The opening focuses the electrons emitted from the cathode onto the anode to a spot size preferably less than 40 nanometers.
Most fuel cells use a polymer electrolyte membrane to separate the cathode and anode.
Those same ions would then flow to the cathode , and after electrons were added, would end up as pure copper.
Therefore, in electrolytic cells, the cathode is the negative terminal and the anode is the positive terminal.
An electron originating near the planar cathode and ultimately collected at electrode A will induce an equal charge at A and B during most of its journey.
Oxygen enters at the cathode , where it combines with electrons and is split into ions that travel through the electrolyte to react with fuel at the anode.
The electrons on the anode migrate via a wire to the cathode , the other electrode in the fuel cell, where they are electrochemically assisted to combine with the protons and produce hydrogen gas.
But because electrons must be supplied to the cathode by an external power source to drive this process, the cathode in an electrolytic cell has a negative charge.
The trouble with the fuel cell is that it requires a barrier between the anode and the cathode because the oxidizing and reducing agents will corrode catalytic elements if allowed to intermix.
Stainless steels are positioned towards the cathodic end of the galvanic series in seawater.