Ultrasonic Spraying of RuO₂ Catalyst

Ultrasonic Spraying of RuO₂ Catalyst – Ultrasonic Coating – Cheersonic

Ultrasonic spraying technology is currently a key process for the preparation of membrane electrode assemblies (MEAs) for RuO₂ catalysts (especially for proton exchange membrane water electrolysis PEMWE). Through precise atomization and deposition, it solves the pain points of traditional processes while improving the activity and stability of RuO₂ catalysts. The following is a detailed explanation from four aspects: technical principles, core advantages, application examples, and performance:

Technical Principles of Ultrasonic Spraying of RuO₂ Catalysts

Ultrasonic spraying technology achieves precise coating of RuO₂ catalysts through a two-step “atomization-deposition” method. The core is to utilize high-frequency ultrasonic vibration to overcome the limitations of traditional spraying, adapting to the characteristics of RuO₂ (a precious metal oxide requiring efficient utilization and uniform distribution):

1. Atomization Stage

The RuO₂ catalyst slurry (containing RuO₂ particles, Nafion ionomer, and solvents such as isopropanol/water) is fed into the ultrasonic atomizing nozzle through a feeding system. The piezoelectric ceramic transducer inside the nozzle generates mechanical vibration under the excitation of a 10-180 kHz high-frequency electrical signal, overcoming the surface tension of the slurry and breaking it into uniform micro-droplets of 1-50 μm, forming a stable “atomizing cone.” – For modified RuO₂ (such as Ta/B-RuO₂, F-RuO₂/FC), ultrasonic dispersion (“ultrasonic dispersion of Ta/B-RuO₂”, “ultrasonic adsorption preparation of F-RuO₂/FC”) is required to ensure uniform particle dispersion before proceeding to the spraying process.

Ultrasonic Spraying of RuO₂ Catalyst - Ultrasonic Coating

2. Deposition Stage

Atomized RuO₂ droplets are sprayed at a controllable speed onto the substrate (such as Nafion membrane, titanium substrate) under the drive of a carrier gas (compressed air or nitrogen). The droplets spread uniformly on the substrate surface, and the solvent evaporates rapidly to form a continuous, pinhole-free RuO₂ catalyst layer, ultimately constructing the anodic catalyst layer of the PEMWE membrane electrode.

Core Advantages of Ultrasonic Spraying for RuO₂ Catalysts

RuO₂, as a precious metal oxide, presents challenges related to the trade-off between activity and stability, as well as high cost. Ultrasonic spraying technology specifically addresses these pain points, with core advantages summarized in four points:

  • Coating Uniformity: Narrow droplet size distribution (deviation ≤ ±5%), combined with precise control via robotic arms/XY platforms, eliminates edge buildup and pinhole defects; ensures uniform exposure of RuO₂ active sites (such as coordinated unsaturated Ru⁴⁺/Ru⁵⁺), avoiding localized insufficient activity or agglomeration.
  • Material Utilization: Strong atomized droplet directionality eliminates overspray waste, achieving a utilization rate of 80%-95% (compared to only 30%-50% with traditional air spraying); Ru is a precious metal (its price is approximately 1/10 that of Ir, but cost control is still necessary), significantly reducing RuO₂ loss and lowering costs.
  • Thickness Controllability: By adjusting atomization power, feed rate, and nozzle movement speed, coating thickness can be adjusted from 100 nm (nanometer level) to 50 nm. Precise μm (micrometer level) control; adaptable to PEMWE membrane electrode requirements: RuO₂ loading needs to be controlled at 1-3 mg/cm², and ultrasonic spraying can precisely match the coating thickness (5-20 μm, meeting PEMWE catalyst layer requirements) corresponding to this loading.
  • Substrate compatibility: Non-contact spraying, no high-pressure airflow impact, does not damage fragile substrates such as Nafion membranes and titanium substrates; protects the integrity of the proton conduction channel (Nafion membrane) of the PEMWE membrane electrode, avoiding physical damage to the substrate caused by traditional coating methods.

