Bionic Leaf

Bionic leaf or ar­ti­fi­cial leaf absorbs car­bon diox­ide in the at­mos­phere to pro­duce fuel and re­lease oxy­gen in the process, im­i­tat­ing the nat­u­ral process of pho­to­syn­the­sis.

Alive - - News - by Ganesh Joshi

Re­searchers like Biswajit Bhat­tacharyya work­ing at the In­dian In­sti­tute of Sci­ence (IISc), Ben­galuru, Kar­nataka have de­vel­oped a Bionic leaf or Ar­ti­fi­cial leaf that absorbs car­bon diox­ide in the at­mos­phere to pro­duce fuel and re­lease oxy­gen in the process, im­i­tat­ing the nat­u­ral process of pho­to­syn­the­sis. The de­vel­op­ment is be­ing viewed as the lat­est ap­proach in tack­ling global warm­ing and cli­mate change while keep­ing the at­mo­spheric car­bon diox­ide lev­els un­der con­trol.

They claim this to be a method to achieve two tar­gets si­mul­ta­ne­ously (1) It pro­vides a source of re­new­able en­ergy, (2) while sig­nif­i­cantly re­duc­ing the car­bon diox­ide in the at­mos­phere, as well as re­leas­ing oxy­gen back in the at­mos­phere.

What is a leaf? A leaf is one of the ex­panded, usu­ally green or­gans borne by the stem of a plant or tree.

Pho­to­syn­the­sis is the process through which plants gen­er­ate their food. Plants ab­sorb the light from our Sun with a green pig­ment called chloro­phyll. In this process car­bon diox­ide is con­verted into or­ganic com­pounds, more specif­i­cally sug­ars, through the en­ergy com­ing from sun­light. Hu­man be­ings ex­ploit that en­ergy when they eat plants, or when they eat an­i­mals that have eaten plants, or when they burn ei­ther plants or sub­stances ul­ti­mately de­rived from plants: fire­wood, coal, oil, nat­u­ral gas.

Bionic leaf is ef­fi­cient

IISc’s sci­en­tists from the Chem­istry depart­ment con­sider their bionic leaf it to be “100 times more ef­fi­cient” than a nat­u­ral leaf in ab­sorb­ing car­bon diox­ide. In their words,” It is com­posed of “com­pletely bio­com­pat­i­ble, earth abun­dant, in­ex­pen­sive el­e­ments”. In the words of Shri Bhat­tacharyya, the first au­thor of the pa­per, “Although sev­eral at­tempts have been made world­wide to repli­cate pho­to­syn­the­sis, the bionic leaf or Quan­tum leaf de­vel­oped at IISc is the most ef­fi­cient de­vice us­ing sun­light to con­vert car­bon diox­ide (CO2) to oxy­gen.”

“This is the most en­er­gy­ef­fi­cient method to con­vert car­bon diox­ide into fuel and oxy­gen us­ing only sun­light. While most plants con­vert less than one per cent of the avail­able so­lar en­ergy into chem­i­cal en­ergy, the ma­te­rial de­vel­oped by us can con­vert about 20 per cent of the in­ci­dent so­lar en­ergy into chem­i­cal en­ergy in the form of fuel and oxy­gen,” He fur­ther added.

In the words of Dr

An­shu Pandey, As­so­ciate Pro­fes­sor, “Quan­tum dots — semi­con­duct­ing nanocrys­tals — made of spe­cific ma­te­ri­als, act as cat­a­lyst to con­vert CO2 into formic acid, that can be used as fuel. “It was made of cheap el­e­ments al­low­ing adap­ta­tion of the tech­nol­ogy in an in­dus­trial scale, with­out pro­vid­ing fur­ther de­tails. The ef­fi­ciency ob­served by us is a ma­jor jump over avail­able meth­ods and is close to the max­i­mum ef­fi­ciency that can pos­si­bly be achieved ar­ti­fi­cially,” he fur­ther added.

Pho­to­syn­the­sis is the process through which plants gen­er­ate their food. In this process car­bon diox­ide is con­verted into or­ganic com­pounds, more specif­i­cally sug­ars, through the en­ergy com­ing from sun­light. The process is car­ried out by Green leaves of plants, which store en­ergy from the sun. Hu­man be­ings ex­ploit that en­ergy when they eat plants, or when they eat an­i­mals that have eaten plants, or when they burn ei­ther plants or sub­stances ul­ti­mately de­rived from

The Sci­en­tists have been ex­plor­ing dif­fer­ent cat­a­lysts to force CO2 re­duc­tion, but so far such re­ac­tions have been in­ef­fi­cient and rely on ex­pen­sive pre­cious met­als such as sil­ver. What they needed was a new fam­ily of cat­a­lysts chem­i­cals with ex­tra­or­di­nary prop­er­ties.

plants: fire­wood, coal, oil, nat­u­ral gas.

