---
title: "Carbon nanofibers in hydrogen electrolysis and fuel cells"
canonical_url: "https://www.smoltek.com/electrolyzers-fuel-cells/14/"
date: 2021-11-06
author: "Thomas Barregren"
featured_image: "https://www.smoltek.com/wp-content/uploads/2022/01/h2-jpg.webp"
categories:
  - name: "Hydrogen"
    url: "https://www.smoltek.com/category/articles/hydrogen.md"
tags:
  - name: "carbon nanotechnology"
    url: "https://www.smoltek.com/topic/carbon-nanotechnology.md"
  - name: "electrolyzers"
    url: "https://www.smoltek.com/topic/electrolyzers.md"
  - name: "hydrogen"
    url: "https://www.smoltek.com/topic/hydrogen.md"
---

# Carbon nanofibers in hydrogen electrolysis and fuel cells

Hydro­gen has emerged as a key to store renew­able ener­gy and mak­ing heavy indus­try car­bon-free. Two appli­ca­tion areas of imme­di­ate vital impor­tance. The core tech­nolo­gies that make this pos­si­ble are hydro­gen elec­trol­y­sis and fuel cells. Elec­trol­y­sis con­verts elec­tric­i­ty into hydro­gen, while fuel cells con­vert the hydro­gen back to elec­tric­i­ty. Nat­u­ral­ly, these con­ver­sions are sub­ject to ener­gy loss­es. Unfor­tu­nate­ly, these loss­es can be pret­ty significant—up to eighty per­cent. How­ev­er, there are solu­tions, and [car­bon nanofiber (CNF)](https://www.smoltek.com/technologies/carbon-nanofibers/) is part of them.

## [](https://www.smoltek.com#the-need-for-hydrogen)**The need for hydrogen**

The inter­mit­tent nature of renew­able ener­gy sources such as solar and wind pow­er cre­ates a demand for solu­tions to store sur­plus elec­tric­i­ty pro­duced on sun­ny or windy days for lat­er use. One method of stor­ing sur­plus elec­tric­i­ty is to con­vert it into hydro­gen by elec­trol­y­sis of water. Fuel cells can then con­vert the hydro­gen back into electricity.

Hydro­gen is expect­ed to become increas­ing­ly impor­tant as a fuel. Hydro­gen-pow­ered vehi­cles are already on the road today. There are even hydro­gen-pow­ered pas­sen­ger cars avail­able for any­one to buy.

Not least, hydro­gen is an increas­ing­ly essen­tial raw mate­r­i­al in heavy indus­try. For exam­ple, hydro­gen is replac­ing coal and coke in the pro­duc­tion of steel, enabling fos­sil-free steel production.

## [](https://www.smoltek.com#industrially-production-of-hydrogen)**Industrially production of hydrogen**

Hydro­gen is pro­duced indus­tri­al­ly in *elec­trolyz­ers*. Basi­cal­ly, an elec­trolyz­er can be described as a tank of water in which two elec­trodes are immersed. When an elec­tric volt­age is applied across the elec­trodes, a cur­rent flows through the water. The cur­rent breaks down the water into its con­stituent parts: hydro­gen and oxy­gen. Hydro­gen bub­bles up at one of the elec­trodes. Oxy­gen at the other.

## [](https://www.smoltek.com#conventional-electrolysis)**Conventional electrolysis**

The old­est and most con­ven­tion­al way of pro­duc­ing hydro­gen is *alka­line elec­trol­y­sis*.

In this process, lye (potas­si­um hydrox­ide or sodi­um hydrox­ide) is added to the water, mak­ing it high­ly cor­ro­sive. The elec­trodes, made of nick­el alloy, are sep­a­rat­ed by a mem­brane which allows hydrox­ide ions (OH-) to flow through, on their way from the cath­ode to the anode, while sep­a­rat­ing the hydro­gen gas pro­duced at one elec­trode from the oxy­gen gas pro­duced at the other.

