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Stanford researchers develop copper-based catalyst that produces ethanol from CO at room temperature; potential for closed-loop CO2-to-fuel process

11 April 2014

Researchers at Stanford University have developed a nanocrystalline copper material that produces multi-carbon oxygenates (ethanol, acetate and n-propanol) with up to 57% Faraday efficiency at modest potentials (–0.25 volts to –0.5 volts versus the reversible hydrogen electrode) in CO-saturated alkaline water.

The material’s selectivity for oxygenates, with ethanol as the major product, demonstrates the feasibility of a two-step conversion of CO2 to liquid fuel that could be powered by renewable electricity, the team suggests in their paper published in the journal Nature. Ultimately, this might enable a closed-loop, emissions free CO2-to-fuel process.

We have discovered the first metal catalyst that can produce appreciable amounts of ethanol from carbon monoxide at room temperature and pressure—a notoriously difficult electrochemical reaction.

—Matthew Kanan, an assistant professor of chemistry at Stanford and coauthor of the Nature study

Two years ago, Kanan and Stanford graduate student Christina Li created a novel oxide-derived copper electrode material. While conventional copper electrodes consist of individual nanoparticles that just sit on top of each other, oxide-derived copper, is made of copper nanocrystals that are all linked together in a continuous network with well-defined grain boundaries. The process of transforming copper oxide into metallic copper creates the network of nanocrystals, Kanan explained.

For the Nature study, Kanan and Li built an electrochemical cell: two electrodes placed in water saturated with carbon monoxide gas. When a voltage is applied across the electrodes of a conventional cell, a current flows and water is converted to oxygen gas at one electrode (the anode) and hydrogen gas at the other electrode (the cathode). The challenge was to find a cathode that would reduce carbon monoxide to ethanol instead of reducing water to hydrogen.

The electrochemical conversion of CO2 and H2O into liquid fuel is ideal for high-density renewable energy storage and could provide an incentive for CO2 capture. However, efficient electrocatalysts for reducing CO2 and its derivatives into a desirable fuel are not available at present. Although many catalysts can reduce CO2 to carbon monoxide (CO), liquid fuel synthesis requires that CO is reduced further, using H2O as a H+ source. Copper (Cu) is the only known material with an appreciable CO electroreduction activity, but in bulk form its efficiency and selectivity for liquid fuel are far too low for practical use. In particular, H2O reduction to H2 outcompetes CO reduction on Cu electrodes unless extreme overpotentials are applied, at which point gaseous hydrocarbons are the major CO reduction products.

—Li et al.

In the Nature experiment, Kanan and Li used a cathode made of oxide-derived copper, with the resulting high yield of ethanol and acetate at 57% Faradaic efficiency (i.e., 57% of the electric current went into producing these two compounds from carbon monoxide). By comparison, conventional Cu nanoparticles with an average crystallite size similar to that of oxide-derived copper produced nearly exclusive H2 (96% Faraday efficiency) under identical conditions.

The researchers attributed the ability to change the intrinsic catalytic properties of Cu for this notoriously difficult reaction to the growth of the interconnected nanocrystallites from the constrained environment of the oxide lattice.

The Stanford team has begun looking for ways to create other fuels and improve the overall efficiency of the process.

In this experiment, ethanol was the major product. Propanol would actually be a higher energy-density fuel than ethanol, but right now there is no efficient way to produce it.

—Matthew Kanan

In the experiment, Kanan and Li found that a slightly altered oxide-derived copper catalyst produced propanol with 10% efficiency. The team is working to improve the yield for propanol by further tuning the catalyst’s structure. Ultimately, Kanan would like to see a scaled-up version of the catalytic cell powered by electricity from the sun, wind or other renewable resource.

For the process to be carbon neutral, scientists will have to find a new way to make carbon monoxide from renewable energy instead of fossil fuel, the primary source today. Kanan envisions taking carbon dioxide (CO2) from the atmosphere to produce carbon monoxide, which, in turn, would be fed to a copper catalyst to make liquid fuel. The CO2 that is released into the atmosphere during fuel combustion would be re-used to make more carbon monoxide and more fuel—a closed-loop, emissions-free process.

Technology already exists for converting CO2 to carbon monoxide, but the missing piece was the efficient conversion of carbon monoxide to a useful fuel that's liquid, easy to store and nontoxic. Prior to our study, there was a sense that no catalyst could efficiently reduce carbon monoxide to a liquid. We have a solution to this problem that’s made of copper, which is cheap and abundant. We hope our results inspire other people to work on our system or develop a new catalyst that converts carbon monoxide to fuel.

—Matthew Kanan

The Nature study was coauthored by Jim Ciston, a senior staff scientist with the National Center for Electron Microscopy at Lawrence Berkeley National Laboratory.

The research was supported by Stanford University, the National Science Foundation and the US Department of Energy.

Resources

  • Christina W. Li, Jim Ciston & Matthew W. Kanan (2014) “Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper,” Nature doi: 10.1038/nature13249

April 11, 2014 in Carbon Capture and Conversion (CCC), Catalysts, Ethanol | Permalink | Comments (16) | TrackBack (0)

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Is this another step towards future electro-fuels?

