Mark Prochaska

Fuel cells are possible power sources for automobiles and portable electronics. When connected to an electric motor, they can operate with greater efficiency than internal combustion engines since they don’t use heat to do work. Using hydrogen fuel cells in cars would reduce environmentally harmful emissions. Methanol fuel cells in portable electronics could be designed to supply power for longer times than rechargeable batteries.

Fuel cells produce electrical power by oxidizing a fuel, such as hydrogen or methanol, at the anode and reducing oxygen gas at the cathode.

The schematic diagram above shows a hydrogen fuel cell. The electrons from the hydrogen oxidation reaction at the anode are carriers of electrical energy through the external circuit. The protons travel across a proton exchange membrane where they meet with the electrons and oxygen gas at the cathode. The fuel cell’s by-product is water. Fuel cells can also use methanol at the anode. In that case, methanol is oxidized to produce protons, electrons, and carbon dioxide.

For the fuel cell to produce enough current to the external electrical circuit, catalysts must help the chemical reactions at the anode and cathode. Most fuel cells use Pt catalysts, a situation that has hardly changed since Sir William Grove built the first fuel cell in 1839! The most significant improvements have been the use of Pt nanoparticles and Pt/Ru alloys. Pt catalysts, however, have many deficiencies. At the cathode, the reaction rate of oxygen reduction is very slow. The fuel cell cannot supply enough current to the circuit and suffers a reduction in voltage, called the overpotential. Methanol oxidation on Pt also suffers from a high overpotential. When hydrogen is the fuel, impurities such as sulfur and carbon monoxide adsorb to the Pt surface and block further oxidation. High-purity hydrogen requirements, along with the scarcity of Pt, contribute to high operation costs.

Clearly, new catalysts are necessary to reduce overpotentials, improve fuel impurity tolerances, and lower operation costs. We are searching for ordered intermetallic compounds with such properties. But there are tens of thousands of compounds that no one has tested! The number of possible binary and ternary compounds would take decades to investigate using traditional synthesis and evaluation methods.

Is there a faster way to test these compounds? The answer is yes! I am using a high throughput method to synthesize and evaluate potentially thousands of binary and ternary compositions in just one sample! I sputter thin films of composition spreads of two or three elements onto silicon substrates. Not only do I produce lots of compositions, but it only takes hours instead of decades.

To test all the compositions for catalytic ability, Jing Jin of the Abruña group uses a fluorescent pH-sensitive indicator to determine the location of good catalysts on the thin film.

We also use scanning electrochemical microscopy (SECM) and pH-sensitive electrodes to confirm the results of the fluorescence test.

Once I know the location of the good catalysts on a composition spread, I can characterize them using several tools. I use x-ray diffraction to determine which chemical phases are present, along with their crystal structure. Microprobe measurements and scanning electron microscopy (SEM) allow me to determine atomic ratios and surface morphology. Once I know the characteristics of the catalyst, I can make the catalyst in bulk and perform other tests on it.