Evaluating the Stability of Co<sub>2</sub>P Electrocatalysts
in the Hydrogen Evolution Reaction for Both Acidic and Alkaline Electrolytes
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Abstract
The evaluation of
the stability of emerging earth-abundant metal
phosphide electrocatalysts by solely electrochemical current–potential
sweeps is often not conclusive. In this study, we investigated Co<sub>2</sub>P to evaluate its stability under both acidic (0.5 M H<sub>2</sub>SO<sub>4</sub>) and alkaline (1.0 M KOH) hydrogen evolution
(HER) conditions. We found that the electrochemical surface area (ECSA)
of Co<sub>2</sub>P only slightly increased in acidic conditions but
almost doubled after electrolysis in alkaline electrolyte. The surface
composition of the electrode remained almost unchanged in acid but
was significantly altered in alkaline during current–potential
sweeps. Analysis of the electrolytes after the stability test shows
almost stoichiometric composition of Co and P in acid, but a preferential
dissolution of P over Co could be observed in alkaline electrolyte.
Applying comprehensive postcatalysis analysis of both the electrode
and electrolyte, we conclude that Co<sub>2</sub>P, prepared by thermal
phosphidization, dissolves stoichiometrically in acid and degrades
to hydroxides under alkaline stability testing