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A Guide To The Hydrogen Fuel Cell


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     • SEE ALSO: The Auto Channel Hydrogen News Archive

By Douglas Crawford
Automotive Industry Alliance
Washington, D.C.
douglascrawford@autoindustryalliance.com

This article contains a guide covering fuel cell cars, how fuel cell vehicles work and the fuel cell economy.

Hydrogen is a chemical element (H) and atomic number 1. With an atomic weight of 1.00794 u, hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the universe, constituting roughly 75% of all baryonic mass. Hydrogen is the simplest element. An atom of hydrogen consists of only one proton and one electron. It’s also the most plentiful element in the universe. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, highly combustible diatomic gas with the molecular formula H2. Since hydrogen readily forms covalent compounds with most non-metallic elements, most of the hydrogen on Earth exists in molecular forms. Despite its simplicity and abundance, hydrogen doesn’t occur naturally as a gas on the Earth – it’s always combined with other elements, like water, a combination of hydrogen and oxygen (H2O).

Hydrogen is also found in many organic compounds, notably the hydrocarbons that make up many of our fuels, such as gasoline, natural gas, methanol, and propane. Hydrogen can be separated from hydrocarbons through the application of heat – a process known as reforming. Currently, most hydrogen is made this way from natural gas. An electrical current can also be used to separate water into its components of oxygen and hydrogen (ibid). This process is known as electrolysis. Some algae and bacteria, using sunlight as their energy source, even give off hydrogen under certain conditions.

Hydrogen is high in energy, yet an engine that burns pure hydrogen produces almost no pollution. NASA has used liquid hydrogen since the 1970s to propel the space shuttle and other rockets into orbit. Hydrogen fuel cells power the shuttle’s electrical systems, producing a clean byproduct – pure water, which the crew drinks.

A fuel cell combines hydrogen and oxygen to produce electricity, heat, and water. Fuel cells are often compared to batteries. Both convert the energy produced by a chemical reaction into usable electric power. However, the fuel cell will produce electricity as long as fuel (hydrogen) is supplied, never losing its charge.

Fuel cells are a promising technology for use as a source of heat and electricity for buildings, and as an electrical power source for electric motors propelling vehicles. Fuel cells operate best on pure hydrogen. But fuels like natural gas, methanol, or even gasoline can be reformed to produce the hydrogen required for fuel cells. Some fuel cells even can be fueled directly with methanol, without using a reformer.

In the future, hydrogen could also join electricity as an important energy carrier. An energy carrier moves and delivers energy in a usable form to consumers. Renewable energy sources, like the sun and wind, can’t produce energy all the time. But they could, for example, produce electric energy and hydrogen, which can be stored until it’s needed. Hydrogen can also be transported (like electricity) to locations where it is needed.

Hydrogen Benefits and Considerations

Hydrogen can be produced from diverse domestic resources with the potential for near-zero greenhouse gas emissions. Once produced, hydrogen generates power in a fuel cell, emitting only water vapor and warm air. It holds promise for growth in both the stationary and transportation energy sectors.

Energy Security

As feared earlier, the United States relies heavily on foreign oil to power its transportation sector. With much of the worldwide petroleum reserves located in politically volatile countries, the United States is vulnerable to supply disruptions. Hydrogen can be produced domestically from resources like natural gas, coal, solar energy, wind, and biomass. When used to power highly efficient fuel cell vehicles, hydrogen holds the promise of offsetting petroleum in transportation. Energy security is no longer compromised.

Public Health and Environment

More than 50 percent of the U.S. population lives in areas where air pollution levels are high enough to negatively impact public health and the environment. Emissions from gasoline and diesel vehicles—such as nitrogen oxides, hydrocarbons, and particulate matter—are a major source of this pollution. Hydrogen-powered fuel cell vehicles emit none of these harmful substances. Their only emission is H2O—water and warm air.

The environmental and health benefits are even greater when hydrogen is produced from low- or zero-emission sources, such as solar, wind, and nuclear energy and fossil fuels with advanced emission controls and carbon sequestration. Because the transportation sector accounts for about one-third of U.S. carbon dioxide emissions (affecting climate change), using these sources to produce hydrogen for transportation can slash greenhouse gas emissions.

