Hydrogen's Dark Side: Pollution And Environmental Impact

Hydrogen fuel has been touted as the clean fuel of the future, with the ability to power vehicles and generate electrical power with minimal emissions. However, the process of producing hydrogen fuel can result in pollution and global warming emissions, depending on the method of production. While hydrogen combustion engines emit lower levels of pollutants than gasoline or diesel engines, the production process, such as steam reforming or electrolysis of water, can generate carbon dioxide and other greenhouse gases. As a result, the overall environmental impact of hydrogen fuel depends on the specific methods and sources used in its production, as well as the efficiency and cost of implementing hydrogen-based technologies.

Hydrogen production methods and their environmental impact

Hydrogen is increasingly being recognized as a clean and reliable energy vector for decarbonization and defossilization. The environmental impact of hydrogen depends on how it is produced and in what type of vehicle it is used. Hydrogen can be produced from diverse domestic resources, including fossil fuels, biomass, and water through electrolysis using electricity. The primary challenge for hydrogen production is reducing the cost of production technologies to make the resulting hydrogen cost-competitive with conventional transportation fuels.

There are several hydrogen production methods in development. Thermochemical water splitting, for example, uses high temperatures generated by solar concentrators or nuclear reactors to drive chemical reactions that split water to produce hydrogen. Photobiological water splitting uses microbes such as green algae to consume water in the presence of sunlight and produce hydrogen as a byproduct. Photoelectrochemical water splitting employs photoelectrochemical systems to produce hydrogen from water using special semiconductors and energy from sunlight. Other production methods include steam methane reforming, electrochemical routes through water electrolysis using renewable power sources, and biological processes.

The environmental sustainability of hydrogen production can be improved by including renewable energy sources, like solar and wind power, in the processes. The carbon impact of hydrogen can be significantly reduced by using renewable electricity for electrolysis or simply powering biomass gasification. The carbon capture and storage technique used in blue hydrogen also reduces toxic emissions significantly.

The U.S. Department of Energy launched the Energy Earthshots Initiative in June 2021 with the Hydrogen Shot, which seeks to reduce the cost of clean hydrogen by 80% to $1 per 1 kg in 1 decade. The Hydrogen Shot Energy Earthshot Research Centers were established in 2023 to further this goal.

Hydrogen fuel cells and their efficiency

Hydrogen fuel cells are highly efficient, with a CE rating (energy efficiency) of around 60%. This is significantly higher than the efficiency of internal combustion engines, which operate at around 25-35% efficiency. Hydrogen fuel cells achieve this high efficiency by directly converting chemical energy into electrical energy, bypassing the losses associated with combustion. This results in a greater energy output from the same amount of fuel. Additionally, hydrogen fuel cells have a short refueling time, allowing operators to get back to work quickly.

However, it is important to note that the process of producing hydrogen fuel cells is energy-intensive. The creation of hydrogen through electrolysis results in a 20-30% energy loss, followed by another 10% loss during compression and storage. Converting hydrogen into electricity results in an additional 30% loss. As a result, the total energy cost per km is three times higher than that of lithium-ion batteries, which have a CE rating of around 99%. The high cost of manufacturing fuel cell stacks and maintaining hydrogen stations also contributes to the overall expense of hydrogen fuel cells.

Despite the higher operating costs, hydrogen fuel cells offer advantages in certain applications. For example, they are valuable in disaster-struck regions where traditional power infrastructures may be compromised. Hydrogen fuel cells can operate independently of the grid, ensuring a dependable energy source for critical applications such as hospitals, emergency response units, and water treatment facilities. Additionally, remote communities can utilize hydrogen fuel cells to efficiently store surplus renewable energy and generate electricity on demand, even during seasons with limited solar power.

The scalability and modular design of hydrogen fuel cells make them versatile across various industries. They can power emergency generators, vehicles, and large-scale power systems. Hydrogen fuel cells also offer notable operational durability, with some designs lasting over 20,000 hours. As hydrogen can be produced from diverse domestic resources, it strengthens national energy security while reducing dependence on petroleum.

Hydrogen as a clean fuel for the future

Hydrogen is the simplest and most abundant element in the universe. It has the potential to be the clean fuel of the future. An engine that burns pure hydrogen produces almost no pollution, making it a desirable source of power. Hydrogen burns with oxygen to make water vapour and only water vapour—no soot, no nitrous oxides, and no carbon dioxide with its potential greenhouse warming.

Hydrogen can be produced from diverse domestic resources with the potential for near-zero greenhouse gas emissions. Hydrogen can be produced domestically from resources like natural gas, coal, solar energy, wind, and biomass. However, currently, 95% of hydrogen is made from fossil fuels, typically via a process known as steam methane reforming (SMR), in which water is heated at high temperatures to produce steam that reacts with natural gas and produces hydrogen and carbon dioxide (CO2). This process emits significant greenhouse gases — 10 kilograms of CO2 equivalent per kilogram of hydrogen (kg CO2e/kg H2) to 14 kg CO2e/kg H2 — an amount similar to the carbon emissions from producing and burning a gallon of gasoline. Fossil-based hydrogen can also be produced from coal gasification, which has even higher emissions.

