Gas Diffusion Electrodes (GDE)

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A gas diffusion electrode (GDE) is a porous, multilayer electrode that facilitates the meeting of a gaseous reactant, a liquid electrolyte, and a solid catalyst at a single, well-defined interface, known as the triple-phase boundary (TPB).

This solves a basic mass-transport problem: gases such as CO₂, H₂, O₂, and N₂ dissolve poorly and diffuse slowly in liquid electrolytes so reactions relying on dissolved gas alone are limited by how much gas can reach the catalyst. GDEs get around this by feeding gas from behind the electrode, cutting transport distances from millimetres to microns and enabling current densities liquid-fed systems can't reach.

Originally developed for chlor-alkali production and fuel cells, GDEs have since expanded to be used in most gas-fed electrochemical energy technologies. Fuel cells, water electrolysers (PEM, AEM, BPM), CO2 electrolysers (such as CO2RR), metal-air batteries (Lithium-air and Zinc-air commonly), and nitrogen reduction systems (NRR) all use some variant of the same layered structure, tuned to the specific gas, electrolyte, and reaction involved.

Browse Gas Diffusion Electrode Cells

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What Is A Gas Diffusion Electrode?

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At the triple-phase boundary:

• The gas arrives through interconnected pores.
• The electrolyte wets the catalyst from the opposite face.
• The electrons move through the conductive carbon (in most cases) backbone.

The reaction rate depends on how much of this TPB is active at any moment, which is why GDE design, rather than catalyst chemistry often decides whether a promising lab result can translate into a workable device.

Rather than a fixed geometric line, the triple-phase boundary is better understood as a dynamic, unevenly distributed microenvironment. This will be affected by local pH, ion concentration, and wettability, which all vary within the pore network and shift during operation. Due to this, GDE performance can drift over the course of an experiment, even when the nominal operating conditions as current, flow rate, and electrolyte concentration kept constant.

GDE Cell Design: Layer by Layer

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A GDE is built from three functional layers, bonded into a single porous stack. These are the substrate (e.g. carbon cloth), a microporous layer and a catalyst layer. The substrate and microporous layer together make the gas diffusion layer. The GDL is the mechanical and electrical backbone of the electrode.

• The substrate in a GDE provides a porous matrix for the gas to migrate through while still being conductive enough to perform as an electrode. The open structure allows the gas to easily flow through towards the catalyst. This facilitates a consistent flow of gas towards and over the reaction site, carrying reactants to the triple phase boundary and products away from it. However, this layer must also maintain high conductivity and reasonable tensile strength.
• The microporous layer acts largely as a barrier layer, preventing the migration of water into the substrate. Flooding into the mesoporous structure will prevent gas flow, limiting GDE functionality. However, layer can limit gas diffusion and conductivity. This layer must be chosen carefully, to smooth pore-size distribution, improve electrical contact, maximize gas flow and preventing product water from flooding the GDE.
• The catalyst layer is where the reaction occurs. This material depends on the reaction you are doing. These catalyst particles are often combined with PTFE fibers that connect the catalyst to the microporous layer.

The microporous and microporous layer together make the gas diffusion layer. The GDL is the mechanical and electrical backbone of the electrode.

Substates: Carbon vs. Metal Substrates

Carbon paper (non-woven) and carbon cloth (woven) are the default choice for CO2RR, PEM fuel cells, and most acidic or neutral systems. However, carbon is prone to corrosion in strongly alkaline or high anodic-potential environment, such as in alkaline electrolysis and some AEM systems. Also, carbon is prone to attacked by oxygen intermediates as singlet oxygen, OH radicals, or by lithium or sodium superoxide forming carbonates. This can passivate the battery cathode surface. Decomposing this passivation requires high charging overpotentials, reducing the Faradaic Efficiency of the system. In such scenarios, metal substrates such as nickel foam, titanium felt or mesh, and stainless-steel mesh are used instead.

Microporous Layer (MPL)

This is usually a thin carbon-black coating sits between the GDL and catalyst layer. This smooths the pore-size distribution, improves conductivity of the electrode, and prevents product water from reaching the catalyst.

Catalyst layer

Reaction catalyst nanoparticles are dispersed with an ionomer or binder to create a catalyst layer that can be directly coated onto the MPL or onto a membrane.

The selection of catalyst materials is application specific. Noble metal/ metal oxide catalysts, like Pt and RuO2, are industrial benchmarks for catalysing HER and OER reactions across applications. However, transition metal oxides and other derivatives perform competitively in alkaline medium in AEM electrolysers related to water splitting, CO2RR, metal-air batteries and related energy applications.

PTFE hydrophobicity treatment

PTFE is applied to the GDL and/or MP, to control wetting (primarily on carbon-based substrates) to make sure the electrolyte is kept close to the tri-phase boundary while preventing flooding into the GDE blocking the gas diffusion pathways.

However, too much PTFE blocks GDE porosity and starves the catalyst of electrolyte contact, while also adding a significant resistance against electron transport. Hence, it is important to properly optimize the amount of PTFE. Alongside PTFE, other materials such as PVDF and FEP can be used instead, offering similar water-management behaviour with different cost and chemical-resistance trade-offs. Metal substrates manage wetting differently, largely through pore geometry and surface coatings rather than PTFE loading.

Gas Diffusion Electrode Properties

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• Porosity

  This governs gas throughput: too low restricts mass transport, too high weakens mechanical integrity.

• Hydrophobicity

  This balances gas access against electrolyte flooding.

• Catalyst Loading

  TMore catalyst doesn’t always guarantee better performance. Excess loading adds resistance and can bury active sites.

• Catalyst loading

  TMore catalyst doesn’t always guarantee better performance. Excess loading adds resistance and can bury active sites.

GDE Applications Across Energy Systems

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The fundamentals of GDE use are shared across applications, but operating requirements differ considering the nature of the reaction and the reaction constraints. A GDE that is optimized for one reaction may not the best fit for another.

One way to choose GDE components is according to whether the reaction consumes or produces gas at the electrode. Gas-consuming reactions such as CO2RR, NRR, and ORR typically need continuous reactant delivery and a stable, extended triple-phase boundary. The GDE cell requires hierarchical pore networks and controlled hydrophobicity.

Gas-evolving reactions as water electrolysis and other anodic processes, generally face the opposite problem: rapid bubble detachment and mechanical robustness matter more than reactant supply. This is because trapped bubbles block ionic conduction and accelerate delamination.

No single pore design serves both regimes well, which is why electrode architecture is usually reaction-specific rather than universal. The following table lists key requirements for few of the common applications

This list isn't exhaustive, and the same architecture also underpins electrochemical hydrogen peroxide synthesis (via the two-electron ORR pathway) and its use in electro-Fenton water treatment, alongside longer-established industrial uses such as chlor-alkali and ozone production. The same porous, controlled-wettability design that prevents flooding in CO2RR is what governs oxygen delivery and radical generation in these processes too.

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