Carbon papers for Fuel Cells & Electrolyzers

Fuels cells and Elec­trolyz­ers are two sides of the same coin. In the case of elec­trol­y­sis we use elec­tric­i­ty to cre­ate hydro­gen while in the case of fuel cells we use hydro­gen to cre­ate elec­tric­i­ty. Their prin­ci­ple and set­up is pret­ty sim­i­lar but with a reverse struc­ture and some cru­cial dif­fer­ences in cat­a­lyst and exchange mem­brane types.

Both fuel cells and elec­trolyz­ers use very sim­i­lar MEA (Mem­brane elec­trode assem­bly) stacks with Gas dif­fu­sion lay­ers, Elec­trodes (Anodes & Cath­odes) and of course the exchange mem­brane.Graphi­tized Car­bon plates, Car­bon papers, car­bon sheets, how­ev­er you want to name them are cru­cial for a big part of these assem­blies, play­ing a role in both the elec­trode and gas dif­fu­sion lay­er side. 

Honda Global | Clarity Fuel Cell - Picture Book

Renew­able ener­gy sus­tain­abil­i­ty — Cour­testy of Hon­da Motor Co., Ltd

Gas dif­fu­sion lay­ers (GDLs) are cru­cial com­po­nents for pro­ton exchange mem­brane fuel cells (PEM­FCs) since they mod­u­late all rel­e­vant trans­port process­es (fuel, reac­tion prod­ucts, elec­tric­i­ty, heat). Gas dif­fu­sion lay­ers act as an inter­face between the flow fields (struc­tur­al cell parts, mil­lime­ter-sized fea­tures) and the elec­tro­cat­a­lysts (reac­tion lay­ers, nanome­ter-size fea­tures), direct­ing the fuel to the active sites while remov­ing heat and reac­tion prod­ucts and elec­tri­cal­ly wiring the reac­tion lay­ers with the cur­rent collectors. 

If we want to get into car­bon plate seman­tics there are two more “lay­ers” that we can look into:

1. Gas Dif­fu­sion Back­ing Lay­er (GDBL)The car­bon plate which is a fibrous back­ing mate­r­i­al that gov­erns the mechan­i­cal prop­er­ties of the GDL (behav­ior upon com­pres­sion, bend­ing, and shear strength) and also impacts the ther­mal and elec­tric properties.

fuel cell | Definition, Types, Applications, & Facts | Britannica

2. Micro­p­orous Lay­er (MPL). Car­bon plates can be treat­ed with extra micro­p­orous lay­ers and PTFE. This is not an essen­tial treat­ment. It is an extra. The main prop­er­ties of GDLs, con­tain­ing GDL treat­ed with PTFE (Teflon), can make the mate­r­i­al hydropho­bic and improve water trans­port. Fur­ther­more, the GDL with MPL treat­ment helps to reduce the con­tact resis­tance between the GDL and cat­a­lyst lay­er, and lim­it cat­a­lyst loss to the GDL inte­ri­or. MPL can also be used as a sub­strate to deposit cat­a­lyst par­ti­cles for the man­u­fac­ture of gas dif­fu­sion elec­trodes (GDEs).

There are mul­ti­ple MPL types that can be adjust­ed for gen­er­al fuel cells, DMFC anodes, dry con­di­tion PEMFC, low humid­i­ty FCV, High humid­i­ty FCV and High dura­bil­i­ty Vehi­cle Fuel cells(FCV).

Typ­i­cal GDL Applications

  • Pro­ton Exchange Membrane(PEM) stacks
  • Direct Methanol (DMFC) stacks
  • Phos­phor­ic Acid (PAFC) stacks
  • Elec­trolyz­er
  • Redox Flow Batteries
  • Oth­er elec­tro­chem­i­cal devices

Manufacturing Process of Carbon Papers

Car­bon paper gas dif­fu­sion lay­ers (pre­pared by the wet lay­ing of chopped PAN-based car­bon fibers) are a pop­u­lar solu­tion since they can be man­u­fac­tured at high vol­umes (scal­a­bil­i­ty) and low thick­ness. Steps are:

1. Chopped car­bon fibers are processed to a pri­ma­ry car­bon fiber web using a paper­mak­ing (wet-lay­ing) tech­nol­o­gy and sub­se­quent thermo-bonding. 

2. The raw paper is then impreg­nat­ed with car­boniz­able resins (car­boniz­able resins with the option­al addi­tion of car­bon fillers), cured, and recarbonized/ graphi­tized. This pro­ce­dure serves to adjust the poros­i­ty and enhance elec­tric and ther­mal conductivity. 

