Choosing the right Ion Exchange membrane for Water electrolyzers and fuel cell applications

Choosing the Right Ion Exchange Membrane for Your Water Electrolyzer and Fuel Cell Applications

Understanding ion exchange membranes

An ion exchange mem­brane (IEM) is a thin bar­ri­er that allows the selec­tive pas­sage of ions from one elec­trode to anoth­er of elec­tro­chem­i­cal devices, includ­ing but not lim­it­ed to water elec­trolyz­ers and fuel cells. 

Structure of an Ion Exchange Membrane

IEMs are com­posed of a three-dimen­sion­al poly­mer matrix func­tion­al­ized with charged (or ion exchange) groups. These fixed charge groups com­plete­ly or par­tial­ly repel sim­i­lar­ly charged ions (co-ions) from the mem­brane and allow the move­ment of dif­fer­ent­ly charged ions (counter-ions) through the mem­brane. In both water elec­trolyz­ers and fuel cells, effi­cient ion trans­port is impor­tant to achieve high per­for­mance, reduce over­po­ten­tials, and ensure the over­all effec­tive­ness of the elec­tro­chem­i­cal process­es involved. 

In this arti­cle, we’ll guide you through the key con­sid­er­a­tions when choos­ing the appro­pri­ate IEM for your water elec­trol­y­sis and fuel cell applications. 

Key considerations when choosing the right IEM

Fuel Cell and Water Electrolyzer Type

Depend­ing on the type of the fixed charge groups found in their poly­mer back­bones, IEMs can be clas­si­fied into two: cation (CEM) and anion (AEM) exchange mem­brane. CEMs con­tain fixed neg­a­tive­ly charged ions, which allows the move­ment of cations across the mem­brane. Con­verse­ly, AEMs have pos­i­tive­ly charged groups to selec­tive­ly allow the trans­port of anions. On top of these two basic clas­si­fi­ca­tions, IEMs can also be pro­ton exchange mem­branes (PEMs), bipo­lar, ampho­teric, and mixed matrix mem­branes. In water elec­trolyz­ers and fuel cells, PEMs and AEMs are the most use­ful. PEM is a spe­cial type of CEMs that trans­ports pro­tons (H+ ions).

Types of Ion Exchange Membranes

The first thing to con­sid­er when choos­ing IEMs is the type of fuel cell and water elec­trolyz­er. Fuel cell and water elec­trolyz­er oper­a­tion involve the trans­port of ions; the type of ion­ic species that need to be trans­port­ed dic­tates the appro­pri­ate type of IEM to be used. Poly­mer elec­trolyte mem­brane water elec­trolyz­ers (PEMWE) and fuel cells (PEMFC), which are oper­at­ed under acidic con­di­tions, require the trans­port of H+ ions. There­fore, a PEM is used for PEMFC and PEMWE. In con­trast, in anion exchange mem­brane fuel cells (AEM­FCs) and anion exchange mem­brane water elec­trolyz­ers (AEMWEs), which run in alka­line envi­ron­ments, OH ions are trans­port­ed. AEM is used in AEMFC and AEMWE.

Anion and Proton Exchange Membrane Water Electrolyzer and Fuel Cell

Once the right type of IEM for your fuel cell and water elec­trolyz­er stack has been deter­mined, it is now time to dig into the spe­cif­ic prop­er­ties that will yield your tar­get effi­cien­cy and performance.

IEM properties and the balance between them

Gen­er­al­ly, the prop­er­ties of IEMs are deter­mined by the prop­er­ties of the poly­mer back­bone and fixed charges that make up their struc­tures. Par­tic­u­lar­ly, the den­si­ty, wet­ta­bil­i­ty (hydropho­bic­i­ty or hydrophilic­i­ty), and mor­phol­o­gy of the poly­mer matrix, as well as the type and con­cen­tra­tion of the charged func­tion­al groups, affect the result­ing prop­er­ties of the IEMs. The mechan­i­cal, chem­i­cal, and ther­mal prop­er­ties of IEMs are pri­mar­i­ly influ­enced by the poly­mer back­bone, where­as the elec­tro­chem­i­cal prop­er­ties, con­duc­tiv­i­ty, and perms­e­lec­tiv­i­ty are deter­mined by the con­cen­tra­tion of the fixed charges. Learn more about the key prop­er­ties of IEMs here.

A high per­for­mance IEM should exhib­it high ion­ic con­duc­tiv­i­ty, high ion exchange capac­i­ty, perms­e­lec­tiv­i­ty close to uni­ty, and excel­lent dimen­sion­al, chem­i­cal, mechan­i­cal, and ther­mal sta­bil­i­ties. How­ev­er, hit­ting all these check box­es is nowhere near as pos­si­ble. We can’t have it all and most of the time, we must find the per­fect bal­ance between these properties.

