CO2 Con­verted Di­rectly into Ethanol with New Cat­a­lyst

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The world has a mas­sive prob­lem with too much car­bon diox­ide from the burning of car­bon-based fu­els. But what if we could re­cy­cle CO2 into new fuel with­out adding any new car­bon to the at­mos­phere?

In a new twist to waste-to-fuel tech­nol­ogy, sci­en­tists at the Depart­ment of En­ergy’s Oak Ridge Na­tional Lab­o­ra­tory have de­vel­oped an elec­tro­chem­i­cal process that uses tiny spikes of car­bon and cop­per to turn car­bon diox­ide, a green­house gas, into ethanol. Their find­ing, which in­volves nanofab­ri­ca­tion and catal­y­sis sci­ence, was serendip­i­tous.

“We dis­cov­ered some­what by ac­ci­dent that this ma­te­rial worked,” said ORNL’S Adam Rondi­none, lead au­thor of the team’s study pub­lished in Chem­istry­s­e­lect. “We were try­ing to study the first step of a pro­posed re­ac­tion when we re­al­ized that the cat­a­lyst was do­ing the en­tire re­ac­tion on its own.”

The team used a cat­a­lyst made of car­bon, cop­per and ni­tro­gen and ap­plied volt­age to trig­ger a com­pli­cated chem­i­cal re­ac­tion that es­sen­tially re­verses the com­bus­tion process. With the help of the nan­otech­nol­ogy-based cat­a­lyst which con­tains mul­ti­ple re­ac­tion sites, the so­lu­tion of car­bon diox­ide dis­solved in wa­ter turned into ethanol with a yield of 63 per­cent. Typ­i­cally, this type of elec­tro­chem­i­cal re­ac­tion re­sults in a mix of sev­eral dif­fer­ent prod­ucts in small amounts.

“We’re tak­ing car­bon diox­ide, a waste prod­uct of com­bus­tion, and we’re push­ing that com­bus­tion re­ac­tion back­wards with very high se­lec­tiv­ity to a use­ful fuel,” Rondi­none said. “Ethanol was a sur­prise -- it’s ex­tremely dif­fi­cult to go straight from car­bon diox­ide to ethanol with a sin­gle cat­a­lyst.”

The cat­a­lyst’s nov­elty lies in its nanoscale struc­ture, con­sist­ing of cop­per nanopar­ti­cles em­bed­ded in car­bon spikes. This nano-tex­tur­ing ap­proach avoids the use of ex­pen­sive or rare met­als such as plat­inum that limit the eco­nomic vi­a­bil­ity of many cat­a­lysts. “By us­ing com­mon ma­te­ri­als, but ar­rang­ing them with nan­otech­nol­ogy, we fig­ured out how to limit the side re­ac­tions and end up with the one thing that we want,” Rondi­none said.

The re­searchers’ ini­tial anal­y­sis sug­gests that the spiky tex­tured sur­face of the cat­a­lysts pro­vides am­ple re­ac­tive sites to fa­cil­i­tate the car­bon diox­ide-to-ethanol con­ver­sion.

“They are like 50-nanome­ter light­ning rods that con­cen­trate elec­tro­chem­i­cal re­ac­tiv­ity at the tip of the spike,” Rondi­none said.

Given the tech­nique’s re­liance on low-cost ma­te­ri­als and an abil­ity to op­er­ate at room tem­per­a­ture in wa­ter, the re­searchers be­lieve the ap­proach could be scaled up for in­dus­tri­ally rel­e­vant ap­pli­ca­tions. For in­stance, the process could be used to store ex­cess elec­tric­ity gen­er­ated from vari­able power sources such as wind and so­lar for use when wind is not blow­ing and the sun is not shin­ing.

The re­searchers plan to re­fine their ap­proach to im­prove the over­all pro­duc­tion rate and fur­ther study the cat­a­lyst’s prop­er­ties and be­hav­ior.

ORNL’S Yang Song (seated), Dale Hens­ley (stand­ing left) and Adam Rondi­none ex­am­ine a car­bon nanospike sam­ple with a scan­ning elec­tron mi­cro­scope.

Cat­a­lyst made of cop­per nanopar­ti­cles (seen as spheres) em­bed­ded in car­bon nanospikes that can con­vert car­bon diox­ide into ethanol.

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