![](https://www.smoltek.com/wp-content/uploads/2022/01/alkaline-electrolysis.png)

Schemat­ic of how alka­line hydrol­y­sis works.

This tech­nique has sev­er­al dis­ad­van­tages. Main­ly is the low effi­cien­cy. The ener­gy val­ue of the hydro­gen gen­er­at­ed is only 45–65% of the ener­gy sup­plied. In addi­tion, the method works poor­ly for renew­able elec­tric­i­ty because of its inter­mit­tent nature.

## [](https://www.smoltek.com#alternative-electrolyzers)**Alternative electrolyzers**

There are alter­na­tives to con­ven­tion­al alka­line elec­trol­y­sis. The table below sum­ma­rizes the most com­mon solutions.

| Type                                                                                | Mem­brane                 | Elec­trolyte                 | Cat­a­lyst                          | Cur­rent den­si­ty \[A/​cm2] | Oper­a­tional tem­per­a­ture \[°C] |
|-------------------------------------------------------------------------------------|---------------------------|------------------------------|-------------------------------------|------------------------------|------------------------------------|
| Alka­line electrolyzer                                                              | Diaphragm                 | KOH dis­solved in water      | Non-noble met­al alloys             | 0.2–0.7                      | 60–80                              |
| High-tem­per­a­ture electrolyzer                                                    | Diaphragm                 | Yttria-sta­bi­lized zirconia | Ni-YSZ alloys or per­ovskite oxides | 0.2–1.0                      | 600–700                            |
| AEM elec­trolyz­er[1](https://www.smoltek.com#6bf9f394-f2dc-4422-a0e8-52e719a4a0e4) | Anion exchange membrane   | Poly­mer                     | Non-noble met­al alloys             | 0.1–0.5                      | 50–70                              |
| PEM elec­trolyz­er[2](https://www.smoltek.com#d9656657-08f0-487a-8449-092e934e23cf) | Pro­ton exchange membrane | Poly­mer                     | Plat­inum and irid­i­um oxide       | 1.0–2.2                      | 50–84                              |

Char­ac­ter­is­tics of com­mon electrolyzers.

*PEM elec­trolyz­ers* are con­sid­ered the most inter­est­ing going for­ward. So let’s take a clos­er look at them before delv­ing into how car­bon nanofibers (CNF) can improve them.

## [](https://www.smoltek.com#pem-electrolyzer)**PEM** electrolyzer

From the out­side and inwards, a PEM cat­a­lyst con­sists of the fol­low­ing parts:

- An elec­trode that is con­nect­ed to a pow­er source. The elec­trode con­nect­ed to the pos­i­tive pole of the volt­age source is called the *anode*. The oth­er is called the *cath­ode*.
- A porous mate­r­i­al that makes it eas­i­er for the gas form­ing on the cat­a­lysts to be released and facil­i­tates trans­porta­tion away from the cat­a­lysts to an outlet.
- A cat­alyt­ic lay­er facil­i­tates the chem­i­cal reac­tions. It is in close con­tact with the poly­mer elec­trolyte mem­brane. Usu­al­ly, irid­i­um oxide is used on the anode side and plat­inum on the cath­ode side.
- A mem­brane of an elec­trolyt­ic poly­mer (usu­al­ly *Nafion*) that allows pro­tons but not elec­trons to pass through.

Water flows through the porous mate­r­i­al at the anode side. Oxy­gen is formed at the anode and hydro­gen at the cathode.

![](https://www.smoltek.com/wp-content/uploads/2022/01/PEM-electrolysis-1.png)

Schemat­ic of how PEM hydrol­y­sis works.