Fuel Storage

Hydrogen’s energy content by volume is low. This makes storing hydrogen a challenge because it requires high pressures, low temperatures, or chemical processes to be stored compactly. Overcoming this challenge is important for light-duty vehicles because they often have limited size and weight capacity for fuel storage.

The storage capacity for hydrogen in light-duty vehicles should enable a driving range of more than 300 miles to meet consumer needs. Because hydrogen has a low volumetric energy density compared with gasoline, storing this much hydrogen on a vehicle currently requires a larger tank than most conventional vehicles.

Production Costs

To be competitive in the marketplace, the cost of fuel cells will have to decrease substantially without compromising vehicle performance. The Department of Energy Hydrogen and Fuel Cells Office make up plans and projections for the future of hydrogen and fuel cells.

Hydrogen can be produced from diverse domestic resources with the potential for near-zero greenhouse gas emissions. Once produced, hydrogen generates power in a fuel cell, emitting only water vapor and warm air. It holds promise for growth in both the stationary and transportation energy sectors (ibid).

Challenges

−Availability. Hydrogen is only available at a handful of locations, mostly in California, though more hydrogen fuelling stations are planned for the future.

−Vehicle Cost & Availability. Fuel cell vehicles (FCVs), which run on hydrogen, are far more expensive than conventional vehicles, and not yet available for sale to the general public. However, costs have decreased significantly, and commercially available FCVs are expected within the next few years. Volkswagen AG felt cars powered by hydrogen fuel cells will probably struggle catching on beyond Japan’s borders. Government subsidies of as much as 3 million yen ($28,500) a vehicle offered in Japan will probably be too high for other countries to match. Even in Japan, refueling will be impractical because handling hydrogen is challenging and building out infrastructure inordinately expensive.

−Onboard Fuel Storage. It is difficult to store enough hydrogen onboard an FCV to go as far as a comparable gasoline vehicle between fillups. Some FCVs have recently demonstrated ranges that are comparable to conventional vehicles—about 300 to 400 miles between fillups—but this must be achievable across different vehicle makes and models and without compromising customer expectations of space, performance, safety, or cost. Other challenges related to FCVs must also be overcome, like:

−Fuel Cell Durability and Reliability. Fuel cell systems are not yet as durable as internal combustion engines, especially in some temperature and humidity ranges. Fuel cell stack durability today is about half of what is needed for commercialization. Durability has increased substantially over the past few years from 29,000 miles to 75,000 miles, but experts believe a 150,000-mile expected lifetime is necessary for FCVs to compete with gasoline vehicles.

−Getting Hydrogen to Consumers. The current infrastructure for producing, delivering, and dispensing hydrogen to consumers cannot yet support the widespread adoption of FCVs. In 2013, H2USA was launched as a public-private partnership between DOE and other federal agencies, automakers, state government, academic institutions, and additional stakeholders to coordinate research and identify cost-effective solutions for deploying hydrogen infrastructure.

In the U.S., hydrogen is transported safely through 700 miles of pipelines, and 70 million gallons of liquid hydrogen is transported annually by truck over U.S. highways without incident. Both indoor and outdoor hydrogen refueling stations are located in several dozen states and have safely dispensed compressed hydrogen for use in passenger vehicles, buses, trucks, forklifts, and other types of vehicles.

−Public Education. Fuel cell technology must be embraced by consumers before its benefits can be realized. As with any new vehicle technology, consumers may have concerns about the dependability and safety of these vehicles when they first hit the market; they must also become familiar with a new kind of fuel. Public education can accelerate this process.

Hydrogen Production and Delivery

Most of the hydrogen in the United States is produced by steam reforming of natural gas. For the near term, this production method will continue to dominate. Researchers at National Renewable Energy Laboratory (NREL) are developing advanced processes to produce hydrogen economically from sustainable resources.

