Exploring how specialized coatings on porous transport layers enhance hydrogen electrolysis efficiency and durability through advanced microstructural characterization.
Imagine a world where we can store solar and wind energy for later use, powering our homes and industries without carbon emissions. This vision is at the heart of the hydrogen economy, where hydrogen gas serves as a clean energy carrier. At the forefront of this transition is proton exchange membrane water electrolysis (PEMWE), an advanced technology that converts water into hydrogen and oxygen using renewable electricity.
While the process may sound simple, the internal components of these electrolyzers face extraordinarily harsh conditions—especially on the oxygen-producing side where highly acidic environments and high potentials create a destructive setting that would quickly degrade most materials.
Enter the unsung hero of hydrogen production: porous transport layers (PTLs). These metal components serve as critical intermediaries, simultaneously managing the flow of electrons, water, and gas bubbles. But what keeps these components functioning reliably under such aggressive conditions? The answer lies in specialized coatings—microscopically thin layers of precious metals and innovative materials that protect against corrosion while maintaining electrical conductivity.
Advanced coatings reduce electrical resistance, improving energy conversion
Microscopic layers shield against harsh acidic environments
Extended lifespan and improved performance lower hydrogen production costs
Think of the porous transport layer as both a complex highway system and a protective shield within the electrolyzer. Positioned between the catalyst layer (where water molecules split) and the bipolar plates (which distribute electrical current), this component must perform multiple critical functions simultaneously 1 3 .
Facilitates electron flow from reaction site to current collector
Distributes liquid water and removes gaseous products to prevent blockages
Provides mechanical support to the membrane assembly
Maintains thermal conductivity to manage operating temperatures
The anode side of PEM electrolyzers presents what materials scientists call an "exceptionally harsh environment"—strongly acidic conditions, high electrical potentials, and an oxygen-rich atmosphere that would rapidly degrade most metals 1 .
Excellent corrosion resistance and conductivity, but vulnerable to oxidation
While titanium has become the material of choice for anode PTLs due to its excellent corrosion resistance and conductivity, it faces a hidden vulnerability: beneath a protective surface oxide layer, pure titanium can still slowly oxidize further during operation, forming increasingly thick, non-conductive oxide scales that dramatically increase electrical resistance over time 1 7 .
This is where specialized coatings enter the picture. By applying thin layers of corrosion-resistant materials, researchers create barriers that prevent oxygen from reaching the titanium surface while maintaining electrical conductivity.
Coating technologies for PTLs have evolved significantly, branching into several material families, each with distinct advantages and trade-offs. The coating landscape includes everything from precious metal coatings like platinum and gold to metal oxide coatings such as iridium oxide, and increasingly, bimetallic combinations that harness synergistic effects between materials 2 4 7 .
| Material Type | Examples | Key Advantages | Limitations |
|---|---|---|---|
| Precious Metals | Platinum, Gold | Excellent conductivity, good corrosion resistance | High cost, can dissolve slowly over time |
| Metal Oxides | Iridium Oxide, Titanium Oxide | Outstanding stability in acidic environments | Lower electrical conductivity |
| Bimetallic | IrPt combinations | Enhanced stability through synergistic effects | Complex deposition process |
| Non-Precious | Stainless steel with protective layers | Significant cost savings | Durability challenges in long-term operation |
The benefits of advanced coatings extend beyond mere corrosion protection. By modifying the surface chemistry and topography of PTLs, coatings can significantly influence the electrochemical activity at the critical interface where the PTL meets the catalyst layer.
Research has shown that coated PTLs enhance the triple-phase boundary—the precise region where electrolyte, catalyst, and reactant converge to enable the water-splitting reaction 5 .
This interfacial enhancement occurs through several mechanisms. Coatings can increase the electrochemically active surface area (ECSA), creating more sites for reactions to occur. For instance, one study demonstrated that a platinum-coated 3D-printed electrode achieved an ECSA approximately 50 times greater than its uncoated counterpart 2 .
