Less Expensive GDLs Sintered Titanium vs Carbon Paper

Why are Graphitized Carbon Panels Cheaper than Sintered Titanium for Gas Diffusion Layers?

In a pre­vi­ous arti­cle, we explored the var­i­ous mate­ri­als com­mon­ly employed as gas dif­fu­sion lay­ers (GDLs). Among these, two stand out as the most com­mon choic­es for fuel cells and elec­trolyz­ers: graphi­tized car­bon fiber paper or pan­el (also called mold­ed graphite lam­i­nate) and sin­tered tita­ni­um.

GDLs play a cru­cial role in both the anode and cath­ode com­part­ments of fuel cells and elec­trolyz­ers. They facil­i­tate the effi­cient deliv­ery of reac­tants to the cat­a­lyst lay­er, ensur­ing uni­form dis­tri­b­u­tion and opti­mal chem­i­cal inter­ac­tions. In pro­ton-exchange mem­brane (PEM) fuel cells, the anode GDL enables the dif­fu­sion of H2 gas to the cat­a­lyst lay­er, where it under­goes the hydro­gen oxi­da­tion reac­tion (HOR), pro­duc­ing H+ ions and elec­trons. These elec­trons trav­el through the exter­nal cir­cuit to the cath­ode, pass­ing through the GDL. At the same time, the cath­ode GDL allows the dif­fu­sion of O2 gas, which reacts with the H+ ions that per­me­ate through the mem­brane, form­ing liq­uid H2O. From this, GDLs not only facil­i­tate gas dif­fu­sion but also aid elec­tron trans­port and assist in water removal to pre­vent stack swelling.

Gas Diffusion Layer in PEM Fuel Cells

Graphi­tized car­bon paper is ver­sa­tile and can effec­tive­ly func­tion as both the anode and cath­ode GDLs in PEM fuel cells. Mean­while, sin­tered tita­ni­um has been used as an alter­na­tive oxi­dant dif­fu­sion medi­um, i.e., cath­ode GDL. For the sake of argu­ment, in this arti­cle, we will focus on the cath­ode side because both sin­tered tita­ni­um and car­bon-based GDLs work well there.

Assum­ing sin­tered tita­ni­um and graphi­tized car­bon fiber paper have equal­ly desir­able prop­er­ties (although they don’t, we’ll dis­cuss this lat­er), the cost of the gas dif­fu­sion lay­er (GDL) becomes a cru­cial fac­tor in mate­r­i­al selec­tion. Let’s delve into the pri­ma­ry fac­tors influ­enc­ing GDL cost and com­pare how they dif­fer for car­bon pan­els and sin­tered tita­ni­um. To begin, let’s out­line the main cost considerations:

  1. Raw mate­r­i­al costs
  2. Man­u­fac­tur­ing process
  3. Scal­a­bil­i­ty
  4. Ener­gy consumption
  5. Appli­ca­tion-spe­cif­ic requirements

Raw Material Costs

Graphi­tized car­bon pan­els are typ­i­cal­ly more cost-effec­tive to pro­duce com­pared to sin­tered tita­ni­um. While sin­tered tita­ni­um is pro­duced from expen­sive tita­ni­um ore, which con­tains tita­ni­um in min­er­als like rutile, ilmenite, or titan­ite, graphi­tized car­bon pan­els are man­u­fac­tured using car­bon-based raw mate­ri­als that tend to be more eco­nom­i­cal. These organ­ic pre­cur­sors include poly­acry­loni­trile, pitch, cel­lu­lose, or lignin.

