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. 

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).

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.

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.

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.