Laminar flow-based fuel cells (LFFCs) utilize the occurrence of laminar flow at the microscale to create a membraneless fuel cell [1]. Mixing is governed by slow molecular diffusion only, so streams of fuel and oxidant can be kept separated without use of a polymer electrolyte membrane (e.g. Nafion). Compared to more conventional fuel cells (e.g. DMFCs), these LFFCs exhibit the following advantages: (i) fuel crossover can be avoided completely leading to high open cell potentials; (ii) anode dry-out and cathode flooding issues are eliminated; (iii) these cells can be operated in both acidic and alkaline conditions [2]; and (iv) one can operate these fuel cells with either formic acid or methanol as the fuel. Earlier generations of these LFFCs were performance limited by slow mass transport of dissolved oxygen to the cathode, but recently we have overcome this issue by incorporating an air-breathing gas-diffusion electrode which enables rapid transport oxygen to the cathode from air due to the 4 orders of magnitude higher diffusion constant [3].

This presentation will summarize the key characteristics of this microfluidic fuel cell. Then the performance of direct methanol LFFCs with gas diffusion electrodes in acidic and alkaline media will be compared. These cells exhibit high open circuit potentials of 0.93 V and 1.05 V in acidic and alkaline media, respectively, which demonstrates control over methanol crossover in these fuel cell designs. A higher maximum power density of 17.2 mW/cm2 was obtained when operating in alkaline media compared to 11.8 mW/cm2 in acidic media. Single electrode studies show that the cathode and anode exhibits better kinetics in alkaline solutions, in accordance with prior electrochemical studies in literature. These LFFCs, however, avoid clogging of membrane pores by carbonate formation in alkaline media, one of the factors that has limited their use in, for example, DMFCs.

[1] E.R. Choban, L.J. Markoski, A. Wieckowski, and P.J.A. Kenis, J. Power Sources 2004, 128, 54; R. Ferrigno, A.D. Stroock, T.D. Clark, M. Mayer, and G. M. Whitesides, J. Am. Chem. Soc., 2002, 124, 12930. [2] E.R. Choban, J.S. Spendelow, L. Gancs, A. Wieckowski, and P.J.A. Kenis, Electrochim. Acta, 2005, 50, 5390; J. L. Cohen, D.J. Volpe, D.A. Westly, A. Pechenik, and H.D. Abruna, Langmuir, 2005, 21, 3544. [3] R.S. Jayashree, L. Gancs, E.R. Choban, A. Primak, D. Natarajan, L.J. Markoski, and P.J.A. Kenis, J. Am. Chem. Soc., 2005, In press