## [](https://www.smoltek.com#the-reactions-within-a-pem-electrolyzer)**The reactions within a PEM electrolyzer**

At the anode-side, an *oxy­gen evo­lu­tion reac­tion* (*OER*) takes place:

1. Water flows in. Some of the water comes into con­tact with the cat­a­lyst. A water mol­e­cule that comes into con­tact with the cat­a­lyst splits into one oxy­gen atom, two elec­trons, and two hydro­gen ions (pro­tons).
2. The elec­trons are drawn to the anode and moves towards the pos­i­tive pole of the pow­er source.
3. The hydro­gen ions are drawn towards the cath­ode and must pass through the mem­brane on the way.
4. Oxy­gen atoms com­bine in pairs to form oxy­gen gas.

At the cath­ode-side a *hydro­gen evo­lu­tion reac­tion* (*HER*) takes place:

1. Elec­trons have been sup­plied to the catalyst.
2. Hydro­gen ions pass through the mem­brane and come into con­tact with the catalyst.
3. Hydro­gen ions and elec­trons com­bine to form hydro­gen atoms.
4. Hydro­gen atoms com­bine in pairs to form hydro­gen gas.

Each indi­vid­ual reac­tion occurs with­in a micro­scop­ic region called the *triple-phase bound­ary* (*TPB*). You can think of TPB as a point where the reac­tion hap­pens because all nec­es­sary con­di­tions are met simul­ta­ne­ous­ly. For OER, this means that a water mol­e­cule comes into con­tact with the cat­a­lyst and the poly­mer elec­trolyte mem­brane. For HER, it means that a hydro­gen ion comes into con­tact with the cat­a­lyst and the poly­mer elec­trolyte membrane.

## [](https://www.smoltek.com#major-advantages)**Major advantages**

One of the most sig­nif­i­cant advan­tages of PEM elec­trol­y­sis is its high effi­cien­cy. Cur­rent­ly, the hydro­gen pro­duced has an ener­gy val­ue of up to 80% of the elec­tri­cal ener­gy sup­plied. The effi­cien­cy is expect­ed to be even high­er in the com­ing years—up to 86% by 2030.

Anoth­er advan­tage to PEM elec­trol­y­sis is its abil­i­ty to cope with rapid changes in the cur­rent sup­ply, which is a chal­lenge with some renew­able ener­gy sources such as solar and wind.

But PEM elec­trolyz­ers also have their share of problems.

## [](https://www.smoltek.com#need-for-rare-and-precious-metals)**Need for rare and precious metals**

PEM elec­trolyz­ers require plat­inum and irid­i­um oxide as cat­a­lysts. They are scarce and pre­cious met­als. For com­par­i­son, gold is 40 times more abun­dant in the Earth’s crust than iridium.

So, to reduce the amount need­ed, a sup­port­ing struc­ture of a cheap­er mate­r­i­al is coat­ed with a thin lay­er of met­als. Alter­na­tive­ly, par­ti­cles of the met­als are dis­persed onto a porous and elec­tri­cal­ly con­duct­ing sup­port­ing material.

How­ev­er, since the total sur­face area of a cat­a­lyst in an indus­tri­al appli­ca­tion is quite large, the cost of cat­a­lysts is still sig­nif­i­cant. And worse, most of it is nev­er used in the reac­tions because they are not at the triple-phase boundaries.

So the main chal­lenge of the PEM elec­trolyz­er is to fur­ther reduce the use of plat­inum and irid­i­um oxide in rela­tion to the gen­er­at­ed current.

## [](https://www.smoltek.com#gas-bubbles-block-the-reaction)**Gas bubbles block the reaction**

The oxy­gen evo­lu­tion reac­tion and the hydro­gen evo­lu­tion reac­tion result in gas that needs to be quick­ly trans­port­ed away from the cat­a­lyst. Oth­er­wise, the gas mol­e­cules may block the reactions.

The porous mate­r­i­al between the elec­trodes and the poly­mer elec­trolyte mem­brane dis­si­pates the gas­es. Yet, on the anode side, prob­lems can arise with oxy­gen gas not being removed effi­cient­ly enough, thus form­ing gas bub­bles in the water, instead.