Recent experimental work exemplifies the innovative approaches scientists are taking to optimize PTL coatings. In a landmark 2025 study published in Scientific Reports, researchers explored the potential of 3D-printed gyroid structures as next-generation PTLs 2 .
Researchers designed four different gyroid structures with varying surface area-to-volume ratios using computer-aided design software.
Using selective laser melting (SLM), they fabricated these designs from SS316 stainless steel powder with micron-level precision.
Using electron-beam physical vapor deposition, the team applied platinum coatings of varying thicknesses (0.20, 0.45, and 1.00 μm).
The experimental results demonstrated the profound impact of combined structural and coating optimization. Among the uncoated samples, the G10 geometry delivered the best performance, achieving a current density of 159.466 mA cm⁻² at 1.9 V. However, the platinum-coated versions of this same structure showed remarkable improvements, with performance scaling directly with coating thickness 2 .
| Electrode Type | Current Density at 1.9 V (mA cm⁻²) | Electrochemically Active Surface Area (cm²) | Corrosion Potential (mV) |
|---|---|---|---|
| Bare G10 | 159.466 | 0.0747 | 248.51 |
| G10-0.20 μm Pt | 342.188 (approx.) | 1.8925 | 437.66 |
| G10-0.45 μm Pt | 463.490 (approx.) | 2.6641 | 457.48 |
| G10-1.00 μm Pt | 584.692 | 3.4355 | 486.17 |
The G10 structure coated with 1.00 μm of platinum achieved approximately 3.7 times higher current density than the uncoated version
The development and optimization of PTL coatings relies on a sophisticated arsenal of research tools and materials. These enable scientists to precisely control coating processes, then meticulously analyze the resulting structures and properties.
The process of evaluating a new PTL coating typically begins with microstructural characterization using techniques like SEM and X-ray CT. SEM provides high-resolution images of the coating morphology, revealing details about grain structure, surface roughness, and potential defects at the nanometer scale.
Meanwhile, X-ray CT constructs detailed three-dimensional maps of the internal pore structure, allowing researchers to quantify parameters like porosity, pore size distribution, tortuosity, and connectivity without destroying the sample 3 9 . This non-destructive analysis is crucial for understanding how coatings might affect mass transport properties.
Following microstructural analysis, researchers proceed to electrochemical testing to evaluate performance under realistic operating conditions. Techniques like cyclic voltammetry measure the electrochemically active surface area, while linear sweep voltammetry assesses current-voltage characteristics.
The development of advanced coatings for porous transport layers represents a fascinating convergence of materials science, electrochemistry, and manufacturing engineering. As we've seen, these microscopic protective layers play an outsized role in determining the efficiency, durability, and cost-effectiveness of hydrogen production systems.
Strategically varying porosity and composition for enhanced performance
3D printing and tape casting enable complex PTL architectures
Machine learning accelerates design and analysis of coating systems
Current research directions suggest several exciting pathways for future development. The emerging trend toward multilayer and graded structures shows particular promise. Rather than applying a single uniform coating, researchers are developing structures with strategically varying porosity and composition.
For instance, triple-layer PTLs with an ultra-high porosity (75%) backing layer demonstrate enhanced oxygen transport while maintaining excellent interfacial contact with the catalyst layer 5 . Similarly, bimetallic and multi-material coatings leverage synergistic effects between different elements to achieve performance characteristics impossible with single materials.
Advanced manufacturing techniques like 3D printing and tape casting enable increasingly complex PTL architectures that were previously impossible to fabricate 2 5 . These methods provide unprecedented control over pore size, shape, and distribution, allowing optimization of both mass transport and electrical contact.
In the broader context, these incremental improvements in coating technology contribute meaningfully to the clean energy transition. By enhancing the efficiency and durability of hydrogen production systems, researchers are helping to lower the cost of green hydrogen, bringing us closer to a sustainable energy future where hydrogen plays a vital role in decarbonizing industry, transportation, and energy storage.