The pi­o­neer­ing work on bionic leaves was car­ried out by Dr Daniel Ge­orge No­cera, an Amer­i­can chemist, work­ing at

Har­vard Univer­sity. In

2011, Dr No­cera, an­nounced a cheap, play­ing-card-size coat­ed­sil­i­con sheet that, when placed in a glass of tap wa­ter and ex­posed to sun­light, split the wa­ter into hy­dro­gen and oxy­gen. The gas could eas­ily be col­lected and ei­ther burned or used to power a fuel cell. He called the de­vice an “ar­ti­fi­cial leaf,” and claimed that ar­ti­fi­cial leaves could one day en­able peo­ple ev­ery­where to live with­out be­ing con­nected to any power grid.

The process could be de­scribed more pre­cisely as so­lar-pow­ered elec­trol­y­sis of wa­ter: us­ing en­ergy from the sun to split wa­ter into hy­dro­gen and oxy­gen. Sci­en­tists led by Dr Amin Salehi-Kho­jin, As­sis­tant Pro­fes­sor at the Univer­sity of Illi­nois at Chicago, USA, have now de­vel­oped "ar­ti­fi­cial leaves" - so­lar cells that cheaply and ef­fi­ciently con­vert at­mo­spheric car­bon diox­ide di­rectly into us­able hy­dro­car­bon fuel us­ing sun­light.

Ar­ti­fi­cial leaf de­liv­ers syn­gas

A so­lar farm of such "ar­ti­fi­cial leaves" could re­move sig­nif­i­cant amounts of car­bon from the at­mos­phere and pro­duce en­ergy-dense fuel ef­fi­ciently. The new so­lar cell is not pho­to­voltaic. It is pho­to­syn­thetic. In the words of Dr Amin Sale­hiKho­jin, “In­stead of burn­ing fos­sil fu­els like coal or crude oil to pro­duce en­ergy as well as green­house gases like car­bon diox­ide , we can now re­verse the process and con­vert at­mo­spheric car­bon diox­ide into fuel us­ing sun­light."

“While leaves in plants pro­duce fuel in the form of sugar, our ar­ti­fi­cial leaf de­liv­ers syn­gas, or syn­the­sis gas, a mix­ture of hy­dro­gen gas and car­bon monox­ide, which can be burned di­rectly, or con­verted into diesel or other hy­dro­car­bon fu­els. If we could con­vert CO2 in the air into fuel at a cost com­pa­ra­ble to a liter of petrol or diesel it would ren­der fos­sil fu­els ob­so­lete.” He fur­ther added.

Chem­i­cal re­ac­tions that con­vert CO2 into flammable forms of car­bon like car­bon monox­ide are called re­duc­tion re­ac­tions, the op­po­site of ox­i­da­tion or com­bus­tion. The Sci­en­tists have been ex­plor­ing dif­fer­ent cat­a­lysts to force CO2 re­duc­tion, but so far such re­ac­tions have been in­ef­fi­cient and rely on ex­pen­sive pre­cious met­als such as sil­ver. What they needed was a new fam­ily of cat­a­lysts -chem­i­cals with ex­tra­or­di­nary prop­er­ties.

They fo­cused on a fam­ily of nano-struc­tured com­pounds called tran­si­tion metal dichalco­genides - or TMDCs - as cat­a­lysts, putting them to­gether them with an un­con­ven­tional liq­uid as the elec­trolyte in­side a twocom­part­ment, three­elec­trode elec­tro­chem­i­cal cell.

The best of sev­eral cat­a­lysts they stud­ied turned out to be nano flake tung­sten dis­e­lenide. "The new cat­a­lyst is more ac­tive; more able to break car­bon diox­ide's chem­i­cal bonds," said Mo­ham­mad Asadi, post­doc­toral re­searcher at Univer­sity of Illi­nois at Chicago, a mem­ber of Dr Amin Salehi-Kho­jin’s, team. In fact, the new cat­a­lyst is 1,000 times faster than no­ble-metal cat­a­lysts like sil­ver, gold or plat­inu­mand about 20 times cheaper.

The ar­ti­fi­cial leaf con­sists of two sil­i­con pho­to­voltaic cells of 18 square cen­time­ters to har­vest light. When light of 100 watts per square me­ter – about the av­er­age in­ten­sity reach­ing the Earth's sur­face – en­er­gises the cell, hy­dro­gen and car­bon monox­ide gas bub­ble up from the cath­ode, while free oxy­gen and hy­dro­gen ions are pro­duced at the an­ode. Fur­ther work is in progress. Re­search on sim­i­lar lines is be­ing car­ried out at num­ber of uni­ver­si­ties in the US and Ger­many. It is felt that re­search on sim­i­lar lines should be taken up more vig­or­ously in In­dia and that too im­me­di­ately.

Re­searchers use bac­te­ria to con­vert so­lar en­ergy into liq­uid fuel.

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