Origins of the Instability of Non-precious HER Catalysts at Open Circuit Potential

Non-precious hydrogen evolution reaction (HER) catalysts commonly suffer from severe dissolution under open circuit potential (OCP). In this work, using calculated Pourbaix diagrams, we quantitatively analyze the stability of a set of well-known active HER catalysts (MoS₂, MoP, CoP, Pt in acid, and Ni₃Mo in base) under working conditions. We determine that the large thermodynamic driving force towards decomposition created by the electrode/electrolyte interface potential is responsible for the substantial dissolution of non-precious HER catalysts at OCP. Our analysis further shows the stability of HER catalysts in acidic solution is ordered as Pt ∼ MoS₂ > MoP > CoP, which is confirmed by the measured dissolution rates using an inductively coupled plasma mass spectrometer. Based on gained insights, we suggest strategies to circumvent the catalyst dissolution in aqueous solution.