Composition and working principle of PEM hydrogen production electrolyzer

Proton exchange membrane (PEM) water electrolysis technology has the advantages of low DC power consumption, high current density, small electrolyzer volume, high operating pressure and differential pressure operation, wide power adjustment range, etc. It has good adaptability to wind power and photovoltaic power with large fluctuations, and has developed rapidly in recent years.

The PEM electrolyzer is the core part of the PEM water electrolysis hydrogen production device. Its main components include compression plates, bipolar plates, gas diffusion layers, anodes and cathodes, and membrane electrode assemblies（MEA）. By understanding the materials and functions of the components in the PEM electrolyzer, we can deepen our understanding of this cutting-edge technology and its role in the field of clean energy.

Composition of PEM electrolyzer

The names of the components of PEM electrolyzer from top to bottom are:

Bolt, compression plate, insulation layer, bipolar plate, insulation rubber ring, titanium mesh (2 layers), titanium felt, membrane electrode, titanium felt, titanium mesh (2 layers), insulation rubber ring, electrode plate, insulation layer, compression plate

1.Compression plate

The compression plate is made of aluminum alloy and is used to fix the entire electrolyzer.

2.Insulation rubber ring

The next one below the pressure plate is the insulation rubber ring, which has insulation and sealing properties.

3.Bipolar plate (BPP)

The bipolar plate (BPP) is a flat separator (with a metal mesh or screen laminate or a thick metal separator with etched flow field channels) used to match the power supply voltage by stacking multiple electrolytic cell units in series. Separate adjacent units and make electronic connections. It needs to have low resistance and high mechanical and chemical stability, fluid distribution and high thermal conductivity, as it also helps promote heat transfer.

Titanium is generally considered a state-of-the-art material because of its excellent strength, low resistivity, high thermal conductivity, and low hydrogen permeability. However, titanium is susceptible to corrosion, especially on the anode side, where the potential may exceed 2V, resulting in surface oxide accumulation, which increases contact resistance and reduces thermal conductivity. To avoid this, a thin platinum coating can be applied to reduce surface resistance.

4.Silicone ring

This is a silicone ring with sealing and fluid transport properties.

5.Gas diffusion layer (GDL)

The gas diffusion layer, or current collector GDL or PTL, acts as an electronic conductor between the MEA and the BPP, ensuring effective mass transfer of liquid and gas between the electrode and the BPP.

At the anode, liquid water is transported from the channels of the BPP through the current collector to the catalyst layer on the membrane, where water is decomposed into oxygen and protons, and the oxygen produced here diffuses into the flow channel in the opposite direction through the current collector.

At the cathode, liquid water and hydrogen are transported from the membrane to the channels 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, other materials must be used because the anode potential is high enough to oxidize carbon materials. Titanium is usually the choice of anode current collector.

6.Membrane Electrode Assembly (MEA)

MEA consists of a proton-conducting membrane, which is coated with porous electrocatalyst layers on both the anode and cathode sides. It is the core component of the electrolyzer. Water is decomposed into gaseous hydrogen and oxygen under the action of 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 an external circuit.

At the cathode, protons gain electrons and are reduced to form hydrogen. Iridium oxide is generally considered to be the most advanced catalyst in PEM water electrolysis. Among single transition oxides, RuO2 has the highest OER activity, but is unstable under electrolyzer conditions. IrO2 is slightly less active than RuO2, but has the advantage of higher corrosion resistance.

Working Principle of PEM Electrolyzer

Water enters the bipolar plate from the water inlet, then enters the gas diffusion layer, and finally enters the proton exchange membrane. By inputting current and voltage, water is decomposed into protons H+ and two O2- by contacting the proton exchange membrane of the electrode. O2- loses electrons e- to form O2.

The lost electrons reach the cathode through the circuit, and H+ reaches the cathode through the proton membrane, where it combines with electrons to form H2.

The anode produces oxygen and the cathode produces hydrogen. The oxygen produced at the anode is output through the anode tube, while the hydrogen produced at the cathode is output through the cathode tube, and then goes up to the water-gas separator to form gas.