Is it possible to use energy from renewable energy sources to break down CO2 and when needed, turn that back into another molecule? Or am I dumb?
And is it efficient?
In: 1
That’s what plants do. The best way we currently have of doing it is to get plants to do it for us and then burn the plants.
Burning fuel into CO2 gives us energy. Turning CO2 back into fuel costs us even more energy. This will not reduce carbon emissions, but it wouldn’t increase them either, and could be used to store power from renewable energy sources.
However other fuels, especially hydrogen, seem better for this same purpose.
Yes, perhaps a process could be considered that uses solar photons to synthesize more complex molecules, such as sugars, from atmospheric CO2. These compounds would then be stored on location, in tall self-assembling structures, packed densely across large swaths of otherwise unusable land such as hills or mountainsides. After an extended period of self-assembly, the structures could then be cut down as needed, to be used as a fuel or even a building material. In this way CO2 could be used as a component of a battery, with a fairly high efficiency.
e.
To charge the battery we could cover it in millions of self-assembling thin film solar panels, designed to convert solar energy directly to chemical energy for easy storage and transport and to do so with a high efficiency. These small charging panels would be subject to high winds, rain, UV exposure etc. so they’ll have to be discarded and re-synthesized on regular intervals. Fortunately they ae fully biodegradable, and pose no environmental threat.
You can break the CO2 apart, but you need energy to do so. It would take more energy to break the molecules apart and store them than you would get back.
Hydrogen as fuel is promising, but it has the same problem. You need to break water apart to get pure hydrogen, spending energy to get the fuel. For this reason, hydrogen is called an “energy vector.” That means it can be used to store or transport energy, but never make more than was put in to obtain the hydrogen in the first place. Same idea with CO2. However, the bonds that bind carbon and oxygen in CO2 are stronger than the bonds that bind hydrogen to oxygen in water. You need more energy to break stronger bonds, so it would not be efficient to do this over using hydrogen.
You are never dumb for asking an honest and complex question. 🙂
CO2 is already one of the lowest energy carbon molecule, if not the lowest energy. So making it into another molecule would not make sense as you can not get all the energy back. However there is actually a process which almost fit your description. It is called the Sabatier process and works by turning hydrogen and CO2 into oxygen and methane. This process can be easily reversed either by burning the methane or by using a fuel cell to get electricity from it slowly. This process is mainly used in spaceflight.
Currently ISS use this process to conserve most of their oxygen, the methane is vented. This means that supply ships do not have to bring any oxygen, and only some water. The carbon and hydrogen atoms all come from the food that is brought up. This cuts the amount of consumables required for each astronaut by about half. There are also plans to use this process on Mars to create fuel using the CO2 in the atmosphere. The energy can come from solar panels or nuclear power. A rocket only have to bring about 20% of the fuel weight in hydrogen which can then be turned into liquid oxygen and liquid methane to fuel the rockets for the return trip. If possible we could find enough water on Mars to make rocket fuel from this instead of bringing inn hydrogen.
As for efficiency though, no it is not. The Sabatier process use a lot of energy and you will not get much back from the methane. This is why it is only used in very specific situations.
You are not dumb:) this is actually an active field of research. “Efficiency” definition is a tricky one and it depends on what product you would like to get. Some are easier than others but overall it’s absolutely doable. It’s not just feasible yet to do it on an industrial scale.
To understand the fundamental obstacle here: CO2 is what you get if you burn an organic thingie. Obviously the thing you get after you burn off all the energy in the other stuff has no energy of its own, else you’d burn that too.
Iceland turns the CO2 into stone somehow, don’t ask me how. But that seems an appropriate analogy for how much energy is in CO2. I don’t think anyone’s tried burning stone.
You ask the right questions. In theory, you could. In practice, it can’t be as efficient as finding other sources (e.g letting plants do the work for us). The reason is that CO2 is the lowest energy molecule you can get with carbon and oxygen. Pulling them apart and making something else requires adding a lot of energy. Worse, chemical reactions like that (where the atoms are bonded together) always take extra energy to drive them forward.
You’re thinking of carbon fuel cells.
The problem is that realistically speaking, it would have to be a carbon monoxide fuel cell, so the fuel would be in a gaseous format. The reason for this is that the triple bond between carbon and oxygen in carbon monoxide is the single strongest bond in all of chemistry, and breaking that bond is hard to do. As far as I understand, you can’t just electrolyze CO2 to oxygen and carbon. That’s not how it works.
But once you go to a gaseous fuel cell, you may as well use hydrogen. The hydrogen and oxygen to water reaction is much easier to manage, and electrolyzing water is way easier than splitting oxygen off of CO2. The oxygen atoms on CO2 are both double bonded to the carbon. But in water two hydrogen atoms each have a single bond to the oxygen, making it easier to reverse by electrolysis.
But even then, electrolytic hydrogen derived from water gives back less energy than it takes to produce it by electrolysis.
We already do that by making ethanol from corn. Does it work? Yes. Is it efficient? No as you waste a lot of energy with farming equipment, processing, transportation, and of course the inefficiency of combustion.
Now if we could make a gasoline fuel cell hybrid that would be pretty interesting as you would double the efficiency vs combustion and give gas cars a reason to still exist.
Latest Answers