Versatile membranes from carbon nanotubes
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Versatile membranes from carbon nanotubes A new type of membrane composed of vertically aligned carbon nanotubes shows promise for boosting the perfor- mance of electrochemical devices such as lithium-ion batteries and fuel cells. Chemistry professor Charles R. Martin, assistant chemistry professor Ellen R. Fish- er, postdoctoral researcher Guangli Che, and graduate student Blinda Β. Lakshmi, at Colorado State University, Fort Collins, created the membranes by chemical vapor deposition of graphitic carbon into an alu- minum template riddled with 200-nm- diameter pores. The group then dissolved away the aluminum template with acid, leaving a freestanding carbon membrane—a clus- ter of ordered nanotubules held together by 20-nm-thick carbon surfacefilms[Na- ture, 393,346(1998)]. The Colorado State method shows that alumina template membranes have a lot of potential that hasn't yet been exploited, says Michael J. Sailor, associate chemistry professor at the University of California, San Diego. "It's very interesting work," he adds. The high surface area of the tubule clusters means that large quantities of elec- trochemically important substances, such as nanoscopic metal catalyst particles, can be embedded in the membrane. Also use- ful is that these membranes are easy to connect to an electrochemical cell. As Martin notes: "You just place the mem- brane on top of an electrode. "In addition, the membrane approach ensures that all of the carbon tubes are bathed in electrolyte because the electro- lyte fills the tubes." Carbon is the typical anode material used in lithium-ion batteries. Martin's group found that the caibon tubule mem- brane reversibly intercalates Li + . The group also grew a second set of even tini- er nanotubules inside the membrane tu- bules and found that these inner tubules doubled the It intercalation capacity of the membrane, Martin says. The tube-within-a-tube morphology is novel, notes Thomas E. Mallouk, chemis- try professor at Pennsylvania State Univer- sity. "It is impressive that one can make these structures rationally," he says. The Colorado State group also showed that the membranes could be imbedded with nanoparticle catalysts such as plati- num, ruthenium, and platinum/ruthenium alloys. They found that the greater surface area of the membranes (compared with Transmission electron micrograph of a tube-wlthln-a-tube membrane: graphitic carbon Inner nanotubules within the outer template-synthesized tubules. that of glassy carbon electrodes) enhanced the rates of electrochemical reactions im- portant to fuel cells, such as oxygen reduc- tion or methanol oxidation. "One of the major problems in elec- trocatalysis is getting the catalyst distrib- uted widely on the surface, and Martin and Fisher's method accomplishes that in a clever and creative way," says Fred C. Anson, chemistry professor at Califor- nia Institute of Technology, Pasadena. However, he notes, "It will be interest- ing to know how stable the carbon nano- tubes are to oxidative conditions encoun- tered in fiiel-cell cathodes." Elizabeth Wilson Science policy: D.C. to get new think tank Columbia University and Georgia Institute of Technology are planning what could become a million-dollar center to assess the practical benefits of science and tech- nology programs. Its tentative name is the Center for Science, Policy & Outcomes, and it will be located in Washington, D.C. "We are in the earliest stages of plan- ning this effort, and we hope to engage a broad cross-section of the R&D policy community in bringing it to fruition," says Michael Crow, professor of science and technology policy and vice provost at Columbia. The lead figure at Georgia Tech in the venture is Barry L. Bozeman, director of its School of Public Policy. Crow, who is seeking foundation fund- ing for the venture, has sent a "Dear Col- league" letter to several hundred policy professionals around the country seeking ideas as to what the center should stress, and he has a few of his own. As he explains in his letter, the center idea grew out of a series of three confer- ences held in the mid-1990s at Columbia that critiqued the so-called Bush model of science policy. That model developed out of the legendary report, "Science— The Endless Frontier," written at the re- quest of President Franklin D. Roosevelt by Vannevar Bush, a Massachusetts Insti- tute of Technology engineer who ran the country's World War II research effort. Bush's report led to the establishment of the National Science Foundation, and for decades it provided the rationale for fed- eral support of science. The Bush model, says Crow in his let- ter, "was appropriate for a Cold War era in which we had one major military compet- itor and no economic ones. In today's complex globalized society, however, this foundation reveals itself to be intellectual- ly and politically unequal to the task of linking our complex research and devel- opment system to the broad outcomes that the system is called upon to achieve and support." Crow then goes on to list four "overrid- ing themes" that emerged from the Co- lumbia conferences: The mission for sci- ence and technology is now much more comprehensive than the national security issues that dominated policy until recent- ly; research is now international; science and technology need to be better integrat- ed with "other forms of human endeavor"; and current science and technology poli- cies focus more on building knowledge bases than on meeting social needs. "Our current science and technology policy framework has not internalized these and similar realities," Crow says. It needs to be similar to those that exist in the environmental, financial, and health care areas that are "supported by an en- ergetic and pluralistic intellectual infra- structure that promotes research and de- bate while seeking to connect theory and practice." Pending success in gathering financial support, the center would open in the spring or summer of 1999. "Everyone wants to get into the act," comments George Washington University's John M. Logsdon, who heads the only other major center for science and technology policy studies in Washington. Logsdon says he welcomes the proposed center and has told Crow he is open to possible collabo- rations. Those seeking a copy of the pro- posal can download it from Columbia's web site at http://www.columbia.edu/cu/ research/ovp/cspo.html. Wil Lepkowski 12 JUNE 1, 1998 C&EN news of the week
Transcript of Versatile membranes from carbon nanotubes
Versatile membranes from carbon nanotubes A new type of membrane composed of vertically aligned carbon nanotubes shows promise for boosting the performance of electrochemical devices such as lithium-ion batteries and fuel cells.
