Fuel Cell/Hydrogen/Hydrogen Extract 01
If you can’t lower the price of the fuel cell, try lowering the cost of hydrogen extraction...
Hydrogen Extraction,More than One Way to Skin the Cat
by Donald Georgi
Today, one of the greatest barriers to the implementation of fuel cell vehicles is the lack of hydrogen at ‘gas stations.’ Hydrogen has low energy density, is highly reactive and requires a totally new infrastructure to allow the fuel cell auto to replace the gasoline powered auto. Initial systems have put reformers on board fuel cell powered autos allowing hydrogen to be extracted from gasoline, methanol or natural gas. Although on-board reformers allow the use of present fuel distribution, the cost and complexity of individual reformers make them little more than experimental stepping stones. There will possibly have to be a number of follow-on stepping stones reached before fuel cell powered transportation is as convenient and economical as today’s petroleum/internal-combustion engine combination. Present efforts include the hydrogen production methods described on the cover, methanol electrolysis, gasoline/natural gas steam reforming and conventional water electrolysis.
Methanol is electrolyzed to hydrogen (the main product) and carbon dioxide (the byproduct). The carbon dioxide is vented, while the hydrogen is purified with a molecular sieve to remove traces of water and methanol before use. ( Reprinted with permission from NASA Tech Briefs, Volume 26, No. 6. page 62
An all too often imagined misconception is that water, having two atoms of hydrogen in each molecule, is a veritable storehouse of free hydrogen fuel energy for our future fuel cell economy. Unfortunately, there is no hydrogen free lunch. Just as the implementation of solar and nuclear energy requires massive amounts of resource to utilize it, so does hydrogen. How the resource is isolated is of utmost importance because total costs are the great measure of the performance, convenience, safety and profitability of an energy system.
Electrolysis of water, the oldest known way to prepare hydrogen, is not new. The principle was first proposed by Michael Faraday in 1820. Today, wall plug household electrolyzers are available to provide hydrogen in a fuel cell auto owner’s garage. Fueling stations produce larger quantities for experimental fleets. To electrolyze and compress one kg of hydrogen requires about 52 kWh, or about $5.20/kg at 10 cent kWh electrical rates. A compressed hydrogen tank of 4.7 liters will power a fuel cell auto about 600 km or about 4 cents per km. Compared to today’s fully accounted gasoline/IC cost of 2.5 cents /km, the running costs of fuel cells are about double that of gasoline. If capital and operating costs were added, the electrolyzed hydrogen system cost could approach $10.00/kg. (Ed. note: Keeping all the costs in perspective, the 10 year straight line depreciation on a $25,000 car driving 10,000 miles/ year, would be 15 cents/km. Today, the motorist perception of fuel costs are only the smaller part of the automobile’s total cost per mile.)
Steam reforming of gasoline or natural gas is moving from the prototype stages to planned production. Ztec has built the above prototype unit which extracts hydrogen from either gasoline or natural gas at costs which may be half that of electrolysis. Using available fuels allows present infrasturcture to implement a hydrogen economy. Sequestering of CO2 could mean zero emissions as a closed system. (Graphic is permission of Ztec Corp.)
In her paper on Hydrogen Refueling Infrastructure for Fuel Cell Vehicles (In BD 58, pp. 3-9), Sheral Arbuckle proposes costs for various hydrogen implementations. The price at the fuel dispensing pump must be in the ballpark of $3/kg. How it gets there has not been deternmined. A pipeline system throughout the country would be a massive and costly effort which cannot be embarked upon until there is a guarantee of demand from fuel cell vehicles. If the pipeline did exist, present estimates put the generation from large scale systems at $0.70/ kg with overhead costs bringing the delivered cost to around $3.00/kg.
Classic electrolysis of hydrogen using electricity is in place now at the SunLine facility in Thousand Palms, California. Due to the cost of electric, this method is too expensive to compete with gasoline IC engine economics today. Sunline can use its photovotaic panel electricity seen in the upper right corner to produce true zero emission fuel while eliminating foreign oil and gas dependence.
Alternatives include hydrogen extraction from gasoline, methanol or natural gas on site, which although more expensive, can be implemented in stepping stone fashion because the delivery infrastructure is in place now.
The cover shows three alternatives in hydrogen preparation - methanol electrolysis (still experimental), steam reforming of hydrocarbons (moving from test to production) and water electrolysis (in place today).
After earlier formulating the concept of electrolysis, Michael Faraday reported electrolysis in his On Electrical Decomposition in the Philosophical Transactions of the Royal Society in 1834. The graphic from his original correspondence, shown at the right, includes many configurations of hardware used in his experiments. Not only was this transaciton a hallmark in electrolysis, but it was also the defining moment at which he coined the following terms: electrode, cathode, anode, ions, cations and anions. All terms were derived from Greek words.
