A new technique developed by a team of Dutch Engineers generates electrical power from a novel mixing of CO2, air, and water — without increasing CO2 emissions.
Carbon dioxide (CO2) is a simple molecule that results from either the natural breakdown of organic matter (by bacterial decomposition), or as a by-product of combustion of hydrocarbon-based fuels (coal, oil, natural gas, etc.). It can be a “food source” for vegetation (though this is limited by other factors such as soil nitrogen), or a source of pollution (a greenhouse gas, or GHG).
The accumulation of this particular GHG in our atmosphere has been the primary focus of much climate research due to its heat-trapping capacity and resultant global warming (from this and other molecules and aerosols).
While policymakers argue over how to reduce this GHG (and by how much by what future date to avoid irreversible climate change) as well as which renewable energy technologies to invest in, researchers from the Netherlands have been working to figure out a way to use this pollutant to generate power — and it seems they have succeeded in their quest.
A Cell Full of Water, Air, and CO2
The breakthrough comes via a modified version of a device called a capacitive electrochemical cell. Similar to a battery, the cell has two porous electrodes: one (the negative, or anode) that attracts/absorbs hydrogen ions, and the other that attracts/absorbs (hydrogen) bicarbonate ions (the positive, or cathode). The supply of each ion type is provided by bubbling CO2 through water. In the first stage of a two-stage process, this CO2-packed water is pumped through the cell resulting in the flow of each ion population from the cell to their respective electrodes. This separation of charges creates the potential to drive an electrical current.
In the second stage (as the electrodes have absorbed the maximum amount of ions), air-bubbled water is then pumped through the cell which drives the ions from their electrodes back into the cell. By continuously alternating between these two active processes (i.e., the two stages), the cell generates almost continuous electrical energy (note: the solutions need to be replenished periodically).
Making the Mix
The technique is based upon the concept of ‘mixing energy’ of fluids; when two different fluids (e.g., with different densities) are mixed, the mixture can release (mixing) energy. This basic physics concept holds for both gases and liquids, but up until now, no technology existed for effectively harvesting this mixing energy from mixed gases (such as CO2 and air, a composite gas).
The breakthrough — and relatively simple and inexpensive technology — could provide an energy source/market with a total annual (global) capacity of 1570 TWh (terawatt hours) potential. This is about 400 times the energy produced by the Hoover Dam each year.
And while the technology does depend on CO2 production, if scaled up, conceivably all the CO2 emissions from a given source (e.g., smokestack emissions, 5–20% of which is CO2) could be captured and harnessed for this purpose — with no additional CO2 inputs (from the technique) to the atmosphere.
[right] Diagram and graph showing the capacitive electrochemical cell with different electrolyte solutions Credit: Hamelers et al/ACS
So far, the researchers have achieved 24% efficiency with the technique using water as the electrolyte (aqueous) solution. The Dutch researchers are experimenting with other electrolyte solutions for greater efficiency of power generation (although these might be somewhat more polluting in terms of their supply for use in the process).
Quoting from the paper abstract (see the diagram, also):
Though not truly a “renewable” energy technology (at least in the very long term), it is arguably “cleaner” and the technology does address an obvious question: if we’re causing pollution (which is waste energy), why not harness this waste to generate more energy (and less waste)?
No doubt the new technique — if widely adopted — will add to the debate over CO2 reduction targets in the near-to-medium term.
The team (Hamelers et al) reported their results online this week in Environmental Science & Technology Letters, under the title: “Harvesting Energy from CO2 Emissions”
Some source material for this post came from the Science Shot piece “A Smokestack’s Hidden Treasure” by Sid Perkins.