I. Abstract of the Paper’s Core Research

This study, based on the Optomec M³D dual‑atomization aerosol jet printing system, prepared ceramic‑specific inks for NiO and YSZ. By dynamically regulating the carrier gas flow rates of two channels, the deposition stoichiometry was precisely controlled, enabling in situ fabrication of a compositionally graded anode interlayer on the anode support substrate. Simultaneously, a dense YSZ electrolyte layer was directly printed via aerosol jetting, leading to the assembly of a complete SOFC button cell. Furthermore, a low‑voltage SEM microstructural characterization technique was developed. The key findings are as follows:

Dual-Path Aerosol Dynamic Gradient Deposition Process

Two independent pneumatic atomization units enable real-time mixing of the aerosol phase within a Y‑shaped nozzle, eliminating the need for pre‑mixing the slurry. By calibrating the deposition rate curve using atomization and exhaust flow rates, the three‑layer gradient is precisely controlled: 50NiO/50YSZ near the substrate, 33NiO/67YS in the middle layer, and 17NiO/83YSZ close to the electrolyte. A total of 12 layers are printed, with an interlayer thickness of 35 μm.

The electrochemical performance of the gradient interlayer is significantly enhanced.

Under 850°C test conditions, the uniform‑layer battery achieves a peak power density of 200 mW/cm², while the gradient‑layer battery reaches 235 mW/cm². The gradient architecture mitigates interfacial thermal stress and reduces ohmic losses at the anode–electrolyte interface; moreover, both substrate drying processes have no significant impact on device performance.

Integrated molding of aerosol‑dense YSZ electrolyte

Single‑channel atomization is used to print pure YSZ ink, which, after sintering at 1400°C, forms a dense, pore‑free barrier layer with a thickness of 12 μm—eliminating the need for a vacuum‑coating process.

Innovative Method for Phase-Resolved Characterization Using Low-Voltage SEM

Under conventional 10–20 kV SEM conditions, the backscattering coefficients of Ni and YSZ are similar, making it impossible to distinguish between the two phases. However, when the accelerating voltage is reduced to 1 kV, a clear contrast emerges, allowing for straightforward identification of interconnected versus isolated nickel phases, as well as the ceramic matrix and porosity, without the need for lengthy EDS mapping scans.

High-Repeatability Ceramic Thin-Film Fabrication

The same set of gas‑flow parameters can be used to replicate the gradient‑layered microstructure in batch, with minimal inter‑batch variation in electrochemical performance, demonstrating potential for pilot‑scale production and mass manufacturing.

II. Complete Preparation Process for Gradient Anode Aerosols

Ceramic Ink Formulation: NiO and YSZ powders were milled separately; a solvent–dispersant–binder system was formulated with a solid content of 34.7 wt%, optimized for pneumatic atomization.

Base pre-treatment: Commercial NiO/YSZ tape‑cast anode support green bodies are sintered at 950°C to achieve dimensional stabilization.

Dual-atomization system calibration: Individually test the deposition rates of NiO and YSZ under varying atomization and exhaust flow rates, and establish calibration curves correlating the composition ratio with the gas flow rate.

Gradient Sandwich Printing: The procedure is divided into three stages: switching between two gas flow rates, sequentially adjusting the Ni content, and preparing two sets of control samples—one subjected to room-temperature drying and the other to constant‑temperature drying at 60°C.

Electrolyte Printing: Single-channel, all‑over deposition of pure YSZ ink;

High-temperature sintering: Laminate layer + electrolyte co-fired at 1400°C; LSM cathode applied by hand coating, followed by a second heat treatment at 1200°C.

Electrochemical Testing and Microstructural Characterization: Hydrogen-fueled testing in a tube furnace, with low-voltage SEM imaging of the cross-sectional Ni/YSZ phase distribution.

III. Five Core Process Advantages of Aerosol Jet Printing for SOFC Ceramic Fabrication

Real-time adjustment of component ratios during printing to achieve a continuous thickness gradient.

Unlike conventional pre‑mixed slurries, this system employs dual‑channel atomized‑flow online mixing, enabling programmable switching between any Ni/YSZ ratio to precisely fabricate a graded transition layer.

Maskless digital fabrication, multi-layer integrated synchronous manufacturing

The anode interlayer and electrolyte can be continuously printed on the same equipment, eliminating the need for multiple tape‑casting and alignment steps and significantly reducing the ceramic sintering process.

High material utilization, with ceramic powder loss significantly lower than that of coating.

Precise deposition within a defined area, avoiding full‑area coverage of the substrate, resulting in significant savings of precious metals and ceramic materials.

It exhibits broad process compatibility and can be used to fabricate porous electrodes and dense electrolytes.

By adjusting only the ink and gas‑line parameters, the same equipment can simultaneously fabricate both a porous anode interlayer and a dense, barrier‑type electrolyte.

Processing at ambient temperature and pressure, with no high-temperature damage to the substrate.

Printing is carried out entirely at room temperature, with only a single high-temperature sintering step performed afterward; this prevents premature deformation and cracking of the green body.

