Elaborate and you'll find the issue with this setup.

Zinc can do this too. But I like silver, its oxide has decent conductivity.

One of the common arrangements on a basic two-electrode sensor is to have one gold electrode to make contact with the electrolyte, and the electrolyte provides conductivity to a sacrificial silver electrode. With electrolyte exposed to the atmosphere through an oxygen-permeable membrane.

As oxygen makes its way through the membrane, it is consumed by the silver at a steady rate and equilibrium is achieved relative to how much oxygen is in the atmosphere. This generates a steady current which is amplified to move a needle on a gauge, where there are knobs to adjust the meter until it displays the correct amount of oxygen during calibration against a known concentration. And must also be calibrated to display zero when there is no oxygen.

Eventually even if the membrane never gets fouled the oxidized silver builds up in the electrolyte chamber and response deteriorates so maintenance is needed. Remove the membrane, polish the silver, put in fresh electrolyte, new membrane, and re-calibrate.

Adding a third electrode opens up a number of further possibilities.

One of them is the option to use an additional inert gold or platinum contact or a salt bridge as electrical reference against the original gold or silver as the sensor. Plus using a more complex circuit than a plain amplifier, apply controlled responsive current to the sacrificial silver at the same time. So rather than directly amplifying the current produced by different concentrations of oxygen existing in the electrolyte (and waiting for it to equilibrate), instead with 3 (or 4) electrodes the ionic silver concentration in the electrolyte can be maintained electronically in a steady state, and as oxygen permeates, the current required to replace the consumed silver is designed to make a dfferent kind of meter move the needle the same way as above. In this way the oxygen concentration in the electrolyte varies to a much more limited extent compared to waiting for it to be depleted from a high amount to zero before the meter will bottom out.

This can be equivalent to constant-ion electrochemical titration.

Disclaimer: I always like to handle things like this like lives depended on it, because lives depended on it.

The big gain comes from a change in how you interpret the presence of electrons.

The older approach converted oxygen to electrical current, the magnitude of current flow relating to magnitude of oxygen depletion. The assumption built into that approach is that low oxygen depletion levels meant low oxygen levels, but that wasn't the only potential cause, because it ignored variation in the permiability of the membrane.

The newer approach equates current flow to oxygen concentration, as the system doesn't deplete the concentration any longer. The permiability of the membrane in this setup only contributes to a longer initial delay as the inner chamber comes to equilibrium with the surrounding concentration.