The Fuel Cell Battery Knowledge

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A fuel cell is an electrochemical device that combines hydrogen fuel with oxygen to produce electricity, heat and water. The fuel cell is similar to a battery in that an electrochemical reaction takes place as long as fuel is available. The hydrogen fuel is stored in a pressurized container and oxygen is taken from the air. Because of the absence of a burning process, there are no harmful emissions, and the only by-product is fresh water. The water emitted from the proton exchange membrane fuel cell (PEMFC) is so pure that visitors to Vancouver’s Ballard Power Systems were served hot tea made from this clean water.

Fundamentally, a fuel cell is electrolysis in reverse, using two electrodes separated by an electrolyte. The anode (negative electrode) receives the hydrogen and the cathode (positive electrode) collects the oxygen. A catalyst at the anode separates hydrogen into positively charged hydrogen ions and electrons; the oxygen is ionized and migrates across the electrolyte to the anodic compartment, where it combines with hydrogen. A single fuel cell produces 0.6–0.8V under load. To obtain higher voltages, several cells are connected in series. Figure 1 illustrates the concept of a fuel cell.

Figure:

Concept of a fuel cell

The anode (negative electrode) receives the hydrogen and the cathode (positive electrode) collects the oxygen.

Source: US Department of Energy, Office of Energy Efficiency and Renewable Energy Fuel cell technology is twice as efficient as combustion in turning carbon fuel to energy. Hydrogen, the simplest chemical element (one proton and one electron), is plentiful and exceptionally clean as a fuel. Hydrogen makes up 90 percent of the universe and is the third most abundant element on the earth’s surface. Such a wealth of fuel would provide an almost unlimited pool of clean energy at relatively low cost. But there is a hitch. Hydrogen is usually bound to other substances and “unleashing” the gas takes technology and a substantial amount of energy. In terms of net calorific value (NCV), hydrogen is more costly to produce than gasoline. Some say that hydrogen is nearly energy neutral, meaning that it takes as much energy to produce as it delivers at the end destination.

Storage of hydrogen poses a further disadvantage. Pressurized hydrogen requires heavy steel tanks, and the NCV by volume is about 24-times lower than a liquid petroleum product. In liquid form, which is much denser, hydrogen needs extensive insulation for cold storage.

Hydrogen can also be produced with a reformer by means of extraction from an existing fuel, such as methanol, propane, butane or natural gas. Converting these fossil fuels into pure hydrogen releases some leftover carbon, but this is 90 percent less harmful than what comes from the tailpipe of a car. Carrying a reformer would add weight to the vehicle and increase its cost. Reformers are also known to be sluggish.

The net benefit of hydrogen conversion is in question because it does not solve the energy problem. With the availability of hydrogen through extraction, the fuel cell core (stack) to convert hydrogen and oxygen to electricity is expensive and the stack has a limited life span. Burning fossil fuels in a combustion engine is the simplest and most effective means of harnessing energy, but this contributes to pollution.

Sir William Grove, a Welsh judge and gentleman scientist, developed the fuel cell concept in 1839, but the invention never took off. This was in part due to the rapidly advancing internal combustion engine, which promised better results. It was not until the 1960s that the fuel cell was put to practical use during the Gemini space program. NASA preferred this clean power source to nuclear or solar power. The alkaline fuel cell system generated electricity and produced the drinking water for the astronauts.

High material costs made the fuel cell prohibitive for commercial use at that time. This did not hinder Karl Kordesch, the co-inventor of the alkaline battery such as Acer TravelMate 290 Battery, Acer TravelMate 4000 Battery, Acer TravelMate 2300 Battery, Acer Aspire 1680 Battery, Acer Aspire 1410 Battery, Acer TravelMate 4500 Battery, Acer LCBTP03003 Battery, Acer Aspire 1300 Battery, Acer BTP-APJ1 Battery, Acer BTP-AQJ1 Battery, Acer BTP-ARJ1 Battery, from converting his car’s power source to an alkaline fuel cell in the early 1970s. Kordesch drove his car for many years in Ohio, USA. He placed the hydrogen tank on the roof and utilized the trunk to place the fuel cell as well as backup batteries. According to Kordesch, there was “enough room for four people and a dog.” The 1990s brought renewed interest in the fuel cell; however, this enthusiasm started to diminish again in the 21st century.

Just as there are different battery chemistries, so also are there several fuel cell systems to choose from. Let’s look at the most common types and examine the applications.

Proton Exchange Membrane Fuel Cell (PEMFC)

The proton exchange membrane, also known as PEM, uses a polymer electrolyte. PEM is one of the furthest developed and most commonly used fuel cell systems; it powers cars, serves as a portable power source and provides backup power in lieu of stationary batteries in offices. The PEM system allows compact design and achieves a high energy-to-weight ratio. Another advantage is a relatively quick start-up when applying hydrogen. The stack runs at a moderate temperature of 80°C (176°F) and has a 50 percent efficiency. (In comparison, the internal combustion engine is only about 25 percent efficient.)

The limitations of the PEM fuel cell are high manufacturing costs and complex water management systems. The stack contains hydrogen, oxygen and water. If dry, water must be added to get the system going; too much water causes flooding. The system requires pure hydrogen; lower fuel grades can cause decomposition and clogging of the membrane. Testing and repairing a stack is difficult, given that a 150V, 50kW stack to power a small car requires 250 cells.

Extreme operating temperatures are a further challenge. Freezing water can damage the stack, and the manufacturer recommends heating elements to prevent ice formation. When the fuel cell is cold, start-up is slow and the performance is poor at first. Excessive heat can also cause damage. Controlling the operating temperatures as well as supplying enough oxygen requires compressors, pumps and other accessories that consume about 30 percent of the energy generated.

If operated in a vehicle, the PEMFC stack has an estimated service life of 2,000-4,000 hours. Start-and-stop conditions induce drying and wetting that contribute to membrane stress. Running continuously, the stationary stack is good for about 40,000 hours. Stack replacement is a major expense. Figure 2 illustrates a portable fuel cell.