Hydrogen fuel cells generate electricity using a chemical reaction. Each fuel cell has two electrodes; a negative anode and a positive cathode. The reaction to produce the electricity happens at these electrodes, with an electrolyte carrying electrically charged particles between them and a catalyst to speed up the reactions.
Hydrogen acts as the basic fuel in a hydrogen fuel cell, but the cell also needs oxygen to work. One of the largest advantages of these fuel cells is that they generate electricity with very little pollution, as the hydrogen and oxygen used to generate the electricity combines to produce water as a by-product. Cells that use pure hydrogen as fuel are completely carbon-free.
Other types of fuel cell system include those that use hydrocarbon fuels like natural gas, biogas, or methanol. Because fuel cells use an electrochemical reaction rather than combustion, they can achieve higher efficiencies than with traditional energy production methods. This can be improved further by with combined heat and power generators that use waste heat from the cell for heating or cooling applications.
The process by which a fuel cell works can be summarised as follows:
- Hydrogen atoms enter at the anode, while oxygen is fed to the cathode
- The hydrogen atoms are separated into protons and electrons at the anode
- The now positively charged protons pass through the membrane (or electrolyte) to the cathode, with the negatively charged electrons take a different route as they are forced through a circuit to generate electricity
- After passing through the circuit and the membrane accordingly, the electrons and protons meet at the cathode where they combine with oxygen to produce heat and water as by-products.
Single fuel cells do not generate a large amount of electricity, so they are arranged into stacks to create enough power for their intended purpose, whether that is powering a small digital device or a power plant.
Fuel cells work like batteries but, unlike batteries, they will not run down or need recharging and can continue to produce electricity while the fuel source (in this case, hydrogen) is supplied.
Being comprised of an anode, cathode and an electrolyte membrane, there are no moving parts in a fuel cell, making them silent in operation and highly reliable.
There are a number of pros and cons associated with hydrogen fuel cells, the benefits include:
- Durability
- Energy Security
- Fuel Flexibility
- High Efficiencies
- Low / Zero Emissions
- Quiet Operation
- Reliability
- Scalability
The challenges associated with fuel cells include:
1. Cost
The cost of fuel cells can be high given the use of platinum as one of the largest component materials. There is work underway to find non-platinum catalyst approaches
2. Hydrogen Extraction
The extraction of hydrogen for use in fuel cells can take a lot of energy to achieve, undermining the green benefits of fuel cell use
3. Infrastructure
There is a need to create the infrastructure to support the growth in fuel cell use, including retrofitting vehicles
4. Safety
The flammable nature of hydrogen poses evident safety concerns for its widespread use
Find out more about the pros and cons here
What are they used for?
Hydrogen fuel cells offer a range of applications, from powering our homes and businesses to moving vehicles like cars, buses and trains and more. Here is a selection of fuel cell uses:
1. Power
Fuel cells act as power sources for a variety of commercial, industrial and residential applications. These range from homes to spacecraft and research stations. Fuel cells are particularly useful for remote locations due to their lack of moving parts, which means they are highly reliable and unlikely to fail. Ideal conditions provide up to 99.9999% reliability, which is equal to less than one minute of downtime every six years.
2. Cogeneration
Fuel cells can be made even more efficient through cogeneration. This is where fuel cell systems are used to generate power while the waste heat produced is used to heat buildings or power cooling systems. Cogeneration systems can reach 85% efficiency (of which 40-60% is electric). However, these systems can be costly and have a relatively short lifetime as well as taking up space with the need for a hot water storage tank.
3. Transport
Fuel cells can be used for a variety of transport applications, from automobiles to buses, ships, trains and aircraft. Fuel cells are also being incorporated into motorcycles, bicycles and scooters.
18,000 fuel cell electric vehicles (FCEVs) had been leased or sold by the end of 2019 and these automobiles have an average range of between 314 and 380 miles between refuelings, while refuelling takes less than five minutes, making this technology competitive against battery-based electric cars that take much longer to charge. In addition, fuel cells running on hydrogen gas use around 40% less energy and emits 45% less greenhouse gas than internal combustion engines. However, to be a truly viable option, many of the challenges around hydrogen storage, transport and extraction will need to be addressed.
Despite the challenges around fuel cell automobiles, fuel cell buses are already proving effective, while forklift trucks are also a key driver of hydrogen fuel demand. Forklifts are of particular interest since they often need to operate indoors where emissions need to be controlled. This means that electric forklifts are often used, but fuel cells provide benefits over battery power, including faster refuelling and a lack of degradation at low operating temperatures, such as in refrigerated warehouses.
Fuel cells have also been used for manned aerial vehicles, often using a combination of technologies, such as a proton exchange membrane fuel cell with a battery hybrid as back-up during testing. Fuel cells are being more widely deployed in unmanned aerial vehicles as well as for providing auxiliary power on aircraft, replacing fossil fuels for applications such as starting the engines and powering on-board electrics.
Fuel cells have also been used for tourist boats on the canals of Amsterdam and the German and Italian navies have used fuel cells to allow submarines to remain submerged for weeks, while also improving silent running operations.
4. Portable Power
Portable fuel cell systems are classified as weighing less than 10kg and producing under 5kW of power. These types of cell have a wide range of applications for powering small devices of 1-50w and for larger power generation of 1-5kW for remote locations.
The smaller microfuel cells are aiming to reach markets such as mobile devices and laptops with advantages including energy density and weight reduction when compared to lithium ion batteries. Market penetration would require some further developments in fuel cell technology to reduce costs, but the promise of longer usage times between charging is appealing.
