Thermo-charged capacitors and the Second Law of Thermodynamics

In this Letter we describe a vacuum spherical capacitor that generates a macroscopic voltage between its spheres harnessing the heat from a single thermal reservoir at room temperature. The basic idea is trivial and it makes use of two concentric spherical electrodes with different work functions. We provide a mathematical analysis of the underlying physical process and discuss its connections with the Second Law of Thermodynamics.