New anode for direct ethanol fuel cells enables peak power and current densities approaching H2 PEM fuel cells
12 December 2014
A team of researchers in Italy has developed a new palladium-doped anode for direct alcohol fuel cells that produces peak power and current densities (using ethanol at 80 °C) approaching the output of hydrogen-fed proton exchange membrane fuel cells (PEMFCs). A paper on their work is published in the RSC journal ChemSusChem.
Direct alcohol fuel cells (DAFCs), which belong to the family of alkaline fuel cells, are electrochemical devices that continuously convert the chemical energy of an alcohol fuel to electricity. Ethanol is becoming a desirable target fuel for use in DAFCs (i.e., a DEFC) because it offers higher energy density compared to methanol; less crossover rate (from the anode to cathode); and can be produced from agriculture and biomass products. In a 2006 paper (Mann et al.), researchers at Princeton observed that:
The direct 12-electron oxidation of ethanol to carbon dioxide and water in a fuel cell reactor offers a potentially attractive energy resource. In contrast to the much studied hydrogen−oxygen fuel cell, ethanol provides a volumetric energy density that approaches that of gasoline (21 MJ L-1 for ethanol vs 31 MJ L-1 for gasoline). As a liquid fuel, ethanol also avoids issues of storage associated with proposed hydrogen systems. Assuming that ethanol is bioderived, this materials is considered to be carbon neutral. The direct ethanol fuel cell’s (DEFC) primary disadvantage is the lack of a catalyst that can initiate complete oxidation at a high rate. In the absence of an electrocatalytic system that can efficiently deliver 12 electrons per ethanol molecule, the optimistic picture suggested above vanishes.
The electrochemical oxidation of ethanol is a difficult task because of the substantial increase in the number of reaction intermediates associated with this 12-electron process. More troublesome is the presence of the C−C bond, which is between two atoms with little electron affinity or ionization energy, thus making it difficult to access electrochemically.
—Mann et al.
| The complete oxidation of ethanol molecule involves the release of 12 electrons and the cleavage of the C-C bond, which is between two atoms with little electron affinity or ionization energy. |
| Anodic ethanol oxidation: C2H5OH + 3H2O → 2CO2 + 12H+ + 12 e- |
| Oxygen reduction reaction: 3O2 + 12H+ + 12e- → 6H2O |
| Full reaction of DEFC: C2H5OH + 3O2 → 2CO2 + 6H2O |
Key to the success of the DEFC is the catalyst. Many catalysts have been developed and demonstrated electrochemically to oxidize small alcohols, but with varying degrees of oxidation.
To avoid the drawbacks of carbon-supported nanoparticle (NP) electrocatalysts, the team ICCOM CNR (Institute of Organometallic Chemistry, National Research Council) in Italy prepared anodes consisting of palladium (Pd) NPs supported on 3 D TiO2 nanotube arrays.
A 2 μm thick layer of TiO2 nanotube arrays was prepared on the surface of the Ti fibers of a nonwoven web electrode. After it was doped with Pd nanoparticles (1.5 mg Pd cm−2), this anode was employed in a direct alcohol fuel cell. Peak power densities of 210, 170, and 160 mW cm−2 at 80 °C were produced if the cell was fed with 10 wt % aqueous solutions of ethanol, ethylene glycol, and glycerol, respectively, in 2 m aqueous KOH.
The Pd loading of the anode was increased to 6 mg cm−2 by combining four single electrodes to produce a maximum peak power density with ethanol at 80 °C of 335 mW cm−2. Such high power densities result from a combination of the open 3 D structure of the anode electrode and the high electrochemically active surface area of the Pd catalyst, which promote very fast kinetics for alcohol electro-oxidation.
—Chen et al.
Resources
Chen, Y., Bellini, M., Bevilacqua, M., Fornasiero, P., Lavacchi, A., Miller, H. A., Wang, L. and Vizza, F. (2014), “Direct Alcohol Fuel Cells: Toward the Power Densities of Hydrogen-Fed Proton Exchange Membrane Fuel Cells,” ChemSusChem doi: 10.1002/cssc.201402999
A. M. Sheikh, Khaled Ebn-Alwaled Abd-Alftah, C. F. Malfatti (2014) “On reviewing the catalyst materials for direct alcohol fuel cells (DAFCs),” Journal of Multidisciplinary Engineering Science and Technology Vol. 1 Issue 3
Jonathan Mann, Nan Yao, and, and Andrew B. Bocarsly (2006) “Characterization and Analysis of New Catalysts for a Direct Ethanol Fuel Cell” Langmuir 22 (25), 10432-10436 doi: 10.1021/la061200c
...Assuming that ethanol is bioderived, this materials is considered to be carbon neutral...
That is quite an assumption, considering all the energetic inputs into the creation of ethanol.