Larger scale portable power shows promise for the leisure sector, the military and geographically remote industrial applications such as weather stations. The advantages for these larger, yet still portable, cell stacks is the amount of power that can be generated per weight compared to batteries.
5. Other Applications
The uses listed above are just some of the examples of where fuel cells could be used. Other applications include power for base stations and cell sites, distributed power generation, emergency power systems as a back-up for when other systems fail, telecommunications, base load power plants, solar hydrogen fuel cell water heating, portable charging stations for small electronic devices, small heating appliances, food preservation for shipping containers (exhausting the oxygen through power generation), and electrochemical sensors.
Who Invented Hydrogen Fuel Cells?
The first fuel cells were invented in 1838 by Sir William Grove, however it was over a century later until fuel cells were first used commercially, following the invention of the hydrogen oxygen fuel cell by Francis Thomas Bacon in 1932.
Alkaline fuel cells, also known as the ‘Bacon Fuel Cell’ after their inventor, have been in use by NASA since the mide-1960s, where they are used to provide power to satellites and space capsules.
How Long Do They Last?
The exact lifetime of a fuel cell depends on what it is being used for, much as with how batteries drain at different rates depending on application. However, as an example, hydrogen fuel cell cars can now average between 312 and 380 miles before they need refuelling.
The fuel cell stacks in cars are designed to last for the lifetime of the vehicle, which is around 150,000 to 200,000 miles. Once they have completed their lifespan, fuel cells can be disassembled and the materials recycled.
Are Hydrogen Fuel Cells a Renewable Source of Energy?
The abundance of hydrogen in the universe means that hydrogen fuel cells are a renewable source of energy. They are also a clean method of energy production, although there are still some concerns over the use of fossil fuels for hydrogen extraction as well as the potential carbon footprint associated with hydrogen transportation, for example.
However, hydrogen fuel cell technology has the potential to be a completely green and renewable source of power, with the only by-products being heat (which can be used elsewhere) and water.
In addition, fuel cells do not run down or need recharging like batteries, so long as there is a constant source of fuel and oxygen.
Are They Dangerous?
Hydrogen has the highest flammability range and lowest ignition energy point of any fuel, leading to obvious concerns over the safety of hydrogen fuel cells. However, despite this, the United States’ National Fire Protection Association have determined that hydrogen fuel cell and battery-powered electric vehicles are no more dangerous than traditional combustion engine vehicles.
Part of the reason for this is the speed at which hydrogen dissipates up into the air. Hydrogen diffuses directly up into space at the rate of 20mph so, as long as it is not trapped inside a container or structure long enough to accumulate into large quantities, it shouldn’t be too hazardous.
There have also been tests done on hydrogen fuel tanks in vehicles, simulating a collision and being shot at point blank range. The military have even strapped a rocket propelled grenade to the side of hydrogen fuel tank to simulate a direct hit and also simulated shrapnel damage. In all cases, hydrogen fuel was found to be no more dangerous than liquid fuels and in most cases less so.
In fact, hydrogen fuel cell vehicles could be argued to be safer than battery electric vehicles (BEV). The energy in a BEV does not vent into the atmosphere as with hydrogen, meaning that there is a danger of neighbouring cells catching fire or exploding at a later point. It is also difficult to extinguish a BEV battery fire, which produces toxic fumes.
Of course, hydrogen fuel cells have been widely used for forklift trucks for over a decade without any major incidents, while thousands of hydrogen fuel cell vehicles are on our roads already.
When used outdoors, hydrogen is deemed safer than other fuel types, but it can still be dangerous where it is stored or held in a place where it cannot escape. That said, experts don’t believe hydrogen to be any more dangerous than other fuels; it is all a matter of learning how to handle it safely.
Are Hydrogen Fuel Cell Cars the Future?
There are a lot of manufacturers who have investigated hydrogen fuel cell technology and some have created hydrogen-powered cars in small numbers, but could they meet our future transport needs?
Hydrogen has been used to power engines for years and is the most abundant element on our planet, while the ability to produce a lot of power in a small device means that hydrogen fuelled cars could travel much further than all-electric vehicles. There are also the benefits with regards to emissions, making it the cleanest fuel available.
The demand for cleaner transport is clear, with sales of battery-powered electric cars rising by 162% in the year up to November 2020 as compared to the previous 12 months. However, this also means that many manufacturers are investing in electric vehicles rather than hydrogen. Another barrier to uptake is the lack of infrastructure, with too few hydrogen fuel stations for drivers to use as they can with petrol and diesel refuelling.
Despite these difficulties, there are a number of reasons why hydrogen fuel cells could be the future of the car; not least the environmental benefits, refuelling times compared to battery charging, and the abundance of fuel.
Many manufacturers are already looking at hydrogen as a complement to electric power, which currently produces the around same amount of CO2 over the lifetime of a vehicle (124g/km for EVs and 120g/km for hydrogen fuel cells). However, the use of biomass to obtain hydrogen could see life-cycle emissions from fuel cell cars drop to around 60g/km of CO2; significantly lower than that achievable with EVs.
However, to truly become the future of the car, hydrogen fuel cells need investment in the technology and the supporting infrastructure to allow readily-available refuelling. Until that happens, hydrogen fuel cells will not be able to compete with EVs or petrol and diesel.
Hydrogen fuel cells have been used for many decades for a wide range of applications, from small electronic devices to vehicles. Hydrogen is the cleanest available energy and is not as hazardous as you may think.
Hydrogen fuel cells are already widely used for vehicles such as forklifts, but there is a need for improved infrastructure before they can really challenge for a place as the primary method of fuelling our transport needs.
However, with many very real benefits, hydrogen fuel cells look set to be part of the power generation future in some form.