Hydrogen gas can be burned as a fuel, with oxygen, leaving only water behind as a by-product. Usable in regular combustion engines, hydrogen fuel itself can be easily produced through methods like the electrolysis of water. If this production is powered by renewable energy, carbon will not be involved at any stage of the process, making it entirely free from greenhouse gases.
On top of this, hydrogen fuel is now being explored as a possible way to store excess renewable energy over the longer term.
Hydrogen is one of the most promising routes towards a carbon-neutral economy.
When the output of wind, solar, and hydroelectric facilities outpaces demand for electricity, that power could be used to produce hydrogen fuel, which could be stored indefinitely. Then, if renewables’ output drops, the hydrogen could be turned back into clean power on demand.
All of these factors have cemented hydrogen’s place as one of the most promising routes towards a carbon-neutral economy: a goal that is becoming increasingly urgent as climate change continues to accelerate.
However, the global-scale rollout of the fuel still has a major barrier to overcome.
The (explosive) challenge: Since hydrogen gas is highly explosive, it must be stored and transported in highly secure fuel cells — where it is either pressurised, or cooled to ultra-low temperatures.
This equipment is not only too costly for everyday users, but it could also cause catastrophic damage if anything malfunctions, raising ever-present concerns about the technology’s safety.
One solution to the problem is chemistry: a reaction that converts hydrogen gas (H2) and carbon dioxide (CO2) into formic acid — a liquid that can be stored easily and safely over a wide range of temperatures and pressures.
However, the chemical catalysts involved in this process often require the use of rare metals or extreme reaction conditions – making the whole thing less attractive from an economic perspective.
Life finds a way: A group of biologists in Germany now have demonstrated a potentially ground-breaking solution to this problem.
In their study, Volker Müller and colleagues at Johann Wolfgang Goethe University, Frankfurt, investigated a species of bacteria that inhabits the deep ocean. To gain the energy it requires, this organism carries an enzyme that catalyses the rapid conversion of H2 and CO2 into formic acid.
The bacteria didn’t require extreme conditions to survive.
Normally, the bacteria would then go on to digest this compound, producing less useful acetic acid and ethanol. Yet through genetic engineering, Müller’s team altered its metabolism to prevent this additional reaction, and even reverse the initial reaction entirely: converting formic acid back into CO2 and hydrogen fuel.
Crucially, these bacteria didn’t require extreme conditions to survive, steadily converting the chemicals at temperatures of just 30 C (86 F) and regular atmospheric pressure.
The experiment: Using a bioreactor, the researchers fed their modified bacteria with hydrogen gas for 8 hours during the day. This simulated the length of time where hydrogen gas could be realistically produced using the energy harvested by solar panels during the south German summertime.
For the remaining 16 hours, they cut off the reactor’s supply of hydrogen, causing any formic acid produced during the day to re-oxidise, and release the hydrogen gas initially consumed by the bacteria.
At the same time, the CO2 released from the bioreactor could be re-captured, ready for use in the next storage cycle.
Müller’s team kept the experiment running for 2 weeks in total, allowing them to assess their fuel cell’s performance over multiple day/night cycles.
Encouragingly, the amount of formic acid produced in the bioreactor remained constant for the first 4 cycles, before the unwanted production of acetic acid began to degrade its performance.
Storing hydrogen safely: The researchers describe their setup as a “bio-battery,” in which the electrons carried by H2 can be stored indefinitely inside formic acid, and then accessed as soon as a user requires.
With further improvements, they hope that their bacteria could maintain their levels of formic acid production across numerous day/night cycles – paving the way for the technology’s industrial-scale rollout.
The tech could provide industries with stronger incentives to capture the CO2 they produce.
If successful, the bio-battery could be used to store excess renewable energy, then release it again as customer demands begin to outpace supply.
This is particularly important in scenarios where renewable energy output is highly variable: for example, when solar panels aren’t generating power during the night; or at drier times of year, when less water is available to drive hydroelectric generators. Wind power is also seasonally variable in different regions.
Since the process also involves storing and recycling CO2, it could also provide industries with stronger incentives to capture the CO2 they produce – potentially bringing a carbon-neutral economy a step closer to reality.
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