What might eventually replace oil and gas in the future?

The United States consumes about 9.2 million barrels of oil per day in the form of gasoline. For a number of reasons, this situation isn’t sustainable in the long-term. Automobiles will have to change radically, deriving their power from something other than gasoline and diesel fuel. The most promising replacement technology exists, and is being perfected at the UH Cullen College of Engineering, in the form of fuel cells, which utilize chemical reactions to create electricity.

Peter Strasser, assistant professor of chemical and biomolecular engineering, is conducting research into polymer electrolyte membrane fuel cells (PEMFCs). In PEMFCs, hydrogen is split into protons and electrons on a fuel cell’s anode side, the section of the cell where chemical reactions begin. The polymer electrolyte membrane in the center of the cell allows the positively charged protons to travel through to its cathode side, where the reactions end.

At the same time, the electrons on the anode side travel through an external circuit to the cell’s cathode side, and in doing so create an electrical current that can be used to power automobiles. When these electrons arrive to the cathode side, they bond with the protons that passed through the electrolyte membrane and with atmospheric oxygen to form water, the only “exhaust” produced by PEMFCs.

While a fuel cell’s basic reactions are simple enough to explain, perfecting these reactions is where the real work comes in. Strasser is developing catalyst materials that make the reactions on the cathode side—where the chain of reactions end—as efficient as possible.

These catalysts must possess several properties. First, they must instigate the chain of reactions that converts oxygen, protons and electrons to water as quickly as possible. They must also be able to withstand the harsh internal environment of fuel cells, which is highly corrosive due to the acidic nature of the electrolyte membrane. Currently, platinum offers the best combination of these features. Pure platinum alone, however, is not ideal; it is too expensive and, on the molecular level, bonds too strongly with oxygen, which slows the water formation at the surface of the cathode catalyst, making the fuel cell less efficient. Instead, platinum is combined with other cheaper metals, such as cobalt or copper, to form platinum alloys to create the conditions that will yield the most efficient catalytic activity.

“We try to find synthetic methods where we can fine-tune the distance between atoms. In our most recently developed method, we removed some of the non-platinum atoms in the top layer of the catalyst and observed that the remaining platinum atoms stayed in the contracted state that was created when they were alloyed with the other metals. We thereby modified the electronic properties of the surface atoms. That changes the interaction of the surface with the reacting molecules, which modifies the catalytic activity,” Strasser said.

With the basic reactions of fuel cells still being perfected, the widespread commercialization of the technology is still years down the road. The efforts undertaken by Strasser and others, however, are key if we are ever to arrive at that future.

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