  • Biological Water Splitting: Certain photosynthetic microbes use light energy to produce hydrogen from water in their metabolic processes. NREL researchers are trying to create new genetic forms of organisms that can sustain hydrogen production in the presence of oxygen. In short, hydrogen is produced from water using sunlight and specialized microorganisms, such as green algae and cyanobacteria.
  • Fermentation: NREL scientists are developing pretreatment technologies to convert lignocellulosic biomass into sugar-rich feedstocks that can be directly fermented to produce hydrogen, ethanol, and high-value chemicals. Researchers are also working to identify a consortium of Clostridium that can directly ferment hemicellulose to hydrogen. In short, hydrogen is produced from the fermentation of renewable biomass materials.
  • Conversion of Biomass and Wastes: Hydrogen can be produced via pyrolysis or gasification of biomass resources such as agricultural residues like peanut shells; consumer wastes including plastics and waste grease; or biomass specifically grown for energy uses. Biomass pyrolysis produces a liquid product (bio-oil) that contains a wide spectrum of components that can be separated into valuable chemicals and fuels, including hydrogen.
  • Photoelectrochemical (PEC) Water Splitting: The cleanest way to produce hydrogen is by using sunlight to directly split water into hydrogen and oxygen. The photovoltaic industry is being used for creating PEC light harvesting systems that split water. In the PEC water splitting process, hydrogen is produced from water using sunlight and specialized semiconductors.
  • Solar Thermal Water Splitting: A High-Flux Solar Furnace reactor concentrates solar energy and generates temperatures between 1,000 and 2,000 degrees Celsius, providing the ultra-high temperatures required for thermochemical reaction cycles to produce hydrogen.
  • Renewable Electrolysis: The renewable electrolysis process uses renewable electricity to produce hydrogen by passing an electrical current through water.
  • Hydrogen Production and Delivery Pathway Analysis: NREL is focusing on sustainable hydrogen production and delivery pathways, ensuring cost effective status improvements via technology advancements. Their primary aim is to provide 150,000-mile durable delivery systems (ibid).

Liquefaction and Delivery in the UK

Hydrogen undergoes liquefaction at a temperature of 20 K (–253 °C). Theoretically, only about four MJ kg-1 must be removed from the gas but the cooling process has a very low Carnot cycle efficiency so even large plants require 30 MJ kg-1 to liquefy hydrogen. However, a substantial amount of expensive electricity is required. The energy efficiency of liquefaction varies from 68 percent to 84 percent, with larger plants being more efficient. Engineers in the UK are working at designing large plants and assuming a 1600 km round-trip (72 deliveries per year) per road tanker. They are also studying transfer by ship, tubes and pipelines.

Fuel Cell Cars

A fuel cell vehicle (FCV) or fuel cell electric vehicle (FCEV) is a type of vehicle which uses a fuel cell to power its on-board electric motor and has the potential to revolutionize our transportation systems. They are more efficient than conventional internal combustion engine vehicles and produce no harmful tailpipe exhaust—they emit water vapor and warm air and are considered Zero Emission Vehicles.

Fuel cell vehicles and the hydrogen infrastructure to fuel them are in an early stage of deployment. The U.S. Department of Energy is leading government and industry efforts to make hydrogen-powered vehicles an affordable, environmentally friendly, and safe transportation option. Hydrogen is considered an alternative fuel under the Energy Policy Act of 1992 and qualifies for alternative fuel vehicle tax credits.

Fuel cells in vehicles create electricity to power an electric motor, generally using oxygen from the air and hydrogen. Depending on the process, however, producing the hydrogen used in the vehicle may create pollutants. Fuel cells have been used in various kinds of vehicles including forklifts, especially in indoor applications where their clean emissions are important to air quality, and in space applications. Commercial production fuel cell automobiles are currently being deployed in California by one auto manufacturer, with additional manufacturers expected to join in. Furthermore, fuel cells are being developed and tested in buses, boats, motorcycles and bicycles, among other kinds of vehicles.

FCEVs use a completely different propulsion system from conventional vehicles and can be two to three times more efficient. They also increase U.S. energy security and strengthen the economy, a concern voiced volubly and referred to earlier in this essay.

FCEVs are fueled with pure hydrogen gas stored directly on the vehicle. Similar to conventional vehicles, they can fuel in less than 10 minutes and have a driving range of around 300 miles. FCEVs can be equipped with other advanced technologies to increase efficiency, such as regenerative braking systems, which capture the energy lost during braking and store it. Major auto original equipment manufacturers started offering production vehicles to the public in certain markets in 2014.

As of now, there is limited hydrogen infrastructure, with 10 hydrogen fueling stations for automobiles publicly available in the U.S., but investments have been planned to build more hydrogen stations, particularly in California. New stations are also planned in Japan and Germany. Critics doubt whether hydrogen will be efficient or cost effective for automobiles, as compared with other zero emission technologies.

