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All descriptions of a Hydrogen fueled fuel cell (such as this one) Start with $H_2$ giving up its electrons to a platinum coated anode. Then the $H^+$ ions (protons really) travel through the electrolyte where they find $O_2$ and the $e^-$ they had previously given up at a platinum-coated cathode. At the cathode, these components come together with a sigh of exothermic relief and $H_2O$ drips out.

I have no sense at all what DRIVES the cell. I am guessing that somehow in some context the $H_2$ giving up its electrons to the platinum anode is energetically favorable, but I can't for the life of me think of how pulling electrons away from protons would be favorable.

So what I really want here is to understand what the forces or pseudo-forces are that drive a Fuel Cell. What drives $H_2$ to give up its electrons to the platinum anode?

Any helpful directions to figuring this out would be appreciated.

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2 Answers 2

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H2 + O2 is exothermic. That drives the fuel cell. Platinum adsorbs H2 and O2. This means it "sticks" those atoms to it so that the offering and accepting of electrons is made easier. This presenting of atoms must have an energy cost and so weakens the diatomic bonds otherwise keeping respective H2 and O2 molecules bound. That is why heterogeneous catalysts work. But what about the structure of Pt and similar metals allows them to adsorb so well I believe remains less well understood.

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Every picture I see does NOT show H or H2 being adsorbed on the platinum anode, but rather the electron from the H going in to the platinum anode and the $H^+$ running away from the platinum so it can diffuse across the membrane and show up at the cathode. –  mwengler Apr 30 at 7:06

Why does the platinum take an electron from the hydrogen? Remember that this happens in a fuel cell, where the other electrode loses electrons to O2. The platinum is effectively only an intermediary. It's a metal, so there are a lot of electrons which are not bound to one specific atom. O2 can easily steal one of those, which would leave the platinum positively charged. Hydrogen in turn loses its electrons to the now-charged platinum.

So, in effect platinum is just an electron carrier between hydrogen and oxygen.

So, what drives this? Well, let's remove the platinum intermediate from the reaction. We already know it's energy-efficient for hydrogen to donate its electrons to oxygen to form water, that's precisely why hydrogen is so flammable. But without the platinum intermediate, the energy from the electron transfer is released uncontrollably - fire, heat, light.

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