Clean hydrogen, on the other hand, is made with nominal or, ideally, no greenhouse gas emissions. Several methods exist to produce clean hydrogen, including natural gas with carbon capture and storage (blue hydrogen) and green hydrogen, which is produced through the electrolysis of water, using renewable energy sources such as wind or solar power. This process emits no CO2, making green hydrogen the most sustainable option. Nuclear (pink hydrogen) can be generated in the same way as electrolytic hydrogen but is powered by nuclear energy instead of wind or solar.

Hydrogen can be used to power highly efficient fuel cell electric vehicles or hydrogen internal combustion engine vehicles. Hydrogen fuel cell vehicles do not produce greenhouse-enhancing carbon dioxide. Hydrogen internal combustion engines emit lower amounts of pollutants than gasoline and diesel engines, while hydrogen-powered fuel cell electric vehicles emit none of these harmful substances—only water (H2O) and warm air.

However, there are also limitations to using hydrogen. Storing and transporting hydrogen can be challenging due to its low energy density. It also requires a significant amount of energy to produce. Furthermore, while fuel cells are becoming more efficient and cheaper, they are still more expensive than conventional combustion engines.

Hydrogen combustion engines and their emissions

Hydrogen combustion engines are a type of hydrogen vehicle that uses an internal combustion engine to burn hydrogen fuel. They are nearly identical to traditional spark-ignition engines, except that they burn hydrogen instead of gasoline. Hydrogen internal combustion engine vehicles (HICEVs) differ from hydrogen fuel cell vehicles (FCEVs), which use hydrogen electrochemically rather than through oxidative combustion.

Hydrogen combustion engines have several advantages. First, they are a zero-emissions technology, as the absence of carbon in pure hydrogen means that no carbon-based pollutants, such as carbon monoxide (CO) or hydrocarbons (HC), or carbon dioxide (CO2) are present in the exhaust. Second, hydrogen combustion engines are a more mature technology than hydrogen fuel cells, with internal combustion engines having been universally used for decades and supported by extensive service networks. This makes them a more familiar and lower-risk option for vehicle manufacturers and fleet operators. Additionally, hydrogen engines can operate with lower-grade hydrogen, which can be produced on-site using steam methane reforming and carbon capture and storage (CCS). This makes them a more flexible option in the transition to high-quality green hydrogen.

However, it is important to note that hydrogen combustion engines are not entirely emission-free. While they do not produce carbon-based pollutants, the combustion of hydrogen in air can produce oxides of nitrogen, or NOx, due to the presence of nitrogen in the air. This is a common issue with high-temperature combustion fuels, such as kerosene, gasoline, diesel, or natural gas, and it is exacerbated by the very high temperatures generated by hydrogen combustion. As a result, hydrogen combustion engines may require exhaust after-treatments to reduce NOx emissions, particularly for indoor use.

Furthermore, while hydrogen combustion engines have the potential to reduce emissions, the production of hydrogen currently involves emissions. In 2021, almost 96% of global hydrogen production was from natural gas (47%), coal (27%), and oil (22%), which all produce emissions. While emissions from burning hydrogen can be negligible, the emissions from producing hydrogen are currently higher than direct combustion of the source. This is a significant consideration when evaluating the environmental impact of hydrogen combustion engines.

Overall, hydrogen combustion engines have the potential to play a significant role in reducing vehicle and transportation emissions, particularly for heavy-duty commercial vehicles. However, it is important to consider both the emissions from the combustion process as well as the emissions from hydrogen production when assessing the environmental impact of this technology.

Hydrogen's potential to reduce nitrogen oxide emissions

Hydrogen has the potential to reduce nitrogen oxide emissions, but the conditions under which it is produced and used must be considered. Hydrogen can be produced from diverse domestic resources, including natural gas, coal, solar energy, wind, and biomass, with the potential for near-zero greenhouse gas emissions. When used as fuel in electric vehicles, hydrogen fuel cells emit only water vapour and warm air, significantly reducing nitrogen oxide emissions compared to traditional gasoline and diesel engines.

However, the combustion of pure hydrogen at very high temperatures (above 1500°C) can produce nitrogen oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2), which are hazardous air pollutants. This is because NOx formation occurs when air, which contains nitrogen and oxygen, is exposed to extremely high temperatures. Hydrogen burns at higher temperatures than natural gas, which may result in higher NOx emissions.

To mitigate this issue, hydrogen can be diluted with additional air, which cools the flame and results in lower-temperature combustion, thereby reducing NOx emissions. Furthermore, hydrogen can be blended with other fuels, such as ethanol and palm oil biodiesel, to reduce NOx emissions from diesel engines. These blends, combined with hydrogen addition, have been shown to improve NOx reduction activity by up to 73%.

Overall, while hydrogen has the potential to significantly reduce nitrogen oxide emissions, particularly in the transportation sector, careful consideration must be given to the conditions under which it is produced and used to ensure that NOx emissions are minimised.

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