High Surface Area Stainless Steel Cathodes as Efficient as Platinum in Microbial Electrolysis Cells for H2 Production
Researchers at Penn State University have found a way to replace the platinum-catalyzed carbon cloth cathodes in their hydrogen-generating microbial electrolysis cells (MEC) (earlier post) with high surface area stainless steel brush cathodes 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.
??”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.
Using a stainless steel brush cathode with a specific surface area of 810 m2/m3, hydrogen was produced at a rate of 1.7 ?± 0.1 m3-H2/m3-d (current density of 188 ?± 10 A/m3) at an applied voltage of 0.6 V. The energy efficiency relative to the electrical energy input was 221 ?± 8%, and the overall energy efficiency was 78 ?± 5% based on both electrical energy and substrate utilization. These values compare well to previous results obtained using platinum on flat carbon cathodes in a similar system.
??”Call et al. (2009)
While the stainless steel brushes show great promise in that they have high current densities and high energy recovery, Logan said, 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.
The American Society of Engineering Education, the National Water Research Institute and the National Science Foundation funded this work.
Resources
Douglas F. Call, Matthew D. Merrill and Bruce E. Logan (2009) High Surface Area Stainless Steel Brushes as Cathodes in Microbial Electrolysis Cells. Environ. Sci. Technol., 43 (6), pp 2179??“2183 doi: 10.1021/es803074x
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