Since iron-iron WE (iron rod plated with iron) does not provide any LEC voltage it appears that the double layer between two different metals is key to provide the observed
This is not yet proven to be the case, being subject to ongoing studies, although double-plating brass (iron plated on top of iron plate) has not so far yielded good results, no 'null' but sub 100mV. I have just taken delivery of some zinc and titanium sheet, since I am interested in expanding the materials research side of things, and also like Stevenson looking again at Frank's own plating methods.