Hydrogen, the most abundant element in the universe, is rapidly becoming a source of hope for the net-zero future. Previously, the cost and complexity of producing hydrogen prevented major advancements in the field. However, with countries around the globe quickly approaching their net-zero targets, hydrogen power developments are beginning to boom.
So, how do hydrogen fuel cells work?
Fuel cells work like batteries, except they do not need recharging.
Output: Electricity, water and heat
Let’s break down how this happens:
- Fuel cells are made up of two electrodes, a positive electrode (also known as a cathode) and a negative electrode (also know as the anode). The anode and cathode are separated by an electrolyte membrane.
- Hydrogen is passed into the anode and oxygen into the cathode.
- At the anode, hydrogen is separated into protons (positively charged ions) and electrons (negatively charged ions) by a catalyst.
- The electrons are unable to travel through the electrolyte membrane and are forced through an external circuit which produces an electric current and heat.
- The protons travel to the cathode via the electrolyte membrane. At the cathode they combine with oxygen and the electrons, producing water.
So you might be starting to wonder where do we get all this hydrogen gas from. Whilst the element is very abundant, the presence of pure hydrogen gas in our atmosphere is scarce.
So how do we produce it?
Hydrogen gas can be produced from a wide range of resources including natural gas, nuclear power, biomass and renewables. There are many processes that can be used to produce hydrogen, lets focus on the two most common processes.
1) Thermal processes (steam reforming)
- Steam reacts with a hydrocarbon fuel at high pressure to produce hydrogen.
2) Electrolytic processes
- Water is split into hydrogen and oxygen using an electric current. This process is the reverse of what happens in a fuel cell.
The way in which hydrogen is produced classifies the hydrogen fuel type, which is broken down into a colour coded system shown below.
Grey Hydrogen - Hydrogen produced using fossil fuels, resulting in greenhouse gas emissions.
Blue Hydrogen- Using grey hydrogen however carbon capture and storage is used, reducing the greenhouse gas emissions.
Green Hydrogen- Hydrogen produced from renewables, e.g. using electricity from renewables to split water in electrolysis.
What are the advantages of using hydrogen as a fuel?
- The output of a hydrogen fuel-cell is water, making it a super clean fuel
- Hydrogen can be produced in a central location or on site using various sources.
- Compared to propane-powered equipment (e.g. forklifts), the energy density of hydrogen fuel cells is high. This means hydrogen-powered equipment can last for longer periods of time without refuelling.
- It is more efficient than traditional combustion engines (two to three times infact)
- The source of hydrogen (water) is entirely renewable and if produced using renewable electricity, then hydrogen is a carbon neutral energy source.
So, what about the disadvantages?
- Fossil fuels are often used to produce hydrogen. Fossil fuels are ultimately finite and thus it becomes and unsustainable fuel source and also results in the production of greenhouse gas emissions.
- To ensure it is a totally clean fuel source we ideally want to use green hydrogen, however the cost of green hydrogen is very high (around 6-7 times more costly than Grey hydrogen).
- It is highly flammable which poses risks for using it as a fuel source.
- Hydrogen is difficult to store and transport. This is because hydrogen is a lightweight element so when it is a gas at room temperature, it takes up a lot of space. Therefore, to store and transport it there are two options; keeping it as a liquid which requires an extremely cold environment or pressurising the gas so that it takes up less space. Both of these are costly.
Facts About The World’s Largest Green Hydrogen Project
Name: Asian Renewable Energy Hub
Location: Western Australia
Amount of hydrogen produced: 1.75 million tonnes per year (this is the equivalent to filling the tank of around 44 million hydrogen powered cars!)
Amount of energy needed: 6GW wind, 10GW solar to power 14GW of electrolysers
Planned completion: 2027-28
So, is hydrogen the future?
With the current climate crisis and the major push towards net zero, we have no choice but to move away from fossil fuels. As discussed above, not all methods of hydrogen production are carbon neutral. With this, green hydrogen is the ultimately the best option for the climate but is currently very expensive. However, with time, the cost of renewables will decrease which will make green hydrogen a more affordable option. Whilst the future of hydrogen is constantly debated, the momentum behind the industry and the exponential increase in investments are promising. It will be interesting to see developments in the hydrogen industry in the next five years, stay tuned …..