Artificial leaves could power tomorrow’s cars – and China may be best placed to lead the way

It’s been described as one of the “holy grails” of 21st century chemistry.

Bill Gates called its potential “magical”.

And it’s one of the World Economic Forum’s Top 10 Emerging Technologies of 2017.

It’s the technology that harnesses solar power to produce energy; but not in the way we might imagine, by using solar panels. What Gates was describing was artificial photosynthesis (AP).

In nature, plants use sunshine to make carbohydrates from water and carbon dioxide. But you can also mimic the process artificially to produce energy-rich fuels and chemicals. This means not only could AP one day soon power our cars, but it could provide energy for whole cities and end our dependence on fossil fuels.

AP uses solar energy to split water and carbon dioxide into hydrogen, oxygen and carbon. Hydrogen can then be used as a fuel directly, or the elements can be combined to create liquid fuels, such as methanol.

AP liquid fuel is especially attractive because batteries are still relatively heavy and bulky compared to liquid fuels.

One of the biggest barriers to making Artificial Photosynthesis commercially viable, however, has been the efficiency with which the conversion of inputs occurs. Natural photosynthesis converts only around 1% of solar energy into the carbohydrates used by plants, an efficiency rate far too low to be commercially viable.

Previously, AP carried out in lab conditions has raised that efficiency rate to 10% and more.

But experts working at Monash University in Melbourne, Australia, have pushed the boundary much further, using an AP process to produce hydrogen at a record rate of 22% efficiency. The process involves passing a solar-powered electrical current through water to separate out hydrogen.

A new leaf for green energy

“Hydrogen can be used to generate electricity directly in fuel cells,” says Professor Doug MacFarlane, leader of the Energy Programme of the ARC Centre of Excellence for Electromaterials Science at Monash.

“Cars driven by fuel cell electric engines are becoming available from a number of car manufacturers. Hydrogen could even be used as an inexpensive energy storage technology at the household level to store energy from roof-top solar cells.”

One of the most exciting aspects of the Monash University breakthrough is that the process will even work using impure river water, allowing it to be deployed in a variety of geographical locations.

In the meantime, methanol is the simplest hydrocarbon that can be used in combustion engines.

China – the world’s largest methanol consumer – is already using it to blend with petrol at low levels of 15% or under and selling it at petrol stations; it also has taxi and bus fleets around the country running on blends as high as 85% methanol.

Blending methanol with petrol means refiners in China can extend gasoline supplies considerably.

Despite the fact that methanol has only 50% the energy per unit of volume compared to petrol, it still holds promise as an attractive alternative to polluting fossil fuels.

Shanghai, China’s most populous city, and 13 of the county’s 23 provinces have approved local standards for blends ranging from 5% to 100% methanol.

Methanol can be converted into petrol, but in China this is far less common than blending it with gasoline.

Elsewhere, research is taking place that uses the fundamentals of this technology to generate a wide variety of fuels and chemicals, even at low CO2 concentrations.

Professor Javier Garcia-Martinez of Alicante University in Spain has described how a variation of the artificial photosynthesis process carried out at Harvard used metabolically engineered bacteria to generate nitrogen-based fertilizer directly in soil, an approach that could increase crops yields in areas where conventional fertilizers are not readily available.

A time is envisaged when such bacteria will “breathe in hydrogen” produced by water splitting and use the hydrogen to produce products ranging from fuels to fertilizers, plastics and drugs, depending on the specific metabolic design of the bacteria.

The future of sustainable fuel

For now, though, research teams around the world are still working to understand the fundamentals of photosynthesis and replicate them at scale in an industrial process.

“Electrochemical splitting of water could provide a cheap, clean and renewable source of hydrogen as the ultimately sustainable fuel,” says Professor Leone Spiccia from the School of Chemistry at Monash University.

“This latest breakthrough is significant in that it takes us one step further towards this becoming a reality.”

(Professor Doug MacFarlane describes his work in this video – Harvesting Sunshine: )

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