Typical Application Examples of Ultrasonic Spraying in RuO₂ Catalysts

Currently, ultrasonic spraying is widely used in the preparation of membrane electrodes for pure RuO₂ and modified RuO₂ (such as Ta/B-RuO₂, F-RuO₂/FC). Specific application scenarios and effects are as follows:

1. Preparation of membrane electrodes for modified RuO₂ catalysts

  • Ta/B-RuO₂ catalyst: The Ta/B-RuO₂ catalyst (2… (mg/cm²) was ultrasonically dispersed in a “5 wt% Nafion + isopropanol + water” system, and then ultrasonically sprayed onto the front side of a Nafion N117 membrane (183 μm) to form a catalytic layer (CCM). A Pt/C cathode was also sprayed. This electrode ultimately outputs a current density of 1 A/cm² at 1.6 V and operates stably for 120 h at 0.2 A/cm², overcoming the “activity-stability trade-off”.
  • F-RuO₂/FC catalyst: F-RuO₂/FC powder was prepared via “ultrasonic adsorption + heat treatment” and then ultrasonically sprayed onto the anode of a PEMWE membrane electrode. This catalyst exhibited an overpotential of only 192 mV at 10 mA/cm² in 0.5 M H₂SO₄ and operated stably for 1440 h (60 days) at 100-1000 mA/cm². The membrane electrode achieved a current density of 500 mA/cm² at 1.58 V and remained stable for 2 months.

2. Industrial Preparation of Pure RuO₂ Catalysts

  • Addressing the issue of pure RuO₂ agglomeration (the original webpage mentioned that nano-RuO₂ agglomeration reduces the active area), ultrasonic spraying, through “first ultrasonic dispersion (breaking up agglomerated particles) + then precise spraying,” ensures that RuO₂ particles are uniformly distributed on the film surface, increasing the active area by more than 30%; simultaneously, combined with the uniform mixing of Nafion ionomers, continuous proton/electron/gas transport channels are constructed.

Ultrasonic Spraying vs. Traditional Processes: Data on RuO₂ Catalyst Performance Improvement

Compared to traditional coating methods (dagger coating, screen printing, air spraying), ultrasonic spraying technology significantly improves the performance of the RuO₂ catalyst membrane electrode assembly (MEA):

1. Catalytic Efficiency: The hydrogen evolution current density of the RuO₂ MEA using ultrasonic spraying is 40% higher than that of the traditional process, resulting in a significantly faster hydrogen production rate; modified RuO₂ (such as Ta/B-RuO₂) has a lower overpotential (170 mV overpotential at 10 mA/cm², far superior to the approximately 230 mV of commercial RuO₂).

2. Material Costs: The RuO₂ material waste rate is reduced from 30%-40% in the traditional process to less than 10%. Based on the cost of Ru precious metals, the material cost per batch of MEA is reduced by 25%-30%. 3. Stability: Due to its uniform structure, the RuO₂ catalyst layer coated by ultrasonic spraying has a reduced lattice oxygen loss rate, extending the lifespan of pure RuO₂ from “tens to hundreds of hours” to “thousands of hours” for modified RuO₂ (such as Ru-Ir), and even reaching 1440 hours for F-RuO₂/FC.

Ultrasonic Spraying of RuO₂ Catalyst - Ultrasonic Coating

Supplement: Extended Applications of Ultrasonic Technology in RuO₂

Preparation Besides spraying, ultrasonic technology is also used for the preparation of RuO₂ nanosheet precursors—ultrasonic exfoliation: RuO₂ bulk is exfoliated into single-layer nanosheets using probe-type ultrasound (1-7 minutes). This process is highly efficient (50% increase in exfoliation amount in 15 minutes) and produces high-quality nanosheets (high conductivity, low resistance). It can serve as a raw material for high-performance RuO₂ catalysts and can be further combined with ultrasonic spraying to form an optimized “ultrasonic exfoliation-ultrasonic spraying” process.

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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