Table of Contents
Hydrogen Properties: Hydrogen is the most abundant element in the universe. In the creation of the universe heavier elements were made from hydrogen or from other elements that were made from hydrogen. Hydrogen is a colorless, odorless, combustible gas. Hydrogen gas is so light and diffusive that uncombined hydrogen can escape from the atmosphere. http://chemistry.about.com/od/elementfacts/a/hydrogen.htm
Hydrogen Uses: Hydrogen is important in the proton-proton reaction and carbon-nitrogen cycle. Great quantities are used for the fixation of nitrogen from the air in the Haber ammonia process. Hydrogen is use in welding, for the hydrogenation of fats and oils, in methanol production, in hydro-dealkylation, hydrocracking, and hydro-desulfurization. Other applications include producing rocket fuel, filling balloons, powering fuel cells, producing hydrochloric acid, and reducing metallic ores. The hydrogen ‘economy’, or the hydrogen ‘age’, is a concept based on using hydrogen as an energy carrier, synonymous to electricity, for the purposes of providing energy to a multitude of applications from homes to vehicles. http://chemistry.about.com/od/elementfacts/a/hydrogen.htm
Hydrogen Sources: Hydrogen occurs rarely in the free state but may be found in volcanic gases and some natural gases. Hydrogen is most often produced by steam on heated carbon, decomposition of certain hydrocarbons with heat, action of sodium or potassium hydroxide on aluminum, electrolysis of water, or displacement from acids by certain metals. There is a strong movement towards the production of green hydrogen; hydrogen produced from renewable resources. http://chemistry.about.com/od/elementfacts/a/hydrogen.htm
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange’s Handbook of Chemistry (1952) International Atomic Energy Agency ENSDF database (Oct 2010)
Climate change and its link to our present and future energy needs are the greatest challenge facing our planet. Hydrogen is regarded as one key element of a potential energy solution for the twenty-first century, capable of assisting in issues of environmental emissions, sustainability and energy security. Hydrogen has the potential to provide energy in transportation, distributed heat and power generation and energy storage systems with little or no impact on the environment, both locally and globally. http://rsta.royalsocietypublishing.org/content/365/1853/1043.long
Hydrogen is thought to be the solution as a clean and renewable future energy vector. The use of hydrogen in a polymer electrolyte membrane fuel cell is likely to be at the centre of power generation for stationary and mobile applications.
Hydrogen and fuel cells have a wide range of applications for use almost any time and anywhere.
Fuel cells are ideal for residential zones. They are virtually silent with no moving parts and provide reliable power 24/7. In addition, a fuel cell big enough to power an entire home is about the size of a traditional Air Conditioning unit. Fuel cells already power thousands of homes in Japan and are beginning to do so in other parts of the world.
Fuel cells can be produced in stacks large enough to power the biggest of office buildings, and only occupy the area of a couple parking spaces. Again, fuel cells are a great fit in this situation as they are noiseless, environmentally friendly, and efficient. Distributed power from fuel cells does not rely on transmission lines and thus eliminates the need for backup power generators.
Major automakers are predicting that commercial fuel cell vehicles will be in showrooms in certain countries in 2015. Already fuel cell powered buses are operating in various jurisdictions throughout the world. There are hundreds of fuel cell vehicles in operation globally with millions of miles/kilometers of performance data and hundreds of thousands of hydrogen fueling operations.
The fuel cell lift truck market is developing in North America since it provides significant productivity improvement over battery-powered lift trucks. Telecommunications towers are using hydrogen-powered fuel cells to provide important, long-term backup power.
Fuel cells are classified primarily by the kind of electrolyte they employ. This classification determines the kind of chemical reactions that take place in the cell, the kind of catalysts required, the temperature range in which the cell operates, the fuel required, and other factors. These characteristics, in turn, affect the applications for which these cells are most suitable. There are several types of fuel cells currently under development, each with its own advantages, limitations, and potential applications.
Polymer electrolyte membrane (PEM) fuel cells—also called proton exchange membrane fuel cells—deliver high-power density and offer the advantages of low weight and volume, compared with other fuel cells. PEM fuel cells use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum catalyst. They need only hydrogen, oxygen from the air, and water to operate and do not require corrosive fluids like some fuel cells. They are typically fueled with pure hydrogen supplied from storage tanks or on-board reformers.
