Alternative Energy Tutorial
Introduction
Batteries
Fuel Cells
Conducting Polymers
High-Purity Inorganics
Liquid Electrolytes
Plasticizers and Binders
Solid Polymeric Electrolytes
Related Products
References
Introduction
Fuel cells and batteries are electrochemical cells used to generate an external electrical current. They consist of an anode, where oxidation occurs, a cathode, where reduction occurs, and an electrolyte through which ions can travel between electrodes (see Figure 1 for a schematic of an electrochemical cell). In fuel cells (discussed below), one or both of the reactants are supplied from an external source to the cell. Though technically fuel cells, when the only reactant supplied to the cell is atmospheric oxygen, the cells are considered batteries (zinc/air or aluminum/air cells for example).
Batteries
Batteries can be divided into two types: primary or disposable batteries and secondary or rechargeable batteries. The main advantages of batteries over fuel cells are their availability, portability, low cost, and wide range of operating conditions. Batteries, however, have much shorter life spans and lack the power output of fuel cells. Power outputs of batteries are typically on the order of 100's of watts, whereas fuel cells can provide kilowatt to megawatt outputs, power enough to light a building or fuel a vehicle for hours. Under heavy energy demands, batteries can build up dangerous levels of heat and pressure, degrading the battery and possibly causing leaks of toxic compounds or even explosions. In addition, the limited life of primary batteries and the limited cycle life (number of times it can be recharged) of most secondary batteries necessitates the need for disposal of often dangerous and toxic battery materials. Table 1 summarizes some of the common types of primary and secondary batteries.
| Battery Type | Anode | Cathode | Electrolyte | Advantages | Disadvantages | |
|---|---|---|---|---|---|---|
| Primary Batteries | Alkaline Cell | Zn | MnO2 | KOH | High energy density, long shelf life, good leak resistance, performs well under heavy or light use. | Costlier than zinc-carbon cell but more efficient |
| Aluminum/Air Cell | Al | O2 | KOH or neutral salt solution | Can operate exposed to sea water (neutral salt solution), easily replaceable electrolytes/electrodes | Anode quickly degrades, short shelf life, short operational life | |
| Leclanché Cell (Zinc Carbon or Dry Cell) | Zn | MnO2 | NH4Cl or ZnCl2 | Cheap and common (oldest available battery type) | Poor performance under heavy or continuous use. | |
| Lithium Cell | Li | Various liquid or solid materials | SOCl2, SO2Cl2, or organic solutions | Very high energy density, long shelf life, long operational life | Poor performance under heavy use, vulnerable to leaks or explosions | |
| Mercury Oxide Cell | Zn or Cd | HgO | KOH | Higher energy density than (Zn/MnO2) alkaline cell | High cost and being phased out due to toxicity concerns | |
| Zinc/Air Cell | Zn | O2 | KOH | Environmentally benign, cheap, very high energy density, and virtually unlimited shelf life | Short operational life, low power density | |
| Secondary (rechargeable) Batteries | Iron Nickel Cell | Fe | Ni(OH)2 | KOH | Long life under a variety of conditions, excellent back-up battery | Low rate-performance, slow recharge rate |
| Lead/Acid Cell | Pb | PbO2 | dilute H2SO4(aq) | Low cost, long life cycle, operates well under a variety of conditions. Common car batteries | Minor risk of leakage | |
| Lithium Ion Cell | C, carbon compounds | Li2O, intercalated into graphite | LiPF6, LiBF4, related compounds | Relatively cheap, high energy density, long shelf life, long operational life, long cycle life | Minor risk of leakage | |
| Nickel/Cadmium Cell | Cd | Ni(OH)2 | KOH | Good performance under heavy discharge and/or low temperature | High cost, can temporary loose cell capacity if not fully discharged before recharging (memory effect) | |
| Nickel/Metal Hydride (NiMH) Cell | Lanthanide or Ni alloys | Ni(OH)2 | KOH | High capacity and power density | High cost, some memory effect | |
| Nickel/Zinc Cell | Zn | NiO | KOH | Low cost, low toxicity, good for high discharge rates | Zinc on the electrolyte tends to redeposit unevenly on anode, severely reducing efficiency | |
| Sodium/Sulfur Cell | Molten Na | Molten S | Al2O3 | Inexpensive materials, long cycle life, high energy and power | High operational temperature lower efficiency, some danger of explosion upon degradation |
The primary component materials of a battery are the anode, cathode, electrolyte, and semi-permeable materials. In addition various catalysts have been used to enhance the performance of electrodes. For example, ruthenium(IV) oxide (Prod. No. 238058) is used as a catalyst in a vanadium redox battery system.1 Table 1 summarizes some of the types of electrodes and electrolytes used in common batteries. Many advanced battery designs focus upon new materials for these key components.
