So-called "turquoise hydrogen" fuel is produced by breaking down methane, the main component of natural gas, but the low-carbon process faces barriers to wide usage. Now, an updated method is more portable and flexible, providing the potential to assist the transition toward a clean energy system.
The currently dominant method for turning methane into hydrogen gas emits substantial amounts of carbon dioxide, so the new technology could allow for a cleaner production of hydrogen, which, when burned, leaves behind only water.
Researchers at West Virginia University and the Pacific Northwest National Laboratory have developed nickel-based compounds that catalyze methane decomposition at high temperatures. The methods are detailed in a pending patent that was published May 6 by the World Intellectual Property Organization.
Nearly all of the world's countries have agreed, as part of the 2015 Paris Agreement, to take actions to limit global warming to below 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial temperatures. This challenging goal requires the rapid reduction of greenhouse gas emissions by retiring fossil fuels and adopting renewable energy sources in the next few decades.
One low-carbon energy source on the table is hydrogen gas, which releases only water when burned and is envisioned by some to be used as a fuel for technologies, such as airplanes, that cannot be electrified and supported directly by renewables.
Interest and research into hydrogen as a clean source of energy is accelerating, though it currently represents only a sliver of global energy and is made mostly with high-emission methods.
Hydrogen can be produced in several ways with varying levels of emissions, and the different processes are commonly color-coded. Gray hydrogen, the most common "color" of the fuel today, is made in a reaction of methane and water in a process called steam reforming, which emits carbon dioxide.
In contrast, green hydrogen is produced by splitting water molecules through electrolysis with renewable energy. It is the cleanest form of hydrogen fuel but represents less than 0.1% of current hydrogen production. Renewable-energy infrastructure will also not be large enough to produce enough green hydrogen necessary in the near-term and midterm future, said John Hu, an inventor of the pending patent and a professor of engineering and mineral resources at WVU.
Hu and his colleagues have been working for the last few years on methane pyrolysis, in which methane exposed to high temperatures breaks down into hydrogen gas and carbon nanotubes. The fuel produced in this process is sometimes called turquoise hydrogen, and the carbon molecules are also a valuable material that can be sold rather than discarded.
Methane pyrolysis lags behind many other "colors" of hydrogen production in terms of development and rollout, although many turquoise-hydrogen plants have recently been funded, and many are under construction.
The reaction does not emit any carbon dioxide, although some emissions are produced if the large amounts of heat required by pyrolysis are generated with fossil fuels and not renewable energy, or if the methane being converted was extracted in a high-emission process, according to a 2020 study.
The inventors' central innovation is a nickel-based catalyst that efficiently decomposes methane at about 600 degrees Celsius (1,110 degrees Fahrenheit), a temperature at which many other catalysts perform poorly. An acid is added to the carbon-catalyst leftovers to break down the catalyst and purify the carbon nanotubes, a useful material in nanotechnology, optics and other scientific fields. The use of catalysts made from other metals is also covered by the pending patent.
This latest iteration of Hu's methane pyrolysis process is relatively efficient, he said, which allows low-carbon hydrogen production to be performed using portable equipment. This makes the technology accessible without the need to build a major chemical plant, according to the professor.
One application he emphasized was avoidance of the flaring of natural gas, in which excess gas is burned at a remote production site. The catalyst technology would be nimble enough to convert would-be flared natural gas into hydrogen and high-value carbon, avoiding the large release of greenhouse gases.
"It is a challenge to the commercial process to handle a small-scale feedback supply," said Hu, who is also the director of the Center for Innovation in Gas Research and Utilization at West Virginia University. "That's why process-intensified modular technology becomes necessary."
He said the technology could also be used to cleanly and efficiently produce ammonia, a major application of hydrogen that is often used as a fertilizer by farmers.
Hu said the trajectory of the researchers' experimental hydrogen technology has been significantly influenced by the U.S.'s goal to halve its greenhouse gas emissions by 2030, announced by President Joe Biden in April.
According to Hu, this "very aggressive goal" is putting pressure on the sectors using fossil-fuel energy. Global natural-gas production has been increasing for decades, despite growing awareness of the size and negative impacts of methane pollution.
He said this could increase demand for the methane-pryolysis production approach, which he and his team have been probing by conducting market research with major fossil-fuel companies.
The application for the patent "Methods and compositions for production of CO2-free hydrogen and carbon nanomaterials by methane decomposition" was filed Oct. 30, 2020, with the World Intellectual Property Organization. It was published May 6 with the application number 2021/087405. The earliest priority date was Oct. 30, 2019. The inventors of the pending patent are John Hu, I-Wen Wang and Lili Li, West Virginia University; and Robert Alexander Dagle, Juan A. Lopez-Ruiz, Mengze Xu and Stephen deLemos Davidson, Pacific Northwest National Laboratory. The assignees are West Virginia University and Battelle Memorial Institute.