  MoS2 nanostructures are promising catalysts for proton-exchange-membrane
(PEM) electrolyzers to replace expensive noble metals. Their broadscale
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 MoS2-based nanocatalysts, but the effect of dopants in the
electrochemical and structural stability is yet to be discussed. Herein, we
correlate operando electrochemical measurements to the structural evolution of
the materials down to the nanometric scale by identical location electron
microscopy and spectroscopy. The range of stable operation for MoS2
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 MoS2. Doping MoS2-based
nanocatalysts is validated as a promising strategy for the continuous
improvement of high performance and durable PEM electrolyzers.