Much of the recent battery work has focused on lithium-ion batteries, since they are the primary power source for the ever-growing field of small, rechargeable electronic devices. Nickel sulfide, for example, was recently explored as a cathode material for rechargeable lithium batteries.2 Current research is also concerned with some very mundane materials in electrodes. New morphologies of graphite flakes (Prod. No. 332461), as a case in point, have been studied as anode material in lithium-ion batteries.3 Electrolytes are also very important in battery performance. An LiBF4 (Prod. No. 451622) solution, for example in a butyrolactone/ethylene carbonate (Prod. Nos. B103608 and E26258) solution has proven to be a highly conductive and highly thermally stable electrolyte for lithium-ion batteries.4
Fuel Cells
Fuel cells offer the promise of a clean energy source for stationary power generation. They produce energy from hydrogen, natural gas, alcohol, or other readily available hydrocarbon fuels (Figure 2). Fuel cells date back to the nineteenth century when Grove, in 1839, first published his work on the generation of electricity by partially immersing two platinum electrodes and separately supplying oxygen and hydrogen to them.5 There is considerable current interest in fuel cells as an environmentally clean alternative to fossil-fuel-burning power sources.
Figure 2.Schematic of a typical polymeric electrolyte membrane (PEM) fuel cell.
Purely fuel cell powered vehicles are currently being tested as prototypes with plans for eventual commercialization by as early as 2010.6 Some of these vehicles are already in operation in municipal organizations around the world. See Table 1 for some examples.
| Automaker | Vehicle Type | Year | Engine Type | Fuel Cell Size/ type | Fuel Cell Mfr. | Range (mi/km) | MPG Equiv.* | Max. Speed | Fuel Type |
|---|---|---|---|---|---|---|---|---|---|
| BMW | Series 7 (745 h) (Sedan) | 2000 | ICE (fuel cell APU) | 5kW/PEM | UTC | 180mi 300km | N/a | 140 mph | Gasoline/ Liquid hydrogen |
| Limited intro in 2000 (Munich Airport Hydrogen Vehicle Project) | |||||||||
| Daihatsu | MOVE EV - FC (micro van) | 1999 | Fuel cell/ battery hybrid | 16kW/ PEM | Toyota | N/a | N/a | N/a | Methanol |
| MOVE FCV – K II (mini vehicle) | 2001 | Fuel cell/ battery hybrid | 30 kW/ PEM | Toyota | 75mi 120km | N/a | 65mph 105km/h | Compress. hydrogen @ 3600 psi | |
| Japan road testing started in early 2003. | |||||||||
| Daimler- Chrysler | NECAR 1 (180 van) | 1994 | 12 fuel cell stacks | 50kW/ PEM | Ballard | 81mi 130km | N/a | 56mph 90km/h | Compress. hydrogen @ 4300 psi |
| NECAR 2 (V-Class) | 1996 | Fuel cell | 50kW/ PEM | Ballard | 155mi 250km | N/a | 68mph 110km/h | Compress. hydrogen @ 3600 psi | |
| NECAR 3 (A-Class) | 1997 | 2 fuel cell stacks | 50kW/ PEM | Ballard Mark 700 Series | 250mi 400km | N/a | 75mph 120km/h | 10.5 gal. of Liquid methanol | |
| First methanol reforming FCV | |||||||||
| NECAR 4 (A-Class) | 1999 | Fuel cell | 70kW/ PEM | Ballard Mark 900 Series | 280mi 450km | N/a | 90mph 145km/h | Liquid hydrogen | |
| Jeep Commander 2 (SUV) | 2000 | Fuel cell/ (90 kW) battery hybrid | 50kW/ PEM | Ballard Mark 700 Series | 118mi 190km | 24 mpg (gas. equiv.) | N/a | Methanol | |
| Jeep Commander 1 came out in 1999. | |||||||||
