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.