ENERGY APPLICATION NOTE
Ultrasonic Spray Coating of Gas Diffusion Electrodes for CO₂ Electrolysis
Deposit copper nanoparticle and Ni-N-C catalyst inks onto Sigracet 28 BC carbon paper as uniform 0.5–2 mg/cm² layers, without plugging a pressure nozzle or flooding the microporous layer. Built around the MicroSpray 120 kHz ultrasonic nozzle, a standalone component that drops into your own lab motion system. A free technical white paper covers materials, process windows, loading math and acceptance criteria.
The application: catalyst layers for CO₂-to-chemicals electrolyzers
Gas diffusion electrodes (GDEs) for CO₂ and CO electrolysis are fabricated much like fuel-cell catalyst layers: a low-viscosity alcohol ink carrying the catalyst and a small ionomer fraction is sprayed onto the microporous layer (MPL) of a carbon-paper GDL. Published work on this exact architecture includes single-atom Ni-N-C catalysts reaching about 95% Faradaic efficiency to CO, Ni–Cu tandem systems producing ethylene, and copper nanoparticle electrodes scaled to 50 cm² stacks at about 80% C2+ Faradaic efficiency.
The fabrication challenge is narrow: Sigracet 28 BC's MPL is hydrophobic (contact angle above 130°) and only about 6 µm rough. Too much wetting drives catalyst into the pores; too-fast drying leaves edge banding and powdery deposits. The coating process, not the chemistry, is usually what limits reproducibility between coupons.
Why a 120 kHz ultrasonic nozzle
Ultrasonic atomization forms droplets from capillary waves on a vibrating tip rather than forcing ink through a fine hydraulic orifice. For nanoparticle suspensions that means low flow, low spray momentum, a narrow droplet-size distribution, and no small pressure orifice to plug, the failure mode that ends airbrush runs. At 120 kHz, the MicroSpray nozzle produces the finest droplet field in our range, suited to low-solids inks on small masked coupons where deposited-mass accuracy and within-area uniformity are the acceptance criteria.
Starting window at 120 kHz, copper nanoparticle ink
- Ink: 5 mg/mL Cu (40–60 nm) in ethanol / 2-propanol, low ionomer fraction
- Flow rate: 0.05–0.20 mL/min
- Substrate temperature: 55–65 °C, MPL side up
- Stand-off: 30–60 mm
- Traverse and overlap: 25–75 mm/s, 50–70% track overlap, alternating orthogonal passes
- Nominal loading: 1.0 mg/cm² from 200 µL over 1 cm², before transfer losses
Working with micron-scale agglomerates or higher solids, typical of Ni-N-C dispersions, start at 60 kHz and move to 120 kHz once the dispersion is stable and submicron. Both frequencies are available across our nozzle family as standalone components: BNC-driven, generator included, no proprietary motion platform required.
Technical white paper
Ultrasonic Spray Fabrication of Copper and Ni-N-C Gas Diffusion Electrodes. Materials, process design, expected outcomes, and supporting literature for Sigracet 28 BC electrodes. The paper defines two spray-deposited electrode architectures, a 40–60 nm copper nanoparticle GDE and an SBA-15-derived Ni-N-C GDE, consolidates the published preparation methods, and establishes conservative ultrasonic spray starting windows.
- Ink formulations aligned to the published patent example (5 mg/mL solids, IPA/Nafion)
- Loading math: converting spray volume and concentration into mg/cm²
- 120 kHz vs 60 kHz nozzle selection by dispersion state
- Development matrix, characterization plan, and acceptance criteria
- 2 → 100 cm² scale-up rules and safety handling notes
Download the white paper (PDF, fully referenced). Free, no sign-up. Prepared September 2026 for an electrode development inquiry from a U.S. Department of Energy national laboratory.
Why ultrasonic spray for GDE catalyst layers
- ✓No fine pressure orifice to plug, the failure mode that ends airbrush runs with nanoparticle inks
- ✓Low spray momentum and many light passes keep catalyst on the MPL surface instead of driving it into the pores
- ✓Narrow droplet distribution for within-area uniformity on masked 1 × 1 and 2 × 2 cm coupons
- ✓Flow rates of 0.05–0.40 mL/min matched to 200–800 µL coupon volumes
- ✓60 kHz tolerates micron-scale agglomerates and higher solids; 120 kHz gives the finest field for low-solids copper inks
- ✓Standalone nozzle, generator and liquid feed that integrate with the XY motion system and fixtures you already have
- ✓Scales from 2 to 100 cm² by holding areal loading, wet-pass density, substrate temperature and track overlap constant
Selected literature
Background on the catalysts, the electrode architecture and scale-up, cited as published. Only the Stryckers paper concerns ultrasonic spray coating itself; the electrode work used air-brush deposition, and none of it was performed on MicroSpray equipment. Published values are literature benchmarks, not guaranteed outcomes.
