Fuel cells have the potential to be a clean and efficient way to run cars, computers and power stations. But the cost of producing them is limiting their use. This is because a key component of the most common fuel cells is a catalyst made from the precious metal platinum.
Researchers from the University of California, Riverside, describe the development of an inexpensive, efficient catalyst material for a new type of fuel cell called a polymer electrolyte membrane fuel cell (PEMFC). This fuel cell turns the chemical energy of hydrogen into electricity and is one of the most promising fuel cell types to power cars and electronics.
The catalyst developed at UCR is made of porous carbon nanofibers embedded with a compound made of a relatively abundant metal like cobalt. Cobalt is 100 times less expensive than platinum. David Kisailus, Winston Chung Endowed Professor in Energy Innovation in UCR’s Marlan and Rosemary Bourns College of Engineering, led the research.
Fuel cells are already being used by some carmakers. Fuel cells offer advantages over conventional combustion technologies, including higher efficiency, quieter operation and lower emissions. Hydrogen fuel cells emit only water.
Similar to batteries, fuel cells are electrochemical devices that are comprise of a positive and negative electrode sandwiched between electrolytes. When a hydrogen fuel is injected onto the anode, a catalyst separates the hydrogen molecules into positively charged particles called protons and negatively charged particles called electrons. The electrons are directed through an external circuit where they do useful work, like powering electric motors, before rejoining the positively charged hydrogen ions and oxygen to form water.
A critical barrier to fuel cell adoption is the cost of platinum. This makes the development of alternative catalyst materials a key driver for mass implementation.
UCR researchers used a technique called electrospinning to make paper-thin sheets of carbon nanofibers that contained metal ions. When heated, the ions formed ultrafine metal nanoparticles that catalyzed the transformation of carbon into a high-performance graphitic carbon. Because of this, metal nanoparticles and residual nongraphic carbon were oxidized. This leads to a highly porous and useful network of metal oxide nanoparticles dispersed in a porous network of graphite.
Kisailus and the team collaborated with scientists at Stanford University to determine that the new materials performed at the same caliber as the industry-standard platinum-carbon systems, but they are a fraction of the cost.
"The key to the high performance of the materials we created is the combination of the chemistry and fiber processing conditions," Kisailus said. "The remarkable electrochemical properties were primarily attributed to the synergistic effects obtained from the engineering of the metal oxide with exposed active sites and the 3D hierarchical porous graphitic structure."
Kisailus said an added benefit of the catalytic nanocomposite was that its graphitic fiber nature provided additional strength and durability, which enables it to serve as a fuel cell catalyst and potentially as a structural component.
"An important challenge in making high-performance vehicles is reducing weight, both from the body of the vehicle as well as extra weight from the battery or fuel cell, without affecting safety or performance," he said. "The material we created may enable automakers to turn structural components, such as the hood or the chassis, into functional elements that help power cars."
A paper on this research was published in the journal Small.