7.02.2016

Bismuth vs Copper as anode in air battery or fuel cell

Copper seems to be marginally better than bismuth as an anode in an air battery or fuel cell.  In my 37% HCL test cell a copper rhenium cell using a little hydrogen peroxide in the cathode gave 1.27v whereas a Bismuth rhenium cell gave 1.24v.  Higher voltages for both were seen with Iridium as the cathode, but the results were inconsistent since my piece of iridium was small, but the voltages were both around 1.45v so iridium is the best cathode but rhenium is easier to test because the inexpensive nature of the metal.

It seems that copper is the best anode in any "new millennium" type of electrochemical cell including fuel cells and wet solar cells.

However the difference is so small that the issue could have been that the bismuth is less conductive which may be why copper scored better.  Bismuth and germanium *should* beat copper but in practice they don't.  But perhaps copper plated with germanium and/or bismuth may beat plain copper because the electrochemical difference from the cathode would be better theoretically and the resistance would be small because the plating layer is very thin.

Resistivities:
Bismuth 1.29 micro ohms per meter
Germanium 1 ohm per meter
Copper 16.78 nano ohms per meter

In conclusion copper may only be better than germanium and bismuth as an anode material because of lower resistance.  Anodes plated in bismuth and/or germanium still need to be tested to see if they can beat a copper anode.  Ideally the anode may be silver (most conductive metal) plated with germanium to achieve greatest voltage.  In practice a method would likely be silver and/or copper plated with bismuth which may or may not be then plated with germanium.  The problem might arise as the anode may slowly be dissolved as the cell discharges (and could be re-plated back during recharge) so in practice a usable amount of bismuth (and/or germanium) on the anode may increase the resistance of the anode so much that the benefit above a purely copper anode might be nullified.  

As far as cathodes are concerned Iridium is the best metal for an air/peroxide or fuel cell and rhenium is quite close and much cheaper than iridium.

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