Development and Characterization of a Dithionite / Air Fuel Cell

With the increase of renewable energy sources in an electrical network, the need for energy storage increases. Depending on the application, there are different ways to store electrical energy. For electrochemical energy storage options exist in the form of batteries, redox flow batteries and fuel cells coupled with electrolysis. The longer the storage time, the lower the cost of energy storage medium must be in order to be competitive with other technologies. Batteries and redox flow batteries use reversible electrochemical reactions, fuel cells do not normally what makes specially adapted electrolysers required. Wherever possible, simple and rapid electrochemical reactions for the reversal of the reactions are required, as for example are found in the redox couple H₂/2H⁺. The reactions of organic redox couples of DMFC and DEFC can be electrochemically not reversed. Another way could be combinations of anodes of dissolved ions with an oxygen cathode, thereby “burning” the salt solutions which results in direct ion liquid fuel cells. A representative is the vanadium / oxygen fuel cell in which divalent vanadium ions are oxidized to trivalent at the anode by means of oxygen at the cathode [1]. The reactions can be reversed by vanadium / water electrolysis in the same cell as a reversible fuel cell (redox flow battery) [2, 3] or externally with a separate electrolysis cell [4].

Here we would like to report a work in which we have built and studied an alkaline fuel cell with the inexpensive redox couple dithionite / sulfite.

Anode:                S₂O₄^2- + 4 OH^- -> 2 SO₃^2- + 2 H₂O + 2 e^-                    E⁰= -0.294 V

Cathode:             O₂ + 2 H₂O + 4 e^- -> 4 OH^-                                           E⁰= +1.227 V

Cell:                    2 S₂O₄^2- + O₂ + 4 OH^- -> 4 SO₃^2- + 2 H₂O                   E = 1.530 V

As with the VOFC the reactions in a separate or the same cell may be reversed, and thus serve as an energy storage. For investigating the feasibility of such a cell a carbon-based anode and a platinum catalyst cathode for the ORR was used. The investigations were carried out by means of polarization curves, discharge tests and impedance spectroscopy using the cell voltage and the half-cell potentials and showed a maximum power density of 2 mW/cm² at room temperature. Under these conditions the oxidation of dithionite at carbon was much slower than the ORR. With a 0.85 M Na₂S₂O₄the cell reached 12.4% energy efficiency and an energy density of 8.6 Wh/L.

1 C. Menictas, M. Skyllas-Kazacos, Journal of Applied Electrochemistry 2011, 41, 1223–1232.

2 S. S. Hosseiny, M. Saakes, M. Wessling, Electrochemistry Communications 2011, 13, 751–754.

3 J. grosse Austing, C. Nunes Kirchner, E.-M. Hammer, L. Komsiyska, G. Wittstock, Journal of Power Sources 2015, 273, 1163–1170.

4 J. Noack, T. Roth, M. Hihn, J. Tuebke, The 7th International Green Energy Conference & The DNL 1st Conference on Clean Energy, Dalian, China, 2012