Coaxial metal disks counter-rotating through an axial magnetic field would have opposite radial currents due to the Lorentz force. Therefore they would become oppositely charged. Although the voltage of Faraday disks is small, the current is large (they are used for rail guns and welding), so across the gap between the disks would be a high electric field. Since the disks are both spinning, incipient arc ends would be continuously pulled apart so power density would not erode the disks. Electrical and mechanical energy in large amounts could be coupled into the molecules between the disks by this dynamic capacitor. The electric field holds them, and the shear tears them apart.

They would accumulate no net charge; the current flow is from the electrons already in the disk.

Yes, radial intra-disk charge separation results from the Lorentz force acting oppositely on the positive and negative free charges that are already present. There would also be inter-disk charge separation across the space between the peripheries of the disks (due to the counter-rotation), so some charges from disk A might pass to disk B through that space once the setup becomes a dynamic capacitor.

Edited July 25, 201114 yr by Wilmot McCutchen