Energy in the Future series: The potential of fuel cells to reduce emissions
A fuel cell is an electrochemical device able to convert the chemical energy of a fuel directly into electric energy.
Latest update: May 2019
The interest in fuel cell technology as a sustainable solution is expanding worldwide as stringent actions are needed to reduce greenhouse gases. The ground propulsion is seeing a strong development of hydrogen-powered vehicles including cars, buses, trains and trucks. Research is actively seeking solutions to reduce all costs associated with the technology as well as improve the hydrogen deployment.
What is fuel cell technology?
A fuel cell is an electrochemical cell that generates electrical energy via a chemical reaction, between a hydrogen-containing fuel and oxygen or another combustion agent. In many cases, water is the only by-product, therefore the technology is free from harmful emissions at the point-of-use.
The main benefits of fuel cells are:
- High efficiency – fuel cells are 60% - 80% energy efficient
- Clean – no harmful emissions at the point-of-use
- No noise – These vehicles produce fewer vibrations than conventional vehicles
- Scalable – can be stacked onto one another
- Low maintenance – Despite the higher initial cost, fuel cells do not require much maintenance
What industries use fuel cell technology?
Within the automotive industry, different companies are developing fuel-cell technology. The most active on this technology are Toyota, Hyundai and Honda, which have already released the first models on the market. The working principle behind these cars is based on the use of compressed hydrogen at 700 bar to produce electricity through the fuel cells and power an electric motor for the traction.
The public transport sector is also trialling fuel cell technology. Various cities worldwide are operating fuel cell buses to demonstrate that this technology can cut emissions and noise pollution while providing good quality public transport. For example, the city of London integrated 10 fuel cell buses within the fleet and showed the first hydrogen-powered double-decker bus in the world.
Within the rail industry, China introduced the first light-rail locomotive with hydrogen fuel cells in 2017. In Germany, Alstom has developed the Coradia iLint which entered passenger service in October 2018. This train uses fuel cells to generate electricity for traction and onboard equipment, and batteries to store and restore energy from the fuel cells and regenerative braking, respectively.
Within the trucking industry, GM, Toyota, Scania and Bosh in partnership with Nikola Motor Company are all targeting to employ fuel cell technology in the upcoming future. First trials have demonstrated good results and confirmed hydrogen benefits compared to other power sources such as batteries.
How will fuel cell technology impact the rail industry?
The UK rail industry has started developing hydrogen-powered trains as a possible solution to replace diesel-only trains by 2040. This could contribute to reducing carbon emission from 40% (brown hydrogen) to 100% (green hydrogen) compared to diesel trains. Since steam is the only by-product, there is the opportunity to improve the air quality in enclosed railway stations, where current diesel trains release harmful emissions. As fuel cells do not have any moving components, the technology requires less maintenance than diesel engines, therefore reducing maintenance costs.
What uncertainties remain in fuel cell technology?
Fuel cell technology is still maturing, and production is expensive. This is due to the use of costly materials (e.g. platinum for catalysts and PTFE for the electrolyte membrane) and because most units are not mass-produced. Although fuel cells do not emit harmful emissions at the point-of-use, there can be harmful emissions due to the sourcing of hydrogen. Most hydrogen is sourced from reforming hydrocarbons due to the low cost, which could negate the environmental advantage of fuel cells over diesel. Alternatively, hydrogen could be sourced from biomass and electrolysers which are costlier extraction methods but have reduced or no emissions. Hydrogen can be stored as compressed gas, a liquid or a solid, but there are different limitations associated with each storage method: compressed hydrogen is costly, has a relatively low energy density and a tank rupture could cause an accident, liquid hydrogen requires very low temperatures which may be expensive, and storage in liquid ammonia can be harmful if ingested.
What is the current state of R&D?
The main barriers for large commercialization of the fuel cell technology are attributable to cost, durability and performance. Volkswagen, in partnership with Stanford University in the US, is developing a new manufacturing process where the platinum atoms are directly applied to a carbon surface, creating particularly thin particles. This allows minimizing the platinum utilised, increasing the lifetime and efficiency of the fuel cell catalysers by three times over the current standards.
At the same time, hydrogen limitations – such as cost of production, storage complications, safety and distribution – are also the reasons for limiting the adoption of this technology. So far, the methods available for breaking down water molecules have been based on highly purified water, which limit future large-scale hydrogen. Researchers at Stanford University have succeeded in exploiting salt water, the most abundant source on Earth, to obtain hydrogen fuel through electrolysis. Thus, fulfilling an important step for large-scale energy production. Sodium chloride, which is negatively charged in salt water, can corrode the positive end, thus limiting the life span of the system. To solve this problem, the team of researchers covered the anode with a layer of iron-nickel hydroxide, rich in negative charges, which were, therefore, able to repel chloride.
The most used methods for hydrogen storage are compressed hydrogen and liquid hydrogen, which have a poor energy density compared to fossil fuels and a large energy loss, respectively. Other storage systems are being tested. An example is the metal hydrides, compounds that host hydrogen, in atomic form, in the interatomic space of the crystal lattice of the host metal. Various European research programs have highlighted how solid-state hydrogen storage is a promising solution, however, their use is currently limited by the operating temperature and reaction heat. Projects like EDEN aim to overcome these obstacles and produce an efficient storage system.
Hydrogen safety covers its production as well as handling and use. Hydrogen flammability is the main concern since it is flammable when mixed even in small amounts with air. R&D activities are, therefore, focused on developing hydrogen sensors for detecting hydrogen leaks. Swedish researchers have recently developed an ultra-fast hydrogen leak detector that can detect 0.1% hydrogen in the air in one second, a benchmark never previously attained.
Hydrogen distribution is currently implemented through tankers. The distribution network through pipelines is present in several countries but with short total lengths. The natural gas grid could provide the key to unlocking hydrogen economy.
What should the rail industry do?
The rail industry should continuously follow the research and technology development aiming to reduce the overall cost of fuel cells and hydrogen production. A cost-benefit analysis to see whether fuel cell technology is economically viable on lines that will not be electrified in the mid-long term may also be valuable. More specifically, the industry could conduct an analysis on the safety elements, associated distribution cost and constraints and the overall carbon impact dependent on production and distribution options.