Unfortunately, hydrogen gas is not as naturally abundant as the molecule itself. It requires other resources such as natural gas, nuclear power, biogas, and solar and wind energy to transform it into a highly versatile power source.
It’s worth the effort. Hydrogen can be used as a low-to-zero emission chemical feedstock and fuel across many energy-intensive sectors including transportation, heavy industry, agriculture, and power. As sustainability mandates and favorable policy frameworks evolve, the demand for hydrogen is expected to nearly double to 180 Mt by 2030, with nearly half of that demand stemming from new applications in heavy industry, power generation and fuels.
Blue Hydrogen vs. Green Hydrogen vs. Clean Hydrogen
Hydrogen’s tremendous promise has captured the attention of governments, private investors, and businesses in recent years. However, only 4% of the world’s current hydrogen supply is produced through sustainable methods. The other 96% is derived from steam methane reforming (SMR), a process that employs natural gas and emits substantial carbon dioxide. This is what is referred to as “gray hydrogen”.
While this production process is carbon intensive, it can be combined with carbon capture and sequestration (CCS) technology to reduce environmental impacts. This process is referred to as “blue hydrogen,” and while better for the environment, its production poses massively increased project complexity and cost. Plus, there’s still the matter of methane leaks that occur during the extraction of natural gas which is still required for blue hydrogen.
In contrast, “green hydrogen” is produced through the electrochemical splitting of water into hydrogen and oxygen, which requires fewer steps and releases zero harmful emissions. As a burgeoning energy source, green hydrogen is the favorable option of the three and should be the focus of significant innovation and investment, particularly as the private sector looks to distance itself from the growing economic and reputational liabilities inherent in fossil fuels.
In an effort to provide greater clarity into hydrogen’s climate footprint, the US government is moving away from the term “green hydrogen” in favor of “clean hydrogen,” which is defined as having less than half the carbon emissions associated with natural gas-derived production of the fuel. Hydrogen varieties will now feature quantitative carbon scores, as opposed to qualitative color labeling (e.g. “blue” or “green” hydrogen). In addition to providing more accurate and up-to-date information for consumers and businesses, this new term will help reduce ambiguity in the hydrogen industry.
What is involved in green hydrogen production?
Green hydrogen production is beginning to ramp up as manufacturing capacity scales and the cost of renewable energy continues to fall. Electrolyzers are at the heart of the process, enabling the chemical conversion by which hydrogen and oxygen molecules are separated using electricity (also known as electrolysis).
A variety of different electrolyzer chemistries exist, including liquid alkaline, proton exchange membrane (PEM), anion exchange membrane (AEM), and solid oxide. While there are some chief differences, they all essentially use water and renewable electricity to produce green hydrogen.
While liquid alkaline has been commercially available for decades, the increased efficiency, compact design, and compatibility with intermittent power input of PEM electrolyzers have led to its adoption and manufacturing by major industry players. AEM and solid oxide electrolyzers have shown substantial promise, but are not yet mature enough for commercial manufacturing.
The iridium catalyst bottleneck in PEM electrolyzers
Electrolyzers require electrocatalyst materials to work, with PEM electrolyzers relying heavily on both platinum and iridium. While existing mining operations and optimized logistics have rendered platinum relatively common and affordable, the same cannot be said for iridium. As an extremely rare earth mineral primarily concentrated in South Africa (80-85%), as well as in Russia and Zimbabwe, less than two tons are made available for electrolyzers annually. Massive supply restrictions combined with the growing demand for green hydrogen solutions have resulted in price increases from more than < $1,000 per ounce in 2017 to approximately $5,000 today. Further increases are almost guaranteed as the demand for PEM electrolyzers and green hydrogen continues to grow, aided by an influx in government tax breaks and subsidies.
R&D challenges for iridium catalyst substitutes
Although it’s exceedingly rare, iridium is critical to PEM electrolyzers because of its durability in highly acidic operating environments. Any substitute material would need to match its operational lifetime or be sufficiently inexpensive and available to justify a modest performance reduction. Yet, existing R&D methods are slow, linear, and ill-suited to discovering potential replacements for the iridium catalyst.
For instance, there is no widely accepted “accelerated stress testing” protocol to quickly evaluate the durability of potential iridium catalyst replacements. As a result, new materials require individual testing for months or even years before results can be verified for end-users, a process which increases expenses while delaying innovation, and thus, limits the number of novel materials that can be evaluated.
A breakthrough catalyst discovery and development approach
With the number of system design combinations in a PEM electrolyzer easily exceeding one trillion (accounting for electrocatalysts composed of arbitrary combinations of metals, the surrounding chemical environment, membrane composition, operating conditions, etc.), testing systems one at a time does not suffice.
Where conventional R&D is slow and linear, advancements in high-throughput experimentation now enable the evaluation of mass quantities of system design combinations in parallel. It’s now possible for millions of materials (nanoparticle alloys of controlled composition) to be synthesized and evaluated per day for their electrocatalytic activity and long-term durability, drastically cutting down on R&D timelines. Generating massive amounts of data, this work can be turbocharged by artificial intelligence (AI), which makes predictions about which system designs should perform the best.
Additionally, utilizing a tight feedback loop with prototype-scale device testing accelerates the holistic optimization of electrochemical systems. This parallelized approach enables the rapid evaluation of catalyst materials’ durability under real-world PEM electrolyzer operating conditions, dramatically reducing the number of materials that need to be tested for extended periods of time.
From materials discovery to widespread commercial deployment
Increased collaboration between industry players, including electrocatalyst, catalyst-coated membrane, and electrolyzer manufacturers, will further expedite the commercialization of industrial solutions. Simultaneously, it’s important that industrially viable accelerated stress testing protocols be created to significantly speed the development of novel and durable electrochemical systems.
To increase green hydrogen production around the world, every stakeholder should have a voice, especially as the needs of manufacturers, project developers, and off-takers evolve and grow. Through enhanced industry collaboration, we can build a stronger and more cohesive ecosystem to meet growing global demand.