Thermionic converter and methods of making and using same
Provided herein are thermionic converters that are capable of operating at lower temperatures and with increased efficiency as compared to conventional thermionic converters. Also provided are methods of using and making the thermionic converters of the disclosure.
1. A thermionic converter, comprising:
a collector;
an emitter;
a gap disposed between the collector and the emitter;
an electrical connection means connecting the collector and the emitter; and,
cesium disposed in the gap adjacent the emitter,
wherein:
the emitter comprises a cold worked metal substrate capable of emitting electrons when heated to temperatures of 800° C. or greater,
the cold worked metal substrate is cold rolled in the direction of grains of a target crystallographic orientation having the lowest surface energy and highest bare work function;
the grains of the target crystallographic orientation are thermally grown such that the grains of the target crystallographic orientation represent at least 40% of the surface area of the metal substrate; and
the grains of the target crystallographic orientation are etched to form a patterned surface, thereby increasing the surface area on a face of the grains.
2. The thermionic converter of claim 1 , wherein the emitter and/or collector comprises one or more of iron, nickel, thorium, tungsten, niobium, tantalum, iridium, rhenium, molybdenum, mixtures, and alloys thereof.
3. The thermionic converter of claim 1 , wherein the metal substrate is:
(a) tungsten or niobium, and the target grains have a or crystallographic orientation; or,
(b) molybdenum, and the target grains have a [110] crystallographic orientation.
4. The thermionic converter of claim 1 , wherein the surface area on a face of the etched target grains is at least 2 orders of magnitude greater than the surface area on a face of the heat grown target grains prior to etching.
5. The thermionic converter of claim 1 , wherein the emitter and/or the collector is free of at least one of a thermionic coating and a dopant.
6. The thermionic converter of claim 1 , wherein the emitter has a work function of about 1.5 eV to about 2.0 eV.
7. The thermionic converter of claim 1 , wherein the collector has a work function of about 0.8 eV to about 1.2 eV.
8. The thermionic converter of claim 1 , wherein the gap is about 20 μm to about 1500 μm.
9. The thermionic converter of claim 1 , wherein the grains of the target crystallographic orientation represent about 40% to about 50% of the surface of the metal substrate.
10. The thermionic converter of claim 1 , wherein the patterned surface comprises a surface structure comprised of a plurality of pyramidal structures having a fractal distribution, a plurality of hemispherical structures, and/or a plurality of single atomic steps.