Stainless Steel Activation for Efficient Alkaline Oxygen Evolution in Advanced Electrolyzers

Abstract

Designing robust and cost‐effective electrocatalysts for efficient alkaline oxygen evolution reaction (OER) is of great significance in the field of water electrolysis. In this study, we introduce an electrochemical strategy to activate stainless steel (SS) electrodes for efficient OER. By cycling the SS electrode within a potential window that encompasses the Fe(II)↔Fe(III) process, we can greatly enhance its OER activity compared to using a potential window that excludes this redox reaction, decreasing the overpotential at current density of 100 mA cm−2 by 40 mV. Electrochemical characterization, Inductively Coupled Plasma – Optical Emission Spectroscopy and operando Raman measurements demonstrated that the Fe leaching at the SS surface can be accelerated through a Fe → γ‐Fe2O3 → Fe3O4 or FeO → Fe2+ (aq.) conversion process, leading to the sustained exposure of Cr and Ni species. While Cr leaching occurs during its oxidation process, Ni species display higher resistance to leaching and gradually accumulate on the SS surface in the form of OER‐active Fe‐incorporated NiOOH species. Furthermore, a potential‐pulse strategy was also introduced to regenerate the OER‐activity of 316‐type SS for stable OER, both in the three‐electrode configuration (without performance decay after 300 h at 350 mA cm−2) and in an alkaline water electrolyzer (ca. 30 mV cell voltage increase after accelerated stress test‐AST). The AST‐stabilized cell can still reach 1000 mA cm−2 and 4000 mA cm−2 at cell voltages of 1.69 V and 2.1 V, which makes it competitive with state‐of‐the‐art electrolyzers based on ion‐exchange‐membranes using Ir‐based anodes.This article is protected by copyright. All rights reserved

Tuning Stainless Steel Oxide Layers through Potential Cycling─AEM Water Electrolysis Free of Critical Raw Materials

“…The gradual cathodic displacement of Ni redox peaks is a key difference separating SS oxide layers from traditional NiFe oxide layers, wherein anodic displacements are noted to signify the inclusion of Fe in the more stable Ni oxides. , Fe is already plentiful in SS, rendering the default potential position of Ni redox peaks significantly shifted to anodic potentials relative to the peak positions noted for pure nickel­(II)­hydroxide . As such, the origin of the cathodic displacement is likely the increase in Ni content in the surface oxide layer through solid-state diffusion.…”

“… 16 , 17 Fe is already plentiful in SS, rendering the default potential position of Ni redox peaks significantly shifted to anodic potentials relative to the peak positions noted for pure nickel(II)hydroxide. 28 As such, the origin of the cathodic displacement is likely the increase in Ni content in the surface oxide layer through solid-state diffusion.…”

“…The use of potential cycling as a general method for modifying an electrode surface has increased in recent years. ,,,− Stainless steel is an inexpensive, ubiquitous material with a very low concentration of critical raw materials (CRMs) which remains stable in alkaline electrolytes. These three facets significantly amplify its potential as an OER electrode if a fair catalytic activity is achieved and sustained over time.…”