Rational Design of Goethite-Sulfide Nanowire Heterojunctions for High Current Density Water Splitting

The preparation of efficient and stable bifunctional electrocatalysts for electrochemical overall water splitting (OWS) to scale up commercial hydrogen production remains a great challenge. Here, we synthesized heterojunction structures consisting of Co₉S₈/Ni₃S₂ nanowire arrays and amorphous goethite (FeOOH, α-phase) particles as efficient OWS catalysts using an interface engineering strategy. The interfacial charge inhomogeneity caused by the heterojunction contact leads to the generation of a built-in electric field, which makes the electron-deficient FeOOH and electron-rich Co₉S₈/Ni₃S₂ favorable for hydrogen/oxygen evolution reaction, respectively, thus ensuring the excellent activity of FeOOH/Co₉S₈/Ni₃S₂ as a bifunctional catalyst. FeOOH/Co₉S₈/Ni₃S₂ exhibits impressive catalytic activity for the oxygen evolution reaction, achieving an ultralarge current density of 1000 mA cm^-2 needed as low as 265 mV overpotential, and its stability was tested up to 1440 h. Furthermore, an excellent OWS output (1.55 V to generate 10 mA cm^-2) is achieved by the bifunctional FeOOH/Co₉S₈/Ni₃S₂ catalysts.