Gas Diffusion Electrodes: an advanced electrochemical solution

Gas diffusion electrodes (GDEs) are emerging as a key enabling technology for advanced electrochemical processes that accelerate industrial decarbonization and support circular resource use.
To know more about them, we interviewed Daniela Galliani, PhD, Program Manager for Emerging Technologies in Energy Transition and Hydrogen at De Nora.

A gas diffusion electrode (GDE) is a type of electrode that speeds up (catalyzes) an electrochemical reaction at the interface between a liquid and a gas. Briefly, the role of the GDE is to transfer electrons effectively between the gas and the liquid, or vice versa. This happens through the GDE's peculiar feature of creating a so-called triple-phase boundary, specific spots where three phases (solid, liquid, gas) can be simultaneously in contact with each other, allowing electrochemical reaction to happen in the most efficient way.

Broadly speaking, GDE consists of two components: a solid substrate, or gas diffusion layer, and an electrocatalyst.
The substrate or gas diffusion layer is a porous structure usually composed of carbon-based material (if the operative condition allows it), such as carbon cloth or carbon paper, while the electrocatalysts, necessary to facilitate the reaction and increase efficiency, are usually transition-metal-based; for instance, the most commonly used in fuel cells are platinum-based catalysts.
A wide variety of parameters can be tuned to manufacture an optimized GDE in which the triple-phase boundary is maximized in correspondence of the catalysts. The development and manufacturing of a GDE are indeed very complex and fascinating challenges that involve formulation chemistry, material engineering, and several physical and chemical characterization methods.

GDEs have unique features that can be exploited in all the industrial processes in which an electrochemical reaction involves the utilization of a gas. With the right product, you can optimize the process and sensibly increase its efficiency.
Such aspects have become extremely important in processes where GDEs are a common state of the art, such as in fuel cells, versatile energy devices that convert chemical energy from fuels (most commonly hydrogen) directly into electricity through electrochemical reactions.
Of course, other processes in the Energy Transition and Circularity field can successfully exploit GDE advantages, for instance, carbon dioxide electrochemical reduction, in which GDEs are used to reduce CO2 to valued-added molecules, or recovery and refining of industrial salts via electrolysis, where GDEs can be implemented to effectively pursue energy saving by cathode and potentially also anode depolarization.

HT PEM FCs are a specific type of FC characterized by high operating temperatures (120–200°C), which offer improved CO tolerance, simplified water management, and easier heat integration compared to low-temperature PEM systems. Within these FC, GDEs are a critical core component that allows the conversion of hydrogen and oxygen into water, powering the systems in which this type of fuel cells are usually implemented, such as heavy-duty mobility means and stationary equipment.

Electrochemical reduction of carbon dioxide is one of the most promising applications of GDEs. This technology could help repurpose carbon dioxide into valuable resources, integrating waste streams into circular economy models. For example, they could be implemented in industrial processes such as fermentation, where carbon dioxide is produced by the biological metabolism of microorganisms.

This technique uses electricity to separate salts, enabling the recovery or purification of industrial salts such as lithium chloride, sodium sulphate, and tetramethylammonium chloride. In GDE applications, these electrodes can be used to depolarize the cathode, thereby reducing cell voltage and energy consumption. This technology is widely employed in hydrochloric acid electrolysis for cathodic depolarization and could potentially and successfully be implemented for anode depolarization as well.

A very interesting growing field is the long-duration energy storage, critical for Energy Transition to happen. There are battery technologies under development for this application, such as metal-air batteries and redox-flow batteries, in which GDEs could be successfully implemented and play an important role in technological advancement.