What is the relationship between the current produced fuel cell, the electrodes and the voltage of a fuel cell?
The electrode materials and the fuel determines the cell voltage.

No current will flow from the cell without an external resistance connected. As the resistance is decreased, the current drawn increases, up to a limit set by the surface area of the electrodes or the amount of fuel being supplied, whichever bites first.

Increasing the limiting parameter, surface area or fuel supply, will increase the limit on the amount of current that can be drawn from the cell.