l-Ascorbic acid as an alternative fuel for direct oxidation fuel cells

doi:10.1016/j.jpowsour.2007.02.023

Journal of Power Sources

Volume 167, Issue 1, 1 May 2007, Pages 32-38

https://doi.org/10.1016/j.jpowsour.2007.02.023 Get rights and content

Abstract

l-Ascorbic acid (AA) was directly supplied to polymer electrolyte fuel cells (PEFCs) as an alternative fuel. Only dehydroascorbic acid (DHAA) was detected as a product released by the electrochemical oxidation of AA via a two-electron transfer process regardless of the anode catalyst used. The ionomer in the anode may inhibit the mass transfer of AA to the reaction sites by electrostatic repulsion. In addition, polymer resins without an ionic group such as poly(vinylidene fluoride) and poly(vinyl butyral) were also useful for reducing the contact resistance between Nafion membrane and carbon black used as an anode, although an ionomer like Nafion is needed for typical PEFCs. A reaction mechanism at the two-phase boundaries between AA and carbon black was proposed for the anode structure of DAAFCs, since lack of the proton conductivity was compensated by AA. There was too little crossover of AA through a Nafion membrane to cause a serious technical problem. The best performance (maximum power density of 16 mW cm⁻²) was attained with a Vulcan XC72 anode that included 5 wt.% Nafion at room temperature, which was about one-third of that for a DMFC with a PtRu anode.

Introduction

Direct methanol fuel cells (DMFCs), in which methanol solution is directly supplied to the anode, have been actively developed as power sources in portable electronic devices such as mobile phones and portable PCs, as alternatives to rechargeable batteries [1], [2], [3]. The use of methanol as a fuel offers several advantages, including high energy density for fuel storage, theoretically complete oxidation to CO₂, and low cost. However, there are still several obstacles to the practical use of DMFCs, such as the need for Pt-based catalysts due to the large overvoltage toward the electrooxidation of methanol [4], large methanol crossover through the polymer membrane [5], and the toxicity of methanol and by-product species, i.e. formaldehyde and formic acid.

We have been trying to identify alternatives to methanol for use in direct-PEFCs [6]. The main purpose of this study is to solve the technical problems in DMFCs described above and to propose a variety of micropower sources with different output scales and characteristics for application in novel fields. For medical applications, which are expected to be one of the most important markets for micropower sources in the near future, the demand for safety is predominant. On that point, we reported for the first time the possibility of using environmentally and biologically friendly l-ascorbic acid (AA), well known as vitamin C, as a fuel for direct-PEFCs [7]. Direct AA fuel cells (DAAFCs), in which AA solution is directly supplied to the anode, offer several advantages compared to DMFCs. In particular, DAAFCs do not require a precious metal anode and do not release any toxic product.

Although many studies have been reported on the electrochemical oxidation of AA in the field of fundamental electrochemistry and its application to electrochemical sensors, there are few research reporting on the use of AA in fuel cells. The electrochemical oxidation of AA has been widely studied on Pt [8], Au [9], and Hg [10] or carbon electrode [11], [12]. In our resent study, DAAFCs using carbon black with a large surface area as an anode were developed and demonstrated that anodic performance was dominated by the electrochemically active surface area of the carbon electrode [13].

Recently, biofuel cells, in which glucose is oxidized to gluconolactone by glucose oxidase, have also been reported as power generators for implantable devices, such as artificial organs, microsurgery robots, and in situ sensors [14], [15], [16]. Glucose is an attractive fuel for both in vivo use and as a biomass energy resource. There has also been interest in the use of bio-ethanol transformed by the fermentation of biomass, i.e. glucose as a fuel for vehicle engines or PEFCs to reduce carbon dioxide emissions [17], [18]. AA is also a biomass-derived fuel, and can be obtained from the fermentation or chemical conversion of d-glucose. Thus, the investigation of DAAFCs may contribute to its application as a regenerative fuel.

In the present study, the fundamental characteristics of DAAFCs were investigated in comparison with DMFCs. Quantitative analysis of the product species during the operation of DAAFCs was carried out to determine the stoichiometry. AA crossover through a Nafion membrane was evaluated in comparison with methanol. The structure of the carbon electrode and the formation of a reaction site in the anode of DAAFCs are also discussed based on the effect of polymer resins and their content when used as binders.

Section snippets

Materials

Unsupported catalysts, Pt, Ru, Pd, Ir, Rh, and PtRu black (Johnson-Matthey, specific surface area is typically 20 m² g⁻¹), were used as electrocatalysts to prepare membrane electrode assemblies (MEAs) in DAAFCs. Vulcan XC72 (Cabot), which is a typical carbon black with a BET surface area of 254 m² g⁻¹, was used after heating at 180 °C for 3 h under vacuum. Three types of polymer resins were used as binders to prepare an electrode layer: poly(vinylidene fluoride) (PVDF, average Mw = 534,000, Aldrich),

I–V performance of DAAFCs with various anode catalysts

The performance of DAAFCs with various anode catalysts was compared. Fig. 1(a) shows the cell voltage versus current plots for DAAFCs using Pt, Ru, Pd, Ir, Rh, PtRu (3.0 mg cm⁻², Nafion 10 wt.%), and Vulcan XC72 (0.3 mg cm⁻², Nafion 5 wt.%) as anode catalysts. The differences in cell performance with the different anode catalysts can be explained by the electrochemically active surface area formed by the catalysts and Nafion electrolyte rather than by the specific catalytic activities. Previous

Conclusions

The fundamental characteristics of DAAFCs, in which AA is used as an alternative fuel for PEFCs, were investigated in terms of cell performance, product analysis, and AA crossover. The best performance was attained using a Vulcan XC72 anode and the maximum power density reached 16 mW cm⁻², which was about one-third of that for DMFCs with a PtRu anode under the same operating conditions. The product analysis suggested that the anode reaction was two-electron oxidation from AA to DHAA, the same as

Acknowledgments

This study was supported by the Industrial Technology Research Grant Program in 2004 from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The authors thank Mr. Kazuya Sako, Ms. Eriko Kasugai, Ms. Yoshiko Murai, and Ms. Yumiko Hayashi for their kind support with the experiments.

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Citation Excerpt :
However, the primary disadvantage of Direct Ethanol gasoline cells is the requirement for a highly effective catalyst to break the C-C bond and to form Carbon dioxide as the end product. Then again, opportunity gasoline wishes to produce excessive strength in terms of energy, widespread availability, and environmentally friendly, thus consequently Ascorbic Acid (AA) is considered as a prominent, alternative, high efficient-sustainable and eco-friendly fuel [10], [11]. Moreover, AA is a bio-energetic molecule that performs a crucial position in diverse biological and chemical reactions.
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l-Ascorbic acid as an alternative fuel for direct oxidation fuel cells

Abstract

Introduction

Section snippets

Materials

I–V performance of DAAFCs with various anode catalysts

Conclusions

Acknowledgments

J. Power Sources

Electrochem. Commun.

J. Power Sources

J. Power Sources

J. Power Sources

Electrochim. Acta

Electrochim. Acta

Electrochem. Commun.

J. Power Sources

Appl. Catal. B: Environ.

J. Chromatogr. A

Electrochim. Acta