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INL team develops new electrode for efficient steam electrolysis at reduced temperatures

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.

Resources

  • 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

Comments

Davemart

This would seem to offer good potential for the production of hydrogen from renewables, as the cost of heat is less than electricity, and concentrated solar might provide it.

The use of renewables can be far more optimised in a system involving hydrogen than attempting to go straight from say, solar input to electricity, as the plants can be put in the most favourable locations and the hydrogen produced and transported at any time of the year.

Engineer-Poet
Dr. Dong Ding

<checks calendar>
<see's it's not April 1>

This would seem to offer good potential for the production of hydrogen from renewables, as the cost of heat is less than electricity

It'll help some but not too much.  The enthalpy of steam at 500 C and 10 bar absolute is 3.47 MJ/kg.  Hydrogen is what, 33.7 kWh/kg (121.3 MJ/kg)?  It takes 9x as much water to make it but that's still only about 30-31 MJ/kg of H2.  Most of your input energy still has to be electricity, and that's ignoring losses in electrolysis.  (How much of that 1.6 volts is overvoltage?  I recall a value of about 1.2 volts from somewhere, so that would suggest considerably higher energy input.)

There are no panaceas here.

Engineer-Poet

Hmmm.  It occurs to me that this membrane might find use in fuel cells designed to separate and sequester CO2.  Hydrogen passes through, but e.g. CO from dissociation of MeOH is left behind.  With a proper catalyst the CO can be steam-reformed to CO2 and H2 at cell temperature.  The effluent is CO2 along with the excess H2O (which can be recycled).

This could have some possibilities for emissions-free power using storable liquid fuels.

SJC

Combine SOFCs running renewable methane with SOECs creating hydrogen using renewable energy. Sell the oxygen.
The SOFC produces heat, the SOEC uses heat.

Davemart

Solar thermal can produce 600C, which is going to cut the amount of remaining electricity needed substantially, and of course it can also provide that:
https://www.theguardian.com/sustainable-business/2016/may/13/tantalisingly-close-is-solar-thermal-energy-ready-to-replace-coal-fired-power

SJC

The problem with using only solar heat is you get production only a few hours per day. It takes longer to pay back the investment.

Davemart

SJC:
Its a trade off of utilisation and efficiency.
Electrolysis equipment is now cheap enough that for instance in Germany it is being used when renewables are in surplus to make hydrogen.
In the case of using solar thermal for heat, the heat energy can be stored in molten salts, but of course the efficiency will go down.

SJC

In general you pay back more quickly when you can produce 24/7.

SJC

An SOFC can take bio methane to produce electricity, CO2 and H20.
Those gases go into an SOEC to produce CO, H2 and O2.
The CO and H2 make hydrocarbon fuels, the O2 is used for other purposes.

Engineer-Poet

SJC:  when done directly in chemistry we call this "reforming".

3 CH4 + 2 H2O + CO2 + Δ -> 4 CO + 8 H2

4 CO + 8 H2 -> 4 CH3OH + Δ (methanol synthesis)
or
4 CO + 8 H2 -> 4 CH2 + 4 H2O + Δ (F-T reaction)

SJC

"we"? you don't exist.

Engineer-Poet

Then stop responding to the voices in your head.

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