Over the past century the demand for energy has grown exponentially. With the growing demand for energy, many different energy sources have been explored and developed. One of the primary sources of energy has been, and continues to be, the combustion of hydrocarbons. However, the combustion of hydrocarbons is usually incomplete and releases non-combustibles that contribute to smog as well as other pollutants in varying amounts.
As a result of the pollutants created by the combustion of hydrocarbons, the desire for cleaner energy sources has increased in recent years. With the increased interest in cleaner energy sources, fuel cells have become more popular and more sophisticated. Research and development on fuel cells has continued to the point where many speculate that fuel cells will soon compete with gas turbines generating large amounts of electricity for cities, internal combustion engines powering automobiles, and batteries that run a variety of small and large electronics.
Fuel cells conduct an electrochemical energy conversion of hydrogen or other fuel and oxygen into electricity and heat. In some cases, conversion of a hydrocarbon fuel to hydrogen can occur within the fuel cell in a process known as “internal reforming.” Fuel cells are similar to batteries, but they can be “recharged” while providing power.
Fuel cells provide a DC (direct current) voltage that may be used to power motors, lights, or any number of electrical appliances. There are several different types of fuel cells, each using a different chemistry. Fuel cells are usually classified by the type of electrolyte used. The fuel cell types are generally categorized into one of five groups: proton exchange membrane (PEM) fuel cells, alkaline fuel cells (AFC), phosphoric-acid fuel cells (PAFC), solid oxide fuel cells (SOFC), and molten carbonate fuel cells (MCFC).
Most fuel cells typically include four basic elements: an anode, a cathode, an electrolyte, and a catalyst arranged on each side of the electrolyte. The anode is the negative post of the fuel cell and conducts electrons that are freed from hydrogen molecules such that the electrons can be used in an external circuit. The anode includes channels to disperse the fuel gas as evenly as possible over the surface of the catalyst.
The cathode is the positive post of the fuel cell, and typically includes channels etched therein to evenly distribute oxygen (usually air) to the surface of the catalyst. The cathode also conducts the electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen ions and oxygen to form water.
One of the difficulties encountered with fuel cells is the regulation of excessive flow and/or pressure from the fuel source feeding the fuel cell. It is quite common to have flow or pressure spikes from the fuel source during fuel cell operation. The flow irregularities may be a result of start up, temperature changes, fluctuations in power demands on the fuel cell, or other phenomena. Flow increases and pressure spikes cause operational instability and flood the fuel cell with fuel that cannot be efficiently used.
Accordingly, there has been some use of flow regulators in fuel cells to reduce pressure and/or flow spikes. The flow regulators often consist of a set of capillaries. However, capillary flow regulators have a small dynamic range, and typical regulators add significantly to the cost of the fuel delivery system. There has also been some use of a bladder and rubber diaphragm to regulate the flow and/or pressure delivered to the fuel cell, but such systems are not sufficiently robust for long-term use and have limited efficacy across varying fuel types.
Thus, there is a need in the art for means of regulating the flow and/or pressure of fuel delivered to a fuel cell.