastically improved: it represents about 64% of the theoretical one. Against, electrochemical performances (I–E curves) are affected by the presence of thiourea.     

Life time test in direct borohydride fuel cell system

The electric performances of direct borohydride fuel cells (DBFCs) are evaluated in terms of power density and life time with respect to the NaBH₄ concentration. A DBFC constituted of an anionic membrane, a 0.6 mg_Pt cm⁻² anode and a commercial non-platinum based cathode led to performances as high as 200 mW cm⁻² at room temperature and with natural convection of air. Electrochemical life time test at 0.55 mA cm⁻² with a 5 M NaBH₄/1 M NaOH solution shows a voltage diminution of 1 mV h⁻¹ and a drastic drop of performances after 250 h. The life time is twice longer with 2 M NaBH₄/1 M NaOH solution (450 h) and the voltage decrease is 0.5 mV h⁻¹. Analyses of the components after life time tests indicate that voltage loss is mainly due to the degradation of the cathode performance. Crystallisation of carbonate and borate is observed at the cathode side, although the anionic membrane displays low permeability to borohydride.     

High-performance high-entropy quinary-alloys as anode catalysts for direct ethylene glycol fuel cells

Noble metals are the most commonly used electrocatalysts, but due to the high-cost and scarcity, improving their utilization has become a hot topic. As the Pt-based high-entropy alloy (HEA) can greatly increase the activity of catalyst and increase the utilization of noble metal, herein, a HEA with promising performance in ethylene glycol oxidation reaction (EGOR) is developed. The EGOR results show that, the onset potential of PtPdAuNiCo/C is 0.55 V, which is 20 mV lower than Pt/C (0.57 V) reference. Besides, the PtPdAuNiCo/C exhibits a high activity of 0.482 A mg^?1_PtPdAu, which is 2.18 times of Pt/C (0.221 A mg^?1_Pt) reference. And the current retention rate of PtPdAuNiCo/C (81.3%) is also higher than Pt/C (73.0%) reference in 500-cycle stability test. When as-obtained PtPdAuNiCo/C assembled into a direct ethylene glycol fuel cell, it exhibits a high-power density of 8.38 mW cm^?2. It is 1.40 times than that of Pt/C (6.00 mW cm^?2) reference. This work would be a good reference to HEA materials application on electrocatalysis in future.     

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.     

Product analysis of the ethanol oxidation reaction on palladium-based catalysts in an anion-exchange membrane fuel cell environment

We report a quantitative product analysis of the oxidation of ethanol in an anion-exchange membrane direct ethanol fuel cell (AEM DEFC) that consists of a Pd/C (or Pd₂Ni₃/C) anode, an AEM, and a Fe-Co cathode. The effects of the operating conditions including temperature, discharging current density, and fuel concentration, on the selectivity of each product of ethanol oxidation are investigated. It is found that incomplete ethanol oxidation to acetate prevails over complete oxidation to CO₂ in the range of testing conditions. Experimental results show that the change in the anode catalyst from Pd/C to Pd₂Ni₃/C leads to a significant increase in the cell performance, but does not help improve the CO₂ selectivity of ethanol oxidation. It is also shown that among the operating conditions tested, the operating temperature is the most significant parameter that affects the CO₂ selectivity: increasing the temperature from 60 to 100 °C enables the CO₂ current efficiency to increase from 6.0% to 30.6% with the Pd/C anode.     

Pd and Pt–Ru anode electrocatalysts supported on multi-walled carbon nanotubes and their use in passive and active direct alcohol fuel cells with an anion-exchange membrane (alcohol = methanol, ethanol, glycerol)

Palladium and platinum–ruthenium nanoparticles supported on multi-walled carbon nanotubes (MWCNT) are prepared by the impregnation-reduction procedure. The materials obtained, Pd/MWCNT and Pt–Ru/MWCNT, are characterized by TEM, ICP-AES and XRPD. Electrodes coated with Pd/MWCNT are scrutinized for the oxidation of methanol, ethanol or glycerol in 2 M KOH solution in half cells. The catalyst is very active for the oxidation of all alcohols, with glycerol providing the best performance in terms of specific current density and ethanol showing the lowest onset potential. Membrane-electrode assemblies have been fabricated using Pd/MWCNT anodes, commercial cathodes and anion-exchange membrane and evaluated in both single passive and active direct alcohol fuel cells fed with aqueous solutions of 10 wt.% methanol, 10 wt.% ethanol or 5 wt.% glycerol. Pd/MWCNT exhibits unrivalled activity as anode electrocatalyst for alcohol oxidation. The analysis of the anode exhausts shows that ethanol is selectively oxidized to acetic acid, detected as acetate ion in the alkaline media of the reaction, while methanol yields carbonate and formate. A much wider product distribution, including glycolate, glycerate, tartronate, oxalate, formate and carbonate, is obtained from the oxidation of glycerol. The results obtained with Pt–Ru/MWCNT anodes in acid media are largely inferior to those provided by Pd/MWCNT electrodes in alkaline media.     

Performance of a direct methanol alkaline membrane fuel cell

A study of a direct methanol fuel cell (DMFC) operating with hydroxide ion conducting membranes is reported. Evaluation of the fuel cell was performed using membrane electrode assemblies incorporating carbon-supported platinum/ruthenium anode and platinum cathode catalysts and ADP alkaline membranes. Catalyst loadings used were 1 mg cm⁻² Pt for both anode and cathode. The effect of temperature, oxidant (air or oxygen) and methanol concentration on cell performance is reported. The cell achieved a power density of 16 mW cm⁻², at 60 °C using oxygen. The performance under near ambient conditions with air gave a peak power density of approximately 6 mW cm⁻².