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Green World

Carbon nanofibers in the hydrogen industry

With our carbon nanofibers (CNFs) fabrication technology, we develop advanced materials engineering solutions for use in water electrolysis and fuel cells for the hydrogen industry.

The demand for sus­tain­ably pro­duced hydro­gen is rising due to its role in avoid­ing green­house gas emis­sions. Pro­duc­tion and use of sus­tain­able hydro­gen is made pos­sible by two core tech­no­lo­gies: Water elec­tro­lys­is, which pro­duces hydro­gen from water using elec­tri­city, and fuel cells, which reverses the reac­tion to gen­er­ate elec­tri­city. How­ever, both tech­no­lo­gies use rare and expens­ive cata­lyst mater­i­als such as plat­in­um or iridi­um. Using car­bon nan­ofibers (CNF) as a cata­lyst sup­port can decrease the amount of expens­ive cata­lyst mater­i­al needed. Smol­tek nano­struc­ture fab­ric­a­tion tech­no­logy can unlock this potential.

The need for hydrogen

Hydro­gen pro­duced by water elec­tro­lys­is can be a solu­tion to sev­er­al prob­lems in the pro­cess of redu­cing green­house gas emis­sions. For example, inter­mit­tent energy sources such as sol­ar and wind power occa­sion­ally pro­duce more elec­tri­city than needed, e.g. on very windy or sunny days. 

Using this elec­tric­al power for water elec­tro­lys­is allows the energy to be stored in the form of pro­duced hydro­gen gas, which can later be used con­ver­ted back to elec­tri­city by a fuel cell form­ing only water vapor in the pro­cess. Anoth­er key driver is to abate the car­bon diox­ide emis­sion in the pro­duc­tion of steel, where coal and coke can be replaced by hydro­gen gas as redu­cing agent for the iron ore emit­ting only water vapor and mak­ing a sig­ni­fic­ant reduc­tion in glob­al car­bon diox­ide emis­sions pos­sible. This enables a fossil-free steel production.

Making hydrogen by electrolysis

Water elec­tro­lyz­ers use two elec­trodes, a pos­it­ively charged anode and a neg­at­ively charged cath­ode, sep­ar­ated by an elec­tro­lyte that allows ions to travel between the elec­trodes. The elec­trodes are also elec­tric­ally con­nec­ted to a power source that sup­plies elec­tric­al power to drive the reac­tion. Oxy­gen gas is pro­duced at the anode through the oxy­gen evol­u­tion reac­tion, and hydro­gen gas is pro­duced at the cath­ode through the hydro­gen evol­u­tion reac­tion. Cata­lysts are used to pro­mote these elec­tro­chem­ic­al reac­tions and allow them to run at a lower energy cost. The reac­tions hap­pen at the act­ive cata­lyst sur­face, i.e. at sur­faces where the cata­lyst is in con­tact with the electrolyte. 

Bene­fi­cial con­di­tions for water elec­tro­lys­is depend on the type of elec­tro­lyte, the oper­at­ing tem­per­at­ure, the pres­sure and the types of cata­lysts. His­tor­ic­ally the industry has mostly relied on low-tem­per­at­ure elec­tro­lyz­ers using an alkaline solu­tion with high pH con­tain­ing potassi­um hydrox­ide in water. They do not require scarce cata­lyst mater­i­al but cause lim­ited cur­rent dens­it­ies and there­fore lim­ited hydro­gen out­put per cell area. This draw­back can be over­come by poly­mer ionomer mem­branes that con­duct either hydro­gen ions or hydrox­ide ions in dir­ect con­tact with anode and cath­ode, so-called zero-gap design. These ion-con­duct­ing poly­mers are known as pro­ton exchange mem­branes (PEM) or anion exchange mem­branes (AEM) respectively.

Schem­at­ic of how PEM elec­tro­lys­is works

Green hydrogen and low-carbon hydrogen

Low-tem­per­at­ure elec­tro­lyz­ers with PEM elec­tro­lytes, known as PEM elec­tro­lyz­ers, are prom­ising not only for their high­er cur­rent dens­ity but also for their excel­lent match with inter­mit­tent power sources and the longev­ity of the com­mer­cially offered pro­ton exchange mem­branes. This enables a com­pact and dur­able elec­tro­lyz­er design. 

For high-cur­rent dens­ity oper­a­tion at low over­po­ten­tial1 PEM elec­tro­lyz­ers need rare and expens­ive of cata­lysts such as plat­in­um on the cath­ode side and iridi­um oxide on the anode side. To real­ize the poten­tial of PEM elec­tro­lyz­ers, it is cru­cial that the cata­lysts are used effi­ciently and that the cata­lyst load, i.e. the amount of cata­lyst per unit area of the elec­tro­lyz­er cell, is kept to a minimum. 

