A nanofluid contact potential difference cell includes a cathode with a lower work function and an anode with a higher work function separated by a nanometer-scale spaced inter-electrode gap containing a nanofluid with intermediate work function nanoparticle clusters. The cathode comprises a refractory layer and a thin film of electrosprayed dipole nanoparticle clusters partially covering a surface of the refractory layer. A thermal power source, placed in thermal contact with the cathode, to drive an electrical current through an electrical circuit connecting the cathode and anode with an external electrical load in between. A switch is configured to intermittently connect the anode and the cathode to maintain non-equilibrium between a first current from the cathode to the anode and a second current from the anode to the cathode.