Regarding the application prospect of this achievement, he said: "As far as the improved electrochemical cell is concerned, the high-performance PCEC (proton fuel cell) enables us to reduce the working temperature of hydrogen production by high-temperature electrolysis of water to 350℃ ... This process can open the door for many applications of" clean and green hydrogen ". More importantly, this technology operates in the same temperature range as several important industrial processes, including ammonia production and carbon dioxide emission reduction. Matching these temperatures will accelerate the adoption of this technology in existing industries. "
As far as interface engineering technology is concerned, the technology reported this time can be widely used in solid-state electrochemical devices, such as all-solid-state lithium batteries. All-solid-state lithium battery is a cutting-edge lithium battery technology, and all countries are developing vigorously. Interfacial wetting is one of the main bottlenecks. Acid treatment technology can effectively improve the interfacial wettability of all-solid-state batteries, thus improving the performance and stability of the batteries.
It is precisely because of its strong application that he is full of confidence in the commercial incubation of this achievement: "Our next research plan is two aspects. One is to integrate a series of existing preparation technologies to expand, modularize and even commercialize electrochemical devices. On the other hand, it is to further expand and deepen cooperation with other universities and research institutions in the fields of chemical electrochemical synthesis and industrial carbon reduction. "
It works well at 350℃, with almost no performance degradation for hundreds of hours.
It is reported that he and his collaborators have proved in experiments that the acid-treated battery produces more hydrogen per unit area at 600℃ 150% than any previous battery, and works well at 350℃ with almost no performance degradation within hundreds of hours. This method can be easily extended and integrated into the manufacture of large batteries and battery packs.
Professor Hu, director of the Material Innovation Center of Maryland Institute of Energy Innovation, said that he was not involved in this work, but his evaluation said: "The author reported a surprising, simple and extremely efficient surface treatment method to significantly improve the interface and improve the battery performance to an' excellent' level.
On April 20th, a related paper was published in Nature, entitled "Interface in Protonic Ceramic Cells Activated by Acid Etching".
According to Wei Wu, renewable energy, including wind energy, solar energy and tidal energy, has provided more and more clean electricity for the society. However, one of the main characteristics of these renewable energy sources is that they are unstable and fluctuate obviously with the weather. Therefore, clean electric energy is generally stored first.
The time for using storage batteries to store electric energy is also very limited and the cost is high. Using these clean electric energy to produce hydrogen and other organic chemicals and fuels is another way of electric energy storage, that is, converting electric energy into chemical energy.
As we all know, hydrogen is a green fuel, partly because when it burns, the product is only water. However, pure hydrogen has no natural source. Most of the hydrogen we use today is obtained by steam reforming hydrocarbons, such as natural gas. This method requires hydrocarbon feed gas and produces carbon by-products, which makes it less suitable for sustainable production.
Therefore, developing more efficient new electrochemical cells, such as solid oxide fuel electrolysis cells, can realize distributed power generation and low-carbon or even carbon-free hydrogen chemicals. Scientists all over the world have also been developing electrochemical cells mainly used to produce hydrogen. Hydrogen produced by these batteries can also be used as fuel for heating, transportation, chemical production or other applications.
But the premise is that scientists must overcome a series of challenges in materials and preparation, including how to make batteries more efficient, more stable and lower manufacturing costs.
Having said that, Wei Wu made a short science popularization: There are three main types of electrochemical electrolytic batteries.
The first one works at room temperature, such as proton exchange membrane batteries. Their main problem is low efficiency and the need for rare metals such as platinum.
The second one is at 700? C or above, such as oxygen ion conductor battery. They have high electrolysis efficiency, but metals are easy to oxidize or react with other elements to form corrosion at high temperature, so the equipment needs strict sealing and insulation technology.
The third one, PCEC, is a more potential electrochemical cell solution. Just as rechargeable batteries use chemical principles to store electrical energy for later use, PCEC can convert excess electrical energy and water into hydrogen. PCEC can also run in reverse, converting hydrogen into electric energy. This technology uses a crystal material called perovskite, which is cheap and can work in a wide temperature range. Meanwhile, the main working range of PCEC is between 300 and 600? C, further reduce the operation and manufacturing costs.
Theoretically, proton conductor has high conductivity and low activation energy, so the performance of PCEC will naturally be superior. However, Wei Wu and his collaborators have long observed that their performance is lower than expected by theoretical simulation. Since 20 17, he and his colleagues in Idaho national laboratory have been trying to understand why.