IV. Five Core Technological Innovations of This Study

Innovation 1: A Novel In-Situ Gradient Ceramic Printing System Based on Dual-Atomization Aerosol Technology

A dual-channel synchronous mixing process is employed in the SOFC anode interlayer to achieve a continuous compositional gradient structure through the thickness.

Innovation 2: Quantitative Calibration and Gradient Formulation for Deposition Rate Matching

A mathematical model of gas flow rate versus deposition amount for NiO and YSZ was established, enabling precise identification of the process window corresponding to the three-layer gradient.

Innovative 3‑phase resolution characterization method for low‑voltage 1 kV SEM ceramics

It addresses the industry’s pain point that conventional electron microscopes cannot distinguish between nickel and zirconia, enabling rapid observation of conductive network connectivity.

Complete Validation of the Innovative Four-Gradient Sandwich Drag-Reduction Mechanism

The microstructural phase distribution explains how the gradient architecture reduces interfacial ohmic resistance, thereby highlighting the advantages of an electrolyte‑rich YSZ composition.

Innovative 5‑layer aerosol ceramic coating with high reproducibility in mass production

Film thickness and compositional uniformity remain stable across batches, addressing the significant variability in screen-printing thickness.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Cast‑film and screen‑printing techniques can only produce uniform anodes with a fixed composition, lacking a graded transition layer.

✅ Dual-channel real-time aerosol ratio control, three-layer continuous gradient one-step forming, mitigating thermal mismatch stress.

Challenge 2: Conventional electron microscopy struggles to distinguish between the Ni and YSZ phases, making it difficult to elucidate the underlying microstructural mechanisms.

✅ Using a 1 kV low-acceleration-voltage SEM, the two-phase contrast is markedly distinct, enabling intuitive observation of the conductive network.

Challenge 3: Multilayer ceramic manufacturing involves numerous process steps, and repeated coating and sintering can easily lead to delamination and cracking.

✅ Aerosol‑based integrated printing of the sandwich layer and electrolyte, with a single high‑temperature co‑sintering step, simplifying the manufacturing process.

Challenge 4: Vacuum sputtering gradient equipment is expensive to acquire, and small‑batch R&D costs are high.

✅ Atmospheric-pressure, desktop‑scale aerosol equipment can achieve compositional gradients, significantly lowering the R&D barrier.

Challenge 5: Poor consistency in the thickness of screen-printed films, leading to significant variability in battery performance.

✅ Aerosol gas flow rate precisely controls deposition quantity, with minimal power output variation between batches.

VI. Future Diversified Industrial Application Scenarios

1 Planar Solid Oxide Fuel Cell Stack

Batch fabrication of gradient anode interlayers enhances the power output of individual cells and reduces stack losses.

2 Miniature Tubular SOFC Portable Power Generation Device

Conformal aerosol printing on irregular ceramic substrates, enabling low-power portable clean energy devices.

3 High-Temperature Electrolysis for Hydrogen Production: SOEC Electrolyzer

Additive manufacturing of integrated gradient porous oxygen and hydrogen electrodes enhances electrolysis efficiency.

4 Ceramic Sensor Multilayer Composite Functional Film

Gradient-conductive ceramic sensing layer, high-temperature industrial gas detection chip.

5 High-Throughput R&D Platform for Ceramic Devices Laboratory

Rapidly switch ceramic composition gradients to perform high-throughput screening of optimal electrode formulations.

Image and Text Guide

• System Architecture : Optomec M³D® (Maskless Mesoscale Materials Deposition) AJP system employs Dual Pneumatic Atomizer Virtual Impactor (PAVI) Unit , with YSZ and NiO inks loaded separately; the two aerosol streams are combined via a “Y”-shaped connector before entering the deposition head. On-demand material mixing , which can be controlled independently or simultaneously, enabling the deposition of either single-component or composite layers.
• Airflow Design : Dry air is used simultaneously as the atomizing gas, the exhaust gas, and the sheath gas; the sheath gas surrounds the aerosol plume, prevents contact with the nozzle walls, and provides focusing; the virtual impactor maximizes the retention of atomized particles while reducing the flow rate, and a vacuum pump together with a PCM regulates the flow.
• Technological significance Unlike conventional dry‑mixing or ball‑milling approaches for preparing composite materials, a dual atomizer enables on‑demand adjustment of the NiO/YSZ ratio during deposition, thereby providing a means to fabricate functionally graded layers with compositional gradients along the thickness direction.

• Base : The commercial laminated green tape, approximately 700 μm thick and composed of 55 wt% NiO/45 wt% YSZ, is sintered at 950 °C to serve as the anode support.
• Type 1 (Non-Gradient) : A total of 12 printing passes, all with a uniform composition of 50/50 wt% NiO/YSZ.
• Type 2 (Functionally Graded) : Along the z-axis, a three-stage gradient is applied—near the anode support, 50/50 for 4 passes → 33/67 for 4 passes → near the electrolyte, 17/83 (NiO/YSZ wt%) for 4 passes, totaling 12 passes.
• Drying process : Type 2 employs two drying procedures, DP-1 (air-drying at room temperature) and DP-2 (drying on a heated plate at 60 °C), as controls.

