As the price at the pump continue to soar, our budget for summer frolicking shrinks. People are choosing either to vacation closer to home or forgo them altogether because of high gas prices. We are all feeling the pinch, and we dream of a gasoline independent world. Will it ever come?
Well, it might soon become a reality through research here at UW-Madison. Using hydrogen as fuel is the basis of fuel-cell technology, and though the average Joe probably can't afford to use it to power his car quite yet, that goal's getting closer. UW-Madison professor Manos Mavrikakis of the chemical and biological engineering department, along with biochemistry professor Bryan Eichhorn from the University of Maryland, are doing their part by designing more efficient nanoparticle catalysts; the details appeared in the April issue of Nature Materials. This new catalyst is designed for a purer hydrogen fuel, and its properties may make production of this fuel less expensive.
Fuel cells produce electricity cleanly and efficiently, and the only byproducts are heat and water. Briefly, the fuel cell separates the hydrogen's proton from its electron. The protons travel through a proton conducting membrane and the electrons travel around a circuit to power your light bulb, your laptop, your car, etc. Next, the electrons meet up with the hydrogen protons at the other end and react with oxygen to produce water and heat. These fuel cells rely on catalysts to improve the efficiency of the reactions that occur.
Hydrogen is produced mainly from methane in a process called steam reforming, where methane and water react to give a mixture of two products: carbon monoxide (CO) and hydrogen. [Steam reforming of methane] is the main source of hydrogen today,"" Mavrikakis said. ""After the oil reserve is depleted we'll have plenty of this.""
If you put the CO/hydrogen mixture directly into a fuel cell, it causes the concentration of CO to become too high, and too much CO poisons the fuel cell catalysts, diminishing the fuel cell's lifetime.
Other upstream reactions reduce the amount of CO in the hydrogen fuel mixture. One such reaction is the preferential oxidation of CO, or PROX. The main goal of Mavrikakis and one of his graduate students, Anand Nilekar, was to improve the catalysis of this PROX reaction. Nilekar used theory and computer modeling to design a new platinum catalyst for the PROX reaction, and Selim Alayoglu from the University of Maryland synthesized the catalyst and tested the effectiveness of the new design in CO oxidation.
What's unique about this catalyst is the architecture: It has a ruthenium core two to four nanometers in diameter and a layer of platinum one to two atoms thick, encapsulating the ruthenium and creating what they called a Ru@Pt core-shell nanoparticle. Basically, the structure is kind of like a caramel apple, where ruthenium is the apple and platinum is the thin layer of caramel. In contrast, the traditional PROX catalyst is a platinum and ruthenium bulk alloy, with both types of atoms on the catalyst surface. It's like putting the caramel and apple in a blender and then meshing it into a ball.
With the new platinum shell design, the entire outer surface of the nanoparticle is available for the catalytic reaction. Plus, these platinum atoms behave differently with ruthenium just below the surface instead of more platinum. The platinum atom on the surface of the core-shell nanoparticle feels a stronger bond to the ruthenium below it, so it doesn't bind as tightly to the poisoning CO, ""which will translate into more available sites [on the catalyst] for other molecules to come and do chemistry,"" according to Mavrikakis.
This new architecture allows for many improvements in the catalysis of the PROX reaction. For example, the reaction can take place at roughly room temperature using this core-shell nanoparticle, while various other PROX catalysts require temperatures anywhere from 60 to 200 degrees Celsius. So, this new catalyst saves money in energy costs because you don't have to heat much above room temperature for the reaction to work.
Furthermore, since the Ru@Pt nanoparticle is less easily poisoned by CO, Mavrikakis and Nilekar are looking into using it as one of the catalysts in fuel cells as well. Not only is this catalyst more effective, but it requires significantly less platinum than the traditional catalysts.
""If you break down the cost of the fuel cell, [the platinum catalyst] is 60 percent of the cost, which is a major factor,"" Nilekar said.
But before this new catalyst technology can be used commercially, production must be translated from small ""lab-scale"" to large ""manufacturing-scale,"" and that processes is still in the works.
With the ever growing concern for foreign oil independence and global warming, fuel cells provide a viable alternative to gasoline. However, depending on just one idea to solve the energy crisis is perhaps ill-advised. ""My opinion is we'll need to diversify as much as we can,"" Mavrikakis said.
Nilekar agreed that more than one solution to the fuel crisis is necessary.
""Fuel cells [are] one of the many possible solutions, and right now they look very promising,"" Nilekar said. ""But as everyone else in the industry will tell you, it's really difficult to say if fuel cells will be the solution coming out of this whole process.""
