May
5
DOE/Idaho National Laboratory’s researchers have developed a new electrode material for an electrochemical cell that can efficiently convert excess electricity and water into hydrogen. When demand for electricity increases, the electrochemical cell is reversible, converting hydrogen back into electricity for the grid. The hydrogen could also be used as fuel for heat, vehicles or other applications.
A new triple-conducting oxide allows protons, oxygen ions and electrons to move through, allowing generation of either hydrogen or electricity through reversible operation in a protonic ceramic electrochemical cell. Image Credit: Idaho National Laboratory. Click image for the largest view.
While energy sources such as wind and solar produce emissions-free electricity, they depend on the sun and the wind, so supply doesn’t always meet the demand. Likewise, nuclear power plants operate more efficiently at maximum capacity so that electricity generation can’t be easily ramped up or down to match demand.
For decades, energy researchers have tried to solve one big challenge: How do you store excess electricity so it can be released back onto the grid when it’s needed?
The results have been published in the journal Nature Communications.
Dong Ding, a senior staff engineer/scientist and chemical processing group leader at INL pointed out researchers have long recognized the potential of hydrogen as an energy storage medium.
“The energy storage grand challenge, with its diverse research and development needs, gave rise to more opportunities for hydrogen,” said Ding. “We are targeting hydrogen as the energy intermediate to efficiently store energy.”
Ding and his colleagues improved one type of electrochemical cell called a protonic ceramic electrochemical cell (PCEC), which uses electricity to split steam into hydrogen and oxygen.
But in the past these devices had limitations, especially the fact that they operate at temperatures as high as 800° C (1472° F). The high temperatures require expensive materials and result in faster degradation, making the electrochemical cells cost prohibitive.
In the paper, Ding and colleagues describe a new material for the oxygen electrode – the conductor that catalyses or facilitates the water splitting and oxygen reduction reactions simultaneously. Unlike most electrochemical cells, this new material – an oxide of a compound called a perovskite – allows the cell to convert hydrogen and oxygen into electricity without additional hydrogen.
Previously, Ding and his colleagues developed a 3D mesh like architecture for the electrode that made more surface area available to split the water into hydrogen and oxygen. Together, the two technologies – the 3D mesh electrode and the new electrode material – allowed for self-sustainable, reversible operation at 400 to 600° C (752° to 1112° F).
Ding said, “We demonstrated the feasibility of reversible operation of the PCEC at such low temperatures to convert generated hydrogen in hydrolysis mode to electricity, without any external hydrogen supply, in a self-sustaining operation, It’s a big step for high temperature electrolysis.”
While past oxygen electrodes conducted only electrons and oxygen ions, the new perovskite is “triple conducting,” Ding said, meaning it conducts electrons, oxygen ions and protons. In practical terms, the triple-conducting electrode means the reaction happens faster and more efficiently, so the operating temperature can be reduced while maintaining good performance.
For Ding and his colleagues, the trick was figuring out how to add the element to the perovskite electrode material that would give it the triple-conducting properties – a process called doping.
Hanping Ding, a materials scientist and engineer for Idaho National Laboratory’s Chemical Processing Group said, “We successfully demonstrated an effective doping strategy to develop a good triple-conducting oxide, which enables good cell performance at reduced temperatures.”
For the future, Dong Ding and his colleagues hope to continue improving the electrochemical cell by combining materials innovation with cutting-edge manufacturing processes so the technology can be used at an industrial scale.
Cutting the process kit temperature by near to half is going to greatly reduce the energy input cost as well as take out the noble metal expense. One still has to wonder how the full economic cycle is going to work out. Splitting water to get hydrogen isn’t cheap and has quite a gap to jump for competing with steam reforming hydrogen sourced from natural gas. This technology is getting there, but how close is yet to be revealed.
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