  • Poly­acry­loni­trile (PAN) is a syn­thet­ic poly­mer pro­duced from acry­loni­trile monomers. It is wide­ly pro­duced on an indus­tri­al scale and accounts for over 90% of car­bon fiber pro­duc­tion. This keeps raw mate­r­i­al costs rel­a­tive­ly stable. 
  • Pitch is a dark-col­ored sub­stance formed dur­ing the process of dis­till­ing coal tar, wood tar, or petro­le­um (bitu­men). It is also known as the nat­ur­al petro­le­um residue, asphalt. It con­tains a high pro­por­tion of car­bon and oth­er organ­ic com­pounds. The cost can change based on crude oil prices and demand. High-qual­i­ty pitch can cost more, but car­bon fibers made from it are usu­al­ly cheap­er than PAN.
  • Cel­lu­lose is a nat­ur­al poly­mer found in plants like cot­ton, bam­boo, or wood pulp. It’s renew­able and wide­ly avail­able. Using it to make car­bon fibers is often cheap­er than syn­thet­ic mate­ri­als like PAN, but costs can vary based on har­vest­ing and processing.
  • Lignin is a byprod­uct of the pulp and paper indus­try and is often con­sid­ered a waste mate­r­i­al. Raw mate­r­i­al costs for lignin-based car­bon fibers may be rel­a­tive­ly low since lignin is read­i­ly avail­able as a byprod­uct. How­ev­er, addi­tion­al pro­cess­ing steps may be required to con­vert lignin into a suit­able pre­cur­sor for car­bon fiber pro­duc­tion, which can affect over­all pro­duc­tion costs.

Let’s briefly com­pare these organ­ic materials. 

Pre­cur­sorAdvan­tagesDis­ad­van­tages
Poly­acry­loni­trile (PAN)High car­bon yield, good mechan­i­cal strengthExpen­sive, requires oxidation
PitchHigh car­bon con­tent, low costHigh pro­cess­ing temperatures
Cel­lu­loseRenew­able, low costLow­er car­bon yield, longer processing
LigninRenew­able, abundantVari­able qual­i­ty, com­plex processing
Advan­tages and Dis­ad­van­tages of Car­bon Fiber Paper Precursors

Manufacturing Process

Man­u­fac­tur­ing sin­tered tita­ni­um pow­der is more cost­ly than pro­duc­ing graphi­tized car­bon fiber papers or pan­els. To gain a deep­er under­stand­ing of how graphi­tized car­bon fiber papers are made, we encour­age you to explore our in-depth blog post on the man­u­fac­tur­ing process. On the oth­er hand, the man­u­fac­tur­ing process for sin­tered tita­ni­um pow­der involves sev­er­al key steps. First, tita­ni­um ore is processed to extract tita­ni­um diox­ide, which is then fur­ther processed into tita­ni­um pow­der. Next, the tita­ni­um pow­der is com­pact­ed into the desired shape and sin­tered at high tem­per­a­tures under vac­u­um. This heat­ing process caus­es the par­ti­cles to bond togeth­er, increas­ing the strength and den­si­ty of the mate­r­i­al. After sin­ter­ing, the sur­face of the tita­ni­um pow­der may under­go addi­tion­al treat­ments to improve its prop­er­ties. Through­out the process, qual­i­ty con­trol mea­sures ensure that the sin­tered tita­ni­um pow­der meets required standards.

Different Stages of Sintering

Over­all, sin­tered tita­ni­um pow­der pro­duc­tion is expen­sive due to the high cost of tita­ni­um ore and the com­plex process­es involved. In con­trast, man­u­fac­tur­ing graphi­tized car­bon fiber pan­els involves less ener­gy and equip­ment, uti­liz­ing tech­niques like wet paper lay­ing, com­pres­sion mold­ing, and graphitization.

Scalability

Scal­a­bil­i­ty in man­u­fac­tur­ing refers to how well a process can ramp up pro­duc­tion with­out dri­ving up costs per unit. For GDLs in fuel cells, scal­a­bil­i­ty plays a cru­cial role in deter­min­ing the pro­duc­t’s over­all cost. 

Graphi­tized car­bon fiber paper GDLs offer sev­er­al advan­tages over tita­ni­um in terms of pro­duc­tion capac­i­ty, man­u­fac­tur­ing tech­niques, cost effi­cien­cy, lead time, and cus­tomiza­tion. These mate­ri­als can be pro­duced in larg­er quan­ti­ties from var­i­ous sources and using ver­sa­tile man­u­fac­tur­ing tech­niques, which can be eas­i­ly scaled up to indus­tri­al lev­els. This scal­a­bil­i­ty leads to economies of scale, result­ing in low­er pro­duc­tion costs per unit com­pared to tita­ni­um. Addi­tion­al­ly, car­bon mate­ri­als typ­i­cal­ly have short­er lead times for pro­duc­tion, allow­ing for more flex­i­bil­i­ty in meet­ing mar­ket demands and reduc­ing inven­to­ry costs. Fur­ther­more, the scal­a­bil­i­ty of car­bon-based mate­ri­als enables eas­i­er cus­tomiza­tion and inno­va­tion in prod­uct design, allow­ing man­u­fac­tur­ers to exper­i­ment with dif­fer­ent for­mu­la­tions and con­fig­u­ra­tions to opti­mize per­for­mance and cost for spe­cif­ic applications.

