There’s a greater sense of urgency than ever to find more sustainable, secure, cost effective and ethical ways to source and store energy. As we look to replace fossil fuels, renewable sources like solar, wind, hydro, tidal and hydrogen have taken centre stage.  

For some time, hydrogen has been seen as a key part of the solution. After all, it is the most abundant chemical element and accounts for around 75% of the mass of the universe. While hydrogen atoms are found in water, plants, animals and natural gas, it rarely exists on its own as a gas. It needs some form of extraction process to produce sufficient quantities to fuel industry, vehicles or homes.

Most processes used to manufacture hydrogen involve some level of carbon – in terms of both input and output. This has given rise to the idea of the ‘hydrogen rainbow’ which uses a colour code to differentiate the different manufacturing methods by their carbon intensity. At the current count there are at least 10 shades in an increasingly crowded rainbow, but the three that most people will be familiar with are a more muted palette of grey, blue and green.

• Grey hydrogen is extracted from fossil gas with CO₂ released into the air.
• Blue hydrogen is extracted from fossil gas with CO₂ emissions captured and stored.
• Green hydrogen is extracted from water using renewable electricity with oxygen released into the air.

Clearly, as it emits zero carbon and uses energy from renewable sources, green hydrogen is most likely to deliver decarbonisation targets, and protect against the supply volatility of the current fossil dependent energy markets.

For green hydrogen to be produced there must be sufficient availability of renewable power to deliver the full environmental benefits. It follows that the hydrogen economy should be developed alongside initiatives to increase renewable energy supply. To enable this, there has to be a concerted effort from governments to provide long-term incentives for the growth of the hydrogen economy. This would encourage market investors, funders, companies and consumers to adopt and use hydrogen in the future. Allocation of government support to help establish the hydrogen market by overcoming the initial risks and technical challenges would allow it to become competitive against alternative energy and fossil fuels.

In search of hydrogen efficiency 
Compared to traditional batteries, hydrogen stores energy much more densely and can refuel faster, but historically it has proved quite inefficient to produce, store and transport. A kilogramme of hydrogen holds 39 kWh of energy; the thermodynamic minimum net energy required to form hydrogen from water. However, the actual amount of energy needed to create that kilo varies by manufacturing process and is typically higher.

Conventional thermochemical processes for manufacturing hydrogen require very high temperatures of between 500–2,000°C. This itself requires a great deal of energy, often from non-renewable sources, and the processes are less energy-efficient than others such as electrolysis.

Despite being more efficient than other thermodynamic processes, at 70–80% efficiency, electrolysis still loses between 20–30% of the energy used during the conversion. So, there is an increasing need for new technology to improve efficiency. That’s where plasma comes in.

The plasma effect 
First of all, let’s remind ourselves what plasma is. It is an electrically charged – or ionised – gas, which is sometimes described as the fourth state of matter. Plasma occurs naturally in lightning, sparks from static electricity and the aurora borealis. Plasma is used in television and display screens, fluorescent lighting and arc welding.

Green hydrogen production made by applying the ‘plasma effect’ is the core feature of an innovative UK-developed technology: Tetronics Hydrogen Plasmolysis (THP).

THP involves applying highly concentrated electrical energy to water under the high temperature and pressure gradients arising from the plasma arc. Using renewable sources of electrical energy makes this the ultimate green hydrogen.

Compared with current benchmark electrolysis technologies, THP offers a step-change in performance and delivers considerable energy efficiency improvements in terms of kWh per kg of hydrogen.

Green hydrogen made by applying the ‘plasma effect’ is the core feature of an innovative UK-developed technology – Tetronics Hydrogen Plasmolysis.

Over the summer of 2022, Tetronics built a first-of-its-kind THP system and ran a series of hydrogen production trials funded by the government’s Department for Business, Energy and Industrial Strategy (BEIS). The system took plasma-based hydrogen production beyond the scale achieved by previous laboratory researchers thanks to the integration of its patented plasma torch technology. The work demonstrated the benefits of plasma-assisted hydrogen production by achieving high hydrogen yields with a lower electricity demand than comparable electrolysis systems.

The feasibility test showed that a specific gross energy requirement of 36–40 kWhe/kg of hydrogen was achieved using a water/bio-methanol electrolyte. This is approximately a 10% improvement in efficiency beyond the theoretical minimum and as much as a 40% improvement over the reported commercial performance of polymer electrolyte membrane (PEM) fuel cells.

With that in mind, what is preventing the uptake of plasma technology? This might be down to the perceived complexity of the use of plasma compared to other technologies, without it being proven at a sufficient scale. Essentially, plasma is viewed as very tricky to deal with. It produces a plasma arc – similar to the high temperature torch that’s used in arc welding – which releases huge amounts of energy. Controlling this energy for more than a few seconds has been the reason why plasma systems haven’t been harnessed effectively in the past.

Tetronics has been researching and developing plasma devices for over 50 years and has more than 100 live and pending patents in plasma technology. This work enables the company to deliver plasma systems that can run continuously and was used to create the 14 kW unit that it tested over the summer.

Tetronics researches the potential of plasma technology for green hydrogen production in this plant
Photo: Tetronics

Keen to demonstrate that the technology can work at a commercial scale, the company is looking to develop a 300 kWe demonstration system. This unit will provide additional learning about the engineering design required for a system to allow for greater simplicity in the design for future plants, for example a reduced number of THP cells. This should reduce the complexity of the design and, when coupled with the anticipated higher hydrogen yield, also demonstrate THP as a viable production method.

No hydrogen production system produces 100% pure hydrogen. The core THP process can be integrated into a flexible downstream process tailored to produce hydrogen at varying grades of purity, depending on the end user’s requirements. Key characteristics of the THP technology allow it to be used in diverse hydrogen applications, both for industrial use for power and heating and for applications that demand more purity from the fuel cell technology.

THP has the additional advantage over an electrolysis installation of being highly scalable. The use of THP to produce hydrogen for industrial applications for heating, power or as a raw material mean that there is an opportunity to install onsite hydrogen production facilities. The smaller physical footprint means that hydrogen production facilities can be located at a manufacturing plant of any size or in locations that are off-grid. This dramatically reduces hydrogen transportation costs in addition to energy savings.

THP presents application opportunities where companies are not connected to a larger hydrogen gas network or require hydrogen for specific purposes. Industrial gas consumption in the UK for systems over 1 MW is 79 TWh/y. THP systems could be installed at sites such as furnace operators and chemical processing plants where there may be sufficient scope to install a hydrogen production facility supported by on-site energy generation.

As even heavy industrial manufacturers adopt a route to net zero, THP using renewable sources of energy could be used as an on-site source of hydrogen in the ferrous and non-ferrous metal industries – such as aluminium manufacturers – or glass producers. The processes they use cannot be completely electrified without investing millions to replace furnaces, and radically transform their operations. Using hydrogen as a fuel or raw material means it is not such a huge step to transition away from natural gas or other non-sustainable fuel sources.

This snapshot of the advantages that THP technology has over other hydrogen production methods points to a competitive, energy efficient, green hydrogen supply solution; based on a unique and inventive assembly of proven technologies.

THP has the advantage of being scalable – requiring a smaller footprint than other electrolysis plants – and is suitable for remote, off-grid locations, which in turn reduces transportation costs and losses that might occur. There is considerable scope for plasma produced hydrogen to make a major contribution to reducing our dependency on fossil fuels.