MEA Electrolyzers

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High-performance electrochemical cells with a layered 'zero-gap' architecture to minimize ohmic resistance and enable higher current densities than standard H-cells or GDE flow cells. Typically operating over 2 A/cm², MEA electrolyzers can achieve a higher hydrogen yield in water electrolyzers, compared to traditional alkaline systems.

Eliminating the gap between electrode and membrane, the catalyst layers or coated gas diffusion electrodes are pressed to the bipolar flow field plates or bonded directly onto a solid polymer membrane. With no liquid electrolyte between the membrane and the catalyst, the membrane itself conducts ions, then gases or reactants are fed to the back of each electrode through flow field plates. This cell architecture is widely recognized for its usability in up-scaling green hydrogen production and CO₂ reduction. The sandwiched central membrane provides a selective, robust barrier which prevents the mixing of produced hydrogen, oxygen, or reduced CO₂ products for high-purity gaseous outputs.

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Visual Membrane Electrode Assembly Electrolyzer

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Membrane Electrode Assembly Electrolyzer

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Core Components

Membrane: solid polymer electrolyte (PEM, AEM, or BPM) that conducts ions and separates cathode and anode compartments.
Gas diffusion electrode or catalyst coated membrane: the catalyst is applied to the gas diffusion electrode or on the membrane surface.
Gas diffusion layers (GDL): porous materials (carbon paper, nickel foam, titanium mesh) that distribute reactant gases and conduct electrons.
Flow field plates: machined plates with serpentine, parallel, mesh, or hybrid channel geometry direct gas flow across the GDLs and provide electrical contact.
Observation window (optional): transparent acrylic windows support further analysis.

Membrane Types

The membrane is the most consequential design choice in an MEA cell, as it determines the ionic environment, compatible catalysts, plate materials, and achievable selectivity. Ossila MEA Electrolysers are compatible with PEM, AEM, and BPM membranes

Key Characteristics

Proton Exchange Membrane (PEM)

Acidic environment

High proton conductivity

Well-established

Requires acid-stable anode plates

Anion Exchange Membrane (AEM)

Alkaline environment

Enables non-precious catalysts (Ni, Fe)

Carbonate formation is main challenge

Bipolar Membrane (BPM)

Decouples cathode and anode pH

Reverse bias most common for CO₂RR

Addresses AEM carbonate crossover

Still emerging as a commercial architecture

Electrochemistry

	PEM	AEM	BPM
Ion Conducted	H⁺ (protons), acidic environment	OH^- (hydroxide), alkaline environment	H⁺ + OH^- via water dissociation at junction layer, decoupled pH on each side
Anode Reaction (OER)	H₂O → 2H⁺ + ½O₂ + 2e^-	2OH^- → H₂O + ½O₂ + 2e^-	Anode side: alkaline (reverse bias) 2OH^- → H₂O + ½O₂ + 2e^-
Cathode Reaction (HER)	2H⁺ + 2e^- → H₂	2OH^- → H₂O + ½O₂ + 2e^-	Anode side: alkaline (reverse bias) 2OH^- → H₂O + ½O₂ + 2e^-
Cathode Reaction (CO₂RR, general)	CO₂ + nH⁺ + ne^- → products (CO, HCOOH, CH₄, C₂H₄ etc.) Acidic cathode favours C1 products (CO, formate); competing HER	CO₂ + nH₂O + ne^- → products + OH^- (CO, C₂H₄, C₂H₅OH etc.) Alkaline cathode improves C₂₊ selectivity on Cu; carbonate crossover	CO₂ + nH⁺ + ne^- → products Acidic cathode (reverse bias), similar to PEM but CO₂ reconverted at junction; reduced crossover loss vs. AEM
Cathode Reaction (NRR)	Not recommended, acidic conditions promote HER	N₂ + nH₂O + ne^- → NH₃ + OH^- Alkaline environment suppresses competing HER on NRR catalysts	Limited reliable literature