| NECAR 4 - Advanced (California NECAR) | 2000 | Fuel cell | 85kW/ PEM | Ballard Mark 900 Series | 124mi 200km | 53.46 mpg equiv. (CaFCP est.) | 90mph 145 km/h | 4 lbs. (1.8kg) of Compress. hydrogen @ 5,000 psi | |
| NECAR 5 (A-class) | 2000 | Fuel cell | 85kW/ PEM | Ballard Mark 900 Series | 280mi 450km | N/a | 95mph 150km/h | Methanol | |
| DMFC go-cart (one-person vehicle) | 2000 | Fuel cell | 3kW/ DMFC | Ballard Mark 900 Series | 9.3mi 15km | N/a | 22mph 35km/h | Methanol (directly) | |
| 6kW DMFC built by DC and Ballard is largest in world | |||||||||
| NECAR 5.2 (A-class) | 2001 | Fuel cell/ battery hybrid | 85kW/ PEM | Ballard Mark 900 Series | 300mi 482km | N/a | 95mph 150km/h | Methanol | |
| Awarded a road permit for Japanese roads. Completed CA – DC drive. | |||||||||
| Sprinter (van) | 2001 | Fuel cell | 85kW/ PEM | Ballard Mark 900 Series | 93mi 150km | N/a | 75mph 120km/h | Compress. Hydrogen @ 5,000 psi | |
| Delivered to Hamburg parcel service, Hermes as part of the W.E.I.T. hydrogen project | |||||||||
| Natrium (Town & Country Mini Van) | 2001 | Fuel cell/ (40 kW) battery hybrid | 54kW/ PEM | Ballard Mark 900 Series | 300mi 483km | 30 mpg equiv. | 80mph 129km/h | Catalyzed chemical hydride - Sodium Boro- hydride | |
| Uses Millennium Cell’s ‘Hydrogen on Demand’ system with a 53 gallon fuel tank | |||||||||
| F-Cell (A-class) | 2002 | Fuel cell/ battery hybrid | 85kW/ PEM | Ballard Mark 900 Series | 90mi 145km | 56 mpg equiv. | 87mph 140km/h | 4 lbs. (1.8kg) of Compress. hydrogen @ 5,000 psi | |
| 60 fleet vehicles in US, Japan, Singapore, and Europe starting in 2003 – small fleet in Michigan operated by UPS. | |||||||||
| Jeep Treo | 2003 | Fuel cell | N/a | N/a | N/a | N/a | N/a | N/a | |
| Unveiled at Tokyo Motor Show – drive by wire technology | |||||||||
| ESORO | Hycar | 2001 | Fuel cell/ battery hybrid | 6.4kW/ PEM | Nuvera | 224mi 360km | N/a | 75mph 120km/h | Compress. Hydrogen |
| Switzerland’s first FCV | |||||||||
| Fiat | Seicento Elettra H2 Fuel Cell | 2001 | Fuel cell/ battery hybrid | 7kW/ PEM | 100mi 140km | N/a | 60mph 100km/h | Compress. Hydrogen | |
| Next generation due in 2003 w/ Nuvera fuel cells | |||||||||
| Seicento Elettra H2 Fuel Cell | 2003 | Fuel cell/ battery hybrid | N/a | Nuvera | N/a | N/a | N/a | Compress. Hydrogen | |
| Being investigated for use in Milan, Italy, where gasoline and diesel fueled vehicles are banned on smoggy days. | |||||||||
| Ford Motor Company | P2000 HFC (sedan) | 1999 | Fuel cell | 75kW/ PEM | Ballard Mark 700 Series | 100mi 160km | 67.11 mpg equiv. (CaFCP est.) | N/a | Compress. Hydrogen |
| First FCV by Ford | |||||||||
| Focus FCV | 2000 | Fuel cell | 85kW/ PEM | Ballard Mark 900 Series | 100mi 160km | N/a | 80mph 128km/h | Compress. hydrogen @ 3,600 psi | |
| TH!NK FC5 | 2000 | Fuel cell | 85kW/ PEM | Ballard Mark 900 Series | N/a | N/a | 80mph/ 128km/h | Methanol | |
| Advanced Focus FCV | 2002 | Fuel cell/ battery hybrid | 85kW/ PEM | Ballard Mark 900 Series | 180mi 290km | ~50 mpg equiv. | N/a | 8.8 lb. (4kg) Compress. H2 @ 5,000 psi | |
| ~40 fleet vehicles introduction Germany, Vancouver & CA in 2004 | |||||||||
| GloCar Concept Only | 2003 | Fuel Cell | N/a | N/a | N/a | N/a | N/a | N/a | |
| Powered by fuel cells, it uses LED lights to change body panel colors, intensity, and frequency. | |||||||||
