Nanoscale movies shed light on one barrier to a clean energy future

Left unchecked, corrosion can rust out cars and pipes, take down buildings and bridges, and eat away at our monuments.

Corrosion can also damage devices that could be key to a clean energy future. And now, Duke University researchers have captured extreme close-ups of that process in action.

"By studying how and why renewable energy devices break down over time, we might be able to extend their lifetime," said chemistry professor and senior author Ivan Moreno-Hernandez.

In his lab at Duke sits a miniature version of one such device. Called an electrolyzer, it separates hydrogen out of water, using electricity to power the reaction.

When the electricity to power electrolysis comes from renewable sources such as wind or solar, the hydrogen gas it churns out is considered a promising source of clean fuel, because it takes no fossil fuels to produce and it burns without creating any planet-warming carbon dioxide.

A number of countries have plans to scale up their production of so-called "green hydrogen" to help curb their dependence on fossil fuels, particularly in industries like steel- and cement-making.

But before hydrogen can go mainstream, some big obstacles need to be overcome.

Part of the trouble is electrolyzers require rare metal catalysts to function, and these are prone to corrosion. They're not the same after a year of operation than they were in the beginning.

In a study published April 10 in the Journal of the American Chemical Society, Moreno-Hernandez and his Ph.D. student Avery Vigil used a technique called liquid phase transmission electron microscopy to study the complex chemical reactions that go on between these catalysts and their environment that cause them to decay.

You might remember from high school that to make hydrogen gas, an electrolyzer splits water into its constituent hydrogen and oxygen molecules. For the current study, the team focused on a catalyst called ruthenium dioxide that speeds up the oxygen half of the reaction, since that's the bottleneck in the process.

"We essentially put these materials through a stress test," Vigil said.

They zapped nanocrystals of ruthenium dioxide with high-energy radiation, and then watched the changes wrought by the acidic environment inside the cell.

To take pictures of such tiny objects, they used a transmission electron microscope, which shoots a beam of electrons through nanocrystals suspended inside a super-thin pocket of liquid to create time-lapse images of the chemistry taking place at 10 frames per second.

The result: desktop-worthy close-ups of virus-sized crystals, more than a thousand times finer than a human hair, as they get oxidized and dissolve into the acidic liquid around them.

"We're actually able to see the process of this catalyst breaking down with nanoscale resolution," Moreno-Hernandez said.

Over the course of five minutes, the crystals broke down fast enough to "render a real device useless in a matter of hours," Vigil said.

Zooming in hundreds of thousands of times, the videos reveal subtle defects in the crystals' 3D shapes that create areas of strain, causing some to break down faster than others.

By minimizing such imperfections, the researchers say it could one day be possible to design renewable energy devices that last two to three times longer than they currently do.

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Reducing steel corrosion vital to combating climate change

Every year, the United States spends nearly a trillion dollars fighting metallic corrosion, an electrochemical reaction that occurs when metals oxidize and begin to rust. By taking on this surprisingly insidious issue, researchers have now estimated how much corrosion is gradually worsening global carbon emissions.

Global steel production has been rising steadily for decades -- and because steel has poor resistance to corrosion, part of that demand is to replace steel used in construction materials that have become corroded over time, in everything from bridges to automobiles. Reducing the amount of steel that needs to be replaced due to corrosion could have measurable effects on how much greenhouse gases are produced to make steel, said Gerald Frankel, co-author of the study and a professor in materials science and engineering at The Ohio State University,

Though previous studies have estimated the current economic cost of corrosion to be about 3 to 4% of a nation's gross domestic product, this new study, led by Ohio State alum Mariano Iannuzzi, is the first to quantify the environmental impact associated with steel corrosion.

The study was recently published in the journalnpj Materials Degradation.

"Given society's reliance on coal fuel, iron and steel production is one of the largest greenhouse gases emitters of any industry," said Frankel. "But most of the costs associated with the industry actually stem from the energy that goes into creating steel, and that energy is lost as the steel reverts to rust, which is similar to its original form of iron ore."

The time it takes steel to corrode largely depends on the severity of the environment and the alloy composition, but this environmentally expensive issue is only getting worse, said Frankel.

Using historical carbon dioxide intensity data to estimate carbon dioxide levels per year beginning from 1960, the researchers found that in 2021, steel production accounted for 27% of the carbon emissions of the global manufacturing sector, and about 10.5% of the total global carbon emissions worldwide. Corroded steel replacement accounted for about 1.6 to 3.4% of emissions.

But there is some good news, the study noted. Due to regulations placed on the steel industry, technological advances in the steelmaking process have resulted in a 61% reduction in energy consumption over the last 50 years.

Despite this improvement, the results of the study are a call to action for policymakers and industry officials to amend and coordinate international policy regarding steel production and corrosion management, Frankel said.

"Coordinated international strategies, as well as decreasing global steel demand, by using best practices for corrosion mitigation, could better improve global corrosion management strategies and drastically reduce the rise in greenhouse gas emissions we're seeing due to repeatedly replacing corroded steel," he said.

If actions to improve steel's carbon footprint aren't taken soon, the study notes that greenhouse gas emissions produced by the steel industry could reach about 27.5% of the world's total carbon emissions by 2030, with corroded steel representing about 4 to 9% of that number. Such a result would make the goals set by the Paris Agreement to limit Earth's warming to 1.5 degrees Celsius as well as the U.S.'s own domestic climate goals almost completely unfeasible. The study notes that management strategies such as taking advantage of machine learning technologies could be one of the best chances we have to reduce Earth's carbon dioxide levels.

That said, if humans cannot meet these conditions, the consequences for Earth's climate will be dire, so more people need to be made aware that a low-carbon steel industry is needed to prevent such a dystopia, said Frankel.

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