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By Kris Nelson

Green or renewable hydrogen generally means using renewable power to split water into hydrogen and oxygen, called water electrolysis. An electrolyzer separates the hydrogen from the oxygen. Assuring the power source is not tainted with fossil fuels requires third-party verification and careful accounting. If the power is not completely from renewable sources, use or purchase of renewable energy credits (RECs) or similar offsets can qualify the power as renewable. Nearly 99 percent of hydrogen today is derived from methane and coal gasification, known as grey hydrogen.

Since renewable power sources are commonly intermittent, and since grid power is mostly from fossil fuel sources, the type of electrolyzer to be used must respond quickly to supply fluctuations (frequency response). In the most common alkaline design, the electrolyzer utilizes an alkaline solution with a porous diaphragm as the electrolyte. The generated oxygen (at the anode) and hydrogen (at the cathode) gases can easily crossover the diaphragm.  The gas crossover prevents rapid startup and shutdown of the electrolyzer, leading to efficiency and revenue losses. Moreover, an increase in ohmic resistance often occurs due to a large gap between the two electrodes, resulting in decreased efficiency.

In more recent electrolyzer designs, the intermittency of renewable power causes little power and efficiency losses. The use of a solid electrolyte and a specialized membrane, known as a proton exchange membrane (PEM), enables the electrolyzer to turn on and off instantly. The PEM can largely reduce the ohmic voltage drops and gas crossovers. The effect is to improve the hydrogen production rate, energy efficiency, and purity.

So far, the catalyst-coated membranes in PEM electrolyzers rely on fluorinated polymers, which contain PFAS chemicals, also known as forever chemicals. The EU has issued a mandate to eliminate these harmful chemicals in a few years. Fortunately for the environment as well as efficiency, MemPro has developed catalyst-embedded nanofibers made of non-PFAS materials. With ultra-high surface area, these conductive fibers can also reduce the use of critical or rare-earth metals such as iridium, platinum, and palladium in membrane catalysts by 90 percent or more. Since the catalyst is not bound to a polymeric membrane but integrated into the fiber, the membrane avoids catalyst breakdown (agglomeration) and will likely extend its life.

With lower-loaded iridium catalysts, the demand for this critical metal will not likely be reduced as the market for green hydrogen grows globally. When we embed the metal oxide catalyst into high surface area nanofibers, we estimate that 95 percent less iridium will be used to achieve higher efficiency performance in PEM electrolyzers. We estimate, at current demand forecasts, that this technology could extend the limited supply of iridium to meet green hydrogen production targets by 2030 at a cost at or below the DOE target of $1/kg.

Another aspect of improving the sustainability of green hydrogen production is to reduce use of fresh water. One area of research MemPro has co-proposed to the Department of Energy is to source seawater, desalinate it with specialized filters, extract the lithium and manganese for battery use, and produce green hydrogen by PEM electrolysis using our catalyst-embedded nanofibers. With new ceramic filters, the cost of desalinization is greatly reduced. The challenge will be to scale operations to reach cost-effective levels. One limitation in deployment is access to salt water, yet if deployed nationwide or even globally along coastlines, this technology would significantly reduce demand for fresh water in producing green hydrogen.

As green hydrogen production becomes more cost-effective, its deployment, similar to the history of photovoltaic solar technology, can become more distributed. If we successfully demonstrate its production at or below $1/kg, demand will increase across the economy. That will afford opportunities to produce it among non-industrial businesses and perhaps even at the residential level, which has been demonstrated in Sweden and New Jersey. Such distributed production will enable further replacement of fossil fuels and reduce emissions from transportation of green hydrogen.