Purple Sun­light Eat­ers: New Path to Green Hydro­gen Fuel?

Argonne nanos­cient­ist Elena Rozhkova and her col­leagues com­bined a pig­ment called bac­teri­orhodop­sin with semi­con­duct­ing nan­o­particles to cre­ate a sys­tem that uses light to spark a cata­lyt­ic pro­cess that cre­ates hydro­gen fuel. Sci­ent­ists have been aware of the poten­tial of titani­um diox­ide nan­o­particles for light-based reac­tions since the early 1970s, when Japan­ese research­ers dis­covered that a titani­um diox­ide elec­trode exposed to bright ultra­vi­olet light could split water molecules in a phe­nomen­on that came to be known as the Honda-Fujishi­ma effect. Since then, sci­ent­ists have made con­tinu­ous efforts to extend the light react­iv­ity of titani­um diox­ide pho­tocata­lysts into the vis­ible part of the spec­trum. The prom­ise of these pho­tocata­lysts promp­ted sci­ent­ists to exper­i­ment with dif­fer­ent modi­fic­a­tions to their basic chem­istry in hope of mak­ing the reac­tion more effi­cient, Rozhkova said. ​“Titani­um diox­ide alone reacts with ultra­vi­olet light, but not with vis­ible light, so we used bio­lo­gic­al photore­act­ive molecules as a build­ing block to cre­ate a hybrid sys­tem that could use vis­ible light effi­ciently,” Rozhkova said. Rozhkova and her col­leagues turned to bac­teri­orhodop­sin – which is respons­ible for the unusu­al purple col­or of a num­ber of salt flats in Cali­for­nia and Nevada – because it uses sun­light as an energy source that allows it to act as a ​“pro­ton pump.” Pro­ton pumps are pro­teins that typ­ic­ally straddle a cel­lu­lar mem­brane and trans­fer pro­tons from inside the cell to the extra­cel­lu­lar space. In the Argonne sys­tem, the pro­tons provided by the bac­teri­orhodop­sin are com­bined with free elec­trons at small plat­in­um sites inter­spersed in the titani­um diox­ide mat­rix. ​“The plat­in­um nan­o­particles are essen­tial for cre­at­ing a dis­tinct spot for the pro­duc­tion of the hydro­gen molecule,” said Peng Wang, an Argonne postdoc­tor­al research­er in Rozhkova’s group at Argonne’s Cen­ter for Nano­scale Mater­i­als. ​“It is inter­est­ing that in bio­logy, bac­teri­orhodop­sin does not nat­ur­ally par­ti­cip­ate in these kind of reac­tions,” Rozhkova said. ​“Its nat­ur­al func­tion really doesn’t have much to do at all with cre­at­ing hydro­gen. But as part of this hybrid, it helps make hydro­gen under white light and at envir­on­ment­ally friendly con­di­tions.” This bio-assisted hybrid pho­tocata­lyst out­per­forms many oth­er sim­il­ar sys­tems in hydro­gen gen­er­a­tion and could be a good can­did­ate for fab­ric­a­tion of green energy devices that con­sume vir­tu­ally infin­ite sources – salt water and sun­light.

Ori­gin­al publication:

Shank­ar Balas­ub­ramani­an, Peng Wang, Richard D. Schaller, Tijana Rajh, Elena A. Rozhkova. High-Per­form­ance Bioassisted Nan­o­pho­tocata­lyst for Hydro­gen Pro­duc­tion. Nano Let­ters, 2013; 13 (7): 3365 DOI: 10.1021/nl4016655 The work was per­formed at Argonne’s Cen­ter for Nano­scale Mater­i­als, which is sup­por­ted by the U.S. Depart­ment of Energy’s Office of Sci­ence. Source: Argonne Nation­al Laboratory