One way of redu­cing the cata­lyst load is to depos­it the cata­lyst mater­i­al on anoth­er mater­i­al known as a cata­lyst sup­port, either in the form of a thin film or as particles with a dia­met­er of a few nano­met­ers. The cata­lyst sup­ports act as a scaf­fold­ing, allow­ing the cata­lyst to be spread over a lar­ger area. An ideal cata­lyst sup­port should have a large sur­face area, an open struc­ture that lets water and gases flow to and from the cata­lyst, excel­lent con­tact with the pro­ton exchange mem­brane and good and stable elec­tric­al con­duct­iv­ity to enable the elec­tro­chem­ic­al reac­tions. Car­bon black is often used as a cata­lyst sup­port on the cath­ode side in PEM elec­tro­lyz­ers, but the iridi­um cata­lyst on the anode side is gen­er­ally used without sup­port due to the harsh acid­ic con­di­tions at the anode.

Better catalysts with carbon nanofibers (CNF)

Car­bon nan­ofibers (CNF) are car­bon struc­tures with a dia­met­er that is typ­ic­ally below 100 nm and a length between 1 and 100 µm. Like many car­bon nan­o­ma­ter­i­als, CNF are elec­tric­ally con­duct­ive and mech­an­ic­ally strong. 

CNF are grown by chem­ic­al vapor depos­ition (CVD) and have the poten­tial to improve on exist­ing cata­lyst sup­ports. The CVD growth meth­od makes it pos­sible to con­trol the ori­ent­a­tion of the CNF so that they are ver­tic­ally aligned with a well-defined aver­age spa­cing, width, and height. This means that the struc­ture of a CNF cata­lyst sup­port can be adjus­ted to achieve the large sur­face area and degree of poros­ity that is needed.

The struc­ture of a CNF cata­lyst sup­port also makes it pos­sible to con­trol the pos­i­tion of the cata­lyst that is depos­ited on it, which in turn opens pos­sib­il­it­ies for optim­iz­ing the act­ive sur­face area of the cata­lyst and redu­cing the cata­lyst load. For example, the cata­lyst can be placed in dir­ect con­tact or even embed­ded into the mem­brane. The CNF can be con­form­ally coated and pro­tec­ted for use on the anode side of the electrolyzer. 

Although redu­cing cata­lyst load is most import­ant in PEM elec­tro­lyz­ers, CNF cata­lyst sup­ports may also be used in AEM elec­tro­lyz­ers and in PEM fuel cells. There are clear advant­ages to using CNF grown by CVD as a cata­lyst sup­port, such as increas­ing the act­ive cata­lyst sur­face area and decreas­ing the needed cata­lyst load. The CVD meth­ods used for CNF pro­duc­tion by Smol­tek can be used to real­ize the poten­tial of CNF in elec­tro­lys­is and fuel cells.

Elec­tro­lyz­er-cell with Smol­tek anode-PTL and catalysts

Radically reducing the price for hydrogen production

For future needs of the PEM elec­tro­lyz­er mar­ket, when the capa­city is scaled to pro­duce Gigawatts of water elec­tro­lys­is yearly it will be cru­cial to man­age a low iridi­um cata­lyst load on PEM anodes to enable cost-effi­cient hydro­gen production.

Smoltek’s nan­ofiber-based cell mater­i­als cre­ates an optim­al anode struc­ture that allows iridi­um cata­lyst nan­o­particles to form a highly act­ive and access­ible sur­face. In prin­ciple, all of the nan­o­particles come into con­tact with the pro­ton exchange mem­brane of the cell poten­tially redu­cing the needed amount of iridi­um by 80% – or more. 

Anoth­er bene­fit is that the cells can be optim­ized for high cur­rent dens­ity, thus the capa­city to pro­duce hydro­gen per cell area increases. This is achieved by a cor­res­pond­ing increase of the iridi­um load. These design choices can cre­ate a 2–3 times lower invest­ment cost for the elec­tro­lyz­er in a hydro­gen plant.

Are you interested in partnering with us?

Our next step is to indus­tri­al­ize our solu­tion for the elec­tro­lyz­er cell mater­i­al (CNF-ECM). We are there­fore look­ing for indus­tri­al partner(s) that, in close col­lab­or­a­tion with us;

  • build and test pro­to­types with dif­fer­ent com­bin­a­tions of sub­strates, nano­struc­ture mor­pho­logy, anti-cor­ro­sion pro­tec­tion and cata­lyst deposition,
  • estab­lish per­form­ance and long-term durability,
  • devel­op a high-volume man­u­fac­tur­ing concept,
  • pro­duces a test series of CNF-ECM to be used in actu­al production.

Is your com­pany a poten­tial part­ner in tak­ing advant­age of our dis­rupt­ive tech­no­logy?
Con­tact us today, and let’s arrange a meet­ing to dis­cuss it further. 

  1. The over­po­ten­tial describes the voltage dif­fer­ence, from the min­im­um pos­sible voltage to trig­ger the reac­tion to the voltage that needs to be reached for a suf­fi­cient cur­rent ↩︎

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