- Scaling CO Electrolyzers for Carbon-Neutral Chemical Synthesis
W. Teng & Y. Wang
ChemElectroChem 12, e202500043 ·
Open access · no paywall
- Metal-impregnated carbon materials
L. Qi, W. Huang, S. Zhang, Z. Yin, L. An & K. Lalit
U.S. Patent Application Publication US 2024/0295038 A1 ·
- General Synthetic Strategy to Ordered Mesoporous Carbon Catalysts with Single-Atom Metal Sites for Electrochemical CO₂ Reduction
Z. Luo et al.
Small 18, 2107799 ·
Open access · no paywall
- Hybrid Catalyst Coupling Single-Atom Ni and Nanoscale Cu for Efficient CO₂ Electroreduction to Ethylene
Z. Yin et al.
Journal of the American Chemical Society 144, 20931–20938 ·
- Layer formation and morphology of ultrasonic spray coated polystyrene nanoparticle layers
J. Stryckers et al.
Physica Status Solidi A 213, 1441–1446 ·
The wetness-versus-evaporation balance that governs ultrasonically sprayed layers.
Recommended Equipment
Zero Air Nozzle
Pure ultrasonic atomization with no shaping air, the lowest-momentum deposition onto a hydrophobic MPL; available at 48, 60 and 120 kHz
View details →Focused Nozzle
Tight air-shaped pattern at 60 or 120 kHz for masked 1 × 1 cm active areas with a clean boundary
View details →Liquid Delivery (Dosing Pump)
Syringe-pump feed for the 0.05–0.40 mL/min windows, with delivered-volume records for the loading calculation
View details →Common Questions from Research Groups
How do I convert spray volume into catalyst loading?
Loading in mg/cm² equals solids concentration in mg/mL, times delivered volume in mL, times transfer efficiency, divided by coated area in cm². At 5 mg/mL, 200 µL over 1 cm² and 800 µL over 4 cm² both give 1.0 mg/cm² nominal; at a measured 80% transfer efficiency that is 0.8 mg/cm² actual. Record both pump delivery and coupon mass gain. A bulk ink density such as 0.8 g/mL says nothing about catalyst mass, so report solids in mg/mL separately.
Should I use Nafion or an anion-exchange ionomer?
Nafion at roughly 10 wt% relative to catalyst matches the published Ni-N-C recipe and lets you compare directly with the literature. An anion-exchange ionomer may suit an alkaline membrane-electrode assembly better. Treat ionomer chemistry as its own branch of the development matrix and don't confound it with catalyst identity or loading in the first comparison.
Is this the same as a fuel-cell catalyst layer?
The architecture is the same, but the device runs the other way: a CO₂ or CO electrolyzer consumes electricity to make products rather than generating it from a fuel. That changes the ionomer, electrolyte, loading and the validation test, which is Faradaic efficiency, current density, cell voltage and stability reported together.
Why isn't the nickel catalyst called nickel-SBA-15?
SBA-15 is a silica template used during synthesis and etched away before the ink is made. The finished catalyst is an ordered mesoporous nitrogen-doped carbon with isolated nickel sites, so the ink should be identified as Ni-N-C (Ni-NAC), not nickel-incorporated SBA-15. Only fully washed, neutralized and dried catalyst should enter the spray process; the HF etch belongs to a separate, dedicated procedure.
What should the first milestone be?
Not maximum activity. Reproducible deposited mass within about 10% of target, within-area uniformity with a coefficient of variation below 10–15% and no edge banding, adhesion, and preserved GDL gas transport. Once those hold, electrochemical testing shows whether ultrasonic deposition matches or improves on the air-brushed literature controls.
Do I need a reduction step for the copper electrode?
Not by default. Don't add a high-temperature reduction unless it is compatible with the GDL, the ionomer and the copper oxidation state you want. Measure oxidation state by XPS or an equivalent method before and after electrolysis, because it is likely to influence selectivity.
Building a GDE program?
MicroSpray nozzles are standalone components: generator, nozzle, and liquid feed that integrate with the motion system and fixtures you already have. Tell us your catalyst, carrier, and coupon geometry and we'll recommend a frequency and starting window.