Most fuel cells are powered by hydrogen, which can be fed to the fuel cell system directly or can be generated within the fuel cell system by reforming hydrogen-rich fuels such as methanol, ethanol, and hydrocarbon fuels.
Direct methanol fuel cells (DMFCs), however, are powered by pure methanol, which is mixed with steam and fed directly to the fuel cell anode. Direct methanol fuel cells do not have many of the fuel storage problems typical of some fuel cells because methanol has a higher energy density than hydrogen—though less than gasoline or diesel fuel. Methanol is also easier to transport and supply to the public using our current infrastructure because it is a liquid, like gasoline.
Alkaline fuel cells (AFCs) were one of the first fuel cell technologies developed, and they were the first type widely used in the U.S. space program to produce electrical energy and water on-board space crafts. These fuel cells use a solution of potassium hydroxide in water as the electrolyte and can use a variety of non-precious metals as a catalyst at the anode and cathode. High-temperature AFCs operate at temperatures between 100°C and 250°C (212°F and 482°F). However, newer AFC designs operate at lower temperatures of roughly 23°C to 70°C (74°F to 158°F)
Phosphoric acid fuel cells (PAFCs) use liquid phosphoric acid as an electrolyte—the acid is contained in a Teflon-bonded silicon carbide matrix—and porous carbon electrodes containing a platinum catalyst. The chemical reactions that take place in the cell are shown in the diagram to the right. The phosphoric acid fuel cell is considered the “first generation” of modern fuel cells. It is one of the most mature cell types and the first to be used commercially. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses.
Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide (LiAlO2) matrix. Because they operate at extremely high temperatures of 650°C (roughly 1,200°F) and above, non-precious metals can be used as catalysts at the anode and cathode, reducing costs.
Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte. Because the electrolyte is a solid, the cells do not have to be constructed in the plate-like configuration typical of other fuel cell types. SOFCs are expected to be around 50%–60% efficient at converting fuel to electricity. In applications designed to capture and utilize the system’s waste heat (co-generation), overall fuel use efficiencies could top 80%–85%. Solid oxide fuel cells operate at very high temperatures—around 1,000°C (1,830°F). High-temperature operation removes the need for precious-metal catalyst, thereby reducing cost. It also allows SOFCs to reform fuels internally, which enables the use of a variety of fuels and reduces the cost associated with adding a reformer to the system. http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html
Hydrogen production is the first step toward a larger goal: the transition to a hydrogen economy. The hydrogen economy is a vision for a future in which hydrogen replaces fossil fuels. The goals are to reduce dependence on non-renewable resources and cut down environmentally harmful emissions. Hydrogen is an abundant element, occurring naturally in fossil fuels, water, and most organic compounds. Once in its pure, diatomic form (H2), hydrogen may be used in fuel cells and hydrogen combustion engines to cleanly release its stored energy.
The first step in the process of producing hydrogen fuel is the conversion of hydrogen to the diatomic form. The energy required for this conversion is either stored within a feedstock to the process or comes from an external energy source. Feedstocks like methane, coal, and biomass are carbon-based, so they will release carbon monoxide or carbon dioxide as a by-product of the conversion process. Water contains only hydrogen and oxygen, so no carbon dioxide is released in its decomposition.
Steam methane reforming is a three step process to produce hydrogen. Methane is first
catalytically reformed at elevated temperature and pressure to produce a syngas mixture of
H2 and CO. A catalytic shift reaction is then carried out to combine CO and H2O to produce the H2 product. The hydrogen product is then purified by adsorption. This method produces the majority of the hydrogen used in the world today. It is the lowest cost method for hydrogen production but does contribute carbon dioxide to the atmosphere.
Like steam methane reforming, coal gasification involves three steps: treatment of coal
feedstock with high temperature steam (1330ºC) to produce syngas, a catalytic shift conversion, and purification of the hydrogen product. Coal gasification is a proven technology, with large-scale processes currently in place for the production of H2 for use in the chemical industry (primarily for ammonia production). Coal gasification is an established technology used in hydrogen production today, but additional technical and economic considerations for capture and storage of CO2 will be necessary.
