Before he gets the DARPA funding he can buy an old CRT TV set. It contains two electrodes and an electric field between them. When the field is large enough (25 kV in a TV) electrons leave the cathode and fly to the anode, closing the circuit. The cathode is heated to facilitate emission of electrons, but it is not strictly required - see Neon lamps. This puts the top limit on the voltage of his capacitor even if we assume that there is no leakage anywhere else. All the discussion about how to use FETs to measure this or that has no bearing on storage of energy.
That’s my take also. This article is much more about a memory device than about some major increase in energy density.
Unless it proves the existence of "global warming" it won't receive any funding.