Heterolayered Ni-Fe Hydroxide/Oxide Nanostructures Generated on a Stainless-Steel Substrate for Efficient Alkaline Water Splitting.

Abstract

Highly active and inexpensive anode materials are required for large-scale hydrogen production using alkaline water electrolysis (AWE). Here, heterolayered nanostructures of Ni-Fe hydroxides/oxides with high activity for the oxygen evolution reaction (OER) were synthesized on a 316 stainless steel (SS) substrate through constant current density electrolysis. The thicknesses, morphologies, and compositions of the nanostructures, generated through dealloying and surface oxidation of the SS elements with severe oxygen microbubble evolution, were dependent on the electrolysis time. Nanostructural analyses showed that the heterolayered Ni-Fe hydroxide/oxide nanostructures were generated during the initial stage of electrolysis, growing nanofiberlike Ni-Fe hydroxide layers with increasing electrolysis time of up to 5 h. The prolonged electrolysis resulted in densification of the nanofiber structures. The OER overpotential at 10 mA/cm2 was estimated to be 254 mV at 20 °C, demonstrating better performance than a standard OER catalyst, for example, Ir oxide, and obtaining the value of the Ni-Fe layered double hydroxide (LDH). Furthermore, the OER property surpassed the Ni-Fe LDH catalysts at high current density regions greater than 100 mA/cm2. Moreover, stable electrolysis was achieved for 20 h under conditions similar to that of the practical AWE of 400 mA/cm2 in 20 and 75 °C solution. Therefore, the simple surface modification method could synthesize highly active nanostructures for alkaline water splitting anodes.