Inside fossil-fuel and nuclear-power plants, as well as in cars and trucks, the lion’s share of energy in fuel is wasted as heat rather than converted into electricity or mechanical power. But the search for a practical material that can convert at least some of this waste heat into electricity has been long and frustrating.
Researchers have long known that some inorganic semiconductors can do this. Indeed, deep-space probes have been powered by using such materials. But these inorganic materials are costly and difficult to make, and have low efficiencies. Now, new research shows that certain organic molecules produce voltage when exposed to heat. Ultimately, they could be much cheaper and thus more practical to implement.
“This is the first demonstration that you can use organic molecules in this kind of energy generation,” says Rachel Segalman, professor of chemical engineering at the University of California, Berkeley, who with her colleagues reported new measurements last week in Science Express. “That’s really significant because they are so inexpensive and abundant,” she says.
Experts had previously theorized that some organic molecules could have the qualities necessary to generate electricity from heat. But until now, they lacked experimental proof, which the Berkeley researchers were able to provide by isolating and measuring the properties of just a few molecules of organic substances called benzene dithiols at a time.
These were “very difficult experiments,” says Brian Sales, a senior research scientist at the Oak Ridge National Laboratory, who was not involved with the work. The researchers trapped a few molecules between a sheet of gold and the ultrafine gold tip of a scanning tunneling microscope, which is so sharp it can end in a single atom. They heated up the gold surface and measured, via the microscope tip, the voltage that was created. “These are the type of difficult experiments that get nanotechnology past the ‘picture’ stage [and] into the realm of real science,” Sales says.
The experiments showed that the organic molecules have the three qualities that make for good thermoelectric materials. The first is the ability to create a voltage. But this works best when the materials have two other qualities: they do not conduct heat, but they do conduct electrons. That way, applying heat, rather than just raising the temperature of the material, actually drives electrons, creating a current.
The results confirmed that the organic molecules could indeed be used to generate electricity from heat. Before they can be put to use, however, it will be important, Sales says, to design the molecules so that they arrange themselves between metal layers to make large-scale thermoelectric materials. What’s more, so far the efficiency is very low, the researchers say. To improve this, they are creating and testing new versions of the molecules.
“These are very simple molecules that the group is looking at,” says J. Fraser Stoddart, professor of chemistry at the University of California, Los Angeles. He’s interested in the researchers’ plans to alter the molecules to improve their thermoelectric properties. “That’s where my heart starts to beat,” he says. “I hope they follow this research up.”
The research is only the first step, the researchers say, and, because much work remains, applications will be many years away.
If all goes well, though, so-called thermoelectric devices based on the molecules could prove to be an important source of power–and a way to reduce greenhouse-gas emissions by making far more efficient use of fossil fuel. “Ninety percent of the world’s electricity is generated by thermal-mechanical means,” says Arun Majumdar, professor of mechanical engineering at UC Berkeley and another researcher on the project. “And a lot of the heat is wasted. One and a half times the power that is generated is actually wasted.”
For example, a typical way to generate electricity is by heating up steam to drive a turbine. After the steam passes through the turbine, it still contains energy in the form of heat, although not enough to drive a turbine, Segalman says. That heat typically escapes into the atmosphere and is wasted. By wrapping thermoelectric materials around exhaust pipes, that heat could be put to work. In cars, thermoelectrics could replace the alternator and save hundreds of millions of gallons of gas a year, according to an estimate from a General Motors researcher. (See “Free Power for Cars.”)
Organic materials are appealing because they cost much less than thermoelectric inorganic materials: even if they are inefficient, they might still be economical. “These molecules are dirt cheap,” Majumdar says. “If the efficiency is low, that’s fine. You’re throwing that heat away anyway.”
