Circularity – using hydrogen in the carbon nanofiber production process

The pro­ject is now com­ing to its end – with prom­ising res­ults to present. Some main take-aways are:

• The feas­ib­il­ity of depos­it­ing car­bon nan­ofibers with a H2-based pro­cess has been demon­strated with some chal­lenges remain­ing to make it com­pletely viable.
• The main area of improve­ment to tar­get is the growth rate of the CNFs.
• Obser­va­tions of the CNF struc­ture in detail gives an under­stand­ing of how to tackle the remain­ing challenges.

The growth of CNFs is a fas­cin­at­ing pro­cess and just like the green hydro­gen pro­duc­tion it requires a cata­lyst. Each fiber grows from a cata­lyst particle and usu­ally the particle can be seen at the tip of the fiber, or at the base. By using a trans­mis­sion elec­tron micro­scope (TEM), cap­able of cap­tur­ing details on the atom­ic scale, the grown fibers were imaged, and the res­ult was rather unex­pec­ted: The cata­lyst particle in this case was elong­ated, almost along the whole fiber. The fibers could be called Fe-filled car­bon nan­otubes (CNT) or Fe/​CNT core-shell fibers.

The beha­vi­or of the cata­lyst particle is intim­ately coupled to the growth and the observed shape is likely related to the issue with low growth rate – lead­ing to plenty ideas of how to solve it. For example, expos­ing the sub­strate to a plasma treat­ment before CNF growth starts might loosen the cata­lyst particle from the sub­strate and change its beha­vi­or dur­ing growth. This type of core-shell struc­ture is not only a prob­lem to solve how­ever, with the fer­ro­mag­net­ic prop­er­ties of the Fe core it could prove inter­est­ing in its own right, per­haps for a future Smol­tek busi­ness area? 

In the near-term the pos­sib­il­ity of using H2 in the pro­cess could lead to new ways of con­trolling the car­bon nan­ofiber struc­ture and increase flex­ib­il­ity when it comes to the plan­ning of scale-up and com­mer­cial­iz­a­tion. One poten­tial up-side with the H2-based pro­cess is the pro­duc­tion of free-stand­ing CNFs which could improve water flow and gas bubble dis­sip­a­tion in the elec­tro­lys­is cell but wheth­er this can be real­ized with longer fibers remains to be seen.

If you are inter­ested, please read more in the full thes­is: Car­bon nan­ofibers as cata­lyst sup­port – Devel­op­ing an H2-based recipe for plasma enhanced chem­ic­al vapor depos­ition.

Top photo: Pic­tur­ing a zoomed out view of grown car­bon nan­ofibers and John Schack, a master’s thes­is stu­dent at Smol­tek Hydro­gen, in the lab, reflec­ted in a 6 inch wafer.