Platinum is highly desired in jewelry and as a catalyst, but in both cases it is expensive. Now, Penn State researchers have found a way to replace the platinum catalyst in their hydrogen generating microbial electrolysis cells with stainless steel brushes without losing efficiency.
"Stainless steel brush cathodes can produce hydrogen at rates and efficiencies similar to those we have achieved with platinum-catalyzed carbon cloth," says Bruce E. Logan, Kappe professor of environmental engineering.
The brushes used were made of 304 stainless steel, had a twisted stainless steel core and were manufactured on an industrial brush manufacturing machine. At an inch in length and an inch in diameter, the brushes had 48 square inches of surface area.
In order to produce hydrogen from microbial electrolysis cells that use organic materials, a small amount of electrical energy is needed. While the electrolysis cells will produce more energy than required to force the reaction, without the added energy they will not produce hydrogen. The researchers, who also include Douglas F. Call, graduate student in environmental engineering and Matthew D. Merrill, postdoctoral researcher in environmental engineering, also found that the stainless steel brush cathode needed to be placed very close to the graphite fiber brush anode for optimum effect.
At an applied voltage of 0.6 volts, the researchers produced about 5.5 amps per cubic foot using the stainless steel cathodes. This was achieved using both anode and cathode brushes cut in half and placed back to back. The researchers reported their work in a recent issue of Environmental Science and Technology.
"Stainless steel brushes show great promise in that they have high current densities and high energy recovery," says Logan. He notes however, "one problem might be the stainless steel brushes' tendency to trap hydrogen bubbles which decreases the active area of the brush. The trapped hydrogen also remains in the reactor longer and is therefore available to microbes that consume hydrogen."
While more stainless steel is required to manufacture the stainless steel brushes than the platinum used as a catalyst in the carbon cloth cathodes, because of the great difference in costs between platinum and stainless steel, the stainless steel brushes are five times less expensive than the platinum catalyzed cathodes.