3. Dif­fer­ent GDL back­ings with dif­fer­ent filler con­tent could be the base for the final fin­ish­ing process­es, such as: 

  • Hydropho­bic treat­ment with PTFE 
  • Coat­ing with a micro­p­orous lay­er (MPL)
  • Sin­ter­ing (ther­mal anneal­ing) to bond the substrate/MPL

Sim­ple Car­bon plate process goes through the fol­low­ing steps

Dis­per­sion > Resin impreg­na­tion > Mold­ing > Car­boniza­tion > Graphitization

These thick­er prod­ucts have high­er ther­mal con­duc­tiv­i­ty, high dura­bil­i­ty, low car­bon cor­ro­sion and are typ­i­cal­ly used for Elec­trolyz­ers and dis­trib­uted pow­er gen­er­a­tors. They are also known as Mold­ed graphite papers or Car­bon plates.

A car­bon paper with MPL treat­ment will tra­di­tion­al­ly go through the fol­low­ing man­u­fac­tur­ing steps:

  1. Dis­per­sion
  2. Resin impreg­na­tion
  3. Low tem­per­a­ture carbonization
  4. High tem­per­a­ture graphitization
  5. Micro­p­orous Lay­er coating
  6. Resing impreg­na­tion
  7. Heat treat­ment (1600 or 2000°C)

These thin­ner car­bon papers that usu­al­ly (but not nec­es­sar­i­ly) come with an MPL coat­ing are typ­i­cal­ly used for Fuel cells. These fuel cells are used in vehi­cles, fork­lifts, drones and res­i­den­tial appli­ca­tions. These vehi­cles tend to need high­er pow­er stacks with robust prop­er­ties in thin assem­blies with high gas per­me­abil­i­ty and porosity. 

Carbon Papers as Fuel cell GDL and Electrodes

In fuel cells, these thin, porous sheets must pro­vide high elec­tri­cal and ther­mal con­duc­tiv­i­ty and chemical/corrosion resis­tance, in addi­tion to con­trol­ling the prop­er flow of reac­tant gas­es (hydro­gen and air) and man­ag­ing the water trans­port out of the mem­brane elec­trode assem­bly (MEA). This lay­er must also have con­trolled com­press­ibil­i­ty to sup­port the exter­nal forces from the assem­bly, and not deform into the bi-com­po­nent plate chan­nels to restrict flow. In sum­ma­ry, GDL mod­u­lates all rel­e­vant trans­port process­es: mass trans­port (fuel, reac­tion prod­ucts), elec­trons trans­port, and heat trans­port), mean­while, pro­vid­ing long-term mechan­i­cal, chem­i­cal, and ther­mal sta­bil­i­ty for PEM fuel cells. 

Car­bon papers can be used as Elec­trodes for the Mem­brane Elec­trode Assem­bly. They are used as a sub­strate to paint the cat­a­lyst ink that deter­mines their Anode or Cath­ode nature.

Gen­er­al­ly car­bon plates can be used on the cath­ode side while sin­tered tita­ni­um is more pop­u­lar and suit­able for the anode side.

Anode is the part of the fuel cells where Hydro­gen enters the pack­age. It is where Hydro­gen is split into ions and elec­trons and where the elec­tron flow starts.

Cath­ode is the part of the fuel cell where Oxy­gen enters the pack­age. Oxy­gen is being bound with the charged hydro­gen ions and the excess is being removed in water form that flows out of the cell.

After all was said and done we man­aged to replace and ful­ly qual­i­fy our LINQCELL Car­bon plate prod­uct line after the dis­con­tin­u­a­tion of Spec­tracarb which left many com­pa­nies hang­ing. With full con­trol over our sup­ply chain and pro­duc­tion we are now offer­ing an excel­lent prod­uct port­fo­lio that has been suc­cess­ful­ly test­ed and qual­i­fied but top indus­try play­ers. Our GDLs range from thin, 100um car­bon papers to thick 2.9mm car­bon plates (or mold­ed graphite papers). They exhib­it excel­lent com­press­ibil­i­ty and elec­tri­cal prop­er­ties and have already become the prod­uct of choice for huge fuel cell man­u­fac­tur­ers and gov­ern­men­tal institutions.

Prop­er­tiesUnitGDL 1500BGDL 1850GDL 2200GDL 2900
Basic Para­me­ters
Basis Weightg/m2670156215501734
Thick­ness @50kpamm1.501.852.202.90
Den­si­tyg/cm30.60.850.600.60
Elec­tri­cal Properties
Resis­tancemΩ cm2<21<14<17<25
TP resis­tiv­i­tymΩ cm 14070.511087.5
Volt­age LossmV3925.53527.6
With MPL+PTFE TreatmentNONONONO

This is a top-lev­el overview of our thick­er grades. Our graphi­tized car­bon paper prod­uct line is much more exten­sive and we can also dis­cuss cus­tom grades if you are inter­est­ed in high quan­ti­ties. Please con­tact us with your appli­ca­tions and prod­uct require­ments and we’ll be hap­py to aid you with prod­uct selection.

About George Kountardas

George is a Jack of all trades with an unappeasable inquiring mind. Obsessed with new products and technologies, he is always pushing forward for better, faster and more efficient applications. Always learning something new.

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