Hydrogen is the most abundant element in the universe. It does not exist by itself in an elemental form, but it can be produced easily by various means from coal, oil, natural gas, biomass, and water. This allows us to produce where and when we need it. A large part (~95%) of the hydrogen used today comes from reforming natural gas. The rest comes from electrolysis using electricity generated from fossil fuels. Hydrogen is ideal in many respects as a fuel as it can be used to generate energy without polluting the atmosphere and without adding to the greenhouse gas emissions. The by-product of hydrogen combustion via a fuel cell is water. Of course generation is only a part of the hydrogen economy.
Hydrogen-powered fuel cells can be highly efficient and emit only water as an unused output. Hydrogen can be produced locally, and then stored for later use, and even shipped via pipeline or containers. All kinds of energy resources, from fossil fuels to renewable fuels like wind, solar, and biomass, can be used to produce hydrogen. Hydrogen can be used in fuel cells to power vehicles and provide electricity and heat for homes and offices.
While this is all great, why has it not happened? A large part of it is economics and safety but there are other issues as well. There are various aspects of this hydrogen economy that have to function together to make this an attractive proposition. Hydrogen technology must be flexible, affordable, safe, and available to all regions of the country. And to truly be sustainable, it must be produced from domestic renewable resources.
Integration of hydrogen production, storage and distribution is an important part of how successfully these can be deployed. Together the system created has to be sustainable, safe and affordable.
Let us look at hydrogen production. The most common method is steam reformation of natural gas. This is not a desired method as it releases carbon-dioxide to the atmosphere with associated energy loss. There are other ways to produce hydrogen and in a purer content. Thermo-chemical methods which heat biomass or fossil fuels with little or no oxygen can be used to generate a hydrogen and carbon monoxide into Syngas and/or liquefied oil by Pyrolysis. This can be steam reformed to hydrogen using a water-gas-shift reaction to generate hydrogen. This has it obvious problems as mentioned earlier. A more attractive method is electrolysis – to split water into oxygen and hydrogen. The method is well understood but you need electricity to carry out the split. Renewable resources such as wind or solar generated electricity can be used to generate hydrogen when there is less demand for it for other things.
Figure courtesy GreenCar Congress
There are biological photolytic methods to generate hydrogen as well using nature itself. Microalgae and Photosynthetic Bacteria which can be made to produce hydrogen instead of sugar and oxygen.
The next factor is hydrogen storage. Hydrogen needs to be stored as well as transported. Due to its low natural density, it has to be compressed in pressurized tanks but even these are bulky and hard to transport. Other methods have involved storing hydrogen in Nano-Structures surfaces such as Carbon-Nano-Tubes or in crystalline structures such as metal hydrides. But these methods have regeneration issues that are possible but not convenient yet. There is also the customer’s (user) fear of safety – the “Lindenburg balloon” disaster is still not forgotten.
Delivery is also a key enabling issue. New infrastructure is required to move hydrogen from production facilities to dispenser. Most likely pipelines will have to be installed to transport hydrogen. Care to prevent leakage and other safety issues will need to be addressed.