Multistep Sulfur Leaching for the Development of a Highly Efficient and Stable NiS_x/Ni(OH)₂/NiOOH Electrocatalyst for Anion Exchange Membrane Water Electrolysis

Nickel (poly)sulfides have been widely studied as anodic catalysts for alkaline water electrolysis owing to their diverse morphologies, high catalytic activities in the oxygen evolution reaction (OER), and low cost. To utilize low-cost and high-efficiency polysulfides with industry-relevant cycling stability, we develop a Ni-rich NiS_x/Ni(OH)₂/NiOOH catalyst derived from NiS₂/Ni₃S₄ nanocubes. Ni-rich NiS_x/Ni(OH)₂/NiOOH shows improved OER catalytic activity (η = 374 mV@50 mA cm^-2) and stability (0.1% voltage increase) after 65 h of a galvanostatic test at 10 mA cm^-2 compared with commercial Ni/NiO and hydrothermally synthesized Ni(OH)₂ (both show η > 460 mV@50 mA cm^-2 along with 4.40 and 1.92% voltage increase, respectively). A water-splitting electrolyzer based on Pt/C||AF1-HNN8-50||NiS_x/Ni(OH)₂/NiOOH exhibits a current density of 1800 mA cm^-2 at 2.0 V and 500 h high-rate stability at 1000 mA cm^-2 with negligible attenuation of only 0.12 mV h^-1. This work provides an understanding of truly stable species, intrinsic active phases of Ni polysulfides, their high-rate stability in a real cell, and sheds light on the development of stable chalcogenide-based anodic electrocatalysts for anion exchange membrane water electrolysis (AEMWE).