# Hydrogen fuel cells in small applications

1. Sep 18, 2016

### Pogona

Hello internet!

Please excuse any silly questions as I am not (obviously) a professionally educated physicist (yet!).

I was doing a school project on alternative energy sources and became rather interested in hydrogen fuel cells, specifically to replace batteries in small scale, high energy requirement situations such as drones. I know that we can make them very small (see https://www.newscientist.com/article/dn16370-worlds-smallest-fuel-cell-promises-greener-gadgets/) however these micro-cells run at very low voltages and currents. Is there any way of calculating/roughly working out how big a fuel cell has to be to produce a certain voltage and/or current? (of course the size of the hydrogen fuel tank would not be taken into consideration here. Assume that there is an external hydrogen supply.) Also does anybody know of a way to calculate how much energy you can get from a certain volume of hydrogen, or how long a certain volume would last if it were being used to make a constant electrical current of x amps at y volts?

Thanks in advance for any insight you can offer!

2. Sep 18, 2016

### Bystander

~100 A/m2.

3. Sep 18, 2016

### Pogona

Could you possibly add an explanation to go with that equation?
I'm guessing it means approximately 100 Amps per m^2 of the surface area of the electrodes (according to this source: http://www.mpoweruk.com/hydrogen_fuel.htm).

Last edited: Sep 18, 2016
4. Sep 18, 2016

### Bystander

"power outputs are about 1 Watt /cm2" ... Looks like I gave you a "lowball" estimate for current output; 0.5 V x 20,000 A = 10 kW. My "bad." Based that on my experience with electropolishing (100 mA/cm2 max) and anodizing (10 mA/cm2 max).

5. Sep 24, 2016

The issue with fuel cells ( esp for a drone) is referred to as their BOP; or balance of plant. Basically all of the auxiliary equipment and systems needed to make it run well and reliably. For any high performance vehicle, and to me a Drone is that, Fuel Cells are not well suited where you want simple, effective and responsive power. For less dynamic loads - buses, fork trucks there have been some pretty good solutions with fuel cells. For fuel cells think low and slow - but the efficiency of conversion is very good.

For hydrogen fueled drones - combustion is the answer. It is very versatile fuel, high energy and can be used in Internal Combustion or Turbine set ups - and still minimal to zero environmental impact ( depending on how you source the H2)

Edit - BTW - and again my opinion, for a school project, detailing what you wanted to do ( Apply a fuel sell to a Drone) and why you learned and accepted that it is maybe not the best idea - and you decided to do "X" differently is a very good report strategy. In the real world I have seen more projects and careers sunk by people so "locked in" to their original ideal and plan - they could never accept, or admit, that their original premise was just wrong. - Humility leads to success and arrogance kills.

6. Sep 24, 2016

### CraigHB

Hydrogen fuel cells output about 700mV per cell so you need a "stack" to produce higher voltages. In terms of current there's the internal resistance of the generator to consider and the plate area required to deliver a particular current. That's already been indicated.

In terms of multi-rotor drones they usually require pretty high burst currents which as already stated is not something fuel cells are particularly well suited for. It would be possible to combine a high drain Li-Ion battery with a fuel cell to provide the burst currents required. However weight is always a big consideration with aircraft and the higher weight of a fuel cell system compared to a battery may be somewhat impractical.

7. Oct 3, 2016

### Pogona

Sorry I didn't reply sooner but my internet has been down for almost two weeks! I followed Windadct's advice for using the hydrogen fuel for combustion instead and got full marks!