A new study from Tel Aviv University has identified a strain of algae that may help produce environmentally sustainable green hydrogen on the scale required to suit industrial production.
The research is another small but promising step in the burgeoning science of hydrogen energy.
Hydrogen can be an entirely sustainable fuel: it burns cleanly to produce just energy and water vapour. It’s touted for use as shipping and aviation fuel, fuel for the cars and trains of the future, and an energy provider in various other industrial processes that currently require burning fossil fuels. The problem is, not all hydrogen is created sustainably.
Brown hydrogen is made through the gasification of brown coal, releasing CO2 or carbon monoxide in the process. Grey hydrogen is made by steam reforming natural gas (methane or CH4), producing CO2 as a by-product. And blue hydrogen, often considered sustainable, suffers from an identity crisis: It’s made through the same process as brown hydrogen, but the released CO2 is in theory captured and stored underground to prevent emissions being released into the atmosphere.
In short, none of these processes is wholly sustainable from start to finish. And there are problems with carbon capture and storage that haven’t yet been fully solved. That’s why some commentators say that the best approach to hydrogen fuel is to go green: green hydrogen is made by separating water into hydrogen and oxygen via electrolysis, using renewable energy.
But the production of green hydrogen using solar panels is expensive, because it requires precious metals and distilled water. So, it may not be appropriate for every context.
That’s the problem this new study is trying to address. According to the authors of the study, published his week in Cell Reports Physical Science, micro-algae produce hydrogen as a by-product of photosynthesis, but most only produce it for a period of minutes at a time. The team wanted to investigate whether algae could be engineered to produce hydrogen for longer periods – days or weeks – at a time.
According to study co-author Iftach Yacoby, the team identified a mutated strain of the algae Chlamydomonas reinhardtii in the lab that was producing hydrogen for a prolonged period of 12 days.
“The new mutant overcomes two major barriers that have so far prevented continuous production of hydrogen,” Yacoby explains.
“The first barrier is the accumulation of oxygen in the process of photosynthesis. As a rule, oxygen poisons the enzyme that produces hydrogen in algae; but in the mutation, increased respiration eliminates the oxygen and allows favourable conditions for continuous hydrogen production.
“The second barrier is the loss of energy to competing processes, including carbon dioxide fixation into sugar. It, too, has been solved in the mutant and most of the energy is being channelled for continuous hydrogen production.”
This longevity of hydrogen production could in theory allow scientists to scale up the production of hydrogen from algae. According to Yacoby, the team is working on a pilot program with larger volumes, and is investigating methods that might allow the hydrogen “harvest” to be extended even longer.
“The rate of hydrogen production from the new mutant reaches one-tenth of the possible theoretical rate, and with the help of further research it is possible to improve it even further,” Yacoby says.