Double-layer heterostructure in situ grown from stainless steel substrate for overall water splitting

Developing free-standing electrode based on cost-effective industrial substrate materials is a promising way for efficient water splitting applications. The common stainless steel (S S) consisting of catalytic active transition metal components (e.g. Ni, Fe, etc.) has the potential to be an ideal substrate to prepare free-standing electrodes. In this work, a facile hydrothermal oxidization treatment was proposed to oxidize three types of SS substrates (i.e. 304, 316L and 310S) to prepare efficient free-standing electrodes for water electrolysis. Compared with the 316L and 310S, the relatively low content of Mo and Cr in 304 SS make it easier to be oxidized by alkaline hydrogen peroxide to produce a well-confined double layer heterostructured catalytic film with Fe-rich microcrystals at the top and Ni-rich nanocrystals at the bottom. Consequently, the as obtained 304-SSO27 sample exhibits low overpotentials of 136 mV and 285 mV at the current density of 10 mA·cm−2 towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Moreover, the bifunctional 304-SS-O27 electrode displays a low cell voltage of 1.67 V to realize overall water splitting at 10 mA·cm−2. These results provide a convincing demonstration of fabricating cost-effective and frees-standing electrodes via a facile one step hydrothermal oxidization for water splitting applications.