Lithium batteries can easily smooth out short-term hiccups in the supply of periodic renewable energy. But they are not ideal for long-term storage as they will slowly unload. They are also not particularly suitable for large amounts of energy ̵
But researchers now report a possible solution to some of these problems: a fuel cell that can be used effectively in both directions, either using hydrogen or methane the production of electricity or the use of electricity to produce these fuels. Their measurements show that, after completing a full cycle, they receive 75% of the electricity they have released to get started.
The limits abound
Batteries, as mentioned above, do not work for long-term storage, as they usually lose charge slowly. They are also expensive because adding capacity means adding more batteries. Flow-through batteries solve some of these problems by storing the charged and diluted forms of a chemical in different tanks; larger or extra tanks are cheap, making expanded capacity relatively simple and inexpensive. But streaming batteries are not as effective as traditional batteries, and the chemicals they use can be toxic or corrosive.
An alternative for longer-term storage is to convert excess electricity into fuel. But these reactions often have their own efficiency problems, which means that part of the energy is lost in the process. Costs can be quite large, as you typically need hardware for both fuel production and power generation as well as very clean water sources and expensive catalysts.
One of the ways to reduce costs is the so- Fuel cells simply emit different parts of the chemical reaction so that the electrons that are transferred during the reaction can be used as a source of electricity. Working forward, the fuel cells will occupy hydrogen or methane as fuel and will produce electricity by combining it with oxygen from the air. By working in the opposite direction, they will use electricity to control the production of hydrogen, starting with water or methane if water and CO are used 2 . This allows a completely reversible cycle through which electricity is stored primarily in the form of hydrogen or methane without the need for separate storage and use hardware. It essentially acts as a big battery. Alternatively, hydrogen and methane are valuable chemical supplies or can be used to power different modes of transport. It is clear that the reversible fuel cell is extremely flexible. Why not use them?
Several species are built, but they all have problems. Some forms require high temperatures to work. They all produce a mixture of hydrogen and water, which is less valuable than pure, dry hydrogen. The efficiency of a two-way trip reaction is often drastically lower than the actual battery can provide. In many cases, the necessary catalysts break down very quickly. You have to remember this). This technology is very effective when it moves forward and requires only what the fuel cells are at moderate temperatures (400-600 ° C). This puts them in the range where the working temperature can be reached by using waste heat from industrial processes or traditional power generation.
Unfortunately, they also lose more than 30% of the energy supplied as electricity when they are moving in the opposite direction. So, the research team did some computer modeling to find out where the energy is going, starting with a combination of Ba / Ce / Zr / Y / Yb and Ba / Co / Zr / Y electrodes. Modeling implies that the loss of current during work is done by holes, areas with a lower than normal number of electrons that can migrate around the material. They found that they can reduce the formation of holes by changing the electrolyte; Once done, they began to test its effectiveness.
These tests included finding an optimal current density in the hardware – too low and hydrogen does not flow through the fuel cell; too high, and the system uses all of its water before it can spread anymore. The optimal operating temperature was around 500 ° C, where more than 97% of the supplied electricity was involved in the chemical response management. With water only, the system will produce hydrogen; Using water and carbon dioxide, it will produce methane.
Using the hydrogen reaction, the overall efficiency of the system – how much electricity you get compared to what you put – is 75%. Not as good as batteries, but do not forget that this can increase to as much hydrogen storage as you can and can keep it indefinitely.
But the key thing can be the stability of the system. Researchers conducted the feedback for more than 1200 hours without significant degradation of some of the critical materials. The image of these materials did not show any obvious structural changes after all use. Obviously, we would like this to work for years, not 50 days, but the fact that it works so well after 50 days of use suggests there will be no unpleasant surprises.
All of this sounds extremely promising, but there are many obstacles that need to be cleared. Although there is nothing similar to platinum catalysts, which are often used to divide water, the tbeburum still works at around $ 14,000 per kilo, which can make hardware shortages more expensive. Someone will also have to show that the hardware can be large, both in terms of production and its functioning as a reversible fuel cell when it is surrounded by standard industrial parts and not by hand-set laboratory equipment.
Finally, we do not currently have an energy architecture to use or store large amounts of hydrogen or to emit heat into hardware like this one.
The Energy of Nature 2019. DOI: 10.1038 / s41560-019-0333-2 (for DOIs).