Ultrasonic Spray Coating for High-Efficiency Catalyst Layers: Parameter Mapping and Morphology Control for PEM Water Electrolysis

Polymer electrolyte membrane water electrolysis (PEMWE) places demanding requirements on catalyst-layer architecture. The oxygen evolution reaction (OER) occurs under strongly oxidizing conditions, and the anode catalyst layer must maintain electrical contact, ionic access, water transport and oxygen release while remaining mechanically stable. Iridium-based catalysts are widely studied for this role, making efficient use of the precious metal an important research objective. Ultrasonic Spray Coating for High-Efficiency Catalyst Layers offers a way to investigate controlled deposition of Ir-based inks, provided that process variables are mapped against morphology and cell response.

1. Translate the electrode requirement into coating targets

Before selecting spray settings, define the electrode configuration: catalyst-coated membrane, catalyst-coated porous transport layer or another architecture. The substrate controls wetting, mechanical support and the direction of transport. Define target catalyst loading, active area, allowable thickness range, coverage requirements and post-treatment. Distinguish the nominal loading calculated from ink solids and delivered volume from the loading actually retained on the substrate. Transfer loss, overspray and material remaining in the feed path can make these values different.

2. Understand the main ultrasonic spray variables

Atomization and liquid delivery

Nozzle drive conditions influence the formation of droplets, while liquid feed rate determines how much ink is presented to the atomizing surface. These variables interact with viscosity, surface tension, solids content and solvent volatility. For Ir oxide or supported Ir catalyst inks, particle morphology and dispersion state can be especially important. A stable liquid feed does not guarantee stable droplet formation if the ink changes during the run. Monitor the nozzle and ink condition throughout a coating sequence.

Motion, overlap and stand-off distance

Traverse speed determines exposure time along a path. Track spacing and overlap determine whether adjacent paths merge into a uniform band or produce visible ridges and gaps. Nozzle-to-substrate distance affects spray footprint and droplet transport, but the best distance depends on the spray plume and substrate geometry. Establish these settings with a repeatable test pattern, then measure the dry coating rather than relying only on the wet appearance.

3. Build a parameter map instead of tuning by intuition

A structured parameter map separates primary effects from interactions. A first screening experiment can vary feed rate, traverse speed, path spacing and substrate temperature while holding ink composition and nozzle configuration constant. A second experiment can refine the useful region and examine interactions such as feed rate by travel speed or temperature by pass count. Use a design of experiments approach when practical, with randomized run order and replicate center points to detect drift.

For every coupon, record the actual spray path, number of passes, coating direction, pause between passes and drying sequence. Include a control coupon from a baseline recipe. A process map is meaningful only when the ink batch, substrate lot and measurement procedure are controlled. If one factor changes between trials, annotate it explicitly so that apparent parameter trends are not overinterpreted.

4. Morphology: thickness, pores and surface uniformity

Layer thickness affects catalyst inventory and transport distances. A thick layer may increase the amount of catalyst but can also increase ionic and gas-transport resistance or complicate oxygen removal. A very thin layer may reduce transport distance yet risk incomplete coverage, local discontinuities or insufficient catalyst inventory. The appropriate thickness is architecture- and operating-condition-dependent, so it should be optimized alongside loading and porosity.

Pore architecture influences water access to active sites and oxygen bubble release. Drying rate, solids content, particle agglomeration and ionomer distribution can all affect the resulting pore network. Surface uniformity is important, but a smooth top surface is not a complete description of the internal structure. Cross-sectional imaging, porosity measurements where suitable, and electrochemical testing should be used together. Mercury intrusion porosimetry may be unsuitable for some fragile or reactive structures and should be selected only after assessing sample compatibility and method limitations.

5. Relate morphology to polarization and durability

Cell polarization reflects multiple contributions, including kinetic, ohmic and mass-transport losses. A coating change that appears favorable in one region of the polarization curve may not improve the full operating range. Control membrane, porous transport layer, compression, water feed, temperature and test protocol when comparing catalyst layers. Report iR correction practices and the basis for calculating current density. Replicate cells are needed where assembly variability is significant.

Durability should be evaluated with a defined protocol rather than inferred from initial activity. Potential cycling, steady operation or other stress procedures probe different degradation pathways. Monitor voltage evolution, high-frequency resistance where available, catalyst-layer morphology and changes in contact or interfacial resistance. An apparent voltage change may reflect hardware, water-management or membrane effects rather than catalyst-layer degradation alone.

6. Practical considerations for Ir-based inks

Ir-based powders differ in oxidation state, support, particle morphology and surface chemistry. These differences influence dispersion, wetting and the balance between catalyst and binder or ionomer. Record the exact catalyst identity and lot, and avoid transferring an ink recipe across materials without checking compatibility. Solvent selection should consider membrane and substrate tolerance as well as dispersion stability. Use appropriate handling and waste procedures for precious-metal-containing suspensions.

When the anode is coated directly on a membrane, solvent exposure and thermal history require special attention. Membrane swelling, dimensional change or wrinkling can compromise layer integrity and later assembly. A transfer route may be preferable for some formulations or membranes. Compare both routes using the same loading and characterization methods before selecting a production approach.

7. A repeatable PEMWE development workflow

First, characterize the ink and substrate. Second, verify the atomization footprint and coating continuity on a witness material. Third, map a controlled set of spray variables. Fourth, measure retained loading, thickness distribution and morphology. Fifth, assemble cells using controlled compression and water-management procedures. Finally, evaluate polarization and durability using a documented protocol. Keep failed samples and images when possible: they help identify the boundary of the process window and prevent repeated troubleshooting.

For equipment discussions, review Cheersonic’s ultrasonic coating equipment solutions and ultrasonic atomizing coating resources. A sample coating trial using the actual ink and substrate is a practical way to assess process compatibility.

Conclusion

PEMWE catalyst-layer optimization requires a direct link between spray parameters, internal morphology and cell-level behavior. Ultrasonic spraying can support systematic experimentation, but no single parameter setting is universally optimal for Ir-based OER layers. A reproducible parameter map, suitable characterization and controlled electrochemical testing provide the evidence needed to select a coating window. Qualified manufacturers, R&D teams and production engineers are invited to contact Cheersonic to discuss their coating project and arrange a sample coating test. Email: market2@cheersonic.com.