Scanning electron microscopy images of sintered titanium powder and titanium felt
Scan­ning elec­tron microscopy images of (A) sin­tered tita­ni­um pow­der and (B) tita­ni­um felt

To address prob­lems relat­ed to scal­a­bil­i­ty and com­plex­i­ty of the man­u­fac­tur­ing process, tita­ni­um fiber felt emerges as a promis­ing alter­na­tive to sin­tered tita­ni­um pow­der. Unlike the intri­cate and ener­gy-inten­sive pro­duc­tion meth­ods involved in sin­ter­ing tita­ni­um pow­der, the man­u­fac­tur­ing of tita­ni­um fiber felt involves com­par­a­tive­ly sim­pler techniques.

This involves the cre­ation of tita­ni­um fibers fol­lowed by sin­ter­ing to form a cohe­sive struc­ture. With its sim­pler man­u­fac­tur­ing process and bet­ter scal­a­bil­i­ty, tita­ni­um fiber felt presents itself as a viable option for var­i­ous appli­ca­tions where tita­ni­um’s excep­tion­al prop­er­ties are desired, pro­vid­ing an acces­si­ble and ver­sa­tile solu­tion for indus­tries seek­ing cost-effi­cient and scal­able mate­r­i­al solutions

Cri­te­riaSin­tered Tita­ni­um Pow­derTita­ni­um Felt
Poros­i­ty and PermeabilityHigh poros­i­ty and permeabilityHigh poros­i­ty, slight­ly low­er per­me­abil­i­ty com­pared to sin­tered pow­der due to fibrous structure
Sur­face AreaLarge sur­face area due to fine particlesRel­a­tive­ly low­er sur­face area com­pared to sin­tered pow­der due to fibrous structure
Mechan­i­cal StrengthLow­er mechan­i­cal strengthHigh­er mechan­i­cal strength due to fibrous structure
Con­duc­tiv­i­tyGen­er­al­ly good elec­tri­cal conductivityGood elec­tri­cal con­duc­tiv­i­ty, depend­ing on man­u­fac­tur­ing process
Cor­ro­sion ResistanceGood cor­ro­sion resis­tance due to tita­ni­um compositionGood cor­ro­sion resis­tance due to tita­ni­um composition
CostCan be more expen­sive due to pro­cess­ing stepsCan be more cost-effec­tive, depend­ing on man­u­fac­tur­ing process
Man­u­fac­tura­bil­i­tyRequires spe­cial­ized equip­ment and processesRel­a­tive­ly eas­i­er to man­u­fac­ture and shape
Com­par­i­son between Sin­tered Tita­ni­um Pow­der and Tita­ni­um Felt as Gas Dif­fu­sion Lay­ers in Fuel Cells and Water Electrolyzers

In con­clu­sion, the cost-effec­tive­ness of graphi­tized car­bon pan­els com­pared to sin­tered tita­ni­um for gas dif­fu­sion lay­ers stems from var­i­ous fac­tors, includ­ing raw mate­r­i­al costs, man­u­fac­tur­ing process­es, and scal­a­bil­i­ty. Graphi­tized car­bon pan­els offer a com­pelling alter­na­tive with their abun­dance of raw mate­ri­als, sim­pler man­u­fac­tur­ing tech­niques, and bet­ter scal­a­bil­i­ty poten­tial. As indus­tries con­tin­ue to seek cost-effi­cient and high-per­for­mance solu­tions for gas dif­fu­sion lay­ers, the advan­tages offered by graphi­tized car­bon pan­els make them an increas­ing­ly attrac­tive choice. For those inter­est­ed in explor­ing avail­able gas dif­fu­sion lay­er options, CAPLINQ offers a range of solu­tions tai­lored to meet diverse appli­ca­tion require­ments, pro­vid­ing reli­able and inno­v­a­tive mate­ri­als to sup­port the advance­ment of var­i­ous industries.

About Rose Anne Acedera

Leave a Reply

Your email address will not be published. Required fields are marked *