Hydrogen production processes that can use nuclear heat or alternative energy sources are endothermic water splitting processes. These processes are generally newer technologies and tend to be more expensive than fossil fuel processes, but do not produce harmful emissions or consume large quantities of non-renewables. Photocatalytic and photobiological processes use solar energy, and thermo-chemical processes use nuclear heat. In the case of electrolysis, electricity supplies the energy required. While this electricity could be produced using fossil fuels, a cleaner alternative is using electricity produced using nuclear heat or alternative energy processes like wind, solar, or water power. These processes are attractive because the water feedstock contains only hydrogen and oxygen, so no carbon dioxide is released in its decomposition.
Electrolysis uses electricity to dissociate water into diatomic molecules H2 and O2. An electric potential is applied across a cell with two inert electrodes containing a conducting medium, generally an alkaline electrolyte solution such as an aqueous solution of potassium hydroxide (KOH). Electrons are absorbed and released at the electrodes, forming hydrogen at the cathode and oxygen at the anode. This describes an alkaline electrolyzer. Proton exchange membrane (PEM) electrolyzers also exist (these are effectively PEM fuel cells operated in reverse). They use a polymeric membrane and no alkaline electrolyte. Solid oxide fuel cells (SOFCs) operated in reverse as a solid oxide electrolyzer cell (SOEC) are also viable methods for hydrogen production.
Because electrolysis is not thermodynamically limited, the efficiency of the electrolyzer may theoretically approach 100%. In practice, somewhat lower efficiencies are observed due to operation of the electrolysis unit at elevated voltages and losses in other equipment.
Electrolysis has the advantage of versatility; a variety of energy sources may be used to produce the electricity for the process. The process is environmentally friendly, producing no harmful greenhouse gas emissions, provided that it is paired with an electricity source that is also environmentally friendly, like solar, wind, or nuclear power.
If traditional fossil fuel processes are used to produce the electricity, the process may still indirectly contribute to the polluting effects of these processes.
High Temperature Water Splitting
High-temperature water splitting (a “thermochemical” process) can be used to produce hydrogen and oxygen. Solar concentrators and nuclear reactors are being used to produce high-temperature heat (500°C–2000°C) that drives a series of chemical reactions that produce hydrogen. Researchers have identified cycles appropriate to specific temperature ranges and are examining these systems in the laboratory. The more than 200 possible cycles identified have been screened and down-selected to about twelve for initial research. Solar- and nuclear-driven high-temperature thermochemical water splitting cycles produce hydrogen with near-zero greenhouse gas emissions using water and either sunlight or nuclear energy.
Biomass conversion includes either thermochemical or biochemical conversions to intermediate products that can then be separated or reformed to hydrogen. They can also include fermentation techniques that produce hydrogen directly. Biomass-to-hydrogen is complex, not only because of the technical details of the conversion processes themselves, but also because of the many process types that could be employed.
Hydrogen storage is a key enabling technology for the advancement of hydrogen and fuel cell power technologies in transportation, stationary, and portable applications. Efforts focus on on-board vehicular hydrogen storage systems that allow for a driving range of greater than 500km while meeting packaging, cost, safety, and performance requirements to be competitive with current vehicles. Storage technologies in stationary and portable applications are driven by space limitations for supply volumes.
The energy density of gaseous hydrogen can be improved by storing hydrogen at higher pressures. This higher pressure requires material and design improvements in order to ensure tank integrity. Advances in compression technologies are also required to improve efficiencies and reduce the cost of producing high-pressure hydrogen. Carbon fiber-reinforced 5000-psi and 10,000-psi compressed hydrogen gas tanks are currently being used in fuel cell buses and cars. By increasing the amount and pressure of hydrogen, a greater driving range can be achieved in a fuel cell vehicle but at the expense of cost and valuable space within the vehicle. Volumetric capacity, high pressure, and cost are thus key challenges for compressed hydrogen tanks. Refueling times, compression energy penalties, and heat-management requirements during compression also need to be considered as the mass and pressure of on-board hydrogen are increased.
The energy density of hydrogen can be improved by storing hydrogen in a liquid state. However, the issues with LH2 tanks are hydrogen boil-off, the energy required for hydrogen liquefaction, volume, weight, and tank cost. The energy requirement for hydrogen liquefaction is high; typically, 30% of the heating value of hydrogen is required for liquefaction. New approaches that can lower these energy requirements and thus the cost of liquefaction are needed.
There are presently three mechanisms known for storing hydrogen in materials: absorption, adsorption, and chemical reaction.
