# US 2021/0242003 A1 · Thermionic converter and methods of making and using same

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- Number: US 2021/0242003 A1
- Document ID: US20210242003A1
- Status: Published application
- Kind: A1
- Application number: 16/783,105
- Filed: 2020-02-05
- Published: 2021-08-05
- Earliest claimed: 2020-02-05
- Assignees: Uchicago Argonne, LLC
- Applicants: Uchicago Argonne, LLC
- Inventors: Abdellatif M. Yacout; Sumit Bhattacharya
- Web page: https://patentgrep.com/patent/US20210242003A1

## CPC

- H01J 45/00: Discharge tubes functioning as thermionic generators {(structural combination of fuel element with thermoelectric element G21C3/40; nuclear power plants using thermionic converters G21D7/04; structural combination of a radioactive source with a thermionic converter, e.g. radioisotope batteries G21H1/10; generators in which thermal or kinetic energy is converted into electrical energy by ionisation of a fluid and removal of the charge therefrom H02N3/00)}
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)

## Abstract

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.

## Claims

### Claim 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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 1)

The thermionic converter of claim 1, wherein the metal substrate is:
(a) tungsten or niobium, and the target grains have a [110] or [100] crystallographic orientation; or,
(b) molybdenum, and the target grains have a [110] crystallographic orientation.

### Claim 4

(canceled)

### Claim 5

(canceled)

### Claim 6 (depends on 1)

The thermionic converter of claim 1, wherein the emitter has a work function of about 1.5 eV to about 2.0 eV.

### Claim 7 (depends on 1)

The thermionic converter of claim 1, wherein the collector has a work function of about 0.8 eV to about 1.2 eV.

### Claim 8 (depends on 1)

The thermionic converter of claim 1, wherein the gap is about 20 μm to about 1500 μm.

### Claim 9 (depends on 1)

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.

### Claim 10

(canceled)

### Claim 11 (depends on 1)

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.

### Claim 12

(canceled)

### Claim 13

(canceled)

### Claim 14 (depends on 1)

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.

### Claim 15

(canceled)

### Claim 16 (depends on 1)

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.

### Claim 17

(canceled)

### Claim 18 (depends on 1)

A method of converting heat into electricity comprising: providing the thermionic converter of claim 1; and exposing the emitter to a heat source, wherein the temperature of the heat source is at least 800° C.

### Claim 19

A method of making an emitter for a thermionic converter, comprising:
heat treating a cold worked metal substrate, the cold worked metal substrate being cold rolled in the direction of grains having a target crystallographic orientation having the lowest surface energy and highest bare work function, wherein the cold worked metal substrate is heat treated under conditions to grow the grains having the target crystallographic orientation while maintaining intrinsic stress in the grains resulting from the cold rolling; and
etching the heat treated metal substrate by immersing the heat treated metal substrate in an etchant, wherein faces of the grains having the target crystallographic orientation preferentially etch.

### Claim 20 (depends on 19)

The method of claim 19, wherein the cold worked metal substrate is heat treated at a temperature of at least about 800° C.

### Claim 21

(canceled)

### Claim 22 (depends on 19)

The method of claim 19, wherein the cold worked metal substrate is heat treated for about 1 hour to about 15 hours.

### Claim 23 (depends on 19)

The method of claim 19, wherein the etchant comprises methanol, oxalic acid, hydrogen peroxide, perchloric acid, sulfuric acid, hydrofluoric acid, ammonium hydroxide, hydrochloric acid, formic acid, or any combination thereof.

### Claim 24

(canceled)

### Claim 25 (depends on 19)

The method of claim 19, wherein the heat treated metal substrate is etched at a temperature of at least about 40° C.

### Claim 26

(canceled)

### Claim 27 (depends on 19)

The method of claim 19, wherein the heat treated metal substrate is etched at an etching voltage of about 0.1 V to about 30 V.

### Claim 28 (depends on 19)

The method of claim 19, wherein the heat treated metal substrate is immersed in the etchant for about 10 minutes to about 45 minutes.

### Claim 29 (depends on 19)

The method of claim 19, further comprising immersing the cold worked metal substrate in a first cleaning solution prior to heat treating the metal substrate and/or in a second cleaning solution prior to immersing in the etchant.

### Claim 30

(canceled)

### Claim 31 (depends on 29)

The method of claim 29, wherein the first cleaning solution and/or second cleaning solution comprises NaOH, KOH, or a mixture thereof.

### Claim at position 32

-38. (canceled)