Operando Insights on the Degradation Mechanisms of Rhenium‐Doped and Undoped Molybdenum Disulfide Nanocatalysts During Hydrogen Evolution Reaction and Open‐Circuit Conditions

Abstract Molybdenum disulfide (MoS 2) nanostructures are promising catalysts for proton‐exchange‐membrane (PEM) electrolyzers to replace expensive noble metals. Their large‐scale application demands high activity for the hydrogen evolution reaction (HER) as well as robust durability. Doping is commonly applied to enhance the HER activity of MoS 2 ‐based nanocatalysts, but the effect of dopants on the electrochemical and structural stability is yet to be discussed. Herein, operando electrochemical measurements to the structural evolution of the materials down to the nanometric scale are correlated by identical location electron microscopy and spectroscopy. The range of stable operation for MoS 2 nanocatalysts with and without rhenium doping is experimentally defined. The responsible degradation mechanisms at first electrolyte contact, open circuit stabilization, and HER conditions are experimentally identified and confirmed with the calculated Pourbaix diagram of Re‐doped MoS 2 . Doping MoS 2 ‐based nanocatalysts is validated as a promising strategy for continuing the improvement of high‐performance and durable PEM electrolyzers.