Nanoporous Ti layer encapsulating stainless steel for alkaline water electrolysis: superior electrocatalytic and structural stability under industrially relevant conditions

Abstract

Alkaline water electrolysis is a promising approach for producing green hydrogen via renewable energy. Among the various catalyst candidates for the sluggish oxygen evolution reaction (OER), stainless steels feature excellent activity that is comparable to that of noble metals. However, these alloys are often thermodynamically unstable during electrolysis under industrially relevant conditions and suffer rapid corrosion, which precludes their application in commercial electrolyzers. In this work, we first revealed the structure of the catalytic layer on the surface of a spent 316L stainless steel electrode. It features a sandwich-like nanostructure comprising an Fe-doped NiOOH active layer on top with gradient porosity. A 10 nm thick dense layer in the middle is enriched with both Ni and Fe, which is prone to delamination from the steel matrix, causing rapid weight loss during corrosion. This fundamental understanding inspired us to design and fabricate a protective layer that strongly anchored the vulnerable Ni-rich layer on the surface. Using pulsed bias arc ion plating and sequential anodic oxidation in acid, we created an ∼300 nm thick nanoporous Ti layer that prevented delamination of the Ni-rich active layer from the steel matrix. The electrode obtained by this method exhibited excellent stability, maintaining high activity even after continuous electrolysis for 900 hours at a current density of 500 mA cm⁻² without suffering weight loss. This study highlights the importance of designing and fabricating OER electrodes with excellent electrocatalytic and structural stability under industrially relevant conditions, offering bona fide solutions for industrial water electrolysis applications.