Application of Series/Parallel connection of DMFC? (Direct Methanol Fuel Cell)

[0Rion]

Hello,

Just as the title asks, what sort of applications would series and parallel connections of Direct Methanol Fuel Cell suit the best? Based from my understanding of Fuel Cells and experimental results, one cell is not enough to power anything, hence they are used in stacks, in addition series connection provided more voltage, whereas parallel gave more current. Moreover, power density peak was reached in a shorter amount of time in parallel connection vs. series, where it took longer (polarization curve). Any ideas where one connection might be preferable to another? (DMFCs are typically used in commercial sectors I believe).

Thanks!

 

[0Rion]

Hello,

To anyone still interested in this topic, even though I haven't gotten any replies associated with the above said question and to correct previous assessments,
Series Connection of the DMFC resulted in increased voltage and reaching maximum power output in a much shorter period of time. Series connection then, would play a significant role in charging and running smaller types of electronics and amplifiers. Parallel Connection on the other hand resulted in increased current output, taking more time in reaching the maximum power level when compared to the series connection. Parallel connection would then suit appliances such as motors and actuators (forklifts, airport tug-vehicles, pneumatic and piezoelectric actuators, relays, thermal bi-morphs). Hope anyone still finds this information useful.

 

[That Neuron]

Hi Orion!
I've actually recently been starting to build a micro-DMFC stack for portable electronics of my own.

From my understanding, each cell, when no current is moving through an external circuit, produces a given OCP (Open Circuit Potential) that is a little less than its theoretical (usually about 0.6-0.8 V) potential due to catalyst kinetics, methanol crossover, proton resistance through the membrane and such.

When you hook the cell up to a given potential drop, say a battery or DC-DC converter, if the potential drop is less than the OCP (say 0.5V) then the extra over potential will drive more reaction and raise the current density of the cell, hence the polarisation curve.

So, let's say that you're trying to power something with 4V of potential, you could hypothetically hook up 6 cells in series (Call the OCP of the cells 0.7 V) and they would together supply 4.2 V at OCP. That 0.2V of over potential is essentially distributed through the cells to drive more reaction, leading to an increase in current density. So now, on the polarisation curve, each cell is actually making 0.66 V at whatever current density the polarisation curve gives.

Normally, in these sorts of situations, the voltage is set by arranging that many cells in series or whatnot and the current density varies based on it.

Hope this clears all that up. I'm still a tiny bit sketchy on these counterintuitive polarisation curves myself.

Feel free to shoot me a message some time regarding research into DMFCs (michael-james.olsen@students.mq.edu.au). It's a lonely world right now.