Chemistry professor Charles R. Martin, assistant chemistry professor Ellen R. Fisher, postdoctoral researcher Guangli Che, and graduate student Blinda Β. Lakshmi, at Colorado State University, Fort Collins, created the membranes by chemical vapor deposition of graphitic carbon into an aluminum template riddled with 200-nm-diameter pores.
The group then dissolved away the aluminum template with acid, leaving a freestanding carbon membrane—a cluster of ordered nanotubules held together by 20-nm-thick carbon surface films [Nature, 393,346(1998)].
The Colorado State method shows that alumina template membranes have a lot of potential that hasn't yet been exploited, says Michael J. Sailor, associate chemistry professor at the University of California, San Diego. "It's very interesting work," he adds.
The high surface area of the tubule clusters means that large quantities of elec-trochemically important substances, such as nanoscopic metal catalyst particles, can be embedded in the membrane. Also useful is that these membranes are easy to connect to an electrochemical cell. As Martin notes: "You just place the membrane on top of an electrode.
"In addition, the membrane approach ensures that all of the carbon tubes are bathed in electrolyte because the electrolyte fills the tubes."
Carbon is the typical anode material used in lithium-ion batteries. Martin's group found that the caibon tubule membrane reversibly intercalates Li+. The group also grew a second set of even tinier nanotubules inside the membrane tubules and found that these inner tubules doubled the It intercalation capacity of the membrane, Martin says.
The tube-within-a-tube morphology is novel, notes Thomas E. Mallouk, chemistry professor at Pennsylvania State University. "It is impressive that one can make these structures rationally," he says.
The Colorado State group also showed that the membranes could be imbedded with nanoparticle catalysts such as platinum, ruthenium, and platinum/ruthenium alloys. They found that the greater surface area of the membranes (compared with
Transmission electron micrograph of a tube-wlthln-a-tube membrane: graphitic carbon Inner nanotubules within the outer template-synthesized tubules.
that of glassy carbon electrodes) enhanced the rates of electrochemical reactions important to fuel cells, such as oxygen reduction or methanol oxidation.
"One of the major problems in elec-trocatalysis is getting the catalyst distributed widely on the surface, and Martin and Fisher's method accomplishes that in a clever and creative way," says Fred C. Anson, chemistry professor at California Institute of Technology, Pasadena.
However, he notes, "It will be interesting to know how stable the carbon nanotubes are to oxidative conditions encountered in fiiel-cell cathodes."
Elizabeth Wilson
Science policy: D.C. to get new think tank Columbia University and Georgia Institute of Technology are planning what could become a million-dollar center to assess the practical benefits of science and technology programs. Its tentative name is the Center for Science, Policy & Outcomes, and it will be located in Washington, D.C.
"We are in the earliest stages of planning this effort, and we hope to engage a broad cross-section of the R&D policy community in bringing it to fruition," says Michael Crow, professor of science and technology policy and vice provost at Columbia. The lead figure at Georgia Tech in the venture is Barry L. Bozeman, director of its School of Public Policy.
Crow, who is seeking foundation funding for the venture, has sent a "Dear Colleague" letter to several hundred policy professionals around the country seeking ideas as to what the center should stress, and he has a few of his own.
As he explains in his letter, the center idea grew out of a series of three conferences held in the mid-1990s at Columbia that critiqued the so-called Bush model of science policy. That model developed out of the legendary report, "Science— The Endless Frontier," written at the request of President Franklin D. Roosevelt by Vannevar Bush, a Massachusetts Institute of Technology engineer who ran the country's World War II research effort. Bush's report led to the establishment of the National Science Foundation, and for decades it provided the rationale for federal support of science.
The Bush model, says Crow in his letter, "was appropriate for a Cold War era in which we had one major military competitor and no economic ones. In today's complex globalized society, however, this foundation reveals itself to be intellectually and politically unequal to the task of linking our complex research and development system to the broad outcomes that the system is called upon to achieve and support."
Crow then goes on to list four "overriding themes" that emerged from the Columbia conferences: The mission for science and technology is now much more comprehensive than the national security issues that dominated policy until recently; research is now international; science and technology need to be better integrated with "other forms of human endeavor"; and current science and technology policies focus more on building knowledge bases than on meeting social needs.
"Our current science and technology policy framework has not internalized these and similar realities," Crow says. It needs to be similar to those that exist in the environmental, financial, and health care areas that are "supported by an energetic and pluralistic intellectual infrastructure that promotes research and debate while seeking to connect theory and practice."
Pending success in gathering financial support, the center would open in the spring or summer of 1999. "Everyone wants to get into the act," comments George Washington University's John M. Logsdon, who heads the only other major center for science and technology policy studies in Washington. Logsdon says he welcomes the proposed center and has told Crow he is open to possible collaborations. Those seeking a copy of the proposal can download it from Columbia's web site at http://www.columbia.edu/cu/ research/ovp/cspo.html.
Wil Lepkowski
12 JUNE 1, 1998 C&EN
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