Key Properties of Ion Exchange Membranes

For exam­ple, high ion­ic con­duc­tiv­i­ty improves cell effi­cien­cy. To achieve it, the IEM should have a high IEC. The down­side to this is that adding more charged func­tion­al groups to the poly­mer matrix may increase the water uptake, which can poten­tial­ly lead to the degra­da­tion of the IEM. For this case, performance–stability trade­offs should be con­sid­ered. Con­verse­ly, when we want a mem­brane that is high­ly dimen­sion­al­ly sta­ble, mem­brane dehy­dra­tion, which decreas­es ion­ic con­duc­tiv­i­ty and con­se­quent­ly the cell per­for­mance, is a pos­si­bil­i­ty. When choos­ing the IEM for your appli­ca­tion, it is nec­es­sary to under­stand IEM prop­er­ties and find the bal­ance between them.

IONOMR Inno­va­tions offers advanced ion exchange mem­branes for next-gen­er­a­tion water elec­trolyz­ers and fuel cells. AEMION+TM and PEMION+TM ion exchange mem­branes demon­strate a del­i­cate bal­ance between these key prop­er­ties. AEMION+TM is a high-per­for­mance AEM that is sta­ble in both high­ly alka­line and strong­ly acidic envi­ron­ments, enabling cost-effec­tive hydro­gen pro­duc­tion and even car­bon cap­ture. PEMION+TM intro­duces a par­a­digm shift in PEM tech­nol­o­gy, replac­ing poten­tial­ly harm­ful mate­ri­als with more envi­ron­men­tal­ly benign hydro­car­bons. Both IEMs seek the bal­ance between high ion­ic con­duc­tiv­i­ty, IEC, and sta­bil­i­ty, rec­og­niz­ing the neces­si­ty of trade-offs in achiev­ing opti­mal per­for­mance, whether for effi­cient hydro­gen fuel cells or water elec­trolyz­er applications.

Operating Conditions

The oper­at­ing con­di­tions, includ­ing tem­per­a­ture, pres­sure, and humid­i­ty lev­els, should also be con­sid­ered when look­ing for the right IEM for your appli­ca­tion. The oper­at­ing con­di­tions do not only affect the per­for­mance but also the sta­bil­i­ty of IEMs. Some IEMs per­form opti­mal­ly at high tem­per­a­tures and pres­sures, while oth­ers are designed for low­er-tem­per­a­ture appli­ca­tions. For wet oper­at­ing con­di­tions, a mem­brane with low water uptake may be suit­able. In con­trast, an IEM with a high water uptake is desired for dry oper­at­ing con­di­tions to avoid exces­sive mem­brane dehy­dra­tion. Ensure that the cho­sen IEM can with­stand your device’s environment.

Cost of the membrane material

Let’s say that we have found a per­fect­ly opti­mized mem­brane with excel­lent per­for­mance and sta­bil­i­ty. Anoth­er fac­tor to con­sid­er is the cost. Often­times, high per­for­mance and sta­bil­i­ty require­ments require high mate­r­i­al costs. As such, bal­anc­ing per­for­mance require­ments with bud­get con­straints is cru­cial, as the cost of the IEM can affect the over­all cost of the fuel cell and water system.

Special requirements (if there are any)

Last­ly, when choos­ing IEMS, any spe­cial require­ments unique to your fuel cell and water elec­trolyz­er design should also be con­sid­ered. Con­sid­er any spe­cial require­ments unique to your appli­ca­tion, such as radi­a­tion resis­tance for space appli­ca­tions or chem­i­cal resis­tance to spe­cif­ic con­t­a­m­i­nants in the envi­ron­ment.

Choos­ing the right ion exchange mem­brane is a piv­otal point in the design of an effi­cient and durable water elec­trolyz­er and fuel cell sys­tem. By care­ful­ly con­sid­er­ing the fac­tors men­tioned above and con­duct­ing appro­pri­ate test­ing, you can make an informed deci­sion that aligns with your spe­cif­ic appli­ca­tion needs. Con­tact us, and our appli­ca­tion engi­neers and in-house water elec­trolyz­er and fuel cell experts will assist you in select­ing the most suit­able prod­ucts tai­lored to your appli­ca­tion. Togeth­er, let’s pave a way for the advance­ment of clean and sus­tain­able ener­gy solutions.

About Rose Anne Acedera

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