| General Motors/ Opel | EV1 FCEV | 1997 | Fuel cell/ battery hybrid | N/a | N/a | N/a | N/a | N/a | Methanol |
| 0-60 mph in 9 seconds | |||||||||
| Sintra (mini-van) | 1997 | Fuel cell | 50kW/ PEM | N/a | N/a | N/a | N/a | N/a | |
| Wants to be 1st automaker to sell 1 million FCVs profitably | |||||||||
| **Hydrogenics works with GM on FC development | Zafira (mini-van) | 1998 | Fuel cell | 50kW/ PEM | Ballard | 300mi 483km | 80 mpg equiv. | 75mph 120km/h | Methanol |
| GM has ceased efforts regarding methanol (2001) | |||||||||
| Precept FCEV Concept only | 2000 | Fuel cell/ battery hybrid | 100kW/ PEM | GM** | 500mi 800km (est.) | 108 mpg equiv. (est.) | 120mph 193km/h | Hydrogen (stored in metal hydride) | |
| These are concept projections | |||||||||
| HydroGen 1 (Zafira van) | 2000 | Fuel cell/ battery hybrid | 80kW/ PEM | GM** | 250mi 400km | N/a | 90mph 140km/h | 16 gal. of Liquid hydrogen | |
| GM plans to sell 75kW hydrogen stationary fuel cell generators in 2005 | |||||||||
| HydroGen 3 (Zafira van) | 2001 | Fuel cell | 94kW/ PEM | GM** | 250mi 400km | N/a | 100mph 160km/h | Liquid hydrogen | |
| Being used by FedEx Corp. in Tokyo, Japan from 6/2003 – 6/2004 | |||||||||
| Chevy S-10 (pickup truck) | 2001 | Fuel cell/ battery hybrid | 25kW/ PEM | GM** | 240mi 386km | 40 mpg | 70 mph | Low sulfur, clean gasoline (CHF) | |
| GM has partnership with Toyota on reforming | |||||||||
| AUTOnomy Concept only | 2002 | Fuel cell | N/a | N/a | N/a | Proj. 100 mpg | N/a | N/a | |
| GM’s 2010 FCV concept Freedom of Design | |||||||||
| Hy-Wire Proof of Concept | 2002 | Fuel cell | 94kW/ PEM | GM** | 80mi 129km | ~41 mpg (gas equiv.) | 97mph 160km/h | 4.4 lbs.(2kg) Compress. h2 @ 5,000 psi | |
| Uses HydroGen3’s powertrain, so range & mpg theoretically could = HydroGen3 | |||||||||
| Advanced HydroGen 3 (Zafira van) | 2002 | Fuel cell | 94kW/ PEM | GM** | 170mi 270km | ~55 mpg (gas equiv.) | ~100mph 160km/h | 6.8lbs. (3.1kg) Compress. h2 @ 10,000 psi | |
| 1st FCV to incorporate 10,000 psi tanks (by Quantum). 6 placed in Washington DC. | |||||||||
| Diesel Hybrid Electric Military truck | 2003 | Fuel cell APU | 5kW/ PEM | Hydro- genics | N/a | N/a | N/a | Low pressure metal hydrides | |
| Turbo diesel ICE/battery hybrid with PEM FC APU. Under eval. for US Army’s new fleet of 30,000 light tactical vehicles. | |||||||||
| GM (Shanghai) PATAC | Phoenix (Mini van) | Oct. 2001 | Fuel cell/ battery hybrid | 25kW / PEM | Shanghai GM** | 125mi 200km | N/a | 70mph 113km/h | Compress. Hydrogen |
| Seventh FCV prototype out of China | |||||||||
| Honda | FCX-V1 | 1999 | Fuel cell/ battery hybrid | 60kW/ PEM | Ballard Mark 700 Series | 110mi 177km | N/a | 78mph 130km/h | Hydrogen (stored in metal hydride) |
| FCX-V2 | 1999 | Fuel cell | 60kW/ PEM | Honda | N/a | N/a | 78mph 130km/h | Methanol | |
| Honda has strict focus on pure hydrogen FCVs (2001) | |||||||||
| FCX-V3 | 2000 | Fuel cell/ Honda ultra capacitors | 62kW/ PEM | Ballard Mark 700 Series | 108mi 173km | N/a | 78mph 130km/h | 26 gal. of Compress. hydrogen at 3600 psi | |
| FCX-V4 | 2001 | Fuel cell/ Honda ultra capacitors | 85kW/ PEM | Ballard Mark 900 series | 185mi 300km | ~50 mpg (gas equiv.) | 84mph 140km/h | 130 L (3.75kg) Compress. H2 @ 5,000 psi | |
