As part of an attempt to convert from fossil fuels to renewable energies, some new technologies have emerged that hold the promise to play a key part in the future of energy production. The two most important developments in this regard are the shift from internal combustion engines to fuel cells for energy generation and the use of hydrogen as primary storage fuel.
Fuel Cells
Fuel Cells can be used to power vehicles and buildings. Fuel cells consist of an electrolyte sandwiched by two electrodes. Different types of fuel cells are: polymer electrolyte membrane (PEM), solid oxide fuel cells (SOFC), phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC) and molten carbonate fuel cells (MCFC). These are designed to run using different types of fuels, such as hydrogen, methanol or natural gas. Pure water is a byproduct of the reaction in a fuel cell and there are no toxic emissions, except for CO2 if a carbon containing fuel like natural gas or methanol is used. However, fuel cells have a higher efficiency than internal combustion engines and avoid the formation of particulates (soot) and NOx. Thus the use of fuel cells reduces pollution and global warming. Most PEM and SOFC fuel cells are in the precommercial testing stages but market ready products are available, e.g. from Ballard Power Systems, IDATech, Siemens-Westinghouse, GE and others.
Hydrogen Economy
Hydrogen is readily available from water and is regarded by many as the fuel of the future. While there are currently technological problems associated with the efficient production, storage and transport of hydrogen, it is nonetheless a very promising fuel. The primary benefit of hydrogen is that it can be easily produced wherever water and electrical energy are available. Also, hydrogen reacts with oxygen to produce electrical energy and water, and it does not contribute to pollution in densely populated areas or to global warming.
Hydrogen Production
Presently hydrogen is commercially produced by steam reforming. In steam reforming the equilibrium between water, CH4 (or any other hydrocarbon), hydrogen and CO is exploited to produce hydrogen. This process is very efficient but only occurs at temperatures exceeding 600°C and it produces the greenhouse gas CO2. Also, some fuel cells require high purity hydrogen which requires an additional cleaning step of the resulting gas stream.
In contrast, electrolysis of water proceeds at room temperature and does not produce greenhouse gases. It uses electrical current to split water directly into hydrogen and oxygen. Unfortunately this process is currently not very effective and novel catalysts are still being developed to improve electrolyzer efficiency. However, electrolysis has the benefit that it can produce very high purity hydrogen needed for many fuel cells and that it can convert electrical energy directly to hydrogen. Rather than using conventional energy to electrolyze water, it is preferable to use renewable energy as it is more economical especially in remote Arctic communities and is environmentally-friendly. Commercial electrolyzers are currently available from Norsk Hydro, Stuart Energies, Teledyne Systems, Proton Energies and many others.
Hydrogen Storage
Various hydrogen storage technologies are known. The most popular ones are liquid storage, compressed storage, and metal hydrides. There are other incumbent technologies such as the storage in microporous materials or nanotubes as well as the adsorption of on ultra high surface area materials. However, all currently available hydrogen storage technologies consist of a storage container which is many times heavier than the stored hydrogen. More development is under way to reduce the container weight with respect to the payload hydrogen. The main driving force for this development is the automotive industry which in addition requires fast hydrogen transfer, small temperature change during filling, low weight and low cost. The currently most promising developments in this area are 5,000 psi and 10,000 psi composite aluminum tanks manufactured by Dynetek and Quantum Technologies.