Production of the Honda FCX Clarity began in 2008, and was available for leasing customers in Japan and Southern California. In 2014 Honda announced the end of production of the FCX Clarity for the 2015 model. From 2008 to 2014, Honda leased a total of 45 FCX units in the US. The Hyundai ix35 FCEV Fuel Cell vehicle is available for lease. In 2014, a total of 54 units were leased. There are over 20 other FCEVs prototypes and demonstration cars have been released since 2009. Automobiles such as the GM HydroGen4, Toyota FCHV-adv and Mercedes-Benz F-Cell are pre-commercial examples of fuel cell electric vehicles. Fuel cell electric vehicles have driven more than 3 million miles, with more than 27,000 refuelings.

Sales of the Toyota Mirai to government and corporate customers began in Japan on December 15, 2014. Pricing started at „6.7 million (~US$57,400) before taxes and a government incentive of         „2 million (~US$19,600). Experts estimate that Toyota will initially lose about $100,000 on each Mirai sold. Initially sales are not available to individual retail customers. In 2014, domestic orders had already reached over 400 Mirais, surpassing Japan’s first-year sales target, and as a result, there is a waiting list of more than a year. Toyota plans to build 700 vehicles for global sales during 2015.

How Fuel Cell Vehicles Work

Schematic of an FCV

Like battery electric vehicles, fuel cell electric vehicles use electricity to power a motor located near the vehicle’s wheels. In contrast to other electric vehicles, fuel cell vehicles produce their primary electricity using a fuel cell powered by hydrogen, rather than drawing electricity from a battery. During the vehicle design process, the vehicle manufacturer controls the power of the vehicle by changing the fuel cell size and controls the amount of energy stored on board by changing the hydrogen fuel tank size. This is different than a battery electric vehicle where the amount of power and energy available are both closely tied to the battery size.

A PEM
Figure 5.   A PEM

The most common type of fuel cell for vehicle applications is the polymer electrolyte membrane (PEM) fuel cell. In a PEM fuel cell, an electrolyte membrane is sandwiched between a positive electrode (cathode) and a negative electrode (anode). Hydrogen is introduced to the anode and oxygen (usually from air) to the cathode. The hydrogen molecules break apart into protons and electrons because of an electrochemical reaction in the fuel cell catalyst. Protons, travel through the membrane to the cathode. The electrons are forced to travel through an external circuit to perform work (providing power to the car) then recombine with the protons on the cathode side, where the protons, electrons, and oxygen molecules combine to form water.

Fuel economy

Comparison of Fuel Economy Expressed in MPGe for Hydrogen FCVs December 2014

Char 9 Source EPA
Vehicle Model year Combined fuel
economy
City
fuel economy
Highway
fuel economy
Range
Honda FCX Clarity 2014 59 mpg-e 58 mpg-e 60 mpg-e 231 mi (372 km)
Hyundai Tucson Fuel Cell 2015 49 mpg-e 48 mpg-e 50 mpg-e 265 mi (426 km)

Note:

  1. One kg of hydrogen is roughly equivalent to one U.S. gallon of gasoline.
  2. Fuel economy expressed in miles per gallon gasoline equivalent (MPGe)

A report by consultancy IHS Auto thought fuel cells were barely going to trouble the scoreboard. IHS Auto felt that by 2020 regular hybrids and plug-in hybrids (PHEVs) will account for almost five per cent of global sales compared with less than one per cent for electric only vehicles. By 2025, battery-only will have slowly expanded to 1.5 per cent, while PHEVs and hybrids will push just past six per cent. Fuel cell vehicles will barely register at all by 2025.

Other applications are buses, boats, forklifts, motorcycles, bicycles, unmanned aerial vehicles, aircraft, submarines and more.

The Future of Hydrogen Vehicles

Possible hydrogen vehicles in the future could be:

  • Vehicles with internal combustion engines using pure hydrogen, or using a mix of hydrogen and natural gas.
  • Vehicles with fuel cells that use hydrogen that’s produced either on-board by converting liquid fuels (gasoline, ethanol, or methanol) to hydrogen, or by using direct hydrogen that has been generated off-board and stored on the vehicle in compressed or liquid form.