| Completed Japanese road testing - 1st FCV to receive CARB & EPA emission certs. | |||||||||
| FCX | 2002 | Fuel cell/ Honda ultra capacitors | 85kW/ PEM | Ballard Mark 900 series | 220mi 355km | ~50 mpg (gas equiv.) | 93mph 150km/h | 156.6 L Compress. hydrogen @ 5000 psi | |
| LA (5 total) Japan’s Cabinet Office (1) leasing at $6500/mo. each (12/2/02) | |||||||||
| Kiwami concept | 2003 | Fuel cell | N/a | N/a | N/a | N/a | N/a | Hydrogen | |
| Unveiled at Tokyo Motor Show | |||||||||
| Hyundai | Santa Fe SUV | 2000 | Ambient pressure Fuel cell | 75kW/ PEM | UTC Fuel Cells | 100mi 160km | N/a | 77mph 124km/h | Compress. Hydrogen |
| Santa Fe SUV | 2001 | Ambient pressure Fuel cell | 75kW/ PEM | UTC Fuel Cells | 250mi 402km | N/a | N/a | Compress. Hydrogen | |
| 2003 – 2004 limited intro. to power utilities & research ins | |||||||||
| Mazda | Demio (compact passenger car) | 1997 | Fuel cell/ ultra capacitor hybrid | 20kW/ PEM | Mazda | 106mi 170km | N/a | 60mph 90km/h | Hydrogen (stored in metal hydride) |
| Premacy FCEV | 2001 | Fuel cell | 85kW/ PEM | Ballard Mark 900 Series | N/a | N/a | 77mph 124km/h | Methanol | |
| Awarded road permit for Japanese roads in 2001 – undergoing public road testing | |||||||||
| Mitsubishi | SpaceLiner Concept only | 2001 | Fuel cell/ battery hybrid | 40kW/ PEM | N/a | N/a | N/a | N/a | Methanol |
| Commercial target date in 2005 | |||||||||
| Grandis FCV (mini-van) | 2003 | Fuel cell/ battery hybrid | 68kW PEM | Daimler Chrysler/ Ballard | 92mi 150km | N/a | 87mph 140km/h | Compress. Hydrogen | |
| Will be launched in Europe in 2004 | |||||||||
| Nissan | R’nessa (SUV) | 1999 | Fuel cell/ battery hybrid | 10kW/ PEM | Ballard Mark 700 Series | N/a | N/a | 44mph 70km/h | Methanol |
| Partnership with Renault for gasoline fueled FCV until 2006 | |||||||||
| **Made prototypes w/ each fuel cell stack | Xterra (SUV) | 2000/ 2001 | Fuel cell/ battery hybrid | 85kW/ PEM | Ballard Mark 900 Series & UTC Fuel Cells** | 100mi 161km | N/a | 75mph 120km/h | Compress. Hydrogen |
| X-TRAIL (SUV) | 2002 | Fuel cell/ battery hybrid | 75kW/ PEM | UTC Fuel Cells (Ambient pressure) | N/a | N/a | 78mph 125km/h | Compress. hydrogen @ 5,000 psi | |
| Approved for Japanese Public road testing – limited marketing later in 2003 | |||||||||
| Effis (commuter concept) | 2003 | Fuel cell/ battery hybrid | N/a | N/a | N/a | N/a | N/a | N/a | |
| Unveiled at Tokyo Motor Show | |||||||||
| PSA Peugeot Citron | Peugeot Hydro-Gen | 2001 | Fuel cell/ battery hybrid | 30kW/ PEM | Nuvera | 186m 300km | N/a | 60mph 95km/h | Compress. Hydrogen |
| PSA Peugeot Citron | Peugeot Hydro-Gen | 2001 | Fuel cell/ battery hybrid | 30kW/ PEM | Nuvera | 186m 300km | N/a | 60mph 95km/h | Compress. Hydrogen |
| Peugeot Fuel Cell Cab "Taxi PAC" | 2001 | Fuel cell/ battery hybrid | 55kW/ PEM | H Power | 188mi 300km | N/a | 60mph 95km/h | 80 Liters Compress. hydrogen @ 4300 psi | |
| H2O firefighting Concept only | 2002 | Battery/ fuel cell APU | N/a | N/a | N/a | N/a | N/a | Catalyzed chemical hydride - Sodium Boro- hydride | |
| Uses Millennium Cell’s ‘Hydrogen on Demand’ system | |||||||||
| Renault | EU FEVER Project (Laguna wagon) | 1997 | Fuel cell/ battery hybrid | 30kW/ PEM | Nuvera | 250mi 400km | N/a | 75mph 120km/h | Liquid hydrogen |
| Partnership with Nissan on gasoline fueled FCV | |||||||||
