Explaining electrical quantities for a fuel cell

[deleted-306866]

Hello,

I was using a Proton Membrane Exchange Fuel Cell (PEMFC) to learn more about electricity and research. This fuel cell is a reversible fuel cell, so I used it both to electrolyze water, and to synthesize it back together. I understand the chemistry behind it, but I am a little confused about the physical analysis.

I recorded the voltage across the fuel cell and across a resistor at different temperatures during the spontaneous generation of water (so energy was given off by the fuel cell). I found that as temperature increased, the average voltage across the fuel cell decreased and the average voltage across the resistor increased (slightly). The current also increased slightly as temperature increased.

I'm confused because I don't know how to explain why the voltage decreased. I know that resistance will increase with increasing temperature, but will that decrease the current or increase the voltage, or both (nothing seems to be held constant in V = IR).

I thought that the increased temperature would increase the voltage because there will be a large difference in electromagnetic potential with a larger resistance, but that didn't really happen.
I might have just used too few trials (I tested about 8 times), or measured something wrong, but I would like some advice on if this makes sense.

Any help would be much appreciated,
Thank you!