The effect of magnetic field on the oxygen reduction reaction and its application in polymer electrolyte fuel cells

doi:10.1016/S0013-4686(02)00720-X

Electrochimica Acta

Volume 48, Issue 5, 15 January 2003, Pages 531-539

https://doi.org/10.1016/S0013-4686(02)00720-X Get rights and content

Abstract

The effect of magnetic field gradients on the electrochemical oxygen reduction was studied with relevance to the cathode gas reactions in polymer electrolyte fuel cells. When a permanent magnet was set behind a cathode, i.e. platinum foil or Pt-dispersed carbon paper for both electrochemical and rotating electrode experiments and oxygen was supplied to the uphill direction of the magnetic field, electrochemical flux was enhanced and the current increased with increasing the absolute value of magnetic field. This magnetic effect can be explained by the magnetic attractive force toward O₂ gas. When magnet particles were included in the catalyst layer of the cathode and the cathode was magnetized, the current of oxygen reduction was higher than that of nonmagnetized cathode. A new design of the cathode catalyst layer incorporating the magnet particles was tested, demonstrating a new method to improve the fuel cell performance.

Introduction

The polymer electrolyte fuel cell system is being considered as an alternative power source for electric vehicles. Of the performance controlling components in a polymer electrolyte fuel cell, the cathode is recognized to be one of the most influential components and its performance depends highly on the oxygen transport rate that is affected by the presence of water.

Oxygen gas is a unique gas that has paramagnetic properties because of its parallel spins in the electron configuration of a molecule [1]. In the 19th century, Faraday carried out experiments about the effect of magnetic force on several kinds of gasses, categorizing them as ‘attractive’ or ‘repulsive’ and found that most gases are rejected from a magnet but oxygen gas is attracted toward the magnet [2]. Generally, the magnetic force, i.e. Kelvin force acting on a unit volume of gas is [3]: $F →_{m} = χ 2μ_{0} &0xEB08;&0xEB08; grad (B^{2})$ where μ₀ (4π×10⁻⁷ H m⁻¹) is the absolute magnetic permeability of vacuum, χ is the volume magnetic susceptibility, B is the magnetic flux density, and grad (B²) is the gradient of the square of B.

It is characteristic that a magnetic force can be induced under a magnetic field gradient and the force along z-axis, is proportional to the value of dB²/dz. For χ>0 (oxygen gas, 1.91×10⁻⁶ at 273 K) [4], the force is attractive, while the force is repulsive for χ<0. In the 20th century, Pauling et al. [5] invented an equipment for measuring the concentration of O₂ gas, utilizing the magnetic attractive force toward O₂ gas. Recently, it has been found that this magnetic attractive force toward O₂ gas induces gas flows [6], [7], [8], and affects chemical reactions related with O₂ gas, for example, combustion in diffusion flames [8], [9] and catalytic combustion [10]. This new research field was named ‘magnetoaerodynamics’. In diffusion flames, combustion reaction occurs at the surface of a flame, i.e. the reaction zone. Magnetic promotion of combustion in a diffusion flame was found when the magnetic force transported O₂ gas toward the reaction zone and removed combustion gases from it. For catalytic combustion, oxidation reactions occur at the surface of catalyst. When the magnetic force increased the supply of O₂ gas to the Pt catalyst and removed the reaction products, the promotion of combustion was also observed. Thus, it is possible to promote oxidation reactions by magnetically controlling the transport of O₂ gas and reaction products.

One of the promising applications of magnetoaerodynamics would be the promotion of oxygen reduction reaction in polymer electrolyte fuel cells, which is the major rate-limiting process, and thus, causes high overpotential and loss of efficiency of the system [11]. If the oxygen gas flow and the diffusion in the cathode gas electrode can be promoted by a magnetic force, this will improve the performance of the fuel cell extensively [12], [13], [14]. The aim of the present paper is to demonstrate if this type of promotion of the cathode gas reaction is realized, and to show a future prospect for such an application of permanent magnets in the cathode of the fuel cell system.

Section snippets

Magnetic effects on a cathode reaction-three electrode electrochemical experiments

Platinum foil of thickness 12 μm was used as the working electrode in the three-electrode glass cell for the electrochemical experiments. The reference electrode was Ag/AgCl (0.588 V vs. RHE, the hydrogen electrode in the same solution), and the counter electrode was platinum plate. One side of the platinum foil was open (diameter 16 mm) to the glass cell, which was filled with 0.05 mol dm⁻³ H₂SO₄. The other side of the Pt foil was in contact with the magnetic pole of Nd–Fe–B rectangular magnet

Spatial distribution of magnetic flux density

For three electrode electrochemical cell measurements and rotating vertical electrode measurements, rectangular and cylindrical bar magnets were used, respectively. According to Eq. (1), the magnetic force is proportional to dB²/dz, but it is almost impossible to measure correctly the spatial distribution of magnetic flux density in the vicinity of the permanent magnet because of the large size of a sensor, i.e. Hall probe (0.4 mm thick) of a Gauss meter (5080, F.W. Bell). Therefore, the

Magnetic effects on a cathode reaction-three electrode electrochemical experiments

Fig. 3 shows the potential-current density curves measured on bare platinum while oxygen gas was bubbled in 0.05 mol dm⁻³ H₂SO₄ with and without a magnetic field when (dB²/dz)₀=−489 T² m⁻¹ (l=30 mm). The potential is cycled at a scan rate of 0.1 V s⁻¹. The cathodic current beginning around 0.8 V versus RHE and increasing at negative potentials corresponds to the reduction current of dissolved oxygen in the solution. Although the amount of dissolved oxygen in 0.05 mol dm⁻³ H₂SO₄ solution, ca.

