Electrochemical cells for hydrogen gas production and electricity generation, and related systems and methods

1. An electrochemical cell, comprising:

a first electrode comprising a three-dimensional nanofiber-structured mesh of Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ ,

wherein 0≤x≤0.9, 0≤y≤0.9, 0≤z≤0.9, and δ is an oxygen deficit,

the three-dimensional nanofiber-structured mesh of Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ including multiple tows of nanofibers of the Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ interweaved together,

at least one of the multiple tows of nanofibers of the Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ being substantially hollow;

a second electrode comprising a cermet material including at least one metal and at least one perovskite; and

a proton-conducting membrane between the first electrode and the second electrode.

2. The electrochemical cell of claim 1 , wherein the first electrode comprises PrNi 0.5 Co 0.5 O 3-δ .

3. The electrochemical cell of claim 1 , wherein the first electrode is substantially free of ions of rare-earth elements.

4. The electrochemical cell of claim 1 , wherein the second electrode comprises a nickel/perovskite cermet.

5. The electrochemical cell of claim 1 , wherein the second electrode comprises a cermet comprising nickel and a yttrium- and ytterbium-doped barium-zirconate-cerate (BZCYYb).

6. The electrochemical cell of claim 1 , wherein the proton-conducting membrane comprises one or more of a yttrium- and ytterbium-doped barium-zirconate-cerate (BZCYYb), a yttrium- and ytterbium-doped barium-strontium-niobate (BSNYYb), a doped BaCeO 3 , a doped BaZrO 3 , Ba 2 (YSn)O 5.5 , and Ba 3 (CaNb 2 )O 9 .

7. The electrochemical cell of claim 1 , wherein:

the proton-conducting membrane comprises BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3-δ ;

the first electrode comprises PrNi 0.5 Co 0.5 O 3-δ ; and

the second electrode comprises Ni—BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3-δ .

8. The electrochemical cell of claim 1 , wherein a through hole extending throughout a length of the at least one of the multiple tows of nanofibers of the Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ has a diameter within a range of from about 1 μm to about 5 μm.

9. A system for H 2 gas production and electricity generation, comprising:

a source of steam; and

an electrochemical apparatus in fluid communication with the source of steam, and comprising:

a housing structure configured and positioned to receive a steam stream from the source of steam; and

an electrochemical cell within an internal chamber of the housing structure, and comprising:

an electrode positioned to interact with the steam stream and comprising a three-dimensional mesh of Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ ,

wherein 0≤x≤0.9, 0≤y≤0.9, 0≤z≤0.9, and δ is an oxygen deficit,

the three-dimensional nanofiber-structured mesh of Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ including multiple tows of nanofibers of the Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ interweaved together,

at least one of the multiple tows of nanofibers of the Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ being substantially hollow;

another electrode comprising a metal/perovskite cermet; and

a proton-conducting membrane between the electrode and the another electrode and comprising a perovskite having an ionic conductivity greater than or equal to about 10'S/cm at one or more temperatures within a range of from about 400° C. to about 600° C.

10. The system of claim 9 , wherein the electrochemical cell is configured to switch between an electrolysis mode for producing H 2 gas from the steam stream and a fuel cell mode for generating electricity from the produced H 2 gas at the one or more temperatures within the range of from about 400° C. to about 600° C.

11. The system of claim 9 , wherein:

the electrode comprises PrNi 0.5 Co 0.5 O 3-δ ;

the another electrode comprises Ni—BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3-δ ; and

the proton-conducting membrane comprises BaCe 0.7 Zr 0.1 Y 0.1 Yb 0.1 O 3-δ .

12. A method of generating electricity, comprising:

introducing steam to an electrochemical cell comprising:

a first electrode comprising a three-dimensional nanofiber-structured mesh of Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ ,

wherein 0≤x≤0.9, 0≤y≤0.9, 0≤z≤0.9, and δ is an oxygen deficit,

the three-dimensional nanofiber-structured mesh of Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ including multiple tows of nanofibers of the Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ interweaved together,

at least one of the multiple tows of nanofibers of the Pr(Co 1-x-y-z , Ni x , Mn y , Fe z )O 3-δ being substantially hollow;

a second electrode comprising a metal/perovskite cermet; and

a proton-conducting membrane between the first electrode and the second electrode;

applying a first potential difference between the first electrode and the second electrode of the electrochemical cell to produce H 2 gas from the steam; and

applying a second potential difference between the first electrode and the second electrode of the electrochemical cell to generate electricity using the produced H 2 gas as a fuel.

13. The method of claim 12 , wherein applying a first potential difference between the first electrode and the second electrode comprises operating the electrochemical cell in electrolysis mode to decompose the steam at the first electrode and produce the H 2 gas at the second electrode.

14. The method of claim 12 , wherein applying a second potential difference between the first electrode and the second electrode comprises operating the electrochemical cell in fuel cell mode to decompose the produced H 2 gas at the second electrode and produce H 2 O at the first electrode.

15. The method of claim 12 , wherein:

applying a first potential difference between the first electrode and the second electrode comprises applying the first potential difference at a temperature within a range of from about 400° C. to about 600° C.; and

applying a second potential difference between the first electrode and the second electrode comprises applying the first potential difference at the temperature within the range of from about 400° C. to about 600° C.