Microbial Fuel Cells (MFC) are a new development whereby
electricity can be generated from biofilms. They are especially useful in
waste-management industries like landfill sites and waste-water treatment
plants and many studies have shown great potential in these areas. However,
currently the construction of MFC’s is very costly due to the need for chemically
catalysed cathodes (based on Platinum-loaded materials) and polymeric
electrolyte membrane (PEM). Previous studies have shown that using a single
chamber MFC (SCMFC) reduces the need for PEM; however none have been done on
different cathodes. Indeed in addition to the cost of a Pt-loaded cathode, the
oxidation by-products made from the degradation of organic substances often can
cover the Pt catalyst reducing the yield long-term.
In this study the electrochemical performances of
membraneless-SCMFC’s with different Pt-loaded cathodes were compared. In
addition two graphite based (Pt-free) cathodes were compared to traditional
Pt-based cathodes over a six month period. Once the biofilms had established the
power output was constant across the cathodes, with a small non-significant decrease
seen in the Pt-free cathode in the beginning, however power output crept up to
the same level as the Pt-loaded cathodes. The output of power was found to be
most sensitive to pH; exceeding 9.5 caused a decrease in energy output. Varying
levels of the chemical oxygen demand also had no effect on power output. The
maximum power density was found to be 0.5Wm-2.
The paper covers a wide array of environmental conditions on
energy generation, but the most important in terms of future research is the
finding that Pt-free cathodes work just as effectively as Pt-loaded cathodes
given time. Therefore long term applications of MFCs in industry are a step
closer with this reduction in start-up costs. It was alittle tricky to understand due to technicalities of power-curves including alot of physics so i encourage you to read the paper if you are interested.
Hi Myles,
ReplyDeleteI'm not sure if you've seen my post or not but I was quite interested in Microbial Fuel Cells too! However you've put that they are a recent development.. but I thought you might be interested to learn Wingard et al. (1982) first described them over 30 years ago!
The authors find that the power output is sensitive to pH level, and that exceedingly alkali conditions caused a decrease in power output, does this mean that acidic pH causes a greater power output? or is it that an optimum pH can be achieved? If so, if this an optimum for the bacteria or an optimum for the generation of an electron gradient? And is this pH level in the whole system or just the anode/cathode?
Also did the authors alter any other abiotic factors (light, salinity etc) or just kept to pH?
Thanks, Harri
Hi Harri,
ReplyDeletePerhaps saying 'new' development was the wrong wording, i meant that relative to other energy power sources ie. wind, coal etc it is a new development :)
It is already known that Neutral or alkaline conditions (typical of wastewaters) decreases the Pt's electrocatalytic activity in a typical cathode. So this study also showed that pH effects Pt-free cathodes. The Authors talk about reactions being thermodynamically possible up to pH 12, which suggests its conditions favourable to bacteria rather than the metals. Although the pH of a solution would probably have an effect on the rate of electron loss by the cathode. This is speculation on my part, as it doesn't specifically say in the paper and my chemistry knowledge is still at Alevel level.
The pH is the whole system, because the anode and cathode are within a single chamber (hence SCMFC).
As for other abiotic factors, they didnt measure any others. However i should just clarify that the authors didnt control the pH, they simply measured it over the six month period and observed the reduction of electrical activity over a pH of 9.
Myles