30 August 2023
By Maia Mulko
 

Does hydrogen have a future as a clean energy source?

Is hydrogen gas the best option for clean energy                          iStock/Petmal

Hydrogen by itself is a clean and sustainable energy source, but hydrogen production requires a lot of energy.
If this energy comes from fossil fuels, that makes the hydrogen much less sustainable.
But new solutions are being developed every day.
Hydrogen is a clean and renewable energy source that has great promise as a sustainable alternative to fossil fuels.

But while hydrogen is the most abundant element in the universe, it is not always readily available on Earth in a usable form. Although hydrogen is present in water (H2O) and in organic compounds (such as carbohydrates and hydrocarbons), in order to use it as an energy source, it must be extracted from these compounds in its pure, gaseous form.

While hydrogen itself is an almost zero-emission fuel, the extraction process can require significant amounts of energy - most of which comes from fossil fuels. This raises concerns about the sustainability and environmental impact of hydrogen use.

Hydrogen as a clean fuel
Hydrogen is not exactly an energy source, but rather, an energy carrier. Meaning, it acts as an intermediary in energy systems, storing and transporting energy from point A to point B. In this process, point A can be both a substance containing hydrogen and/or the energy used to separate the hydrogen from the other elements in that chemical compound.

Once produced, hydrogen can be burned with oxygen or used in fuel cells to generate thermal and electrical energy with only water vapor (H2O) as a byproduct.

Fuel cells convert the chemical energy of a fuel, such as hydrogen, into electricity and heat, without combustion and without the byproducts of combustion, such as CO2.

In a hydrogen fuel cell, hydrogen is fed to the anode, and air is fed to the cathode. A catalyst at the anode separates hydrogen molecules into protons and electrons. The electrons go through an external circuit, creating a flow of electricity. The protons migrate through the electrolyte to the cathode, where they unite with oxygen and electrons to produce water and heat.

Hydrogen can also be burned directly in combustion engines, where it reacts with oxygen and produces heat and high-pressure gasses. These gasses expand rapidly and push a piston within the engine. The piston's movement is converted into mechanical energy, which drives the wheels, producing only water and small amounts of nitrogen oxides (NOx) as byproducts.

Illustration of a hydrogen-powered car in the future. iStock/UniqueMotionGraphics

Hydrogen production methods

Hydrogen is a highly reactive element. It has only one electron in its outermost shell, which is also its first and only energy level. As a result, it naturally seeks to achieve a stable electron configuration, and therefore, it tends to readily form chemical bonds with other elements. That’s why it isn’t commonly found in its pure form on Earth, and needs to be purified to use as an energy source.

Common methods for purifying hydrogen include:

Electrolysis, where an electric current splits water molecules into hydrogen and oxygen;

Steam methane reforming, which extracts hydrogen from natural gas (CH4); and

Biomass gasification, which produces hydrogen from organic materials retrieved from plants and animals.

Electrolysis requires a lot of energy. This can come from either fossil fuels or renewable energy sources like wind, solar, or hydroelectric power. If powered using renewable sources, the hydrogen is considered 'clean' energy and is generally referred to as green hydrogen.

Green hydrogen production via electrolysis.   iStock/newannyart

Green hydrogen can also be produced using biomass gasification. This method has a low carbon footprint and can promote the reutilization of waste materials. However, it relies on a consistent supply of biomass feedstock, which is in limited supply and has low energy density.

For these reasons, the most common method for hydrogen production is steam methane reforming (SMR), which is generally carried out using existing natural gas infrastructure.

In steam-methane reforming, methane reacts with steam under pressure and in the presence of a catalyst. This method produces hydrogen, carbon monoxide, and a small amount of carbon dioxide. It also requires energy in the form of heat in order for the reaction to proceed.

Overall, SMR is cost-effective because it extracts hydrogen from low-cost natural gas feedstock. But natural gas is not a renewable resource, and the process releases greenhouse gases in the form of carbon monoxide and carbon dioxide as byproducts, so is not a sustainable hydrogen production method in the long term. That is why hydrogen produced by this method is referred to as grey hydrogen.

