It should be electric potential energy. E = W = UABQ = (φ A-φ B) Q Capacitance C=εS/d=S/4πkd (vacuum) = q/u.

EMF E = W/Q (E is EMF) In the ohm's law of closed circuit, the EMF formula E = IR+IR (this only applies to pure resistance circuits) E = internal U+ external U.