Chuck Hayes, Global Technical Lead, Swagelok

The need for alternatives to fossil fuel production has spurred intense research into the most suitable replacement. One fuel source gaining support among environmental activists and fuel companies alike is hydrogen (H₂), which can reduce or eliminate carbon dioxide (CO₂) emissions. Whether H₂ truly falls into the sustainable fuel category depends on how it is produced. There are three ways to achieve H₂ fuel production, and each successive method is more sustainable than the last.

H₂ FUEL VARIANTS AND HOW THEY ARE PRODUCED

As with generating any type of fuel, making H₂ to serve as a fuel takes energy. Where the energy comes from determines how sustainable it is. Different forms of H₂ fuel are designated with specific colors that reflect the energy sources used to produce it.

Gray H₂. While gray H₂ reduces CO₂ emissions when burned, the production process may release enough CO₂ emissions to offset the benefits. Steam methane reforming and coal gasification—the two processes most often used— release CO₂ into the atmosphere, making it the least sustainable H₂ fuel production option. Its advantage over other production methods is that it is the least expensive, making it the most common type of H₂ fuel generation (FIG. 1).

FIG. 1. By most measures, gray hydrogen is the least sustainable form of the fuel because fossil fuels are used during the production process.

Blue H₂. Blue H₂ also uses fossil fuels in its production; however, instead of releasing the CO₂ into the atmosphere, it is captured by filters and stored. By sequestering the carbon, blue H₂ is considered a low-carbon option, but it is slightly more expensive than its gray alternative (FIG. 2).

FIG. 2. Blue hydrogen production adds an additional step to gray hydrogen production by capturing and sequestering the carbon dioxide. This makes it more sustainable, but the addition of carbon capture technology increases its costs.

Green H₂. To produce green H₂, electrolysis is used to split water molecules into their component H₂ and oxygen atoms. To qualify as green H₂, the electricity employed must be from renewable sources like solar, wind, hydro or geothermal. In those situations, green H₂ produces no CO₂ emissions. As renewable energy prices continue to fall, it will become more attractive to pursue the production of green H₂ vs. other forms of H₂ (FIG. 3).

Fig. 3. The most sustainable form of hydrogen fuel is called green hydrogen because the fuel used to produce it comes from renewable energy sources like hydro, solar, geothermal and wind.

UNDERSTANDING THE DECLINE IN H₂ FUEL COSTS

The world is reaching a tipping point where blue and green H₂ make more sense to produce than their fossil fuel competitors. Major oil producers are cutting back on how much fuel they produce, raising the prices to consumers and making H₂ options more attractive. Furthermore, renewable energy prices continue to come down and in some areas of the country are already cost competitive, which will reduce the costs of producing green H₂. Finally, governments around the world are beginning to implement more stringent CO₂ emissions standards and offering incentives to consumers who shift to more environmentally friendly forms of fuel.

Why this matters. H₂ can be produced sustainably and is one of the most environmentally friendly alternatives to fossil fuels currently on the market. And despite the varying sustainability profiles of different types of H₂, even gray and blue H₂ minimize CO₂ emissions at their point of use. Meanwhile, significant investment in green H₂ is only increasing throughout the world, with industry stakeholders working to find more ways to improve production efficiencies and drive down prices for end users.