High-temperature fuel cells, particularly solid oxide fuel cells (SOFCs), operate in demanding environments where interconnects play a critical role in ensuring long-term performance and efficiency. Interconnects must exhibit exceptional oxidation resistance, maintain stable electrical contact, and closely match the thermal expansion coefficients of adjacent components to prevent mechanical failure. Conventional metallic alloys, such as ferritic stainless steels, are commonly used due to their cost-effectiveness and manufacturability. However, their susceptibility to oxidation and chromium volatilization at elevated temperatures (600–900°C) necessitates protective coatings. Nanomaterials, including chromium-based coatings and perovskite films, have emerged as promising solutions to enhance interconnect durability and functionality.

Oxidation resistance is a primary concern for metallic interconnects in SOFCs. Unprotected alloys form oxide scales, such as Cr2O3, which increase electrical resistance and may lead to spallation during thermal cycling. Chromium evaporation further degrades cell performance by poisoning cathode materials. Nanocrystalline Cr coatings, deposited via physical vapor deposition or electroplating, provide a dense barrier that slows oxidation kinetics. Studies indicate that Cr-coated alloys exhibit a parabolic oxidation rate constant an order of magnitude lower than uncoated counterparts after 1000 hours at 800°C. The nanoscale grain structure of these coatings promotes rapid diffusion of protective oxides, forming a continuous Cr2O3 layer that minimizes further oxygen ingress. Additionally, doping Cr coatings with reactive elements like yttrium or lanthanum enhances adhesion and reduces scale growth by segregating to grain boundaries and blocking cation diffusion.

Perovskite coatings, with the general formula ABO3 (e.g., LaCrO3, Sr-doped LaMnO3), offer superior stability in oxidizing environments. Their crystalline structure accommodates oxygen non-stoichiometry, enabling them to resist phase changes under thermal stress. Nanostructured perovskite films, fabricated by sol-gel or pulsed laser deposition, achieve full coverage at thicknesses below 1 µm, reducing interfacial resistance. Research demonstrates that La0.8Sr0.2CrO3 coatings reduce the area-specific resistance of interconnects to below 0.01 Ω·cm² after 5000 hours at 750°C, outperforming uncoated alloys by a factor of 10. The nanoscale morphology of these films also mitigates crack propagation, as fine grains deflect microcracks and preserve coating integrity.

Electrical contact stability is another critical parameter for interconnect performance. The growth of resistive oxide scales increases energy losses, while interfacial reactions between coatings and adjacent components can degrade conductivity. Nanomaterials address these challenges through tailored composition and microstructure. For instance, bilayer coatings combining a Cr inner layer with a conductive perovskite outer layer balance oxidation protection and low contact resistance. The Cr layer acts as a diffusion barrier, while the perovskite surface maintains stable electrical properties. Measurements show that such bilayers maintain contact resistance below 20 mΩ·cm² after thermal aging, meeting SOFC stack requirements. Nanocomposite coatings, such as Cr-Cu or Cr-Ag systems, further enhance conductivity by embedding metallic nanoparticles within a Cr matrix. These composites exhibit metallic-like conductivity while retaining oxidation resistance, with Ag-containing coatings demonstrating resistivities as low as 5 µΩ·m at 800°C.

Thermal expansion matching is essential to prevent delamination or warping during SOFC operation. Mismatched coefficients of thermal expansion (CTE) between interconnects and ceramic components induce stresses that can fracture cells or break electrical connections. Nanomaterial coatings can be engineered to bridge this mismatch. For example, LaCrO3 perovskites have CTEs of 9–11 × 10⁻⁶ K⁻¹, closely aligning with ferritic steels (10–12 × 10⁻⁶ K⁻¹) and yttria-stabilized zirconia electrolytes (10.5 × 10⁻⁶ K⁻¹). Graded coatings, where composition varies nanoscale from metal-like to ceramic-like, further reduce thermal stresses by providing a gradual transition in mechanical properties. Finite element modeling confirms that graded LaCrO3 coatings reduce interfacial stresses by 30–40% compared to homogeneous films.

Long-term stability under operational conditions remains a key focus for nanomaterial-coated interconnects. Accelerated aging tests reveal that Cr-perovskite systems maintain performance for over 40,000 hours at 700°C, with minimal increase in resistance or oxide scale thickness. The self-healing capability of certain nanomaterials, such as those doped with mobile cations (e.g., Sr²⁺ in perovskites), further enhances durability by filling microcracks via diffusion. Environmental factors, such as humidity or sulfur contaminants, can degrade coatings, but nanostructured barriers with high-density grain boundaries exhibit improved tolerance to such impurities. For instance, sulfur uptake in nanocrystalline Cr coatings is 50% lower than in conventional coatings due to reduced defect density.

Manufacturing scalability and cost are practical considerations for deploying nanomaterial coatings in commercial SOFCs. Techniques like atmospheric plasma spraying or roll-to-roll deposition enable large-area coating of interconnects at competitive costs. Advances in inkjet printing of perovskite precursors have also reduced material waste and processing time. Comparative analyses indicate that nanomaterial-coated interconnects add less than 5% to total stack costs while extending lifetime by 2–3 times, offering a favorable economic trade-off.

In summary, nanomaterials for high-temperature fuel cell interconnects provide a multifaceted solution to oxidation, electrical resistance, and thermal expansion challenges. Chromium-based and perovskite coatings, optimized at the nanoscale, deliver exceptional performance and longevity under SOFC operating conditions. Continued refinement of coating architectures, coupled with scalable fabrication methods, will further solidify their role in advancing fuel cell technology.