| Suzuki | Covie Concept only | 2001 | Fuel cell | N/a | GM | N/a | N/a | N/a | N/a |
| Mobile Terrace | 2003 | Fuel cell | N/a | GM | N/a | N/a | N/a | Hydrogen | |
| Unveiled at Tokyo Motor Show | |||||||||
| Toyota | RAV 4 FCEV (SUV) | 1996 | Fuel cell/ battery hybrid | 20kW/ PEM | Toyota | 155mi 250km | N/a | 62mph 100km/h | Hydrogen (stored in metal hydride) |
| RAV 4 FCEV (SUV) | 1997 | Fuel cell/ battery hybrid | 25kW/ PEM | Toyota | 310mi 500km | N/a | 78mph 125km/h | Methanol | |
| FCHV-3 (Kluger V/ Highlander SUV) | 2001 | Fuel cell/ battery hybrid | 90kW/ PEM | Toyota | 186mi 300km | N/a | 93mph 150km/h | Hydrogen (stored in metal hydride) | |
| Toyota is developing a Japanese residential 1kW stationary fuel cell system for 2005 | |||||||||
| FCHV-4 (Kluger V/ Highlander SUV) | 2001 | Fuel cell/ battery hybrid | 90kW/ PEM | Toyota | 155mi 250km | N/a | 95mph 152km/h | Compress. Hydrogen @ 3,600 psi | |
| Completed Japanese road testing | |||||||||
| FCHV-5 (Kluger V/ Highlander SUV) | 2001 | Fuel cell/ battery hybrid | 90kW/ PEM | Toyota | N/a | N/a | N/a | Low sulfur, clean gasoline (CHF) | |
| Partnered with GM on gasoline CHP reforming technology | |||||||||
| FCHV (Kluger V/ Highlander SUV) | 2002 | Fuel cell/ battery hybrid | 90kW/ PEM [122 hp] | Toyota | 180mi 290km | N/a | 96mph 155km/h | Compress. hydrogen @ 5,000 psi | |
| 3 leased to UC Irvine, 3 to UC Davis & 4 to Japanese gov’t agencies (12/2/02) for 30 months at $10K/mo. each. 6 more to be leased to Japanese local gov’ts and private co.’s | |||||||||
| FINE-S Concept only | 2003 | Fuel cell | N/a | N/a | N/a | N/a | N/a | N/a | |
| Toyota’s freedom of design concept | |||||||||
| VW | EU Capri Project (VW Estate) | 1999 | Fuel cell/ battery | 15kW/ PEM | Ballard Mark 500 Series | N/a | N/a | N/a | Methanol |
| Involved Johnson- Matthey, ECN, VW, and Volvo | |||||||||
| HyMotion | 2000 | Fuel cell | 75kW/ PEM | N/a | 220mi 350km | N/a | 86mph 140km/h | 13 gal. Of Liquid Hydrogen | |
| HyPower | 2002 | Fuel cell/ super capacitors hybrid | 40kW/ PEM | Paul Scherrer Institute | 94mi/ 150km | N/a | N/a | Compress. Hydrogen | |
Figure 3.Oxidation/Reduction reaction in a fuel cell.
The hydrogen used in fuel cells can be supplied directly or indirectly from a fuel reformer that converts alcohol, natural gas, or other hydrocarbon fuels into hydrogen. Since the primary exhaust of fuels cells is water, they offer the promise of an environmentally friendly power source.
Table 3 provides a comparison of some currently available fuel cells. In addition, some fuel cells currently under development include:
- Regenerative fuel cells. In these cells, water is converted to hydrogen and oxygen by a solar-powered electrolyzer. The cell then coverts this fuel into electricity, heat, and water. The water is then recycled into the electrolyzer. NASA is currently spearheading this technology.
- Zinc-air fuel cells (ZAFC). In ZAFCs, atmospheric oxygen is passed through a gas diffusion electrode and converted to water and hydroxyl ions. The ions then travel through an electrolyte to a zinc anode where it reacts to form zinc and electricity. Much like a rechargeable battery, the zinc electrode can be regenerated. Unlike a battery, however, this process takes only about five minutes.
