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Scientists Have Created Batteries Using Carbon Dioxide From Atmosphere (thelatestnews.com)
An anonymous reader writes: While climate change talks progress on how to reduce carbon dioxide emissions, an interdisciplinary team of scientists have worked out a way to reduce carbon dioxide already existing in the atmosphere. The focus is on the batteries used by electric automobiles. Researchers have found out that the graphite electrodes in the lithium-ion batteries could be replaced with carbon electrodes sourced from atmospheric carbon dioxide. The experiment started with the use of a solar-thermal electrochemical process (STEP) to convert carbon dioxide into carbon. STEP uses solar energy as the source of the thermal and electrical energy required for the dissolution of the atmospheric carbon dioxide to its constituent elements -- carbon and oxygen. The team then used the carbon generated to create carbon nanotubes/nanofibers. They then incorporated these carbon nanotubes into lithium-ion batteries by using them as the positive electrode or anode. While the carbon is used in the manufacture of carbon nanotubes, the oxygen is channeled back to the generator to boost the combustion efficiency of the generator. The increased efficiency will balance the electricity consumption of STEP. In the end, the fossil fuel electrical power plant could have zero net carbon dioxide emissions.
His math is right. The bulk of the energy release when creating CO2 is from the step going from atomic carbon and atomic oxygen (dG = 0).to CO2 (dG = -394.4 kJ/mol), not the decomposition of for example CH4 (methane, dG = -50.8 kJ/mol). In fact it would take more energy to go from CO2 to atomic carbon and oxygen, than was originally released when you burned the CH4.
Basically, this process amounts to you taking the exhaust and soot from someone else burning a tree, then you burn 2-3 trees to generate enough energy to convert that soot and CO2 back into its atomic constitutents, then you convert it into a battery. So yeah batteries don't grow on trees, but it would take less energy to make the battery starting with the tree than what these guys are doing.
CO2 and H2O aren't just byproducts of chemical reactions which can be converted into C, H2, and O2 if you "just" knock the atoms apart. They sit very far down the energy potential well. All the energy that you get when you burn fossil fuels comes from lowering the C, H, and O down the energy potential well (creating CO2 and H2O in the process). Decomposing them back into their constituent atoms (knocking the atoms apart) requires pumping an equivalent amount of energy back into them.
Factor in inefficiencies and you're usually looking at having to put 2-3x as much energy in as you originally got out when you burned the fossil fuel. At that point you're better off just using that energy directly as electricity to power society - prevent the fossil fuel from being burned in the first place, instead of trying to uncreate the CO2 that was formed from burning the fossil fuel.