I watched a video yesterday that had Mats Lewan (a Rossi believer and reporter for NY Teknik) say that inside the reaction chamber, the reactants were the same size as a potato.To the very best of my knowledge, no one has seen the inside of an E-Cat reactor other than Rossi. What Rossi has occasionally shown was the inside of an external box that held the reactor.
I wouldn't argue with "potato-sized" description of the volume of the original E_Cat. Here is a picture of it (the reactor is the "lump" in the middle):
Assuming that's a metric scale, it appears to be about 6 cm (2.5 in) wide.
I assume, the nickel reactant is a spongy material so it has the maximum area to react with.Again, to the best of my knowledge, no one other than Rossi has seen the "catalyst". Rossi has stated that it contains Nickel, which he has "enhanced" to increase certain isotopes (apparently another revolutionary breakthrough, since enriching specific isotopes in gram or kilogram quantities is a major industrial process). I have heard it described as a powder, but I have no idea if that originated with Rossi or with one of his minions.