One way to minimize the release of greenhouse gases from this process is to use it in combination with carbon capture and storage (CCS) technologies. However, this is not a complete solution, as it makes SMR more complex and expensive. Hydrogen produced using SMR in conjunction with CCS is referred to as blue hydrogen.

Other production methods
Apart from the three main types of hydrogen extraction and purification described above (green, grey, and blue), there are others:

Gasification is a thermochemical process that extracts hydrogen from carbon-rich materials, such as biomass or coal. In both cases, carbon dioxide is released. In the case of biomass, however, the CO2 released is somewhat offset by the fact that the biomass is made up of carbon dioxide which was previously removed from the atmosphere by plants. Gasification using coal, however, is not offset, and so hydrogen produced by this method is the most harmful to the environment and is referred to as brown or black hydrogen.

Hydrogen produced through electrolysis powered by nuclear energy is called pink hydrogen. According to the French bank Lazard, nuclear-powered electrolysis can produce 63% more hydrogen than green hydrogen plants. But pink hydrogen may not be not as sustainable as it seems because it has low thermal efficiency.

Electrolysis, when powered by solar energy, produces so-called yellow hydrogen. This is a very clean hydrogen production method but it is limited by the availability of solar power.

White hydrogen refers to naturally occurring hydrogen found on Earth, specifically in underground deposits. It is believed to be scarce and, currently, it is primarily accessible through fracking — a method that is extremely controversial because it is resource-intensive and is linked to groundwater contamination, air pollution, land degradation, and earthquake induction, among other negatives.

Turquoise hydrogen refers to the product of a method known as methane pyrolysis. Like SMR, methane pyrolysis breaks down natural gas molecules to obtain hydrogen. But this reaction is typically carried out at high temperatures, usually above 1000°C, in the absence of oxygen. As a result, its byproduct is not carbon dioxide (CO2) as in SMR, but solid carbon. This is a promising option if a) the carbon can be safely stored or used without being released into the atmosphere; and b) if it can be produced using renewable sources of energy.

How clean is hydrogen, really?
Hydrogen is not really an energy source by itself, but an energy carrier that relies on production, storage, and transportation methods to become usable. And it certainly can't be a source of green energy if the energy needed to produce, store, or transport it is derived from fossil fuels.

As of now, hydrogen can only become a truly clean energy source if it is produced through renewable energies. Research indicates that most hydrogen produced today is actually grey and brown hydrogen.

In addition, blue hydrogen may actually involve much less CCS than its producers report (12% versus 80-90%). The performance of CCS technologies is likely to be oversold by blue hydrogen producers because, in the end, blue hydrogen production employs natural gas infrastructure. This also gives the fossil fuel industry a perfect pretext to keep drilling and building this infrastructure.

However, there are proposals to improve hydrogen production. For example, the Korea Research Institute of Standards and Science (KRISS) has recently presented a method of clean hydrogen production based on solar-powered water splitting, a type of artificial photosynthesis. This involves using a material that can absorb sunlight to initiate the splitting of water molecules into hydrogen and oxygen.

One caveat is that water-based hydrogen production methods require a lot of pure water, which becomes wastewater after the process, and treating this wastewater can release yet more CO2 emissions.

To address this issue, Chinese researchers are working to produce hydrogen directly from wastewater using peroxymonosulfate (PMS). This substance appears to break down pollutants in wastewater that hinder hydrogen production.

As you can see, there is still a long way to go before we can establish hydrogen as a completely clean energy source. In the meantime, the creation of new sustainable hydrogen production technologies is working to make truly green hydrogen a reality.


 

Green Play Ammonia™, Yielder® NFuel Energy.
Spokane, Washington. 99212
509 995 1879 Cell, Pacific Time Zone.
General office: 509-254 6854
4501 East Trent Ave.
Spokane, WA 99212