The closed cycle cleanliness of a fuel/power generator is only as clean as the source of electricity to power the unit. If coal fired electrical generation plants were the source, the resulting hydrogen fueled vehicle would still be a net polluter. If obtained from solar or wind generated electric, the hydrogen could be ‘green.’ (Technically, if the PV or wind machines were built or serviced with polluting energy, the system would not be completely green.)
Making Hydrogen by Electrolysis of Methanol
The cost is about half that of making hydrogen by electrolysis of water
NASA’s Jet Propulsion Laboratory, Pasedena, California
Reprinted with permission from NASA Tech Briefs, Volume 26,, No. 6. page 62
Scientists at NASA’s Jet Propulsion Laboratory are developing apparatuses for electrolysis of methanol to produce pure hydrogen for use at industrial sites, in scientific laboratories, and in fuel cells. The state-of-the-art onsite hydrogen generators now in use are based on electrolysis of water to produce hydrogen, with oxygen as a by-product that has no commercial value in this context. The developmental methanol electrolyzers consume less than half the electrical energy of a given amount of hydrogen. Even when the cost of methanol is included, the cost of producing hydrogen by electrolysis is still only about half that of producing hydrogen by electrolysis of water.
Figure 1 (on the front cover) schematically illustrates a methanol-electrolysis apparatus. The heart of the apparatus is an electrolysis cell that contains a unitary membrane-electrode structure. Typically, this structure comprises a solid electrolyte in the form of a proton-conducting polymeric membrane, with a catalytic anode (e.g., containing a Pt/Ru catalyst) deposited on one side and a cathode (e.g., containing Pt or Pd as the catalyst) deposited on the other side as described, for example, in “Improved Fabrication of Electrodes for Methanol Fuel Cells” (NPO-19941), NASA Tech Briefs, Vol. 23, No. 4 (April 1999), page 38.
An aqueous solution of methanol is circulated past the anode, where methanol and water undergo the reaction
CH3OH + H20 !C02 + 6H+ + 6e-
The hydrogen ions pass through the membrane to the cathode, where they are reduced to hydrogen molecules in the reaction
6H+ + 6e- ! 3H2
Thus, the net reaction in the cell is: CH30H ! C02 + 3H2
with carbon dioxide liberated on the anode side and hydrogen liberated on the cathode side. Because the membrane is not totally impermeable by water and methanol, traces of these substances pass through along with the protons. However, the water and methanol can easily be removed from the hydrogen stream by use of a molecular sieve, as is routinely done to remove traces of water and oxygen from hydrogen streams produced in water electrolyzers.
If the solid-electrolyte membrane in the cell is made of NafionTM (or equivalent) perfluorosulfonic acid-based proton-conducting polymer, then the cell can be operated in the temperature range from 5 to 1200C. The concentration of methanol in the aqueous solution can range from 0.1 to 8 molar. The membrane is the electrolyte, and it is not necessary to acidify the solution to make it electrically conductive. The theoretical operating potential of the cell is 0.02 V, though in practice, a useful amount of electrolysis is not achieved until the potential is raised to 0.3 V. In contrast, the potential needed to electrolyze water is more than 1.4 V, even in the most efficient electrolyzers. As shown in Figure 2, the potential needed to obtain a given current density in electrolysis of methanol is more than 1 V below the potential needed to obtain the same current density in electrolysis of water. The electrical power consumed in electrolysis is reduced proportionately.
Figure 2. Less Voltage is needed to electrolyze methanol than to electrolyze water at the same current density, as indicated by these plots of data from an experiment with a prototype methanol electrolyzer and a commercial water electrolyzer.
This work was done by Sekhafipuram Narayanan, William Chun, Barbara Jeffries-Nakamura, and Thomas L Valdez of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at wwwnasatech.com/tsp under the Physical Sciences category.
In accordance with Public Law 96517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Intellectual Prop Group
Mail Stop 202-233
4800 Oak Grove Drive Pasadena, CA 91109
But all hydrogen generation, to both reduce pollution and dependence on foreign oil or gas, has a prerequisite for methods which require realistic implementations today. To make the cost improving step-up from water electrolysis, steam reforming of gasoline or natural gas has two major desirable features: lower cost of hydrogen generation and an in-place distribution infrastructure. If the need for hydrogen were placed on the ‘gas stations’ of today, the only new requirement would be the addition of the hardware such as that which is being pursued by Ztec Corp. In the upper right cover photo, their prototype unit, constructed in 1997-1998, has provided over 20,000 hours of hydrogen production from gasoline and is also able to function on natural gas or propane.
