An artificial leaf to fuel world trade

While renewable energy technologies such as wind and solar have become significantly cheaper and more available in recent years, many challenges still need to be overcome to achieve decarbonization in most industries. To help supplement energy needs, researchers from the University of Cambridge have designed an ultrathin, flexible device intended to mimic nature's best energy convertor – leaves!

For several years, Professor Erwin Reisner's research group at Cambridge has been working to address the high energy costs in the production of gasoline or petrol, as it is called over the pond, by developing an artificial leaf.

In 2019, they managed to create a prototype that makes syngas – a key intermediate in the production of many chemicals and pharmaceuticals – from sunlight, carbon dioxide, and water.

Outdoor tests of the new lightweight leaves on the River Cam showed that they could convert sunlight into fuels as efficiently as plant leaves.

This is the first time that clean fuel has been generated on water, and if scaled up, artificial leaves could be used on polluted waterways, in ports, or even at sea, and could help reduce the global shipping industry's reliance on fossil fuels.

The 2019 prototype generated fuel by combining two light absorbers with suitable catalysts. However, it incorporated thick glass substrates and moisture-protective coatings, which made the device bulky, cumbersome, and all-around impractical.

"Artificial leaves could substantially lower the cost of sustainable fuel production, but since they're both heavy and fragile, they're difficult to produce at scale and transport," said Virgil Andrei, the paper's lead author and doctor at Cambridge's Yusuf Hamied Department of Chemistry.

For the new iteration, the researchers took their inspiration from the electronics industry, where miniaturization techniques have led to the creation of smartphones and flexible displays, revolutionizing the field.

"We wanted to see how far we can trim down the materials these devices use, while not affecting their performance," said Erwin Reisner, research lead for the project. "If we can trim the materials down far enough that they're light enough to float, then it opens up whole new ways that these artificial leaves could be used."

For Cambridge, the challenge was in how to deposit light absorbers onto lightweight substrates and protect them against water infiltration.

To overcome this, the team used thin-film metal oxides and materials known as perovskites, which can be coated onto flexible plastic and metal foils.

You can read about perovskites and how they function at New perovskite solar consortium founded in the May 6, 2020, edition of Metal Tech News.

With an ultrathin, lightweight device covered with a micrometer-thin, water-repellant carbon-based layer that prevents moisture degradation, a breakthrough in artificial leaves was made.

Cambridge not only ended up with a device that works but also looks like an actual leaf.

"This study demonstrates that artificial leaves are compatible with modern fabrication techniques, representing an early step towards the automation and up-scaling of solar fuel production," said Andrei. "These leaves combine the advantages of most solar fuel technologies, as they achieve the low weight of powder suspensions and the high performance of wired systems."

Tests of the new artificial leaves showed that they could split water into hydrogen and oxygen or reduce CO2 to syngas. As for further development, additional improvements will need to be made before they are ready for commercial applications; the researchers go on to say that this development opens entirely new avenues in their work.

"Solar farms have become popular for electricity production; we envision similar farms for fuel synthesis," added Andrei. "These could supply coastal settlements, remote islands, cover industrial ponds, or avoid water evaporation from irrigation canals."

This is not the only work on artificial leaves Cambridge is undertaking. You can read about a similar project at Solar fuel made from artificial leaves in the June 15, 2022, edition of Metal Tech News.

"Many renewable energy technologies, including solar fuel technologies, can take up large amounts of space on land, so moving production to open water would mean that clean energy and land use aren't competing with one another," added Reisner. "In theory, you could roll up these devices and put them almost anywhere, in almost any country, which would also help with energy security."

While the potential of such artificial nature devices presents a new facet of innovation and discovery, the enormous energy needs of an industry that keeps the world going will be a colossal undertaking.

Global shipping

Although many industries still rely on fossil fuels, a paradigm shift toward decarbonization has exploded into the scene in recent years. While land-based industries have multiple options at their disposal, the most vital shipping sector requires a little more power than what solar or wind could provide.

A large container ship is often around 1,400 feet long and roughly 200 feet wide and can weigh up to 220,000 tons when fully loaded – that's right, tons.

According to The Guardian, in one year, a single large container ship emits roughly the same amount of carcinogens as that of 50 million cars. That is if it follows the Suezmax standard, which is the term used to define the largest ships capable of transiting the Suez Canal fully loaded.

Yet not only are shipbuilders resetting the world record for size on a regular basis but so are the diesel engines that propel them. Once one of the longest container ships in the world, the 1,300-foot Emma Mærsk also had the world's largest reciprocating engine.

At five stories tall and weighing 2,300 tons, this 14-cylinder turbocharged two-stroke monster put out roughly 84.4MW (114,800 horsepower) – and up to 90MW when the motor's waste heat recovery system is taken into account. Therefore, these mammoth engines consume approximately 16 tons of fuel per hour or 380 tons per day while at sea.

Around 80% of global trade is transported by cargo vessels powered by diesel, yet, according to Cambridge, the sector receives remarkably little attention in discussions regarding climate change.

Although great advances are being made in generating electricity from renewable energy sources such as wind power and photovoltaics, Reisner says the development of synthetic petrol is vital, as electricity can currently only satisfy about 25% of our total global energy demand.

"There is a major demand for liquid fuels to power heavy transport, shipping and aviation sustainably," he said.

While neither announcement regarding Cambridge's artificial leaf explicitly mentions power output, it can be imagined that an astronomical quantity of them would be needed to offset the energy needs of beasts like the Emma.

With hopes to scale up the technology, we can only wait to see if further breakthroughs can one day provide the necessary output to fuel the world's goods transportation.