- Protonic Ceramic Fuel Cells (PCFC). These cells use high operating temperatures (700 °C) and ceramic electrolytes with high protonic conductivity. As a high temperature cell they have similar advantages to MCFCs while also integrating many of the advantages of PAFCs such as high proton conduction. In addition, they electrochemically oxidize fossil fuels at the anode, eliminating a hydrogen producing step.
| Fuel Cell Type | Electrolyte | Availability | Operating Temp. | Efficiency | Advantages | Disadvantages | |
|---|---|---|---|---|---|---|---|
| Phosphoric Acid (PAFC) | Phosphoric acid soaked in a matrix | Currently available | 150-200 ºC | 40%, 85% cogener- ation | Can use impure H2 as fuel. Can tolerate up to 1.5% CO at operating temp. | Uses expensive Pt as catalyst, relatively low current generation and large size and weight | |
| Proton Exchange Membrane (PEM) | Polyperfluoro- sulfonic acid | Under develop- ment, prototypes in use | 80 ºC | High power density, can quickly vary output (good for vehicles), solid electrolyte | Sensitive to fuel impurities | ||
| Molten Carbonate (MCFC) | Carbonate solution | Under develop- ment, prototypes in use | 650 ºC | 60%, 85% cogener- ation | High operating temperature, therefore, no expensive noble metal catalysts and can operate on cheap fuels. | High operating temperature accelerates corrosion of cell components | |
| Solid Oxide (SOFC) | Yttria-stabilized zirconia, or more recently, lanthanide doped ceria | Under develop- ment, prototypes in use | 1000 ºC | 60%, 85% cogener- ation | High operating temperature, therefore, no expensive noble metal catalysts and can operate on cheap fuels | High operating temperature accelerates corrosion of cell components | |
| Alkaline | KOH(aq) soaked in a matrix | Used by NASA on space missions for decades | 150-200 ºC | up to 70% | Aqueous electrolyte promotes fast cathode reaction and high performance | High cost | |
| Direct Methanol Fuel Cell (DMFC) | Similar to PEM, however, uses methanol directly | Under develop- ment, prototypes in use | 50-100 °C | 40% | Due to the low operating temperature, good for small portable devices | Problems with fuel passing over the anode with producing electricity | |
Fuel cells have the same basic components as batteries: anode, cathode, and electrolyte. Yttria-stabilized zirconia (Prod. Nos. 572349 and 572322) is one of the most commonly used electrolytes in solid oxide fuel cells.5 Lanthanide-doped ceria (Prod. Nos. 572330, 572357, 572365, or 572381) is also gaining favor as a fuel cell electrolyte due to its improved properties at lower temperatures.8 Furthermore, doped cerium oxide electrolytes exhibit an ionic conductivity three to five times greater than that of yttria stabilized zirconia. Platinum black (Prod. No. 205915) and platinum-based alloys are the most common electrodes for fuel cells. Recent work by Scherer and coworkers have recently developed a good model to examine the surface area effects of platinum electrodes as well as glassy carbon (Prod. No. 484164) electrodes.9
Catalysts for Fuel Cells
Platinum is the most common catalyst for fuel cells, however, due to its high cost it is often doped with palladium, ruthenium, cobalt/nitrogen complexes, or more recently iridium or osmium. In addition to its high cost, platinum is also quite rare. In fact, there is not enough platinum in the world to equip every vehicle in use today with a traditional (Pt-catalyst) proton exchange membrane (PEM) fuel cell. For this reason, new catalysts, doped-platinum catalysts, and new platinum-deposition techniques are all being developed to reduce the amount of platinum needed for fuel cell catalysts.
Conducting Polymers
The discovery over twenty five years ago of relatively high electrical conductivity (~10+3 S/cm) of doped polyacetylene10 sparked extensive research in the application of conjugated polymers in such diverse fields as electronics, energy storage, catalysis, chemical sensing, biochemistry, and corrosion control.11,12 Unfortunately, the conducting polymers were found to be unstable in air and difficult to process. Significant advances in improving the desired electrical, optical, and mechanical properties, while simultaneously enhancing processability and stability, have been realized by cross-disciplinary collaborations between chemists, physicists, materials scientists, and engineers.
Polyaniline is becoming the conducting polymer of choice in many applications for several reasons: its electronic properties are readily customized, it exhibits excellent chemical stability, and is the least expensive of the conducting polymers.
