Sr-induced Fermi Engineering of β-FeOOH for Multifunctional Catalysis

Designing a multifunctional electrocatalyst to produce H₂ from water, urea, urine, and wastewater, is highly desirable yet challenging because it demands precise Fermi-engineering to realize stronger π-donation from O 2p to electron(e^-)-deficient metal (t_2g) d-orbitals. Here a Sr-induced phase transformed β-FeOOH/α-Ni(OH)₂ catalyst anchored on Ni-foam (designated as pt-NFS) is introduced, where Sr produces plenteous Fe⁴⁺ (Fe³⁺ → Fe⁴⁺) to modulate Fermi level and e^--transfer from e^--rich Ni³⁺(t_2g)-orbitals to e^--deficient Fe⁴⁺(t_2g)-orbitals, via strong π-donation from the π-symmetry lone-pair of O bridge. pt-NFS utilizes Fe-sites near the Sr-atom to break the H─O─H bonds and weakens the adsorption of *O while strengthening that of *OOH, toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Invaluably, Fe-sites of pt-NFS activate H₂-production from urea oxidation reaction (UOR) through a one-stage pathway which, unlike conventional two-stage pathways with two NH₃-molecules, involves only one NH₃-molecule. Owing to more suitable kinetic energetics, pt-NFS requires 133 mV (negative potential shift), 193 mV, ≈1.352 V, and ≈1.375 V versus RHE for HER, OER, UOR, and human urine oxidation, respectively, to reach the benchmark 10 mA cm^-2 and also demonstrates remarkable durability of over 25 h. This work opens a new corridor to design multifunctional electrocatalysts with precise Fermi engineering through d-band modulation.