Posted by: Nick Lyons | 12 December 2014 at 07:43 AM
The problem is that there is many different technologies and the manufacturers and goverments and consumers don't know where to go. First of all if that fuelcell is cheap and efficient, than there will be enouph ethanol to feed them. can we put it in big trucks contrary to hydrogen as a big truck cannot store enouph hydrogen gas to be useful.
Posted by: gorr | 12 December 2014 at 07:43 AM
If commercialized at a reasonable cost, this would make the future of H2 FCVs very dim. Brazil has shown how well bio derived ethanol can be adopted. With double the efficiency, it just gets that much more attractive.
Posted by: electric-car-insider.com | 12 December 2014 at 08:21 AM
Any liquid based fuel cell would be a huge boon.
So much easier to store and transport.
Even one that ran on gasoline or diesel.
Now, I wonder could you run it on E85, or does it need E100 ?
Either way, you would probably end up using it in a hybrid configuration, more like a range extender than the main power source.
Posted by: mahonj | 12 December 2014 at 08:34 AM
20-50kWh electric car with 20kW ethanol fuel cell range extender in my opinion is car of the future especially in colder climate
Posted by: As Aha | 12 December 2014 at 08:50 AM
You'd probably need E-100 (or even wet ethanol, since the process generates water and is obviously tolerant of it). I've never heard of an alcohol FC catalyst that also handled alkanes.
Posted by: Engineer-Poet | 12 December 2014 at 09:17 AM
The papers are all behind paywalls, and I saw nothing in the abstracts that mentioned efficiency.
Suppose 70% efficiency is achieved. 21 MJ of ethanol yields 14.7 MJ of electricity (roughly 4 kWh). At 250 Wh/mile, 1 liter of EtOH drives the vehicle 16 miles or roughly 60 MPG. 60 miles... on a gallon of alcohol.
If you use PHEV to replace about 2/3 of liquid fuel with grid power, and go from 25 MPG to 60 MPG after cutover, you've very nearly covered demand with the 10% ethanol that's currently blended into gasoline.
Posted by: Engineer-Poet | 12 December 2014 at 09:28 AM
80c is where the fuel cell runs, so heating ethanol is not a problem. The problem with most direct methanol fuel cells is pass through, where the alcohol ends up on the other side, if they can get past that they could have something.
E100 from cellulose is a good idea, you can synthesize ethanol from biomass as well as ferment and distill. The farm equipment can run on methanol and/or ethanol, gasified biomass can be used to create nitrogen fertilizer. It is not done because oil and natural gas have been less expensive, that may not be the case forever, even considering fracking and lower oil and gas prices now.
Posted by: SJC | 12 December 2014 at 10:43 AM
It seems that there are not many A.biofuels currently available
Though Brasil has some 6 or so suppliers. Brasil is a special case with two crops per year possible in some areas.
I suggest that Nicks comment above is justified.
There are reasonably current numbers on ethanol gasoline equivalent ranging from a little as -20% to +120% for say miscanthus where the -20% comes from the underground plant root system that can be held for the regulated time frame I.E. 30years land use change. Sounds rubbery?
the + 120% is due to the energy lost growing corn ethanol at less than optimum energy efficiency Ie energy intensive inputs
and or land use changes.
US regulated imported Brazillian sugarcane ethanol from the six advanced biofuel approved suppliers is rated at <50% gasoline equivalent (CO2)
=
Posted by: Arnold | 12 December 2014 at 05:41 PM
Apology
Makes more sense if you invert the -'s and +'s
Posted by: Arnold | 12 December 2014 at 05:44 PM
What "imported Brazilian sugarcane ethanol"? Brazil is in the midst of a severe drought, and imports ethanol from the US!
For what it's worth, there is probably no limitation on the types of alcohol that qualify for this catalyst.The mixture of different types will improve the availability of heat, fuel density, and desired reactants at all stages of the fuel/intermediate expenditure. This is more or less why you have gasoline blends. Note how critical the availability of water is, which is generated and then recycled for the final combustion of carbon and free hydrogen.
The addition of THF or equivalent may help, as this helps tie up some hydrogen to be effectively utilized by neighboring molecules, including free oxygen. This should reduce inefficient water buildup, and help increase the end availability of H+ for the cathode.
A very promising line of research.
Posted by: kalendjay | 13 December 2014 at 08:00 PM
"...a new palladium-doped anode.."
As long as the ethanol is pure with few contaminants it could last. There can not be any CO created by partial reaction, but keeping the catalyst clean could prevent that.
Posted by: SJC | 14 December 2014 at 04:40 PM
Alcohol FCs could eventually become one way to transform stored energy cleanly, closer to end users.
Excess wind and solar e-energy could be transformed into alcohol for delayed use by AFCs.
Both could work if it can be done efficiently.
Posted by: HarveyD | 16 December 2014 at 09:47 AM