Ultra-low loading and ionomer-free anodes for cost-effective PEM water electrolysis using successive ion layer adsorption and reaction (SILAR)

While iridium catalysts offer a good balance of activity and stability for the oxygen evolution reaction (OER) in acidic media, their high cost, coupled with the limitations of perfluorosulfonic acid (PFSA) membranes and ionomers, hinders large-scale Proton Exchange Membrane (PEM) water electrolysis. This work addresses these challenges by introducing a novel ionomer-free electrode design. Porous titanium felts were engineered with a thin iridium oxide layer using sequential ion layer adsorption and reaction (SILAR). Crucially, surface fluorination via NH 4 F treatment significantly enhanced OER performance, leading to a drastic decrease in onset potential and a 400-fold higher OER current density for the optimal F6.8 composition compared with the least active composition within fluorinated series. The prepared ultra-low iridium loading porous transport electrodes (<0.4 mg cm −2 ) maintained excellent activity while demonstrating superior stability than the IrO 2 porous transport layer reference under intensive potential cycling tests. This approach paves the way for cost-effective and durable PEM water electrolyzers by minimizing noble metal usage and ruling out the expensive and toxic PFSA-based ionomer.