Polythiophenes have been studied extensively for use in light emitting diodes, among other applications, due to the chemical variability offered by substitution at the 3- and 4- positions. The regularity of the side-chain incorporation strongly affects the electronic band gap of the conjugated main chain and is critical to device performance.13 We offer highly regiocontrolled alkylsubstituted polythiophenes (P3HT): almost completely regioregular head-to-tail (HT) P3HT (Prod. Nos. 698997 and 698989) and regiorandom (1:1 HT/HH) P3HT (Prod. No. 510823).14
High-Purity Inorganics
Wemaintain the highest standards for quality control and quality assurance. Our high-purity materials are rigorously analyzed by a variety of techniques including trace metals analysis by ICP, which can detect impurities an order of magnitude below ppm levels. Fuel cells and batteries often require high-purity components. For example, the electrolytes in low-temperature rechargeable batteries can be from alkyl carbonates and high purity lithium salts such as LiPF6 (Prod. No. 450227) and LiAsF6 (Prod. No. 308315).15
High-purity inorganics also find significant industrial usage. More than 60% of the industrially used cadmium is in Ni-Cd batteries, of which 75% is found in cellular phones. Much of the remainder of this portion is also used in the telecommunications industry as materials in emergency power supplies for electronic telephone exchanges.
Liquid Electrolytes
The type of electrolyte used for a fuel cell depends upon the choice of fuel cell (see Table 2). The key role of the electrolyte is to create a medium through which ions can move between the anode and the cathode. Electrolytes can also act as a kind of filter, preventing undesirable ions or electrons from disrupting the desired chemical reactions.
Plasticizers and Binders
The use of plasticizers in commercial polymer formulations to decrease Tg and the internal viscosity, and to increase bulk flexibility is a well-established practice in a multitude of industrial applications. In fact, the "new car smell" enjoyed by many car owners results mainly from the phthalate plasticizer vaporized in the closed car interior, and actually advertises the deterioration of the vinyl upholstery. To improve the permanence of the plasticizer higher-molecular-weight phthalates are commonly used for modern car interiors. A number of criteria are considered in choosing a plasticizer, including cost, compatibility, stability, ease of processing, and permanence. In addition to the aforementioned uses, a growing body of research has emerged over the past two decades on the application of plasticized polymers in areas that involve properties not usually associated with polymers. For example, the introduction of oligomeric poly(ethylene glycols) (PEG) and derivatives as plasticizers, to effect a significant increase in ionic conductivity as solid polymer electrolytes (SPEs), for use in high energy density batteries and other solid-state electrochemical devices.16-18
Cellulose triacetate membranes, plasticized with 2-nitrophenyl octyl ether (Prod. No. 365130), are used as materials for separations. They are impermeable to metal cations, but allow anion exchange19 and are also remarkably permeable to neutral, mono- and disaccharides.20 Highly efficient photorefractive polymer composites can be formed using 9-ethylcarbazole (Prod. No. E16600) (ECZ) as a plasticizer in guest-host polymers.21
Solid Polymeric Electrolytes
NASA's jet propulsion laboratory is currently investigating SPEs formed by reacting lithium salts (e.g. LiClO4, LiPF4, and LiCF3SO3) with cyanoresins for rechargeable batteries and electrochemical cells. Specifically, SPEs would be used as separators between carbon composite anodes and cathodes. It has been proposed that these batteries would have an energy density of 80 W·h·lb-1 and be viable for 1000 recharge cycles. Polyacrylonitrile (Prod. No. 181315), polyvinyl pyrrolidone (Prod. Nos. 234257 and 856568), and polyethylene (Prod. No. 427772) have dielectric constants between 4 and 5 and lithium-ion conductivities between 10-6 and 10-5 S·cm-1. Unfortunately these room-temperature conductivities are too low for effective power generation. SPE's formed from amorphous cyanoresins such as cyanoethyl polyvinyl alcohol (CRV), cyanoethyl pullulan (CRS), and cyanoethyl sucrose (CRU) have dielectric constants as high as 20 or more and lithium-ion conductivities 100 times greater than conventional SPEs.15
We also carry a complete line of Nafion® resins. Nafion® resins are perfluorinated ion-exchange materials composed of carbonfluorine backbone chains and perfluoro side chains containing sulfonic acid groups. Solid polymer fuel cells for pulse power delivery are based on Nafion® solid polymeric electrolytes.22
References
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