Thermo-charged capacitors and the Second Law of Thermodynamics

In this paper we describe a simple vacuum spherical capacitor able to generate a macroscopic voltage between its conductors out of a single thermal source at room temperature: it is a sort of thermo-charged capacitor. The basic idea is trivial and it makes use of two cathodes with different work functions: an inner cathode with work function φ . 1 eV (for example the photo-cathode Ag–O–Cs with φ . 0.7 eV), and an external cathode with φ > 1 eV. In our approach we provide a mathematical analysis of the physical process and discuss its implications and connections with the Second Law of Thermodynamics. PACS (2008): 79.40.+z, 67.30.ef, 65.40.gd, 84.32.Tt