Review of Direct Methanol Fuel Cells

Abstract

Direct Methanol Fuel Cells (DMFCs) are galvanic electrochemical flow systems that convert chemical energy from methanol and oxygen directly to electrical energy. This direct conversion avoids the limitations of the Carnot cycle that constrains the performance of engines and gives DMFCs a higher theoretical efficiency. DMFCs were first investigated in the 1950’s and research on these systems had a renaissance in the 1990’s with the advent of Nafion® use for fuel cell applications.^1–3 DMFCs are akin to Proton Exchange Membrane Fuel Cells (PEMFCs) with the main difference being that DMFCs oxidize methanol (1) on the anode to produce protons while PEMFCs oxidize hydrogen (2) to produce protons:

$$ CH_3 OH + H_2 O \to CO_2 + 6H^ + + 6e^ - (E^\circ = 0.02V vs. SHE) $$

((1))

$$ 3 H_2 \to 6H^ + + 6e^ - (E^\circ = 0.00V vs. SHE) $$

((2))

Both DMFCs and PEMFCs reduce oxygen on the cathode according to (3):

$$ \frac{3} {2}O_2 + 6H^ + + 6e^ - \to 3 H_2 O (E^\circ = 1.23V vs. SHE) $$

((3))

This makes the over all,

$$ CH_3 OH + \frac{3} {2}O_2 \to CO_2 + 3 H_2 O (E^\circ _{cell} = 1.21V vs. SHE) $$

((4))

$$ 2 H_2 + O_2 \to 2 H_2 O (E^\circ _{cell} = 1.23V vs. SHE) $$

((5))

The theoretical potentials of both reactions are nearly equal and looking at logistical issues appears to give DMFCs many advantages over PEMFCs and lithium ion batteries.