Hydrogen A to Z Series: H For Hydrogen Production

By: GenH2 Staff
Read Time: 7 minutes

Defining The Hydrogen Economy from A to Z: H is for Hydrogen Production

Continuing in our Defining Hydrogen from A to Z series, were exploring the letter H and discussing Hydrogen Production. Hydrogen is considered the energy carrier of the future, but hydrogen production and hydrogen cells have been around for a long time. In 1766 Henry Cavendish discovered a lightweight gas that turned into water when burned. Antoine Lavoisier named the gas “hydrogen” in 1787, the name combined the roots hydro and genes, literally “water former”. The first electrolysis process was developed soon after in 1800 when scientists William Nicholson and Sir Anthony Carlisle determined that applying electric current to water generated hydrogen and oxygen gases and the first hydrogen electric cell (now known as the “fuel cell” today) was developed in 1838 to generate electricity.

Hydrogen has been deemed the energy of the future ever since that first fuel cell was developed, and today we finally have the technology to make that future a reality.

Why do we care so much about hydrogen as an energy carrier? Hydrogen is the most abundant element in the universe and has much higher gravimetric energy density than any other energy carrier. It also has the unique ability to react with oxygen, giving off heat (combustion) or electricity (electrochemical cell) with the only product being pure water. For these reasons, it is considered by many to be the energy of the future.

Hydrogen is very reactive and is rare in its pure form as H₂. It is often bound to other molecules such as oxygen (water), hydrocarbons (crude oil), and plants (cellulose). Because of this, producing pure hydrogen requires an energy input. This means that hydrogen is considered an energy carrier rather than a raw fuel. It has the potential to power the transportation sector through fuel cell cars.

To truly discuss hydrogen production, professionals in the energy and hydrogen production and storage industries have developed nicknames, in the form of colors, known as the hydrogen color spectrum. These colors do not describe the final hydrogen product in any way, hydrogen is colorless as a liquid or a vapor. The hydrogen color spectrum ranges from grey to blue to pink, and more colors continue to be added as new developments are made. Here we will discuss the meaning behind each color and the positive and negative values related to each.

Grey hydrogen:

Grey hydrogen is currently the most common form of hydrogen being produced. This hydrogen is created through the process of steam-methane reformation (SMR). In SMR high-temperature steam is reacted with a natural gas feed stock to produce hydrogen and carbon monoxide, or syngas, along with some carbon dioxide. The carbon monoxide is then run through a water-gas shift process to produce more hydrogen and carbon dioxide. None of the greenhouse gases are captured during this process.

The SMR production of hydrogen is low cost, often under $1/kg, is capable of the large-scale production of hydrogen needed to run the proposed hydrogen economy, and the technology is fully matured. The issues with green hydrogen are obvious, if we want are to create a carbon neutral energy grid, we can not produce and release carbon dioxide while producing hydrogen. Furthermore, large amounts energy is used to reach the temperatures needed to drive the reactions, if the energy is not derived from renewable resources, more carbon dioxide is produced in the process.

Blue Hydrogen:

Blue hydrogen uses the same SMR processing as grey hydrogen, but the greenhouse gases are mitigated through carbon capture storage (CCS) in some way. While blue hydrogen can still be produced at a much lower cost than greener methods, green house gases are still created in the process and there is a question of what is to be done with this large amount of carbon monoxide being created.

While blue hydrogen may not be the perfect the best hydrogen production method, and the large amounts of energy are still needed to run the process, it can serve as a bridge until developing industries are able to provide hydrogen on the scale needed to support the worlds energy and transportation grids.

Brown or Black Hydrogen:

Black or brown hydrogen, the two colors are used interchangeably, describes hydrogen produced through coal gasification, which is the process that converts coal, petroleum coke, or biomass into carbon monoxide and hydrogen, or syngas. Much like the SMR process, the carbon monoxide is run through a water-gas shift process to generate more hydrogen and carbon monoxide.  Other byproducts of coal gasification are hydrogen sulfide and slag, a waste product containing contaminants in a solid form.

Hydrogen produced from coal gasification can cost as low as $1.30/kg, but like the methods above greenhouse gases are produced, along with other waste. Current efforts are under way to make the process greener by using CCS and other postproduction processing to mitigate the carbon monoxide and other waste stream products. Other than basic mitigation efforts, future endeavors include transforming the waste products into consumer goods to offset the extra cost involved with these post-production methods.

Green Hydrogen:

Currently green hydrogen is produced via electrolysis – the process of separating water into hydrogen and oxygen – using renewable sources for electricity. Green hydrogen is currently seen as the better hydrogen choice because it is emission-free, leaving nothing but oxygen as a by-product. This eco-friendly color involves an electric current produced by renewable electricity that is used to separate water into oxygen and hydrogen, using electrolysis. Electrolysis employs an electric current to split water into hydrogen and oxygen in an electrolyzer. Green hydrogen has previously been very expensive due to high costs of supply chain logistics and electrolyzers, but the declining cost of renewable energy and other incentives are contributing to a significant growing interest in green hydrogen on the color prism.

While electrolysis can be considered the most environmentally friendly method of hydrogen production, leaving only oxygen as a byproduct, many technological hurdles to surpass before it can become fully viable to produce the scale of hydrogen needed for todays energy and transportation grid. Membrane technologies need to be advanced to allow for further durability form both mechanical and chemical stress, electrolyzers, while becoming more efficient as technologies mature, still require more electricity than other methods of hydrogen production, and finally current electrolyzers require large amounts of pure water for both electrolysis and for the coolers to run the larger scale instruments.

While electrolysis uses less water over all than many current energy production methods, accessible fresh water makes up less than 1% of the Earths water supply. In areas where fresh water is becoming scarce, electrolysis would not be the best solution for hydrogen production.

Turquoise hydrogen:

Turquoise hydrogen is made using methane pyrolysis, a thermal process which produces hydrogen and solid carbon. Because turquois hydrogen does not use oxygen in the reaction, the process results in low to zero CO₂ gas emissions.  This process also requires up to 50% less energy than the current state of the art electrolysis without the drain on clean water resources in water impoverished areas. Turquoise hydrogen provides a promising option for reaching the goal of net-zero emissions by 2050, the technology is currently at a low level however, and full grid scale production has not been currently obtained

Methane pyrolysis is like electrolysis in that it splits natural gas like electrolysis splits water. The difference is that instead of using an electrical current to split the water, it incorporates very high temperatures, ~850 C or ~1550 F, to decompose methane into hydrogen gas and solid carbon. This has the benefit of eliminating CO₂ as a byproduct altogether and instead forms solid carbon, which can be sold as an additional product.  Although this does eliminate the CO₂ produced in similar processes such as SMR, dealing with solids in the chemical industry is notoriously difficult. This is due to their potential to gather on various surfaces such as the catalyst (if used), pipes, and various equipment. Because of this, this technology requires additional research in scaling up from a lab environment to compact, modular units.

Pink, Purple, or Red Hydrogen:

Pink, purple, or red hydrogen refer to hydrogen produced using power from nuclear energy.

At GenH2 we are dedicated to finding hydrogen production and storage for every local. We understand that no one solution works for every environment or time scale, that is why our team of experts are working to develop multiple solutions with modular designs to work for the infrastructure that will make the future of clean hydrogen power a reality. Join us next week as we discuss the letter I and find out what Innovation means and how it relates to the hydrogen economy.

 

Blog written by GenH2 team member: Windy Ancipink