In absorptive hydrogen storage, hydrogen is absorbed directly into the bulk of the material. In simple crystalline metal hydrides, this absorption occurs by the incorporation of atomic hydrogen into interstitial sites in the crystallographic lattice structure.
Adsorption may be subdivided into physisorption and chemisorption based on the energetics of the adsorption mechanism. Physisorbed hydrogen is more weakly and energetically bound to the material than is chemisorbed hydrogen. Sorptive processes typically require highly porous materials to maximize the surface area available for hydrogen sorption to occur and to allow for easy uptake and release of hydrogen from the material.
The chemical reaction route for hydrogen storage involves displacing chemical reactions for both hydrogen generation and hydrogen storage. For reactions that may be reversible on-board a vehicle, hydrogen generation and hydrogen storage take place by a reversal of the chemical reaction as a result of changes in the temperature and pressure. Sodium alanate-based complex metal hydrides are an example. In many cases, the hydrogen generation reaction is not reversible under modest temperature/pressure changes. Therefore, although hydrogen can be generated on-board the vehicle, getting hydrogen back into the starting material must be done off-board. Sodium borohydride is an example.
An approach to utilize stranded renewable assets like wind and solar systems is to produce hydrogen during low demand periods when these devices supply electricity. The electricity can be converted to hydrogen and that hydrogen stored within natural gas transmission lines or in natural gas salt caverns. This technique is gathering momentum in Europe to capitalize on installed renewable assets and the existing gas transmission system.
The widespread use of hydrogen will require an extensive infrastructure to produce, distribute, store and dispense it as a vehicular fuel or for electric generation. Depending on the source from which hydrogen is produced and the form in which it is delivered, many alternative infrastructures can be envisioned. The technology is already in place to transport hydrogen, whether it is by pipeline or in pressurized or liquefied containers. Hydrogen has been safely produced, transported and distributed for over 100 years. With respect to vehicle refueling there have been tens of thousands of refueling events at over 100 global refueling stations.
Codes and standards provide the information needed to safely build, maintain, and operate equipment, systems, and facilities. They help ensure uniformity of safety requirements and give local inspectors and safety officials the information they need to approve systems and installations.
Codes are guidelines for the built environment – buildings and facilities. They are generally adopted by local jurisdictions, thereby achieving the force of law. Codes often refer to or invoke standards for the equipment used within the given built environment.
Standards are rules, guidelines, conditions, or characteristics for products or related processes, and generally apply to equipment or components. Although they’re not regulations, standards achieve a regulation-like status when they are referred to in codes or through other government regulations.
Codes and standards are being adopted, revised, or developed for vehicles; fuel delivery and storage; fueling, service, and parking facilities; and vehicle fueling interfaces. Codes and standards are also being adopted, revised, or developed for stationary and portable fuel cells and interfaces, as well as hydrogen generators.
Hydrogen is non-toxic. It is a naturally occurring, basically benign element found freely in the atmosphere. By comparison, petroleum fuels are extremely toxic.
Hydrogen is less flammable than gasoline. The auto-ignition temperature of hydrogen is 932 degrees Fahrenheit. Compare that to gasoline’s auto-ignition temperature of 536 degrees Fahrenheit (auto-ignition temperature is the minimum temperature at which a fuel will ignite without a spark or flame). Yes, it’s actually easier for gasoline to spontaneously combust.
Hydrogen disperses quickly in the atmosphere. Because hydrogen is so light (about 15 time lighter than air) it easily dissipates and if a leak or spill does occur, the hydrogen becomes rapidly sparse and difficult to ignite. And even if it does catch fire, it burns itself out very quickly. By contrast, heavier fuels such as diesel oil and gasoline do not rapidly dissipate and remain a fire threat for a longer period of time.
Hydrogen stores safely. The tanks used to store hydrogen, whether in its gaseous or liquid form, undergo demanding testing procedures. They must endure extreme heat and external pressure forces as well as collision impacts. Conventional gasoline and diesel fuel tanks are, in most instances, simple stamped steel shells that do not undergo these stringent stress tests.
Hydrogen is clean.
The single emission from burned hydrogen is water vapor—that’s it. Compare that to particulate matter (soot), NOx, CO, CO2 and—among other toxic emissions—from burned petroleum fuels.