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Ndani ya mitambo ya nishati ya makaa ya mawe na nyuklia, na pia katika magari na malori, sehemu kubwa ya nishati katika mafuta hutumiwa kama joto badala ya kubadilishwa kuwa umeme au nguvu za mitambo. Lakini kutafuta nyenzo inayoweza kugeuza angalau sehemu fulani ya joto hilo la taka kuwa umeme kumekuwa kazi ndefu na yenye kuvunja moyo. Watafiti wamekuwa wakijua kwa muda mrefu kwamba baadhi ya vifaa visivyo vya kibiolojia vinaweza kufanya hivyo. Kwa kweli, chombo cha kuchunguza anga za juu kimetumiwa kutokeza nishati kwa kutumia vifaa hivyo. Lakini vifaa hivyo visivyo vya kikaboni ni vya gharama kubwa na vigumu kutengeneza, na vina ufanisi mdogo. Utafiti mpya unaonyesha kwamba molekuli fulani za kikaboni hutokeza voltage zinapowekwa kwenye joto. Hatimaye, wanaweza kuwa nafuu sana na hivyo kuwa rahisi zaidi kutekeleza. "Hii ni maonyesho ya kwanza kwamba unaweza kutumia molekuli za kikaboni katika aina hii ya uzalishaji wa nishati, ""Rachel Segalman, profesa wa uhandisi wa kemikali katika Chuo Kikuu cha California, Berkeley, ambaye pamoja na wenzake waliripoti vipimo vipya wiki iliyopita katika Sayansi Express." "Hilo ni jambo muhimu sana kwa sababu ni la bei nafuu na la wingi", asema. Wataalamu walikuwa wamedokeza kwamba baadhi ya molekuli za kikaboni zinaweza kuwa na uwezo wa kutokeza umeme kutokana na joto. Hata hivyo, utafiti huo haukuweza kuthibitishwa kwa njia ya majaribio, na watafiti wa Berkeley waliweza kuupima kwa kutenganisha na kupima mali za molekuli chache tu za kemikali za kikaboni zinazoitwa benzeno-dithiol. Hizi zilikuwa "majaribio magumu sana", anasema Brian Sales, mwanasayansi mwandamizi wa utafiti katika Maabara ya Kitaifa ya Oak Ridge, ambaye hakuhusika katika kazi hiyo. Watafiti hao waliweka molekuli chache kati ya karatasi ya dhahabu na ncha ya dhahabu ya microscope ya kuchunguza ya tunneling, ambayo ni kali sana inaweza kuishia katika atomu moja. Walipasha joto uso wa dhahabu na kupima, kupitia ncha ya darubini, voltage iliyotengenezwa. "Hizi ni aina ya majaribio magumu ambayo kupata nanotechnology zaidi ya hatua ya "picha" [na] katika ulimwengu wa sayansi ya kweli", Sales anasema. Majaribio yalionyesha kwamba molekuli za kikaboni zina sifa tatu zinazofanya vifaa vizuri vya umeme wa joto. Ya kwanza ni uwezo wa kuunda voltage. Lakini hii inafanya kazi bora wakati vifaa vina sifa nyingine mbili: haviongozi joto, lakini huongoza elektroni. Kwa njia hiyo, kutumia joto, badala ya tu kuongeza joto la nyenzo, kwa kweli huendesha elektroni, kuunda mkondo. Matokeo yalithibitisha kwamba kwa kweli molekuli hizo za kikaboni zingeweza kutumiwa kutokeza umeme kutokana na joto. Hata hivyo, kabla ya kutumiwa, ni muhimu, anasema Sales, kubuni molekuli hizo ili ziweze kujipanga kati ya tabaka za chuma ili kutengeneza vifaa vikubwa vya umeme wa joto. Zaidi ya hayo, hadi sasa ufanisi ni chini sana, watafiti wanasema. Ili kuboresha hali hiyo, wanaunda na kupima matoleo mapya ya molekuli hizo. "Hizi ni molekuli rahisi sana ambazo kikundi hicho kinatazama", anasema J. Fraser Stoddart, profesa wa kemia katika Chuo Kikuu cha California, Los Angeles. Yeye ni nia ya watafiti mipango ya kubadilisha molekuli ili kuboresha mali zao thermoelectric. "Hapo ndipo moyo wangu unapoanza kupiga", asema. "Natumaini wataendelea na utafiti huu. Utafiti huu ni hatua ya kwanza tu, watafiti wanasema, na, kwa sababu kazi nyingi inabaki, maombi yatakuwa miaka mingi mbali". Hata hivyo, ikiwa kila kitu kitaenda vizuri, vifaa vinavyoitwa vya umeme wa joto vinavyotegemea molekuli hizo vinaweza kuthibitika kuwa chanzo muhimu cha nishati - na njia ya kupunguza uzalishaji wa gesi za chafu kwa kutumia mafuta ya visukuku kwa ufanisi zaidi. "Ninini asilimia ya umeme duniani hutengenezwa kwa njia ya joto-mechanical,"" anasema Arun Majumdar, profesa wa uhandisi wa mashine katika UC Berkeley na mtafiti mwingine juu ya mradi huo. <unk>Na joto nyingi hutumiwa bure. Kwa mfano, njia ya kawaida ya kutengeneza umeme ni kwa kupasha joto mvuke ili kuendesha turbine. Baada ya mvuke kupita katika turbine, bado ina nishati katika fomu ya joto, ingawa si ya kutosha kuendesha turbine, Segalman anasema. Kwa kawaida joto hilo huingia angani na kupotea. Kwa kuzunguka vifaa vya umeme wa joto kuzunguka mabomba ya kutolea nje, joto hilo lingeweza kutumiwa. Katika magari, thermoelectrics inaweza kuchukua nafasi ya alternator na kuokoa mamia ya mamilioni ya galoni ya gesi kwa mwaka, kulingana na makadirio kutoka kwa mtafiti wa General Motors. (Tazama <unk>Free Power for Cars.<unk>) Vifaa vya kikaboni ni vya kuvutia kwa sababu vina gharama ndogo sana kuliko vifaa vya inorganic vya joto: hata kama havina ufanisi, bado vinaweza kuwa vya kiuchumi. "Molekuli hizi ni za bei nafuu sana", Majumdar anasema. <unk>Kama ufanisi ni chini, hiyo ni sawa. "Kama vile, ""Ukiangalia teknolojia ya 10 ya Kuboresha 2024 kila mwaka, tunatafuta teknolojia za kuahidi zilizo tayari kuwa na athari halisi ulimwenguni.""" Hapa ni maendeleo ambayo tunafikiri ni muhimu zaidi sasa hivi. Wataalamu wa afya wamegundua dalili za ugonjwa wa Covid-19 katika damu Zinaweza kuongoza kwenye matibabu mapya. Uharibifu wa sehemu fulani ya mfumo wa kinga inaweza kuwa chanzo cha baadhi ya kesi za muda mrefu za COVID-19, utafiti mpya unaonyesha. AI kwa kila kitu: Teknolojia 10 za Kuboresha 2024 Vifaa vya Generative AI kama ChatGPT vilipata kupitishwa kwa wingi kwa muda wa rekodi, na kuweka upya mwendo wa tasnia nzima. "Kama ""Mwanzoni mwa mwaka wa 2020,"" ""Mwaka wa 2020"" au ""Mwaka wa 2020,"" ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020"" au ""Mwaka wa 2020."""