Understanding PEM Electrolyzer Components and Their Functions

Proton Exchange Membrane (PEM) electrolyzers are gaining popularity for their efficiency in hydrogen production through water electrolysis. In this article, we will explore the main components of a PEM electrolyzer, including the compression plate, bipolar plates, gas diffusion layer, anode and cathode processes, and membrane electrode assembly. We dismantled a PEM electrolyzer. By understanding the materials and functions of these components, you can deepen your knowledge of this cutting-edge technology and its role in the clean energy landscape.

Compression Plate

The compression plate is made of aluminum alloy, used for fixing the entire electrolysis cell.

Bipolar Plates (BPP)

Bipolar plates (BPP) are flat separator plates (either with metal mesh or screen lamination or with etched flow field channels thick metal separators) used to match the power supply voltage by stacking multiple electrolysis cell units in series. Separate adjacent units and connect them electronically. It needs to have low low resistance and high mechanical and chemical stability, fluid distribution, and high thermal conductivity as it also helps to promote heat transfer.

Titanium is generally considered the most advanced material because it has excellent strength, low resistivity, high thermal conductivity and low hydrogen permeability. However, titanium is prone to corrosion, especially on the anode side, where potentials may exceed 2V leading to the accumulation of surface oxides, thereby increasing contact resistance and reducing thermal conductivity. To avoid this, a thin platinum coating can be applied to reduce surface resistance.

Gas Diffusion Layer (GDL)

The gas diffusion layer or called the current collector GDL or PTL, as an electronic conductor between the MEA and BPP, ensures efficient mass transfer of liquids and gases between the electrodes and the BPP.

At the anode, the liquid water transports from the passages of the BPP to the catalyst layer on the membrane through the current collector, where the water is decomposed into oxygen and protons. The oxygen generated here diffuses in the opposite direction through the current collector into the flow passages.

At the cathode, liquid water and hydrogen are transported from the membrane to the passages of the BPP through the current collector. Electrons start from the catalyst layer on the anode side, pass through the current collector and BPP, and then reach the cathode side. In PEM electrolyzers, the anode potential is high enough to oxidize carbon materials and other materials must be used. Titanium is often a choice for current collectors at the anode. 

Membrane Electrode Assembly (MEA)

The MEA consists of a proton-conducting membrane coated with porous electrocatalyst layers on both the anode and cathode sides, which is the core component of the electrolyzer, where water is decomposed into gaseous hydrogen and oxygen by electric current. At the anode, water is oxidized into oxygen and protons. The hydrated protons then migrate to the cathode. Electrons flow to the cathode through the external circuit.

At the cathode, protons gain electrons and are reduced to form hydrogen gas. Iridium oxide is generally considered the most advanced catalyst in PEM water electrolysis. Among single transition oxides, RuO2 has the highest OER activity, but it is not stable under electrolyzer conditions. IrO2 has slightly lower activity than RuO2 but has the advantage of higher corrosion resistance.