Introduction to the preparation process of PEM and AEM membrane electrodes

Membrane electrode (MEA) is a key component of AEM electrolyzer, PEM electrolyzer and hydrogen fuel cell. The membrane electrode composition of the three products is similar, generally including proton exchange membrane/anion exchange membrane, catalyst layer and gas diffusion layer; the gas diffusion layer of PEM electrolyzer is titanium mesh, while that of AEM electrolyzer is replaced by nickel mesh

Schematic diagram of membrane electrode structure

I. Preparation process of MEA core components

1. Proton Exchange Membrane

Membrane electrodes used in fuel cells and PEM electrolyzers generally use proton exchange membranes, which are mainly made of perfluorosulfonic acid resin membranes. The production process of perfluorosulfonic acid resin membranes with reinforcement layers is similar. The main difference between the products is the thickness. The proton exchange membrane of fuel cells is thinner than that of PEM electrolyzers.

The preparation process of proton exchange membranes is generally to use a double die head to make a coating on the base membrane first, attach a reinforcement layer, and then apply a layer of resin solution, dry it, and then perform subsequent treatment.

Preparation process of proton exchange membrane

2. Anion exchange membrane

The preparation process of anion membrane without reinforcement layer is relatively simple. In addition to the traditional casting method, it can also be prepared by coating, that is, directly coating on the base membrane and leveling it and then drying it.

Preparation process of anion exchange membrane

II. MEA preparation process

Currently, the membrane electrode generally adopts the CCM process, that is, the catalyst slurry is directly deposited on the proton exchange membrane/anion exchange membrane. This process route improves the utilization rate and durability of the catalyst to a certain extent. It is the membrane electrode process route with a high degree of commercialization and has achieved mass production.

The first step in the preparation process of membrane electrode is pulping. This step is similar for the three products. After pulping, coating, five-in-one, hot pressing, airtightness detection and other processes are carried out. Since both proton exchange membrane and anion membrane have the characteristics of swelling, the coating generally uses the transfer process, that is, the slurry is first applied to the transfer membrane, and then transferred to the proton exchange membrane or anion exchange membrane.

Slurry preparation process

PEM electrolyzer membrane electrode preparation CCM process

AEM electrolyzer membrane electrode preparation CCM process

In the AEM membrane electrode preparation process, the cathode and anode catalyst layers are slurries made of catalysts, hydrophilic materials/hydrophobic materials and ionomers. The catalysts include precious metal PGMs and non-precious metal catalysts, such as molybdenum disulfide for the cathode and nickel-iron layered double hydroxide for the anode.

In addition, there is another preparation process for membrane electrodes for AEM electrolyzers, which is the CCS method, in which the catalyst is deposited on a substrate such as a gas diffusion layer or a porous transport layer.

The main process can be expressed as follows: at the cathode end, the catalyst coating is deposited on the carbon cloth, and at the anode end, the catalyst coating can be deposited on the nickel foam, which can be applied by spraying or slit extrusion; after the coating is applied, the carbon cloth, nickel foam and anion membrane are stacked together by dispensing to obtain a membrane electrode.

The CCS method is easy to control the manufacturing process and forms a solid and stable catalyst layer; the CCM method improves the contact between the catalyst layer and the membrane interface and improves the ion conductivity, but the catalyst layer structure is unstable, which affects the stability of the ion membrane, and the membrane surface may change during the catalyst deposition process. The actual production process can select a suitable process route according to the application scenario.