It said: "After the same experimental design and observation, we found that the problem is the transmission of protons (positively charged hydrogen atoms) at the electrode/electrolyte interface. Specifically, the combination of electrode and electrolyte is not ideal. Subsequently, in the process of battery preparation, we added simple acid treatment steps to realize the close combination of electrodes and electrolytes, thus achieving more effective ion transmission. "
After a series of detailed characterization, it was found that acid treatment increased the contact area between electrode and electrolyte. The increased surface area makes the bond between the electrode and electrolyte closer, thus allowing more efficient proton transport. In addition, the stability of the battery under some extreme conditions is also significantly improved.
Significantly improve the performance, thermodynamics and electrochemical stability of the battery.
In more detail, the core point of this paper is that the proton ceramic membrane electrochemical cell is expected to operate below 350. Although the high proton conductivity of electrolyte has been proved, it can not be completely used in electrochemical whole cells for unknown reasons. In this study, Wei Wu et al. revealed that these problems originated from the poor interface contact between oxygen electrode and electrolyte after secondary treatment at high temperature.
This study proves that simple acid treatment can effectively repair the electrolyte surface after secondary treatment at high temperature, so as to produce reactive bonding between oxygen electrode and electrolyte and improve electrochemical performance and stability.
This method can be as low as 350? C has excellent performance of proton ceramic membrane fuel cell, which can maintain 600? The peak power density at point C is 1.6W per square centimeter, 450? C is 650 milliwatts per square centimeter, 350? C is 300 milliwatts per square centimeter, while in 1.4V and 600? The current density at stable electrolytic operation and C is greater than 3.9 amperes per square centimeter.
It is reported that proton ceramic membrane fuel/electrolytic cell (PCFCs/PCECs) is expected to realize reversible conversion of chemical energy and electric energy in the application field of medium temperature (300-600) due to its high efficiency and zero emission.
One of their key components is perovskite oxide electrolyte. Because of its low activation energy and high proton conductivity, SOFCs can operate at a lower temperature than SOFCs/soec.
However, there are still some electrolyte-related challenges that limit the application of PCFC/PCEC. Firstly, although the sintered electrolyte shows high proton conductivity (for example, at 500 >: 10mS cm 1), the ohmic resistance in the electrochemical cell is larger than the theoretical value estimated only from the bulk ion conductivity, and it has an "unknown source". This inconsistency is believed to be due to poor contact between the oxygen electrode and the electrolyte. Secondly, the mechanical properties of the interface between oxygen electrode and electrolyte are weak, which will lead to delamination and other forms of loss, especially under the cycle of electrolytic cell with high current density.
It should be known that the proton ceramic membrane fuel/electrolytic cell is usually sintered at a high temperature of T 1, then screen printed or painted on the oxygen electrode layer, and then sintered for the second time at a lower temperature of T2.
However, the densification of proton ceramic membrane electrolyte is difficult and requires high temperature sintering. Although it seems to have nothing to do with the performance of the whole battery at 400-600°C, Wei Wu and others believe that low real contact area and high interfacial impedance have the same root cause as poor sinterability caused by low-rate mass transfer.
In fact, the situation of T2 sintering is worse (about1000 C): the porous oxygen electrode must be diffusion bonded to the fully annealed electrolyte surface (taking limited sintering on a single crystal substrate as an extreme analogy), and T2 must be low enough to avoid roughening of the porous oxygen electrode and allow gas transmission and catalysis.
Considering the above situation, the team proposed an acid treatment method to activate and repair the surface of high-temperature annealed electrolyte before combining with oxygen electrode. They proved that this method can completely restore the theoretical proton conductivity in electrochemical cells, and significantly improve the performance, thermodynamics and electrochemical stability of the cells.
Wei Wu said that the cooperation and dedication of all team members are indispensable for the project from project initiation to achievement announcement. This work was completed by three organizations, including Idaho National Laboratory, Massachusetts Institute of Technology and University of Nebraska. The team maintains weekly video conference communication, and everyone can share, discuss and study countermeasures immediately when encountering problems.
Like most scientific research work, there will be challenges and problems from putting forward ideas to realizing them. Many times, hard work may not be rewarded. "We can only do what we have learned, do what we can, rely on the collective strength to solve scientific problems, and leave the rest to luck. We are all very happy that this work has achieved some results. This time luck is on our side. " He said.
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Support: Wang Beibei.
Reference:
1, Bian, Wu, Wang, etc. Acid corrosion activation of proton ceramic battery interface. Nature 604,479–485 (2022). https://doi . org/ 10. 1038/s 4 1586-022-04457-y