The production of hydrogen production via water electrolysis using solid oxide electrolysis cells (SOECs) offers favorable thermodynamics and kinetics, and is considered the most efficient and low‐cost option for hydrogen production from renewable energies. Using a proton‐conducting electrolyte (H‐SOECs) can reduce the operating temperature from beyond 800 to 600 °C or even lower due to its higher conductivity and lower activation energy.
Now, researchers at Idaho National Laboratory have developed a self‐architectured ultraporous (SAUP) 3D steam electrode for efficient proton‐conducting electrolyte (H‐SOECs) below 600 °C. The H‐SOEC with SAUP steam electrode demonstrates excellent performance, promising next‐generation steam electrolysis at reduced temperatures. An open-access paper in the journal Advanced Science details the advances in the production of hydrogen.
We invented a 3D self-assembled steam electrode which can be scalable. The ultrahigh porosity and the 3D structure can make the mass/charge transfer much better, so the performance was better.—Dr. Dong Ding, corresponding author
The researchers demonstrated high-performance electrochemical hydrogen production at a lower temperature than had been possible before. This was due to a key advance: a ceramic steam electrode that self-assembles from a woven mat.
Today, hydrogen is mainly obtained by steam reforming hydrocarbons, such as natural gas. This process, though, requires fossil fuels and creates carbon byproducts, which makes it less suited for sustainable production.
Steam electrolysis, by contrast, needs only water and electricity to split water molecules, thereby generating hydrogen and oxygen. The electricity can come from any source, including wind, solar, nuclear and other emission-free sources. Being able to do electrolysis efficiently at as low a temperature as possible minimizes the energy needed.
Among all the steam electrolysis techniques, solid oxide electrolysis cells (SOECs) at elevated temperatures provide several benefits over low‐temperature electrolysis technologies, including the reduced electricity demand, fast electrode kinetics, and less expensive materials (e.g., Ni rather than Pt) can be used as electrode catalysts.
SOEC is the reversible operation of solid oxide fuel cell (SOFC), and can be divided into two categories due to the different types of the electrolyte: the oxygen ion‐conducting SOECs (O‐SOECs) and the proton‐conducting SOECs (P‐SOECs).
… P‐SOEC … are able to operate at lower temperatures due to the higher ionic conductivity of proton‐conducting electrolytes compared with that of oxygen ion‐conducting electrolyte at reduced temperatures. In addition, P‐SOECs produce pure and dry H2 only at hydrogen electrode side since the proton‐conducting electrolyte is nonpermeable to both oxide ions and molecular gases at low temperatures.As nickel is widely used in the hydrogen electrode for SOECs, P‐SOECs can prevent the Ni oxidation at high steam concentration, which is one of the reasons for performance degradation in O‐SOECs. Therefore, for these advantages toward traditional O‐SOEC, P‐SOECs have gained much attention in recent years.—Wu et al.
A P-SOEC has a porous steam electrode, a hydrogen electrode and a proton-conducting electrolyte. When voltage is applied, steam travels through the porous steam electrode and turns into oxygen and hydrogen at the electrolyte boundary. Due to differing charges, the two gases separate and are collected at their respective electrodes.
The construction of the porous steam electrode is critical. The researchers started with a woven textile template, put it into a precursor solution containing elements they wanted to use, and then fired it to remove the fabric and leave behind the ceramic. The result was a ceramic version of the original textile.
They put the ceramic textile in the electrode and noticed that in operation, bridging occurred between strands. This should improve both mass and charge transfer and the stability of the electrode, according to Dr. Wei Wu, the primary contributor to this work.
The electrode and the use of proton conduction enabled high hydrogen production below 600 ˚C. That is cooler by hundreds of degrees than is the case with conventional high-temperature steam electrolysis methods. The lower temperature makes the hydrogen production process more durable, and also requires fewer costly, heat-resistant materials in the electrolysis cell.
At 600 °C, the electrolysis current densities reaches −2.02 A cm−2 at 1.6 V. Constant activation was observed during long‐term electrolysis at applied voltage of 1.6 V at 500 °C. Our approach suggested a great prospective strategy of developing high‐performance SOECs at reduced temperature.—Wu et al.
W. Wu, H. Ding, Y. Zhang, Y. Ding, P. Katiyar, P. K. Majumdar, T. He, D. Ding (2018) “3D Self‐Architectured Steam Electrode Enabled Efficient and Durable Hydrogen Production in a Proton‐Conducting Solid Oxide Electrolysis Cell at Temperatures Lower Than 600 °C” Adv. Sci. doi: 10.1002/advs.201800360