Solid oxide electrolysis cell (SOEC) has the potential to be cost-effective, environmentally friendly, and highly efficient for the production of hydrogen from water. There are two types of SOECs, based on the electrolyte materials: oxygen ion conducting SOECs (oxygen-SOECs) and proton conducting SOECs (proton-SOECs).
Researchers in South Korea, with colleagues at Georgia Tech, have now developed an SOEC based on a mixed-ion conductor that can transport both oxygen ions and protons at the same time; they call it a “Hybrid-SOEC”. In a paper in the journal Nano Energy, the researchers reported that the hydrogen yield from their Hybrid-SOEC was 1.9 L per hour at a cell voltage of 1.5 V at 700 °C—four times higher hydrogen production efficiency of the existing high-efficient water electrolytic cells.
The proposed system has attracted much attention as a new promising option for the cost-effective and highly-efficient hydrogen production, as it shows excellent performance compared with other water-electrolysis systems, they said.
The work was led by Professor Guntae Kim in the School of Energy and Chemical Engineering at UNIST in collaboration with Professor Tak-Hyoung Lim of Korea Institute of Energy Research (KIER) and Professor Jeeyoung Shin of Sookmyung Women’s University.
An SOEC consists of two electrodes and a solid-state electrolyte; the solid-state electrolyte obviates the need to replenish lost electrolytes, while eliminating corrosion problems. SOECs also operate at relatively high temperatures (700-1000 °C), helping to offer reduced electrical energy consumption.
Existing SOEC electrolytes allow the transport of either only one of the hydrogen or oxygen ions to the other electrode. For SOEC electrolytes that transport oxygen ions, water electrolysis occurs at the anode and this results in the production of hydrogen. The SOEC electrolytes that transport hydrogen ions cause water electrolysis to occur at the cathode and this results in the production of oxygen. Here, hydrogen travels through the electrolyte to the anode.
The Hybrid-SOEC concept is based on the mixed ionic conducting electrolyte, allowing water electrolysis to occur at both hydrogen and air electrodes.
Theoretically, using electrolytes that transport both hydrogen and oxygen ions allows the production of two electrolysis products—hydrogen and oxygen—on both sides of the cell. This could improve hydrogen production rate greatly. In the study, the research team focused on the control of properties of electrolytes.
In comparison to other SOECs and representative water-electrolysis devices reported in the literature, the proposed system demands less electricity for hydrogen production, while exhibiting outstanding electrochemical performance with stability. Moreover, the Hybrid SOEC exhibits no observable degradation in performance for more than 60 hours of continuous operation, implying a robust system for hydrogen production.
By controlling the driving environment of the hydrogen ion conductive electrolyte, a mixed ion conductive electrolyte in which two ions pass can be realized. In Hybrid-SOEC where this electrolyte was first introduced, water electrolysis occurred at both electrodes, which results in significant increase in total hydrogen production.—Junyoung Kim, lead author
Junyoung Kim, Areum Jun, Ohhun Gwon, Seonyoung Yoo, Meilin Liu, Jeeyoung Shin, Tak-Hyoung Lim, Guntae Kim (2017) “Hybrid-solid oxide electrolysis cell: A new strategy for efficient hydrogen production,” Nano Energy, Volume 44, Pages 121-126 doi: 10.1016/j.nanoen.2017.11.074