Measuring the EMF of an electrochemical cellWatch
that's for the top bit that is connected to the circuit - and if you're talking about the immersed electrode - then same applies - needs to be clean to maximise surface area and have an unpolluted electrolyte
at CERN we used to often clean in beam tube electrical components with paper & alcohol, then cleaned them in an oven pyrolitically, then plasma cleaned, then pumped down to UHV whilst baking in-situ at around 400 celsius. All preparation for this was done with a desk covered with a fresh sheet of alcan/bacofoil, the cleanest thing around in many labs.
in fact, I'll go further, adding religion to particle physics , quoting the famous Austro/Swiss/US physicist, Wolfgang Pauli (nobel prize winner),
“God made the bulk; the surface was invented by the devil.”
Pauli explained that the 'evil' characteristic of surfaces was due to the fact that a solid surface shares its border with the external world, and all sorts of things are happening at the macro, micro, nano and femto scale on that border!