Recipe for Low-Cost, Bio­mass-Derived Cata­lyst for Hydro­gen Production

In a paper to be pub­lished in an upcom­ing issue of Energy & Envir­on­ment­al Sci­ence (avail­able online), research­ers at the U.S. Depart­ment of Energy’s Brookhaven Nation­al Labor­at­ory describe details of a low-cost, stable, effect­ive cata­lyst that could replace costly plat­in­um in the pro­duc­tion of hydro­gen. The cata­lyst, made from renew­able soy­beans and abund­ant molyb­denum met­al, pro­duces hydro­gen in an envir­on­ment­ally friendly, cost-effect­ive man­ner, poten­tially increas­ing the use of this clean energy source. The research has already garnered wide­spread recog­ni­tion for Shilpa and Shweta Iyer, twin-sis­ter high school stu­dents who con­trib­uted to the research as part of an intern­ship under the guid­ance of Brookhaven chem­ist Wei-Fu Chen, sup­por­ted by pro­jects led by James Mucker­man, Etsuko Fujita, and Kotaro Sasaki. ​“This paper reports the ​‘hard sci­ence’ from what star­ted as the Iyer twins’ research pro­ject and has res­ul­ted in the best-per­form­ing, non-noble-met­al-con­tain­ing hydro­gen evol­u­tion cata­lyst yet known — even bet­ter than bulk plat­in­um met­al,” Mucker­man said. The pro­ject branches off from the Brookhaven group’s research into using sun­light to devel­op altern­at­ive fuels. Their ulti­mate goal is to find ways to use sol­ar energy — either dir­ectly or via elec­tri­city gen­er­ated by sol­ar cells — to con­vert the end products of hydro­car­bon com­bus­tion, water and car­bon diox­ide, back into a car­bon-based fuel. Dubbed ​“arti­fi­cial pho­to­syn­thes­is,” this pro­cess mim­ics how plants con­vert those same ingredi­ents to energy in the form of sug­ars. One key step is split­ting water, or water elec­tro­lys­is. ​“By split­ting liquid water (H₂O) into hydro­gen and oxy­gen, the hydro­gen can be regen­er­ated as a gas (H₂) and used dir­ectly as fuel,” Sasaki explained. ​“We sought to fab­ric­ate a com­mer­cially viable cata­lyst from earth-abund­ant mater­i­als for applic­a­tion in water elec­tro­lys­is, and the out­come is indeed superb.” This form of hydro­gen pro­duc­tion could help the sci­ent­ists achieve their ulti­mate goal. ​“A very prom­ising route to mak­ing a car­bon-con­tain­ing fuel is to hydro­gen­ate car­bon diox­ide (or car­bon monox­ide) using sol­ar-pro­duced hydro­gen,” said Fujita, who leads the arti­fi­cial pho­to­syn­thes­is group in the Brookhaven Chem­istry Depart­ment. But with plat­in­um as the main ingredi­ent in the most effect­ive water-split­ting cata­lysts, the pro­cess is cur­rently too costly to be eco­nom­ic­ally viable. Com­se­wogue High School stu­dents Shweta and Shilpa Iyer entered the lab as the search for a cost-effect­ive replace­ment was on. The Brookhaven team had already iden­ti­fied some prom­ising leads with exper­i­ments demon­strat­ing the poten­tial effect­ive­ness of low-cost molyb­denum paired with car­bon, as well as the use of nitro­gen to con­fer some res­ist­ance to the cor­ros­ive, acid­ic envir­on­ment required in pro­ton exchange mem­brane water elec­tro­lys­is cells. But these two approaches had not yet been tried togeth­er. The stu­dents set out to identi­fy plen­ti­ful and inex­pens­ive sources of car­bon and nitro­gen, and test ways to com­bine them with a molyb­denum salt. ​“The stu­dents became excited about using famil­i­ar mater­i­als from their every­day lives to meet a real-world energy chal­lenge,” Chen recoun­ted. The team tested a wide vari­ety of sources of bio­mass — leaves, stems, flowers, seeds, and legumes — with par­tic­u­lar interest in those with high pro­tein con­tent because the amino acids that make up pro­teins are a rich source of nitro­gen. High-pro­tein soy­beans turned out to be the best. To make the cata­lyst the team ground the soy­beans into a powder, mixed the powder with ammoni­um molyb­d­ate in water, then dried and heated the samples in the pres­ence of inert argon gas. ​“A sub­sequent high tem­per­at­ure treat­ment (car­bur­iz­a­tion) induced a reac­tion between molyb­denum and the car­bon and nitro­gen com­pon­ents of the soy­beans to pro­duce molyb­denum carbides and molyb­denum nitrides,” Chen explained. ​“The pro­cess is simple, eco­nom­ic­al, and envir­on­ment­ally friendly.” Elec­tro­chem­ic­al tests of the sep­ar­ate ingredi­ents showed that molyb­denum carbide is effect­ive for con­vert­ing H₂O to H₂, but not stable in acid­ic solu­tion, while molyb­denum nitride is cor­ro­sion-res­ist­ant but not effi­cient for hydro­gen pro­duc­tion. A nano­struc­tured hybrid of these two mater­i­als, how­ever, remained act­ive and stable even after 500 hours of test­ing in a highly acid­ic envir­on­ment. ​“We attrib­ute the high activ­ity of the molyb­denum-soy cata­lyst (MoSoy) to the syn­er­gist­ic effect between the molyb­denum-carbide phase and the molyb­denum-nitride phase in the com­pos­ite mater­i­al,” Chen said. Struc­tur­al and chem­ic­al stud­ies of the new cata­lyst con­duc­ted at Brookhaven’s Nation­al Syn­chro­tron Light Source (NSLS) and the Cen­ter for Func­tion­al Nan­o­ma­ter­i­als (CFN) are also repor­ted in the paper, and provide fur­ther details under­ly­ing the high per­form­ance of this new cata­lyst. ​“The pres­ence of nitro­gen and car­bon atoms in the vicin­ity of the cata­lyt­ic molyb­denum cen­ter facil­it­ates the pro­duc­tion of hydro­gen from water,” Mucker­man said. The sci­ent­ists also tested the MoSoy cata­lyst anchored on sheets of graphene — an approach that has proven effect­ive for enhan­cing cata­lyst per­form­ance in elec­tro­chem­ic­al devices such as bat­ter­ies, super­ca­pa­cit­ors, fuel cells, and water elec­tro­lyz­ers. Using a high-res­ol­u­tion trans­mis­sion micro­scope in Brookhven’s Con­densed Mat­ter Phys­ics and Mater­i­als Sci­ence Depart­ment, the sci­ent­ists were able to observe the anchored MoSoy nano­crys­tals on 2D graphene sheets. The graphene-anchored MoSoy cata­lyst sur­passed the per­form­ance of pure plat­in­um met­al. Though not quite as act­ive as com­mer­cially avail­able plat­in­um cata­lysts, the high per­form­ance of graphene-anchored MoSoy was extremely encour­aging to the sci­entif­ic team. ​“The dir­ect growth of anchored MoSoy nano­crys­tals on graphene sheets may enhance the form­a­tion of strongly coupled hybrid mater­i­als with intim­ate, seam­less elec­tron trans­fer path­ways, thus accel­er­at­ing the elec­tron trans­fer rate for the chem­ic­al desorp­tion of hydro­gen from the cata­lyst, fur­ther redu­cing the energy required for the reac­tion to take place,” Sasaki said. The sci­ent­ists are con­duct­ing addi­tion­al stud­ies to gain a deep­er under­stand­ing of the nature of the inter­ac­tion at the cata­lyst-graphene inter­face, and explor­ing ways to fur­ther improve its per­form­ance. In the paper, the authors — includ­ing the two high-school stu­dents — con­clude: ​“This study unam­bigu­ously provides evid­ence that a cheap and earth-abund­ant trans­ition met­al such as molyb­denum can be turned into an act­ive cata­lyst by the con­trolled sol­id-state reac­tion with soy­beans. The pre­par­a­tion of the MoSoy cata­lyst is simple and can be eas­ily scaled up. Its long-term dur­ab­il­ity and ultra-low cap­it­al cost sat­is­fy the pre­requis­ites for its applic­a­tion in the con­struc­tion of large-scale devices. These find­ings thus open up new pro­spects for com­bin­ing inex­pens­ive bio­mass and trans­ition metals, to pro­duce cata­lysts for elec­tro-cata­lyt­ic reac­tions.”

