Hydrogen- A Carbon-neutral Fuel for the Future?

What is hydrogen?

Hydrogen is the first and lightest element on the Periodic Table. It is the most abundant chemical substance in the Universe, and exists in abundance on Earth in molecular form with other compounds e.g. water, natural gas, coal, crude oil, etc. Hydrogen is used for a variety of purposes, and by 2019, just over 70 million metric tons of hydrogen was being produced globally, the majority consumed by the crude refining industry and the production of ammonia. Hydrogen, at standard conditions, is a flammable gas that emits no CO2 when it burns, meaning it provides a greenhouse gas (GHG)-emission free alternative to conventional fuels such as natural gas. However, the manner in which it is produced determines the extent to which it prevents GHG emissions and currently, the global production breakdown of hydrogen production is as follows: 76% from steam reforming of natural gas, 22% from the gasification of coal and 2% from electrolysis of water. The total production from fossil fuel sources is responsible for 830 million tonnes of CO2 emitted into the atmosphere per year, equivalent to the total annual CO2 emissions of Indonesia and the United Kingdom combined. This process of production, i.e. from fossil fuel sources, results in what is known as ‘grey’ hydrogen. Combining this approach to hydrogen production with carbon capture and storage technology results in what is known as ‘blue’ hydrogen, resulting in hydrogen that is considered carbon neutral. However a more accurate description of blue hydrogen would be ‘low carbon’, since generally only 90% of the CO2 is captured, and also fugitive emissions of natural gas (its main component, methane, is a powerful GHG) to the atmosphere regularly occurs during the extraction process.  However, for hydrogen to truly be a player in the future transition to clean energy, a zero-emission production method is required. There are various carbon-emission free types of hydrogen, however in the case of ‘pink’ hydrogen they are not attractive enough to investors, while ‘turquoise’ hydrogen, which involves decomposing natural gas into hydrogen gas via a pyrolysis process with a solid carbon residue as a waste product, is still in an experimental phase. There is a promising process which uses renewable electricity to generate hydrogen via the electrolysis of water, with nothing but oxygen as a by-product (and hence is carbon free); hydrogen generated this way is known as ‘green’ hydrogen.

Graphic showing hydrogen production pathways. Image: Olumide Hassan

Importance of (green) hydrogen

The Paris Agreement set a goal of limiting global warming to well below 2, preferably 1.5, degrees Celsius compared to pre-industrial levels. To reach this, countries signed up to reducing their global greenhouse gas emissions as soon as possible to enable a climate neutral planet by 2050. Some progress has been made in recent years, for example for the first time in the UK, renewable sources were the main source of electricity in 2020, and battery electric vehicles (BEVs) had a 4.3% share of the car market, a 132% increase since 2019. In the same year in Norway, electric vehicles made up the majority of new car sales. However, no single fuel or technology is by itself the solution to climate change, and this is no more evident than in sectors such as the steel and cement making industries (which make up a total of approximately 15% of global CO2 emissions). The materials from these industries are things that are integral to economies including infrastructure, buildings, vehicles (including land, sea and air based transportation machines) and consumer goods, and are also things society will continue to need to produce well into the future. Production processes in these industries require high energy density fuels due to the intense heating required for their operations, meaning electricity as an energy carrier is impracticable. Green hydrogen could provide a suitable alternative to fossil fuels to enable the decarbonization of these industries.

Hydrogen has also long been touted as a replacement for hydrocarbon fuels in the automotive industry, but the process of manufacturing green hydrogen means the electricity first needs to be converted to hydrogen via electrolysis, and it is then compressed, chilled and transported before being pumped into a car after which it is converted back to electricity to move the vehicle. Once the electricity is generated, from the supply of the energy carrier (hydrogen or electricity into a battery) to powering the vehicle equates to total energy losses of approximately 60% for a hydrogen fuel cell vehicle (FCV) compared to losses of only 20% for a battery electric vehicle (BEV). However, current battery technology (lithium-ion) requires mining for finite minerals, while advancements in technology are to be expected with hydrogen generation technology. In fact, a company backed by Bill Gates have claimed to create a technology that generates hydrogen at an efficiency of 95% with significantly lower costs than current electrolysers. This would provide one pathway to green hydrogen production costs of circa $US1/kg, at which point it will be cheaper than grey hydrogen and when compared per unit of energy, it would be on par with current gasoline prices in the United States.

Advantages of green hydrogen

The supply of green hydrogen (water) is abundant and does not require environmentally damaging mining of materials such as those used in lithium-ion batteries. And while the economic, efficiency and emissions-reduction benefits of FCVs over BEVs, in particular small and medium sized road vehicles, is often disputed, hydrogen provides a range of uses that battery technologies (currently) do not provide. Hydrogen is used as a feedstock for various industrial processes, including in oil refining, ammonia, methanol, and steel production. As mentioned earlier, virtually all this hydrogen is generated from fossil fuels, hence there is significant scope for reducing CO2 emissions by using green hydrogen in these industrial processes. Also, the oxygen produced as a by-product of the green hydrogen production has a market value for industrial and medical applications

Hydrogen can be used to store renewable energy. Due to its intermittent nature, the excess renewable energy from wind and solar is stored (usually in batteries) to provide electricity at night (solar) or when the wind falls below certain thresholds (wind). (Green) hydrogen produced this way can be used not only for converting the energy back into electricity, but also to generate a zero-carbon energy carrier for fuelling other processes. Green hydrogen can also be converted into ammonia, which has a higher energy density than liquid hydrogen and can be stored at much less energy-intensive temperatures of -33oC compared to a cryogenic temperature of -253oC for liquid hydrogen. This ‘green ammonia’ can easily be transported as a fuel to wherever it is needed for use in powering ships, aeroplanes, and power plants.

One important advantage of (green) hydrogen is that it can be transported via existing natural gas pipeline networks. This allows for the use of legacy infrastructure (with modifications, as hydrogen is known to leak in pipelines easily), as opposed to building brand new ones. Green hydrogen used in this way can replace fossil-based natural gas to provide heating energy for buildings.