Never Change Your Batteries Again!

Ryan O'Hayre
Department of Electrical Engineering
Stanford University
December 2001

Are you frustrated when your laptop, CD player, or cell phone runs out of batteries? You may soon be able to replace those clunky batteries with a better power source, known as a fuel cell. Compared to conventional batteries, fuel cells can pack a lot more energy in the same volume. As a result, your portable electronics might one day run on micro-fuel cells that last 10 times as long as current batteries.

Fuel cells work by reacting a fuel, such as alcohol (methanol) or hydrogen (H2) with air. This reaction generates energy, some of which is extracted by the fuel cell in the form of electricity. In an ideal world, a fuel cell would be 100% efficient. In other words, it could convert every last drop of the reaction energy into electricity. However, in reality, this is not possible. Some of the reaction energy is always lost as heat. The efficiency of a real fuel cell is thus always less than 100%.

In order to have a fuel cell that can last 10 times as long as a battery of the same size, there are two important design goals. The first is to design a fuel cell that is as efficient as possible. The second is to miniaturize the fuel cell device, so that it is the same size as conventional batteries. Our lab works on both of these design aspects. My research in particular focuses on making the fuel cell more efficient.

The best way to make a fuel cell more efficient is to use catalysts. Catalysts are materials that promote or speed up a reaction. The rare and expensive metal platinum is an example of a catalyst. The catalytic converter of a car's engine uses platinum to help the car run more cleanly. Platinum is also used as a catalyst in fuel cells, where it promotes the conversion of fuel into electricity.

I try to understand how catalyst materials work in order to improve them. One of the most important characteristics of a catalyst is the catalyst structure. Catalyst structure simply refers to form that the catalyst takes-for example, if it's a powder, a film, a block, or mixed with other ingredients, etc. The best catalyst structures distribute the catalytic material as a very fine powder. Many tiny particles of platinum are far more active than one large chunk of platinum, just like fine shavings of wood catch fire more easily than a large block.

I compare the effectiveness of prototype fuel cells that have different catalyst structures in them. This allows me to understand which catalyst structures are the most effective. I accomplish the comparison of catalyst structures through a series of electrical tests and measurements. I'm currently working on a way to generate high resolution "maps" of the catalyst structures. These maps will pinpoint "hot spots" where electricity generation is highly efficient and "cold spots" where electricity generation is highly inefficient. By understanding what catalyst features lead to hot spots, and what catalyst features lead to cold spots, I hope to generate a high performance fuel cell where the whole device is "hot".

As fuel cell research advances, hand held power will pass from dream into reality. Breakthroughs in "hot" catalysts and miniaturization techniques are powering the technology towards commercialization-- and when fuel cells finally are commercialized, you may never have to change your batteries again.