Conclusions

The effect of magnetic fields on the electrochemical oxygen reduction was studied with relevance to the cathode gas reactions in polymer electrolyte fuel cells where oxygen gas is reacted with H⁺ to produce water on platinum catalyst. The key points of the present study are as follows.

(1) When a permanent magnet was set behind the cathode, i.e. platinum film or platinum dispersed carbon paper for both electrochemical and rotating vertical electrode experiments and O₂ gas was supplied to the

Acknowledgements

The authors thank Dr. Akira Nakanishi in Sumitomo Special Metals Co. Ltd. for useful discussions and his encouragement through the research.

References (20)

G. Herzberg
M. Faraday
Philos. Mag.
(1847)
McGraw-Hill Encyclopedia of Science and Technology, vol. 10, 7th ed., MacGraw-Hill, New York, 1992, p....
Chemical Society of Japan (Ed.), Kagaku Binran (Tables of Physical and Chemical Data), 2nd ed., Maruzen, Tokyo, 1975,...
L. Pauling et al.
J. Am. Chem. Soc.
(1946)
N.I. Wakayama
J. Appl. Phys.
(1990)
B. Bai et al.
AIAA J.
(1999)
N.I. Wakayama
Combust Flame
(1993)
N.I. Wakayama et al.
Combust Flame
(1996)
N.I. Wakayama
Jpn. J. Appl. Phys.
(2000)

There are more references available in the full text version of this article.

Cited by (64)

