Green Hydrogen: Importance and Uses in Transportation and Beyond

Introduction to Green Hydrogen Green hydrogen is produced by the electrolysis of water, using electricity derived from renewable energy sources such as solar, wind, or hydroelectric power. This process splits water into hydrogen and oxygen, and because it uses renewable energy, it results in zero greenhouse gas emissions. This distinguishes green hydrogen from other forms such as grey hydrogen (produced from natural gas with emissions released into the atmosphere) and blue hydrogen (produced similarly but with carbon emissions captured and stored).

Applications of Green Hydrogen

Transportation: Green hydrogen is particularly advantageous in the transportation sector, where it can power fuel cell vehicles. Unlike conventional internal combustion engines, hydrogen fuel cells produce water as the only byproduct, offering a significant reduction in pollution. Buses, trucks, and even personal cars are increasingly adopting hydrogen technology due to its efficiency and rapid refueling capabilities.

Aviation: In aviation, green hydrogen has the potential to significantly reduce the carbon footprint. It can be used directly as a fuel or indirectly by producing synthetic fuels. The high energy density makes it suitable for aircraft, and ongoing research aims to overcome challenges such as storage and distribution at airports.

Space Exploration: For space exploration, hydrogen is already a critical component as both a propellant and a power source in fuel cells for spacecraft and extraterrestrial bases. Green hydrogen enhances the sustainability of these operations, making long-term space missions more viable and environmentally friendly.

Economic and Mathematical Analysis of Carbon Credits and Green Hydrogen

Carbon Credits: Carbon credits are permits that allow the holder to emit a certain amount of carbon dioxide or other greenhouse gases. One credit typically permits the emission of one tonne of CO2. These credits can be traded on carbon markets, and their price is influenced by supply and demand.

Economic Sustainability: The production of green hydrogen can be associated with the generation of carbon credits. By avoiding CO2 emissions through the use of renewable energies, companies can earn credits which they can sell. The revenue from these sales can offset the higher initial costs of green hydrogen production facilities.

Mathematical Model: Consider the cost of producing green hydrogen is CgCg​ per kilogram, and the market price for carbon credits is PcPc​ per tonne of CO2 avoided. If producing one kilogram of green hydrogen avoids $E$ kg of CO2 emissions compared to a conventional method, the effective cost reduction per kilogram due to carbon credits is:

Thus, the effective cost per kilogram of green hydrogen becomes:

This model shows how the economics of green hydrogen can be viable through the sale of carbon credits, particularly as the price of renewable energy continues to decrease and the market for carbon credits matures.

Green hydrogen represents a transformative approach to reducing carbon emissions in several heavy industries and sectors. Its application across transportation, aviation, and space exploration shows its versatility and potential to contribute significantly to global decarbonization efforts.

AIR Hydrogen

Extracting hydrogen directly from the air isn’t a common or straightforward process. Typically, hydrogen is not freely available in the atmosphere in its molecular form (H2) because it is extremely light and escapes into outer space. Instead, hydrogen is found in combined forms such as water (H2O) and organic compounds.

Here are a few notable methods and concepts related to extracting hydrogen or its constituents from the air:

1. Water Vapor Extraction:
   • While not directly extracting hydrogen from air, extracting water vapor from the air and then using electrolysis to split it into hydrogen and oxygen is a conceivable method. This involves first condensing the water vapor from air and then applying electrolysis.
   • Technologies like atmospheric water generators capture humidity (water vapor) from the air, which could theoretically be a source of water for hydrogen production.
2. Photocatalytic Water Splitting:
   • Another futuristic concept involves using sunlight and specialized catalysts (photocatalysts) to split water into hydrogen and oxygen directly. If such systems could extract and condense water vapor from the air and then perform photocatalysis, it would be a direct method to produce hydrogen using resources drawn from the air.

The other method, such as Direct Air Capture (DAC) of carbon dioxide, is not directly related to hydrogen production but can be part of a broader system that uses green hydrogen for synthesizing fuels, thereby contributing to carbon-neutral or carbon-negative processes if integrated with renewable energies.

None of these methods involve directly extracting molecular hydrogen from the air, as hydrogen’s low density and high reactivity make it nonviable to exist freely and be harvested directly from the atmosphere. Instead, these methods focus on extracting other components of the air or utilizing the air as a medium to obtain water vapor, which can then be processed to produce hydrogen.

Hydrogen Production without Electricity

Producing hydrogen without using electricity involves a few alternative methods that primarily rely on chemical reactions or thermal processes. Here are some of the most notable methods:

1. Steam Methane Reforming (SMR):
   • This is currently the most common method for producing hydrogen. It involves reacting methane (CH4) with high-temperature steam (water vapor) under pressure in the presence of a catalyst to produce hydrogen and carbon monoxide. A subsequent reaction converts carbon monoxide and more steam to produce additional hydrogen and carbon dioxide. While this method does not use electricity, it is not a green method because it uses fossil fuels and produces significant CO2 emissions.
2. Partial Oxidation (POX):
   • In partial oxidation, a hydrocarbon fuel is partially oxidized with a small amount of oxygen, usually in a controlled environment. It’s similar to combustion but occurs at a lower oxygen-to-fuel ratio. The resulting gas mixture, known as syngas (a mixture of hydrogen and carbon monoxide), is then processed further to separate out the hydrogen. Like SMR, this method also does not rely on electricity but is not environmentally friendly due to its reliance on fossil fuels and CO2 emissions.
3. Thermochemical Water Splitting:
   • Thermochemical water splitting uses high temperatures—obtained from nuclear reactions or concentrated solar power—to drive a series of chemical reactions that ultimately split water into hydrogen and oxygen. This process does not require electricity if the heat is supplied directly through solar thermal energy or nuclear heat. It has the potential to be a green method if the heat source is renewable and carbon-free.
4. Biomass Gasification:
   • This method converts organic materials, such as plant or animal waste, into hydrogen, carbon monoxide, and CO2 by reacting the material at high temperatures with a controlled amount of oxygen and/or steam. The hydrogen can then be separated from the other gases. The green credentials of biomass gasification depend on the biomass source and the lifecycle emissions of the process.
5. Photochemical Water Splitting:
   • Using light, typically from the sun, and a photocatalyst to split water into hydrogen and oxygen. This process mimics natural photosynthesis but is engineered to produce hydrogen. It doesn’t require electricity in the traditional sense but does need light, which can be considered a form of energy.

Methods like Steam Methane Reforming (SMR) and Partial Oxidation (POX), although not using electricity, typically rely on fossil fuels and are not considered green due to significant carbon dioxide emissions unless combined with carbon capture and storage technologies, which would then align them more with blue hydrogen production.

Each of these methods has its own advantages and limitations in terms of efficiency, cost, scalability, and environmental impact. For truly green hydrogen production without electricity, the focus would typically be on processes that can utilize renewable heat or biomass sources, as these can potentially operate with a lower carbon footprint compared to fossil-based methods.

References:

• International Energy Agency (IEA)
• Hydrogen Council Reports
• Academic Journals on Renewable Energy and Sustainable Practices