The hydrogen dispensing station at the Sunline facility provides fuel for experimental vehicles. Built and installed by Stewart, the system includes the water electrolyzer shown on the cover. Sunline has its own photovoltaic system which can power the electrolyzer, and wind energy is available in the local area. Results from pioneering facilities such as Sunline are contributing field information on hydrogen production, safety and utilization. (BD Staff photo)
The prototype steam reformer provides 600 scfh of hydrogen at full capacity with 85% efficiency. By using the high temperatures of steam, the need for precious metal catalyzing elements is removed, reducing the costs for the total system and possibly extending the reformer’s life (another cost improvement). It occupies a space of six feet on a side and sequesters the carbon dioxide to provide possible net zero emissions. Finding an economical process and market for the CO2 is a future challenge.
The unit is able to use in-place fuel sources available today, and it can produce the hydrogen at costs which may be close to half that of water electrolysis. If comparisons were to be made with equivalent utilization, capital and maintenance costs, steam reforming of natural gas would produce 600 scfh with only $2.29 worth of electricity and natural gas. The same hydrogen produced by water electrolysis would require 84 kW of electricity at about $8.40. The estimated costs for capital, electrolysis and compression for water electrolysis is in the ballpark of $10.50/kg. The costs for the capital, fuel and compression of steam reformed hydrogen are estimated to be in the range of $6.50/kg. As these units evolve, waste heat use is projected to increase system efficiency to the 90% region. Such imporvements should help to drive the hydrogen costs down. Real performance will hone both the technology and the numbers including balance of plant, operating costs, service and replacement.
A cutaway shows the components of the future fueling station steam reformer. Utilizing an internal fuel cell as power needed for the process, both electricity for electric vehicles and cogeneration heat canprovide additional economics. Expanding from the R & D fuel cell systems today, these reformers can offer proof of concept with daily performance in customer accessible locations. (Graphic is courtesy of Ztec.)
The first production version is to be available in late 2002 and will provide 4,000 scfh per hour with a purity of five nines. The unit, ten feet on each side, will be small enough to fit within spaces in existing gas stations, yet productive enough to provide hydrogen for a fleet or a neighborhood of fuel cell powered autos. (Ed. note: 4000 scfh weighs 10.18 kg, enough to power a small auto about 750 miles.)
Ztek is not unique in the quest for capturing a share of the hydrogen production market with steam reforming. Others are actively working toward operational units. The feature which gives Ztec a prominent position in this field is the combination of thousands of hours of prototype experience and the commitment to deliver product this year.
Any plan has to include the object of the endeavor, and in the year 2002 when we ask who needs copious quantities of hydrogen, the answer is no one other than the handful of experimenters who are driving the myriad of PEM fuel cell powered autos. Unfortunately, the limited number does not spell success for production quantities of new steam reformers. But, with the announcement by Toyota that they are providing limited numbers of fuel cell powered FCHV-4 SUVs in Japan and the U.S. this year, the demand begins to unfold much sooner than expected. By mid-2002, Toyota already had orders for 20 vehicles. Not a pig-in-a-poke, the FCHV-4 has been in road testing since June of 2001 and has rolled up over 68,000 miles. Based on the technological shattering success of Toyota’s gas-electric Prius hybrid, which has already sold nearly 100,000 units, Toyota will not take its quality image lightly when offering the FCHV-4.
By the end of 2000, Honda is planning to make a small number of FCX fuel cell vehicles available in both Japan and the U.S. Both the EPA and CARB have given approval for the compressed hydrogen powered FCX. The range will be 221 miles on one tank.
DaimlerChrysler is launching a program of providing 30 fuel cell busses in Europe, and Ford will put five fuel cell vehicles in California this year. Most people still place the earliest mass production in 2010 and beyond, but the funding from the U.S. Government and the public acceptance, first of hybrids and the novelty of fuel cells, could put them on a faster track...requiring hydrogen fuel availablity at convenient locations for reasonable prices. It is implicit that safety must be so good than everyone forgets about the potential danger of hydrogen. Already, Lithium-ion battery safety has proven itself in the past decade with technological excellence despite the potential for thermal runaway. Hopefully, comparable dedication in the field of hydrogen transportation will provide its needed safety.
While the excitement builds and ancillary items such as the Ztec reformer become available, there are other problems to be solved. One major problem is the cold weather performance. California is quite temperate, but the harsh 350 below temperatures of Minnesota hardly allow present designs to have suitable starting and operation. Reliability still needs to be demonstrated and the ability to have enough platinum or other precious metal must be considered. The biggest hurdle is the cost of the fuel cell itself - not that dropping pricing would solve any technical issues. Early fuel cell powered vehicles will have to receive government subsidies to be competetive. Beyond that, costs will have to be pared by technological advancements. These steam reforming methods promoted by Ztec, which seriously cut the hydrogen preparation costs, make a significant positive impact on that goal.