Green hydrogen: how we produce this fuel of the future
As global average temperatures continue to rise, engineers around the world search for practical alternatives to carbon-intensive energy sources.
The transportation sector presents one of the biggest challenges to decarbonization—in 2021, it accounted for 35% of U.S. carbon emissions. Renewable sources of energy like solar and wind can only power vehicles through batteries, which currently hold only 15% of the energy that gasoline provides per pound.
Hydrogen gas may be the solution. It’s abundant, highly compressible, and each kilogram provides as much energy as one gallon of gas. Best of all, it produces only water vapor when burned, making it an ideal candidate for both transportation and renewable energy storage.
Let’s take a look at our current ability to make and use hydrogen as a clean fuel.
How hydrogen generates power
Like fossil fuels, the combustion of hydrogen can be used to generate heat, drive turbines with steam, and power combustion engines. When burned, the only products are heat and water vapor—a clean reaction that’s easy on both the environment and machinery. As the smallest element, molecules of hydrogen gas are also highly compressible, making it an energy-dense fuel option.
But handling hydrogen gas in a traditional engine is tricky. Hydrogen’s small size means it can easily slip through any cracks in even a well-maintained system. Like gas, this escaped hydrogen is flammable and can be dangerous.
These engines are also inefficient due to energy lost in combustion, and aren’t technically emission-free thanks to the oils required to lubricate them—they produce trace amounts of CO2 and nitrogen oxides.
These problems are solved by hydrogen fuel cells. A hydrogen fuel cell uses stored hydrogen gas and oxygen from the air to break apart the hydrogen molecules and directly produce water vapor and electrons, generating electricity. When coupled with an electric motor, hydrogen fuel cells produce a vehicle up to three times more efficient than a gas-powered combustion engine.
Fuel cell electric vehicles, or FCEVs, are already in production. They’re clean and efficient, can fill in less than four minutes, and have a range of over 300 miles. Since the vehicle is electric, it can also be equipped with other energy-efficient technology, like regenerative braking.
Despite the advantages that hydrogen fuel cells offer, hydrogen combustion engines still have their place. They’re robust machines that can output a lot of power, burn lower-quality hydrogen, and withstand harsh operating conditions—not to mention our decades of experience working with combustion engines.
Regardless of whether we burn hydrogen directly or use it in fuel cells, we’ll need lots of hydrogen gas. So how can we produce it?
How we produce hydrogen today
Hydrogen is a promising clean fuel, but it’s difficult to refine. Our main methods of producing hydrogen rely on the processing of hydrocarbons like natural gas, which produces emissions, or on the electrolysis of water, which is energy-intensive and inefficient.
Today, around 95% of all hydrogen produced is manufactured through steam reforming of natural gas. In this process, natural gas is heated alongside steam and a catalyst to produce carbon monoxide and hydrogen.
Although carbon monoxide is not a greenhouse gas itself, the process is extremely energy intensive and requires natural gas, making it both inefficient and unsuitable for long-term hydrogen production. Powering vehicles with hydrogen produced this way only cuts the emissions generated by half when compared to gas-powered vehicles.
The other 5% of hydrogen is produced by electrolyzers. These machines operate like a fuel cell in reverse, using electricity to separate water into hydrogen and oxygen molecules.
Unfortunately, they’re not all very efficient. Producing a kilogram of hydrogen with a traditional electrolyzer can cost up to 52.5 kWh of energy, but a kilogram of hydrogen only provides 39.4 kWh when used—and that’s assuming it’s burned at perfect efficiency.
This means losing valuable energy whenever hydrogen is produced this way—and emitting a lot of carbon if the electrolyzer isn’t powered by a renewable source. Additionally, commercial electrolyzers rely on pure water, an increasingly valuable resource that is costly to refine from seawater. They also often require precious metals for their catalysts, further driving up their cost.
These barriers aren’t all insurmountable—companies like Hysata have recently claimed up to 95% efficiency in their newest commercial electrolyzers. But even with this level of efficiency, the energy lost in producing and using hydrogen adds up at every stage, from purifying and electrolyzing water, transporting hydrogen, hydrogen leakage, and inefficient conversion of hydrogen back into heat or electricity.
This inefficiency is a big part of why steam reforming is still the main method of hydrogen production today—but recent advances in catalysis and engineering seek to change that.
Recent breakthroughs in hydrogen electrolysis
Researchers around the world are working to develop catalysts for hydrogen production that are cheaper, more efficient, and more robust. In January 2023, one such project published the promising results of their work.
Researchers at the University of Adelaide in Professor Shizhang Qiao’s research group say they have developed a new low-cost, high-efficiency catalyst for hydrogen production. In addition to these benefits, this new catalyst is also capable of efficiently generating hydrogen from seawater.
Most electrolyzers require highly purified, deionized water to avoid damage to their precious metal catalysts. The big draw of the Qiao group’s breakthrough is that their electrolyzer works on raw seawater—the only treatment needed was filtration of solids and microbes.
Using a modified cobalt and chromium catalyst—much cheaper than the usual platinum and ruthenium—they were able to achieve nearly 100% efficiency, comparable to modern commercial electrolyzers.
Even better, the technology operates by applying an inexpensive coating to an existing catalyst, meaning it could be applicable to electrolyzers of all shapes, sizes, and catalyst types.
Although promising, this technology isn’t ready just yet. The team will still need to work to test the system with various catalysts, electrolyzers, and scales of production. But for areas with access to plenty of seawater and renewable energy, this development looks promising.
Improved electrolyzers aren’t our only option. Other possible future methods of hydrogen production include solar-driven processes, in which sunlight directly drives hydrogen production, and biological processes, in which microbes generate hydrogen through biological reactions.
These projects and more aim to make hydrogen production a cheap and efficient option for our future.
The bottom line
Hydrogen gas is a clean, energy-dense fuel with the potential to transform the transformation energy sector. Although there are obstacles to the efficient production of hydrogen in bulk, those barriers are quickly being broken down by advances in hydrogen electrolyzer technology.
References
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Thomas Praisner—Freelance Writer 