Wednesday, December 7, 2011

Using Hydrogen Fuel Cells For Power

When people think of hydrogen fuel cells, they mainly think of them as a way to power automobiles. The reason is that fuel cells generate electricity as long as they have fuel – hydrogen – so they work similar to internal combustion engines in that regard. They do not have to store electricity like battery-powered cars, thus they are seen as a way of making electric cars work similar to gasoline powered cars – fuel up and go, without waiting for a recharge (or using a very long extension cord).

However, that idea may be getting in the way of adopting hydrogen fuel cells. Fuel cells are much more efficient than an ICE – an ICE loses much of its useful energy in heat, noise and vibration (your car is a testament to this). But the infrastructure to deliver hydrogen is difficult to build and expensive.

So, maybe we should be thinking about another type of fuel cell. There is another option besides a fuel cell that works exclusively on hydrogen. Some fuel cells can use existing types of fuel. The solid oxide fuel cell is one of these:

[...] Another problem, Wachsman says, is America's fixation on vehicles. "It will take decades to create a nationwide hydrogen distribution and storage system, and to convert every gas station into a hydrogen filling station. That reality has turned fuel cells into a 'future technology' and has resulted in a drastic reduction in the funding of fuel cell research by the DOE in favor of developing electric cars, when in fact fuel cells can be used right now in many stationary and mobile applications, including centralized power distribution and power generation for homes, businesses, and industry."

Most people are unaware that there are two kinds of fuel cells. The one in the public eye, the proton exchange membrane (PEM) fuel cell, uses hydrogen to generate power. The type of fuel cell Wachsman and his colleagues have worked to perfect, the solid oxide fuel cell (SOFC), has a distinct advantage over its PEM-based sibling.

"Solid oxide fuel cells are unique because they can oxidize any fuel," Wachsman explains. "They can run off of gasoline, diesel and natural gas today, and biofuels and hydrogen in the future, whenever that infrastructure is in place."

Being able to use multiple fuels is a big plus, since ‘pure’ hydrogen does not exist in nature. Creation of hydrogen has been problematic, as it takes energy to do so. It is also difficult to store and transport hydrogen:

In a recent study, fuel cell expert Ulf Bossel explains that a hydrogen economy is a wasteful economy. The large amount of energy required to isolate hydrogen from natural compounds (water, natural gas, biomass), package the light gas by compression or liquefaction, transfer the energy carrier to the user, plus the energy lost when it is converted to useful electricity with fuel cells, leaves around 25% for practical use — an unacceptable value to run an economy in a sustainable future. Only niche applications like submarines and spacecraft might use hydrogen.

Why a hydrogen economy doesn't make sense (PhysOrg)

Although there are some promising developments:

Harvesting "limitless hydrogen" from self-powered fuel cells (BBC)

The problem with solid oxide fuel cells is that they operate at a much higher temperature than PEM cells. If that changes, however, even electric cars powered by gas may be possible:

"That is the issue," he explains. "It's the reason why the automotive companies are using PEM fuel cells. PEM fuel cells operate at around 80 degrees Celsius [180 degrees Fahrenheit], which allows them to startup fairly quickly. Current solid oxide fuel cells currently operate at 800 degrees Celsius [1500 degrees Fahrenheit], so it takes a long time to warm up to operating temperature, making them more applicable to stationary power generation."

Wachsman and his colleagues are working to change that. In an article in the November 18 issue of Science, the team outlines the technology behind a new world record power density SOFC that generates two watts of power per square centimeter at 650 degrees Celsius [1200 degrees Fahrenheit]. The cell uses a bi-layer electrolyte developed by Wachsman that is more than 100 times more conductive than the conventional zirconia-based electrolyte operating at the same temperature also a world record. When the cells are assembled into a stack they should produce three kilowatts of electricity per kilogram of material, more than an internal combustion engine at approximately one-third the size.

The paper lays out a strategy to further lower temperature. The team believes its improvements to SOFC electrolytes and nanostructured-electrode designs could ultimately reduce the cells' operating temperature to only 350 degrees Celsius [660 degrees Fahrenheit]. At that temperature they could start up fast enough for automotive applications, and would be more efficient and more affordable than current SOFCs because they could be manufactured from less expensive materials.

Whatever their applicability for automobiles, the sold oxide fuel cell’s range of fuels seems to be an attractive option to bring electricity to remote areas. We’ve previously shown how biogas is being harvested as cooking fuel. That biogas could also power an efficient fuel cell with no moving parts to produce electricity. We also pointed out the many ways bacteria can produce biofuels from agricultural waste and non-food crops. Using these methods in combination with fuel cells to produce electricity may be a promising development. Agricultural communities using proper sanitation can harness human and animal waste, along with cellulose plant material, to produce electricity, cooking gas, food, and fiber, while preventing disease and helping the environment, and some of the fuel cell's waste product would be potable water. That seems like a better use for fuel cells than preserving suburbia.

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