Published on September 27th, 2015 | by Tina Casey1
Enzymatic Fuel Cells Are Creeping Slowly Along Thanks To Gold Nanoclusters
September 27th, 2015 by Tina Casey
Way back in 1911, the first enzyme-based fuel cell made its way into being, and ever since then, researchers have been chasing the dream of a fuel cell that could almost literally run on soda pop. In the latest development, a team of researchers over at Los Alamos National Laboratory has found a way past one of the main obstacles, potentially leading to the development of fuel cells that use enzymes instead of metals as catalysts.
Enzymes And Fuel Cells
Enzymes are proteins that catalyze chemical processes in the human body and other living systems. As the results of millions of years of evolution, enzymes are incredibly efficient, as described to CleanTechnica earlier this month by Novozymes CEO Peder Holk Nielsen:
Enzymes may accelerate reactions by factors of a million or even more. Carbonic anhydrase…is one of the fastest enzymes known. Each molecule of the enzyme can hydrate 100,000 molecules of carbon dioxide per second. This is ten million times faster than the nonenzyme-catalyzed reaction.
The idea of harnessing enzymes to convert sugar into power in a mechanical system — an enzymatic fuel cell — first popped up in 1911 according to our friends over at the Electrochemical Society, but progress was slow until the 1960’s. The pace has picked up since then, and in 2007, the US Air Force Office of Scientific Research doubled down with a coordinated effort to develop a fuel cell that runs on simple sugars, involving multiple universities and federal laboratories.
The Los Alamos Enzymatic Fuel Cell
That brings us up to the Los Alamos enzymatic fuel cell. The lab tackled one key problem, which is the ability of the enzyme-active sites to accept and donate electrons. The problem is that the active sites are typically “buried” under the surface of the enzymes, making it difficult to transfer electrons back and forth to the electrode.
The solution was to develop a mediator or “relaying agent” that would enhance electron transfer, and more specifically, one that requires the least amount of energy input to get the job done.
The team focused on gold nanoclusters. Commonly used for chemical catalysis, gold nanoclusters belong to a class of ribbon-like metal nanoclusters (silver, platinum, and copper are also used) known for their unique electronic properties.
Using DNA as a template, the team created a self-assembled gold nanocluster with carbon nanotubes to help the enzyme stay attached to the electrode. Here’s the result:
…the AuNC acts to enhance the electron transfer, and it lowers the overpotential of oxygen reduction by a significant ~15 mV (as opposed to ~1-2 mV observed using other types of mediators) compared to the enzyme alone. The AuNC also causes significant enhancement of electrocatalytic current densities…
Finally, the presence of AuNC does not perturb the mechanism of enzymatic O2 reduction. Such unique application of AuNC as facilitator of ET by improving thermodynamics and kinetics of O2 reduction is unprecedented.
You can get all the details from the Journal of the American Chemical Society under the title, “A Hybrid DNA-Templated Gold Nanocluster For Enhanced Enzymatic Reduction of Oxygen.”
Meanwhile, don’t hold your breath for a fuel cell that will enable you to refuel your FCEV by feeding it jelly donuts. The Los Alamos study demonstrates a path leading to an effective cathode for enzymatic fuel cells, but it’s still a long path.
Speaking Of “Natural” Fuel Cells…
All this news about enzymatic fuel cells got me to thinking about another class of bio-based fuel cells: namely, microbial fuel cells (microbial fuel cells use a whole biological cell, not just an enzyme). CleanTechnica has been following that field since 2009, when the work of University of Massachusetts researcher Derek Lovley crossed our radar.
Lovley has been exploring a mud-loving bacteria called Geobacter for use in microbial fuel cells, since he first discovered the little fellow frisking about on the banks of the Potomac River more than 20 years ago. Geobacter has a unique ability to generate electricity from organic matter and conduct it through tiny, wiry appendages, almost like copper wire.
Our bad for not paying much attention this year. Professor Lovley has made the Thomson Reuters “Highly Cited Researchers” list for 2015. The list is quite exclusive:
About three thousand researchers earned this distinction by writing the greatest number of reports officially designated by Essential Science Indicators as Highly Cited Papers — ranking among the top 1% most cited for their subject field and year of publication, earning them the mark of exceptional impact.
Last year, Lovley also joined the Science Advisory Board for LanzaTech, which has received multiple millions from the US Energy Department to develop and commercialize a microbe-based system for capturing waste gas and converting it to useful products, so stay tuned.
Image: Gold nanoclusters for enzyme fuel cells via Los Alamos National Laboratory.