So anoth­er chal­lenge of the PEM elec­trolyz­er is to fur­ther improve gas trans­porta­tion away from the cat­alyt­ic surfaces.

## [](https://www.smoltek.com#carbon-nanofibers-cnfs-to-rescue)**Carbon nanofibers (CNFs) to rescue**

A [*car­bon nanofiber* (*CNF*)](https://www.smoltek.com/technologies/carbon-nanofibers/) is a car­bon-made mate­r­i­al so thin that its diam­e­ter is mea­sured in nanome­tres (1 nm = 0.001 µm). Its length is tens of thou­sands of times longer than its diam­e­ter. Typ­i­cal­ly a CNF has a diam­e­ter of 1–100 nm and a length of 1–100 μm.

Smoltek has devel­oped and patent­ed a tech­nol­o­gy to pro­duce CNFs with extreme pre­ci­sion by chem­i­cal vapor depo­si­tion (CVD). The tech­nique allows the cre­ation of straight rows and columns of ver­ti­cal CNFs.

![](https://www.smoltek.com/wp-content/uploads/2021/12/cultivation-of-precisely-placed-carbon-nanofibres-1200x800.webp)

An array of car­bon nanofibers (CNFs) pre­cise­ly placed in rows and columns.

In addi­tion, the tech­nique allows nano-par­ti­cles, such as a few atoms of plat­inum or irid­i­um oxide, to be placed on each indi­vid­ual fiber. In con­junc­tion with CNFs elec­tri­cal con­duc­tiv­i­ty with low resis­tance, that can be used to solve both issues of the PEM electrolyzer.

The solu­tion is sim­ple. Start from the porous mate­r­i­al that will dif­fuse the gas that will be formed. On its sur­face towards the mem­brane, place a large num­ber of CNFs arranged in rows and columns. Attach to each of them nano-par­ti­cles of the cat­alyt­ic met­al. Embed the pre­pared CNFs in the poly­mer elec­trolyte mem­brane. Each CNF becomes a “cru­cible” where the reac­tion takes place.

![](https://www.smoltek.com/wp-content/uploads/2022/01/catalytic-nanoparticles-embedded-in-ion-exchange-membrane-1200x737.png)

Schemat­ic pre­sen­ta­tion of a mem­brane with embed­ded car­bon nanofibers with nano-par­ti­cles of cat­alyt­ic metal.

The advan­tage of this is that the amount of plat­inum or irid­i­um oxide need­ed is sig­nif­i­cant­ly reduced, as very lit­tle of these rare and expen­sive met­als are used and only where they are instrumental.

More­over, the array of CNFs improves the gas trans­port, par­tic­u­lar­ly on the anode side where the prob­lem of gas bub­bles in water block­ing the trans­port may occur.

This tech­nol­o­gy pro­duces two to three times more hydro­gen com­pared to exist­ing tech­nol­o­gy. This is because two to three times more cat­a­lyst par­ti­cles can be in con­tact with the mem­brane simul­ta­ne­ous­ly. This, in turn, can lead to sav­ings of up to 30 per­cent for hydro­gen pro­duc­tion plants.

## [](https://www.smoltek.com#fuel-cells-and-other-applications)**Fuel cells and other applications**

It’s not only the PEM elec­trolyz­er that uses an *ion exchange mem­brane (IEM)* such as a poly­mer elec­trolyte mem­brane. They are also used in fuel cells. Thus, Smoltek’s CNF solu­tion applies to those as well.

## [](https://www.smoltek.com#read-more)**Read more**

Read more about how car­bon nanofibers can improve PEM elec­trolyz­ers in our whitepa­per [*Intro­duc­ing Smoltek Elec­trolyz­er Tech­nol­o­gy*](https://www.smoltek.com/introducing-smoltek-electrolyzer-technology/1976/).