About

Addi­tion­al col­lab­or­at­ors in this research were Chiu-Hui Wang and Yimei Zhu of Brookhaven Lab. This research was fun­ded by the DOE Office of Sci­ence, Brookhaven’s Labor­at­ory Dir­ec­ted Research and Devel­op­ment pro­gram, its Tech­no­logy Mat­ur­a­tion pro­gram, and fund­ing through the Office of Sci­ence for Brookhaven’s Office of Edu­ca­tion­al Pro­grams. NSLS and CFN are also sup­por­ted by the DOE Office of Sci­ence. The Cen­ter for Func­tion­al Nan­o­ma­ter­i­als is one of the five DOE Nano­scale Sci­ence Research Cen­ters, premi­er nation­al user facil­it­ies for inter­dis­cip­lin­ary research at the nano­scale sup­por­ted by the U.S. Depart­ment of Energy, Office of Sci­ence. Togeth­er the NSRCs com­prise a suite of com­ple­ment­ary facil­it­ies that provide research­ers with state-of-the-art cap­ab­il­it­ies to fab­ric­ate, pro­cess, char­ac­ter­ize and mod­el nano­scale mater­i­als, and con­sti­tute the largest infra­struc­ture invest­ment of the Nation­al Nan­o­tech­no­logy Ini­ti­at­ive. The NSRCs are loc­ated at DOE’s Argonne, Brookhaven, Lawrence Berke­ley, Oak Ridge, San­dia and Los Alam­os Nation­al Labor­at­or­ies. For more inform­a­tion about the DOE NSRCs, please click here. DOE’s Office of Sci­ence is the single largest sup­port­er of basic research in the phys­ic­al sci­ences in the United States, and is work­ing to address some of the most press­ing chal­lenges of our time. For more inform­a­tion, please vis­it sci​ence​.energy​.gov. Source: U.S. Depart­ment of Energy, Brookhaven Nation­al Laboratory