Catalyst Deposition Techniques

Catalyst Deposition Techniques – Hydrogen Electrolyzers Coatings – Cheersonic

There are many strategies for depositing catalysts onto membranes or transport layers. These deposition strategies affect the type and nature of active sites, the degree of exposure of active sites, and the electronic and ionic conductivity networks between catalyst particles and between the catalyst and the transport layer or membrane.

The most commonly used technique is to spray a catalyst slurry consisting of catalyst particles, ionomer, water, and an alcohol (e.g., n-propanol or isopropanol, ethanol, etc.) onto a substrate (e.g., a membrane or transport layer). This approach has also been widely used in PEMWE studies. Typically, spraying can be performed using an automated ultrasonic spray system, both of which provide varying degrees of control over deposition uniformity.

Typically, the tuning variables for these spray techniques include slurry composition (including solvent selection and concentration and catalyst/ionomer ratio) and preparation (including sonication and dispersion procedures), deposition parameter settings. Slurry composition needs to be optimized for each catalyst-ionomer pair. The water and alcohol content of the slurry solution affects the surface tension of the slurry, which in turn affects dispersion and drying speed, all of which can significantly affect the microstructure of the catalyst layer. Ionomer content also affects slurry rheology and catalyst dispersion, which has been shown to have a significant impact on catalyst layer microstructure in PEMFCs and PEMWEs. Catalyst agglomeration in the slurry results in a less-than-ideal catalyst surface area, which can affect activity.

Different sonication procedures can help mitigate catalyst and ionomer agglomeration, as demonstrated in PEMFCs, and such procedures must be designed based on the catalyst-ionomer used. The choice of slurry design can have a significant impact on catalyst layer structure; lessons learned from these results can be important transferable to AEMWEs. Although optimizing each variable is challenging and time-consuming, the rich array of tuning variables can provide a high degree of control in catalyst layer thickness and microstructure. These spray coating techniques also have the advantage of being easily scalable, adaptable to existing commercial manufacturing methods (i.e., roll-to-roll coating), and capable of further optimization to meet cost and processing requirements.

Spray coating slurries often require the use of ionomers to adhere the catalyst to the substrate (i.e., membrane or transport layer). Ionomers can also serve as ion conductors, helping OH- to and from the catalyst active sites through the catalyst layer. This is particularly important in pure water operation, where the ionomer phase is the only ionic conductor. However, such ionomers inhibit the electron conduction pathways between catalyst particles and between the catalyst and transport layer, and block catalyst active sites, leading to reduced cell performance. The catalyst also promotes oxidation and loss of the ionomer, leading to instability within the catalyst layer and long-term durability issues.

In the use of a supporting electrolyte, anions in the bulk liquid phase provide additional OH- conductivity, and the ionomer may not be required as an ionic conductor. Therefore, catalyst deposition techniques that do not require the use of ionomers or polymer binders can be used, thereby reducing concerns about ionomer site blocking and suppressed electronic conductivity. If desired, ionomers can be integrated after electrode coating to facilitate operation in pure water feeds. Such “direct” deposition methods that bypass the use of ionomers include electrodeposition, chemical vapor deposition, physical vapor deposition, and plasma deposition, which differ in the way they deposit the active catalyst onto the cell components.

In electrodeposition, a substrate (usually a transport layer) is immersed in an electrolyte containing metal ions of the desired catalyst type, and an electrical potential is applied to deposit the metal on the substrate. These materials can be grown as oxides or oxidized in situ to the desired form. Unlike spraying, electrodeposition avoids slurry rheology issues and variations; instead, the thickness and structure of the catalyst layer can be precisely controlled by varying the concentration and properties of the electrolyte solution as well as the electrodeposition time and potential. This allows the catalyst layer to be formed on a nanoscale, which has the advantage of maximizing the active surface area and minimizing mass transfer losses associated with gas escaping from the catalyst and transport layers. Several recent studies have created three-dimensional structures and enhanced OER and HER performance by increasing the active surface area and tuning morphological properties.

Other strategies include thermochemical deposition, where the catalyst material is grown directly on the transport layer or membrane without the use of an applied potential. Vapor deposition techniques typically involve evaporating a metal precursor into an inert carrier gas (e.g., Ar, N2, or He) and then depositing it on a substrate to form a thin catalyst layer. These vapor deposition techniques include chemical vapor deposition, physical vapor deposition (e.g., sputtering), and plasma deposition.

It is also important to consider the compatibility of different electrode deposition methods with existing manufacturing methods (e.g., doctor blade, slot coating, gravure printing, roll-to-roll coating, etc.).

Hydrogen production by electrolysis of water is the most advantageous method for producing hydrogen. Utrasonic coating systems are ideal for spraying carbon-based catalyst inks onto electrolyte membranes used for hydrogen generation. This technology can improve the stability and conversion efficiency of the diaphragm in the electrolytic water hydrogen production device. Cheersonic has extensive expertise coating proton exchange membrane electrolyzers, creating uniform, effective coatings possible for electrolysis applications.

Cheersonic ultrasonic coating systems are used in a number of electrolysis coating applications. The high uniformity of catalyst layers and even dispersion of suspended particles results in very high efficiency electrolyzer coatings, either single or double sided.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

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