The trick is to get from CO2 to CO.

"The trick is to get from CO2 to CO" All it takes is energy as the reaction wants to go the other way. Basically, you can make anything if you have enough energy. However, I am really tired of hearing how we are going to make fuel out of surplus renewable electric power. We do not have surplus renewable electric nor do I believe that we ever will have. Maybe, we could use nuclear power especially if you can use the hear directly and skip the stage of generating electric power.

Sure, it takes energy to make energy., that has to do with that "efficiency" thing.

@sd,
We can erect solar PV Panels and wind turbines that are dedicated to the production of synthetic fuels like H2 and alcohols and methane. This is called "energy farming"... (vs energy hunting & gathering like we are doing now with oil and gas exploration and mining.) As any civilization will advance, the hunting & gathering practice will have to yield to steady Farming methods for sustainability and growth of the civilization. Only 1-5% of land surface area of any country is sufficient to collect enough of solar energy to satisfy all future energy demand. Already developed land areas such as rooftops, parking lots, streets could be covered with solar PV to satisfy all energy demands.

There is no need for any surplus renewable electric power because most of future solar and wind energy can be used for production of synthetic fuels. Base load power can use nuclear energy instead. Nuclear energy is too valuable as base load power supply to use for making fuel. Intermittent but low-cost solar and wind energy would be more economical and can be deployed much more rapidly.

We already have the archaebacterial scheme for converting CO2 to methane at 80% coulombic efficiency.  Fermenting methane to ethanol or oxidizing it to methanol might be simpler than finding an electrochemical way to reduce CO2 to CO.

True renewability requires not just CO production from CO2, but CO2 capture from the environment.  This is easier said than done; the navy's scheme for the carrier-based fuel production system requires roughly 1 MJ per mole of CO2.  With overhead like that, the cost of the product is going to be mighty high.

I get the feeling that the cheapest and easiest scheme might involve something like purification of landfill gas or bio-gas, electro-biological conversion of the CO2 to CH4, and storing it for later use.  Exactly how much of current energy demand this could displace and how much carbon emissions would be prevented, I am in no position to speculate at this time.

@EP:
'There’s a limit to how much fuel waste-treatment plants can provide, he said. Installing similar hydrogen-making systems at most of California’s major waste-treatment plants would generate enough hydrogen to power about 10 percent of all the cars on the state’s roads, Brouwer said.'

http://www.koreaherald.com/view.php?ud=20140216000086

Still, 10% of cars running on sewage is nothing to sniff at!

Future electro-fuels may become one more option to store exess:

1. daylight time Solar energy.
2. unused Wind energy.
3. spring time excess hydro energy.
4. unused CO and CO2

Electro-fuels may be a good source of cleaner fuels for commercial airplanes etc.

HarveyD, I am with you. Just as we now throw away natural gas by flaring it off, we should conserve what we make. There WILL be excess electric from the sources you note. We should not squander it. The cost, on the other hand, I do not know about.

DaveMart, I have no problem with proposals for 10% as long as they don't ignore the other 90%.

I would love to see some sort of scheme for the reformed landfill gas that either converts the CO2 (both from the biogas and from the reformer) to useful products or sequesters it.  We need energy systems that are carbon-negative.

EP:

"We already have the archaebacterial scheme for converting CO2 to methane at 80% coulombic efficiency."

What process is it, where is it working at pilot scale, and what currently prevents extensive use?

The phenomenon was discovered in 2009.  Here's a writeup from 2012:

http://www.sciencedaily.com/releases/2012/07/120727144534.htm

At the time, they were talking about prototype electro-bioreactors in 3 years:

http://www.ecomagination.com/microbes-make-methane-from-waste-wind-power

Thanks, E-P. I dug up a paper I was given (print version) from Sapienza University of Rome, also '09, that discusses CO2 to CH4 conversion using a methanogenic culture. If I can find a link I'll share it in another thread. Lots of data; looks interesting.

Like the Stanford/PSU work, it's all lab scale and I haven't seen a pilot of any appreciable size. In my tour of duty in refining I saw the Catalyst of the week from many people, and was just starting to see the bioelectrochemical stuff. Problem is that very few of these survive pilot-level demo for any number of reasons that were unforeseen in the lab. That's the source of my skepticism.

I have a daughter at PSU doing a bioscience PhD. I tried to talk her into doing something with termite cellulose digestion for her thesis, but she's really into disease vectors. Kids these days...

I was hoping they'd manage to get a methanogenic culture from thermophilic communities, and be able to use the waste heat for space heat or DHW or something.  The hotter the bugs like it, the easier they are to keep at their preferred temperature when you're cranking power into the system.

3 years won't be up until sometime in 2015, so let's not hold their feet to the fire just yet.

Personally I am hopeful that holding their feet to the fire might initiate just the sort of bacteriological action that we are looking for.
It would in my feet, anyway.

Stored H2 or H2 pumped into NG distribution networks may be one of the best way to store surplus or specially produced clean energy.

Stored H2 could be used for future FCEVs or for generating clean electricity with large FCs on an as required basis.

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