Inverse tunneling of electrons in field emission heat engines

The field emission heat engine (FEHE) is a novel thermionic converter with strong electric fields applied on the anode and/or cathode, to set up quantum tunneling barriers, so that electrons with energies lower than the surface vacuum level can still escape the cathode, transit the vacuum gap, and `inverse tunnel´ into the anode [1]. Notably, by lowering the effective work function of just the anode with electric fields, we can linearly increase the thermodynamic efficiency, and exponentially increase the power density of any thermionic converter. We model that a single-grid FEHE with only the anode electric field could reach efficiencies >60% of Carnot across a wide range of temperatures, with power densities on the order of 100 W/cm². We perform experiments to demonstrate inverse tunneling, i.e. the quantum tunneling of free vacuum electrons through a potential barrier into a solid.