Charge redistribution in FeOOH nanoarray by ecological oxygen-reduction deposition for boosting electrocatalytic water oxidation

The exploration for economic and ecological strategies to fulfill macro-synthesis of highly efficient nano-electrocatalysts has always been a key concern for electrocatalytic energy conversion field. Herein, a room-temperature oxygen-reduction deposition method was proposed to achieve the scaled-up preparation of Ni incorporated polycrystalline FeOOH (Ni-FeOOH) nanosheets on Fe metal. Due to the reduction potential difference between Fe metal and O2 in the atmosphere, the O2 reduction would thermodynamically occur in the designed Ni2+ liquid layer covered on Fe metal. Therefore, Ni-FeOOH nanosheets would be in-situ generated on the surface within a short cycle of 20 min. Furthermore, the Ni heteroatom induced the charge redistribution in FeOOH, where the average valence of both Fe and Ni cations was shifted to high states. As a result, the decreased Fermi level and increased electron acceptor significantly reduced the energy barrier of rate-determining step (by ∼1.4 eV). Finally, polycrystalline Ni-FeOOH shows a low overpotential of 239 mV at 10 mA/cm2, a low Tafel slope of 33 mV dec-1, and a dramatically increased TOF value (32.6 times higher than pristine sample), which even surpass some mainstream electrocatalysts consisting of noble-metal composition. This work provides an in-depth insight on Ni-Fe interaction mechanism, as well as a highly economic and ecological strategy to design and synthesize scaled-up FeOOH based electrocatalysts for water oxidation.