June 25, 2012 | 3 Comments
Engineers at the University of Wisconsin-Milwaukee (UWM) have identified a catalyst of nitrogen-enriched iron-carbon nanorods that works in microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) at 5% of the cost of platinum.
One is beginning to think that some of these nitrogen enriched iron based catalysts are going to get to commercial scale.
The UWM catalyst provides the same level of efficiency in MFCs as the currently used platinum catalyst. The catalyst also has the potential to replace the platinum catalyst used in hydrogen-producing MECs.
Sixty percent of the cost in making microbial fuel cells is the platinum component, so the discovery may lead to much more affordable energy conversion and storage devices.
UWM Professor Junhong Chen, who created the nanorods and is testing them with Assistant Professor Zhen (Jason) He said, “Fuel cells are capable of directly converting fuel into electricity. With fuel cells, electrical power from renewable energy sources can be delivered where and when required, cleanly, efficiently and sustainably.”
Before we get too far, MFCs generate electricity while removing organic contaminants from wastewater. On the anode electrode of an MFC, colonies of bacteria feed on organic matter, releasing electrons that create a current as they break down the waste. On the cathode side, the most important reaction in MFCs is the oxygen reduction reaction (ORR). This is where platinum speeds the slow reaction, increasing efficiency of the cell, but the platinum is expensive.
Obviously water with organic material is in abundant supply and more can be made up very easily.
On the other use, MECs are related to MFCs. But instead of electricity, MECs produce hydrogen. In addition to harnessing microorganisms at the anode, MECs also use decomposition of organic matter and platinum in a catalytic process at their cathodes.
The UWM team also found that the nanorod catalyst outperformed a graphene-based alternative being developed elsewhere. In fact, the pair tested the material against two other contenders to replace platinum and found their nanorods’ performance consistently superior over a six-month period.
The results of the team’s work was published in the March issue of the journal Advanced Materials.
This development offers two interesting options, go straight to electric power or go to stored fuel in hydrogen form.
Chen and He’s nanorods incorporate the best characteristics of other reactive materials with nitrogen attached to the surface of the carbon rod and a core of iron carbide. Nitrogen’s effectiveness at improving the carbon catalyst is already well known. Iron carbide, also known for its catalytic capabilities, interacts with the carbon on the rod surface, providing “communication” with the core. Also, the material’s unique structure is optimal for electron transport, which is necessary for the ORR.
The UWM catalyst isn’t perfected yet. When the nanorods were tested for potential use in the hydrogen producing MECs, the material did a better job than the graphene-based catalyst material, but it was still not as efficient as straight platinum.
He points out, “But it shows that there could be more diverse applications for this material, compared to graphene, and it gave us clues for why the nanorods performed differently in MECs.”
The team’s paper for the MEC results was published this June in the journal Nano Energy.
Chen said the nanorods have been proven stable and are scalable but more investigation is needed to determine how easily they can be mass-produced. More study is also required to determine the exact interaction responsible for the nanorods’ performance.
There’s getting to be a lot of platinum alternatives in research and development. Just which one will be efficient enough, low cost enough and go to scale isn’t known yet, but its looking like there will be competition – a very good thing.