Materials and Compatibility

	PEM	AEM	BPM
Electrolyte/Feed	High-purity deionized water (acid-sensitive membrane)	Dilute KOH, carbonate solution, or deionized water	Deionized water (water dissociation at BPM junction provides H⁺ and OH^-)
Catalysts (frequently reported)	Precious metals: Pt (HER), IrO₂ (OER), Sn/Bi (CO₂RR formate)	Earth-abundant metallic derivatives of Ni, Fe, Co (OER/HER), Cu (CO₂RR C₂₊), Mo (NRR)	Flexible: acidic cathode suits Pt, Sn/Bi, while alkaline anode suits Ni/Fe
Recommended Membranes (commercial)	Nafion 117/212, Aquivion E87, Gore-Select	Sustainion X37, Aemion AF1, Fumasep FAA-3, PiperION	Fumasep FBM, Xion composite BPM (reverse bias for CO₂RR)
Plate Materials	Cathode: Graphite or Ti Anode: Ti (mandatory, acid-stable) Premium: Pt-coated Ti	Cathode: Graphite or Ni, Au-coated Ni (Premium) Anode: Ni or Au-coated Ni (Premium) (Ti also compatible)	Cathode: Ti (or Graphite) Anode: Ti or 316L SS (alkaline anode suits SS)
Maturity	Fully commercialized and widely deployed at scale	Emerging / R&D and early commercial stage, fast-growing field	Emerging technology with well-developed CO₂RR literature
Main Limitation	High catalyst cost (Pt, Ir); limited success in CO₂RR and NRR	Membrane durability; carbonate crossover in CO₂RR	Additional energy penalty from water dissociation; more complex assembly

Plate Material Configuration

Flow field plates are one of the key elements of the MEA architecture as it simultaneously support three main functions: electron conduction, reactant distribution, and mechanical support. Choosing the right plate material provides chemical stability under your desired operational conditions. Historically, titanium plates provide excellent stability across a wider pH range. Nickel and stainless steel is limited to neutral or mild alkaline solutions, while and Au- and Pt-coated titanium are a reasonable choice for wide range of applications across different pH regions.

Configuration (cathode plate, anode plate, membrane)	Best Suited	Reasoning
Titanium, titanium, PEM/BPM	- Water electrolysis - CO₂RR - CO₂RR (formic acid/formate) - ORR	Fully acid-compatible on both the cathode and anode. Slightly higher contact resistance than Pt or Au-coated Ti at high current density, but suitable for most research applications. Common choice for PEM cells. Also suitable for BPM CO₂RR cells. BPM (reverse bias) decouples cathode and anode pH via water dissociation at the junction layer, addressing carbonate crossover in AEM cells. BPM is well-suited to formate production because the acidic cathode environment favours Sn/Bi catalyst selectivity toward formate/formic acid.
Pt-coated titanium, Pt-coated titanium, PEM	- Water electrolysis - ORR	Premium PEM configuration for high current density and long-duration testing. Pt coating significantly reduces interfacial contact resistance vs. bare Ti and prevents TiO₂ passivation layer formation over extended operation (ACS Catal. 2024, 14, 921). Best choice when minimising ohmic losses is the priority. Not required for standard CO₂RR screening where Ti/Ti suffices, and Pt can trigger HER
Graphite, titanium, PEM	- Water electrolysis - CO₂RR - CO₂RR (formic acid/formate)	A widely recommended PEM combination. Graphite is electrochemically stable at the reductive cathode potential and does not corrode under PEM cathode conditions. Titanium is mandatory at the anode: the acidic OER environment corrodes carbon and stainless steel. PEM is preferred over AEM for formate production because formate does not cross a cation exchange membrane, giving higher product purity.
Nickel, nickel, AEM	- Water electrolysis	All-Ni configuration suited to alkaline AEM conditions. Good electrical conductivity and corrosion resistance in KOH/alkaline media. Lower cost than Au-coated option. Not recommended for CO₂RR or NRR as Ni is catalytically active for HER and may reduce selectivity toward CO₂RR or NRR products.
Au-coated nickel, Au-coated nickel, AEM	- Water electrolysis - CO₂RR - NRR	Premium AEM configuration for long-duration stability. Au coating prevents Ni passivation and minimises contact resistance under alkaline conditions. Preferred when experiment duration and reproducibility outweigh cost considerations. Not listed for formate: AEM formate crossover limits long-term product purity regardless of plate material.
Titanium, stainless steel (316L), BPM	- CO₂RR - CO₂RR (formic acid/formate)	Most common BPM CO₂RR configuration reported in the literature (e.g. Appl. Chem. Int. Ed. 2023; EES 2021). In reverse bias, the anode sees alkaline conditions where 316L SS is stable, reducing cost vs. all-Ti. The Ti cathode is stable at reductive potentials. Decoupled pH allows efficient OER with earth-abundant catalysts at the alkaline anode while maintaining acidic cathode selectivity.

Note: Graphite flow fields are currently not available from Ossila.

Resources

CO₂ Reduction (CO₂RR)

Electrochemical carbon dioxide reduction reactions (CO₂RR) uses electrical energy to drive the reduction of CO₂ in an aqueous or solid-state electrolyte environment. This article introduces the science underpinning electrochemical CO₂ reduction.