Atomic layer deposition (ALD) has emerged as a critical technique for fabricating nanoscale catalyst coatings in fuel cells, offering unparalleled precision in thickness control and uniformity. This method is particularly advantageous for depositing platinum (Pt) and non-precious metal catalysts, where atomic-level accuracy can significantly enhance catalytic activity and durability. The self-limiting, sequential surface reactions inherent to ALD enable the deposition of conformal and pinhole-free films, even on high-aspect-ratio substrates, making it ideal for optimizing fuel cell electrodes.

The application of ALD for Pt catalysts involves alternating exposures to Pt precursor gases and reducing agents, such as oxygen or hydrogen, at controlled temperatures. Each cycle deposits a sub-monolayer of Pt, allowing precise tuning of particle size and distribution. Studies have demonstrated that ALD-synthesized Pt nanoparticles with diameters below 3 nm exhibit improved mass activity for the oxygen reduction reaction (ORR) compared to conventional methods. The ability to control Pt loading at the atomic level minimizes material waste while maximizing catalytic efficiency, addressing one of the key cost barriers in fuel cell commercialization.

For non-precious metal catalysts, ALD offers a pathway to engineer transition metal oxides, nitrides, and carbides with tailored electronic and structural properties. For instance, ALD of cobalt oxide (CoOx) or iron nitride (FeNx) on carbon supports can create active sites that mimic Pt-like behavior for ORR. The layer-by-layer approach ensures uniform coverage and prevents agglomeration, which is a common challenge in nanoparticle synthesis. By carefully selecting precursors and process parameters, ALD can produce non-precious catalysts with competitive performance and enhanced stability under fuel cell operating conditions.

Thickness control is a hallmark of ALD, with deposition rates typically ranging from 0.1 to 0.3 nm per cycle. This precision allows for the optimization of catalyst layers to balance activity and transport limitations. For example, a Pt ALD film with a thickness of 2 nm may provide optimal surface area and conductivity, while thicker films could lead to increased resistance without proportional gains in activity. Similarly, for non-precious catalysts, ALD enables the creation of ultrathin coatings that expose a maximum number of active sites while minimizing bulk material usage.

Uniformity across large-area substrates is another advantage of ALD, critical for scaling up fuel cell production. Unlike physical vapor deposition or wet-chemical methods, ALD produces consistent film properties regardless of substrate geometry. This is particularly important for porous fuel cell electrodes, where conventional techniques often result in uneven coating depths. ALD’s conformality ensures that even the interior surfaces of porous structures receive uniform catalyst layers, enhancing overall electrode performance.

Scalability remains a consideration for ALD in fuel cell manufacturing. While batch-type ALD systems are well-established for research-scale applications, transitioning to roll-to-roll or spatial ALD configurations is necessary for high-throughput production. Recent advancements in multi-wafer and continuous-flow ALD reactors have demonstrated deposition rates compatible with industrial requirements. However, the cost of precursors and the need for precise environmental controls can still pose economic challenges, particularly for Pt-based systems.

Cost reduction strategies for ALD include the development of cheaper precursors and the optimization of cycle times. For non-precious metal catalysts, ALD can offset costs by minimizing material usage and improving catalyst longevity. The ability to deposit atomically precise layers reduces the need for excess material, and the enhanced durability of ALD coatings can extend the operational lifespan of fuel cells. When combined with substrate engineering and hybrid deposition approaches, ALD presents a viable route to lowering overall manufacturing expenses.

The unique capabilities of ALD also enable the fabrication of advanced catalyst architectures, such as core-shell nanoparticles and alloyed surfaces. For example, Pt shells deposited via ALD on non-precious metal cores can achieve high activity with reduced Pt content. Similarly, ALD can create gradient or layered compositions that optimize interfacial properties for specific reactions. These designs are difficult to achieve with other deposition techniques but are readily accessible through ALD’s sequential processing.

In summary, atomic layer deposition provides a powerful tool for engineering nanoscale catalyst coatings in fuel cells, with exceptional control over thickness, composition, and uniformity. Its application to both Pt and non-precious metal catalysts offers pathways to enhance performance while addressing cost and scalability challenges. As ALD technology continues to advance, its role in fuel cell development is expected to grow, enabling more efficient and economically viable energy conversion systems. The precision and versatility of ALD make it a cornerstone technique for next-generation catalyst design, with implications for both research and industrial applications.