Science Buddies: "Ask an Expert"

I am currently doing a science fair project on fuel cell efficiency. However, I can't get the right formulas together to find the efficiency.
According to my research, I have to do delta G divide by delta H then times 100 to get the percentage. My problem is how to find delta h and delta g
with variable temperature and voltage. I don't know if I should use the set values for these pieces of data at 25C for the equations, dH=mcdT to find delta h and dG=dH-TdS .
Thanks for the help.

Hello technoaaron,

What are you using to fuel you fuel cell? And, what is your fuel cell powering? If you can describe your fuel cell in more detail, we will be better able to help you. Efficiency is the ratio of the useful output energy to the input energy, so you should be able to calculate the fuel cell's efficiency without resorting to Gibb's equation. But, we will need more details (including the answers to the questions I asked above) to help you do so.