Tuning the d-Band States of Ni-Based Serpentine Materials via Fe 3+ Doping for Efficient Oxygen Evolution Reaction.

The serpentine germanate materials are promising oxygen evolution reaction (OER) electrocatalysts due to their unique layered crystal structure and electronic structure. However, the catalytic activities still need to be improved to satisfy the practical applications. Adjusting the d-band center of metal active site to balance the adsorption and desorption of intermediates is considered an effective approach to improve the OER activity. In this work, an element dopant strategy was proposed to optimize the d-band state of Ni 3 Ge 2 O 5 (OH) 4 serpentine to improve the OER activity. The density functional theory calculations revealed that Fe 3+ doping increased the d-band center of the Ni 3 Ge 2 O 5 (OH) 4 serpentine, which optimized the adsorption strength of intermediates on surface Ni and Fe atoms so that the Fe 3+ doped Ni 3 Ge 2 O 5 (OH) 4 (Ni 2.25 Fe 0.75 Ge 2 O 5 (OH) 4 ) exhibited much reduced Gibbs free energy changes in the rate-determining step compared with pristine serpentine. Inspired by the theoretical calculations, the Ni x Fe 3- x Ge 2 O 5 (OH) 4 nanosheets with different amounts of doped Fe 3+ were designed and synthesized. The structural characterizations indicated that Fe 3+ was successfully doped into Ni 3 Ge 2 O 5 (OH) 4 and replaced the Ni 2+ . The Fe 3+ doped Ni x Fe 3- x Ge 2 O 5 (OH) 4 nanosheets showed greatly improved OER activity than Ni 3 Ge 2 O 5 (OH) 4 and Fe 3 Ge 2 O 5 (OH) 4 . Further electrochemical analysis illustrated that Fe 3+ doping reduced the adsorptive/formative resistance of intermediates and the charge transfer resistance and facilitated the kinetic process of OER. The in situ Raman spectra indicated that the Fe 3+ doped Ni 3 Ge 2 O 5 (OH) 4 possesses a more active Ni-O bond than pristine Ni 3 Ge 2 O 5 (OH) 4 . This work provides an effective strategy to tune the d-band center of serpentines for efficient electrocatalytic OER.