Key Findings
Direct Atomic Layer Deposition (ALD) enables the creation of ionomer-free catalyst layers with significantly lower iridium (Ir) loading than traditional methods. Thermal ALD using O3 as a counter-reactant resulted in an electrode Ir loading of 0.21 mg·cm-2, which is 7 times lower than commercial catalyst-coated membrane anodes while maintaining comparable cell-level performance. This performance was sustained over an accelerated durability test equivalent to 600 hours of intermittent operation. When paired with a low-loading ALD-made cathode, the total platinum group metal loading was reduced to 0.24 mg·cm-2.
Technical Details
The approach utilizes custom-made microporous substrates and the Ir(EtCp)(CHD) precursor. Two ALD processes were evaluated:
- Thermal ALD: Yields mostly metallic Ir/IrOx and achieves the 0.21 mg·cm-2 loading.
- Plasma-enhanced ALD: Further reduces Ir loading to 0.04 mg·cm-2 by tailoring catalyst distribution, although it yields lower-activity IrO2.
Because the process deposits the catalyst directly onto the porous transport layer (PTL), it eliminates the need for ionomer-bearing inks. This makes the anodes compatible with various membrane materials, including anion exchange membranes for CO2 electrolysis to hydrocarbons.
Background & Context
Proton exchange membrane water electrolysis (PEMWE) is critical for renewable energy storage and chemical feedstock production. However, the scarcity of iridium, the standard catalyst for the oxygen evolution reaction (OER), poses a scaling bottleneck. Technological roadmaps suggest reducing Ir loading from typically >1 mg·cm-2 to ≤0.2 mg·cm-2 or ≤0.4 g·kW-1. Traditional wet deposition methods—involving catalyst synthesis, ink formulation, and coating—struggle in the sub-mg·cm-2 range due to catalyst particle size, which causes inhomogeneity and increases overpotential.
Significance & Outlook
By uniting synthesis and deposition into a single step, direct ALD reduces fabrication complexity and eliminates the electrical contact issues associated with non-contiguous layers in traditional wet deposition. This method provides a pathway to high power densities and compatibility with intermittent electricity supplies while mitigating the risks associated with the inelastic supply of platinum group metals.
Source: https://arxiv.org/html/2610.15798v1
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