• Trend : At a fixed atomization gas flow rate (Fat = 1000/1250/1500 sccm) and a sheath gas flow rate of 3000 sccm, the deposition rates of both NiO and YSZ decrease with increasing exhaust flow rate (Fex) according to a polynomial relationship; however, this polynomial trend does not hold in the low-exhaust-flow regime.
• Comparison : All Fat‑based YSZ deposition rates exceed those of NiO—maximum wet‑weight deposition rates are approximately 15 mg/min for YSZ and 12 mg/min for NiO; this is attributed to the larger particle size of NiO and its higher ink viscosity (BET surface areas: NiO, 4.53 m²/g; YSZ, 6.98 m²/g).
• Purpose : The gas flow conditions for on‑line mixing of two components, as selected by the deposition rate matrix, are used to control the NiO/YSZ composite ratio during flight.
• Quality loss : After drying, the wet weight loss ranges from 15% to 28%, increasing with rising mist flow rate (the difference between atomizing gas and exhaust flow), likely due to the virtual impactor removing some particles as the flow rate decreases.

• 50/50 : NiO 1000 sccm/760 sccm → 6 mg/min; YSZ 1000/940 → 6 mg/min.
• 33.3/66.7 : NiO 1000/840 → 4 mg/min; YSZ 1000/860 → 8 mg/min.
• 16.7/83.3 : NiO 1000/900 → 2 mg/min; YSZ 1250/1160 → 10 mg/min.
• 0/100 : YSZ only, 1250/1000 → 12 mg/min.
• Key points : As the YSZ content increases, the deposition rate rises from 6 to 12 mg/min, while that of NiO decreases from 6 to 0—achieved by precisely controlling the mist and exhaust flow rates to obtain the desired compositional gradient (in this study, the mist flow rate did not exceed 250 sccm).

• Open-circuit voltage Both battery groups stabilized at approximately 1.20 V.
• Performance Comparison : The maximum power density of the functionally graded anode interlayer (curves b and c) is approximately   235 mW/cm² (≈ 500 mA/cm²), which is superior to that of the non‑gradient interlayer (curve a)   200 mW/cm² 。
• Drying process : Curves b and c correspond to the DP-1 (room temperature) and DP-2 (60 °C) drying protocols, respectively, with no significant difference in performance between the two.
• Reproducibility : The results of sets 1 and 2 are highly consistent, demonstrating the high reproducibility of the AJP printing method.

• (a)   1 keV low-voltage SEM (SEI, ETD positive bias +300 V): Bright white areas correspond to Percolating nickel (percolating Ni) , the dark area highlighted by the black box is Non-seepage nickel Moreover, the two phases are clearly distinguished from YSZ and the pores—something that conventional 10–20 kV imaging cannot achieve.
• (b)   Qualitative X-ray microanalysis phase identification diagram: Green = Ni, Blue = YSZ , a black highlight box indicates the non‑percolating Ni location; it is used to confirm the phase composition in secondary electron images.
• Key Points for Sample Preparation : Prior to imaging, plasma cleaning is required to prevent electron-beam–induced carbon deposition, which can significantly reduce interphase contrast; the sample is not coated with a conductive layer.

• Voltage sequence : The primary beam energy is stepped down from 30 keV to 20, 10, 5, and 1 keV (negative‑bias ETD acquisition of pure BSE images), with an additional 1‑keV positive‑bias ETD reference image.
• Key Conclusions : Except for the two images at 1 keV, Z-contrast (atomic-number contrast) essentially vanishes at all other voltages; only at  1 keV  Only when the backscattering coefficients of Ni and YSZ diverge does a distinct interphase contrast emerge—thus confirming the low‑voltage BSE contrast mechanism proposed by Thydén et al.
• Mechanism : At low voltages, the backscattering coefficient η is strongly dependent on the accelerating voltage (η = E^mC); the η values for Ni and YSZ differ, enabling differentiation of the two phases in BSE/SE images; a carbon coating eliminates this contrast.

• Layered structure : The dense YSZ electrolyte is approximately 12 μm thick, and the anode interlayer is about 35 μm thick (both cells are identical); an enlarged view of the interlayer region at the top.
• Type 1 : In the interlayer, Ni and YSZ are uniformly distributed (50/50); Type 2 : Near the electrolyte region, a compositional gradient of 17/83 → 33/67 → 50/50 (NiO/YSZ) is observed, with the YSZ volume fraction increasing markedly toward the electrolyte side.
• Performance Correlation : The increase in YSZ and the decrease in Ni near the electrolyte (below the percolation threshold of approximately 30 vol%) render this region predominantly ionically conductive, thereby reducing ohmic resistance and enhancing the electrochemical performance of the gradient battery; moreover, the reproducibility of layer thickness and microstructure is also confirmed.