Rugae-like FeP nanocrystal assembly on a carbon cloth: an exceptionally efficient and stable cathode for hydrogen evolution

Abstract

There is a strong demand to replace expensive Pt catalysts with cheap metal sulfides or phosphides for hydrogen generation in water electrolysis. Earth-abundant Fe can be electroplated on carbon cloth (CC) to form high surface area rugae-like FeOOH assembly. Subsequent gas phase phosphidation converts the FeOOH to FeP or FeP<inf>2</inf> and the morphology of the crystal assembly is controlled by the phosphidation temperature. FeP prepared at 250°C presents lower crystallinity and that prepared at higher temperatures of 400°C and 500°C possesses higher crystallinity, but lower surface area. The phosphidation at 300°C produces nanocrystalline FeP and preserves the high-surface area morphology; thus, it exhibits the highest HER efficiency in 0.5 M H<inf>2</inf>SO<inf>4</inf>, i.e., the required overpotential to reach 10 and 20 mA cm^-2 is 34 and 43 mV, respectively. These values are lowest among the reported non-precious metal phosphides on CC. The Tafel slope for FeP prepared at 300°C is around 29.2 mV dec^-1, which is comparable to that of Pt/CC; this indicates that the hydrogen evolution for our best FeP is limited by the Tafel reaction (same as Pt). Importantly, the FeP/CC catalyst exhibits much better stability in a wide-range working current density (up to 1 V cm^-2), suggesting that it is a promising replacement of Pt for HER.