Where does the Oxygen come from to form Copper oxides. The reactor is presumably full of Hydrogen, so any traces of O2 would quickly be bound into H2O.
Problem is oxidation right after copper plating process. It can be prevented but only in strict handling in inert gas.
In any case I can confirm secondary transition metal is not required to obtain excess heat. Nickel is more than enough. The most says just for COP around 1.2 but it all depends on how efficiently you can work with heat.
Well prepared fuel is able to produce excess heat even during hydrogen desorption but also during loading. When hydrogen is released the EVOs can fill up the reactor. And they immediately react with all nearby elements while it can live there for very long time.
From years of our experience EVOs can exist even when Hydrogen is not present and even when reactor is open.
We still dont know how to treat them but we know it is extremely reactive and is causing transmutation to all nearby elements even with no input energy.
Experiments that were running for long time have higher chance for generating excess heat. That is because when you will leave such Mesh or other fuel running for long time in hydrogen atmosphere at right pressure they are generated all the time. With high surface area, high hydrogen flux the chance is highest.
For better imagination I am attaching plots from our early experiments from I think 2016. Here you can see that only one element is enough. And that even with so small amount of fuel you can see heat after death. And that it can work well even with Protium. This is what can be achieved with any transition metal after proper processing. Plot contains processed and unprocessed fuel temperature and corresponding pressure curve.