Flow characteristics analysis and performance evaluation of a novel rotary proton exchange membrane fuel cell
2024, International Journal of Hydrogen Energy
This paper proposes a new type of rotary proton exchange membrane fuel cell (R-PEMFC) and its simulation model is established and verified based on experimental data. Then the effects of different rotational angular speeds (RASs) on reactant flow characteristics and electrochemical reactions are investigated. Also, the key quantitative indexes, such as average value, uniformity index and effective mass transfer coefficient (EMTC) are adopted, while combining the polarization curve and net power to estimate the comprehensive R-PEMFC performance. The results indicate that the R-PEMFC effectively ameliorates uneven distribution and improves the transmission capability and output performance. Compared with the static state (0 rpm), the EMTC and maximum power density are enhanced by 65.86 % and 8.51 % respectively at the RAS of 1080 rpm, and the net power density can reach 5316 W·m⁻².
Synthesis and characterization of Pt<inf>3</inf>Co alloy magnetic nanoparticles in multidomain region for oxygen reduction reaction catalysts in PEMFCs
2024, International Journal of Hydrogen Energy
The structural and electrochemical characteristics of Pt₃Co alloy nanoparticles as novel magnetic catalysts are investigated experimentally to improve the performance of the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Pt₃Co alloy nanoparticles are synthesized using a wet chemical reduction and seed-mediated method. The synthesized Pt₃Co alloy nanoparticles are annealed at 400 °C (Pt₃Co-400) and 700 °C (Pt₃Co-700) to increase the remanent magnetizations. The synthesized Pt₃Co alloy nanoparticles for magnetic catalysts are characterized using physicochemical and electrochemical methods. Physicochemical tests confirm that the Pt₃Co alloy nanoparticles are properly synthesized with the desired atomic ratio for magnetization in the multidomain region. The remanent magnetizations of the Pt₃Co alloy nanoparticles substantially increase after annealing at 400 °C. For the rotating ring-disk electrode tests, the electrocatalytic performance improvement of Pt₃Co alloy nanoparticles by magnetization is very small under the liquid electrolyte condition. However, the performances of PEMFCs using Pt₃Co-400 alloy nanoparticles are substantially improved after magnetization owing to the enhanced ORR activities and oxygen diffusivity. In addition, the optimal operating conditions for PEMFCs using Pt₃Co-400 magnetic catalysts are determined to be a higher reactant flow rate and lower operating temperature with a Pt-to-Pt₃Co-400 mass ratio of 8:2.
Experimental improvement of the performance of the open cathode-direct methanol fuel cell stack by magnetic field effect
2024, International Journal of Hydrogen Energy
Open Cathode Direct Methanol Fuel Cell (OC-DMFC) stack performance is achieved at different methanol temperatures (25, 40, 55 and 70 °C), methanol concentrations (0.5, 1, 2 and 4 M) and air flow rates (3.5, 4.8 and 6.4 m/s). Each parameter, whose performance was tested separately, was presented by making comparisons within itself. The effect of performance changes on peak power densities under relatively low electromagnetic fields (4.7, 12.4, 28 and 35 mT) was investigated by exposing the 10-cell OC-DMFC stack to a magnetic field with the help of ferritic magnets. Ferritic magnets placed on the OC-DMFC stack anode and cathode surfaces, It is designed to create an electromagnetic field. Thus, the magnetic field affected both surfaces. When the magnetic field was 35 mT, the OC-DMFC reached a power density of 17.5 mW cm⁻². When the DMFC stack is exposed to the magnetic field, its performance is increased by ∼16%.
Performance characteristics of novel magnetic-field applied polymer electrolyte membrane fuel cells under various operating conditions
2022, Energy Conversion and Management
In this study, the oxygen reduction reaction (ORR) performance improvement of polymer electrolyte membrane fuel cells (PEMFCs) is investigated using a low magnetic field density. The transient performance of a PEMFC using a magnetic field (MF-PEMFC) was measured and analyzed by varying the cell temperature, voltage, relative humidity, and pre-humidification time. Based on the results, the mechanism of the performance improvement of MF-PEMFC was revealed, and a strategy to maximize its performance was proposed. Enhanced oxygen mobility by a magnetic field led to a higher ORR performance and membrane humidification was accelerated by the vigorous ORR. The performance improvement of MF-PEMFC was more substantial under unfavorable membrane humidification conditions such as high temperature and low operating voltage. The maximum performance improvement of MF-PEMFC compared to that of normal PEMFC was 8.6% at 40% relative humidity, 0.30 V voltage, and 80 ℃ cell temperature due to an enhanced self-humidification effect. In addition, the maximum performance improvement and stability of MF-PEMFC were obtained with the proper pre-humidification time. In conclusion, using a magnetic field can improve the performance and stability of PEMFCs under unfavorable operating conditions.
Photovoltaics and its magnetic-field promotion effect in dye-sensitized solar cells with BiFeO<inf>3</inf> + TiO<inf>2</inf> composite photoanodes
2022, Solar Energy
In dye-sensitized solar cells (DSSCs), the light absorbance of photoanode is the most important factor in power conversion efficiency (PCE). Here the authors report on an alternative modified TiO₂-based photoanode for obtaining enhanced photovoltaic (PV) properties in DSSCs. Multiferroics BiFeO₃, which possesses excellent magnetic, electric, and photocatalytic performances, was employed to construct BiFeO₃ + TiO₂ composite photoanode for DSSCs. In this type of DSSCs with BiFeO₃ + TiO₂ composite photoanodes, BiFeO₃ with suitable bandgap may also act as photoelectric conversion medium, which is generally acted by dye in DSSCs, and increases photogenerated carrier transport channels, which improves the PCE of DSSCs with BiFeO₃ + TiO₂ composite photoanodes. More importantly, magnetic-field enhanced PV properties in abovementioned DSSCs was firstly obtained, which may result from magnetic-field-suppression the recombination of charge carriers and magnetoresistance effect in BiFeO₃. The investigated results offer both an alternative method to improve PV properties in DSSCs, and a referential train of thought to manipulate photoelectric properties of solar cells.
The possible implications of magnetic field effect on understanding the reactant of water splitting
2022, Chinese Journal of Catalysis
Electrochemical water splitting consists of two elementary reactions i.e., hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Developing robust HER and OER technologies necessitates a molecular picture of reaction mechanism, yet the reactants for water splitting reactions are unfortunately not fully understood. Here we utilize magnetic field to understand proton transport in HER, and hydroxide ion transport in OER, to discuss the possible implications on understanding the reactants for HER and OER. Magnetic field is a known tool for changing the movement of charged species like ions, e.g. the magnetic-field-improved Cu²⁺ transportation near the electrode in Cu electrodeposition. However, applying a magnetic field does not affect the HER or OER rate across various pH, which challenges the traditional opinion that charged species (i.e. proton and hydroxide ion) act as the reactant. This anomalous response of HER and OER to magnetic field, and the fact that the transport of proton and hydroxide ion follow Grotthuss mechanism, collectively indicate water may act as the universal reactant for HER and OER across various pH. With the aid of magnetic field, this work serves as an understanding of water might be the reactant in HER and OER, and possibly in other electrocatalysis reactions involving protonation and deprotonation step. A model that simply focuses on the charged species but overlooking the complexity of the whole electrolyte phase where water is the dominant species, may not reasonably reflect the electrochemistry of HER and OER in aqueous electrolyte.

View all citing articles on Scopus

¹: ISE member.

View full text

The effect of magnetic field on the oxygen reduction reaction and its application in polymer electrolyte fuel cells

Abstract

Introduction

Section snippets

Magnetic effects on a cathode reaction-three electrode electrochemical experiments

Spatial distribution of magnetic flux density

Magnetic effects on a cathode reaction-three electrode electrochemical experiments

Conclusions

Acknowledgements

Philos. Mag.

J. Am. Chem. Soc.

J. Appl. Phys.

AIAA J.

Combust Flame

Combust Flame

Jpn. J. Appl. Phys.