Sr-induced Fermi Engineering of ß-FeOOH for Multifunctional Catalysis.

ABSTRACT

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 (t2g) d-orbitals. Here a Sr-induced phase transformed ß-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+(t2g)-orbitals to e--deficient Fe4+(t2g)-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.