Boosting Electrocatalytic Activity of 3d-Block Metal (Hydro)oxides by Ligand-Induced Conversion.

The 3d-transition-metal (hydro)oxides belong to a group of highly efficient, scalable and inexpensive electrocatalysts for widespread energy-related applications that feature easily tailorable crystal and electronic structures. We propose a general strategy to further boost their electrocatalytic activities by introducing organic ligands into the framework, considering that most 3d-metal (hydro)oxides usually exhibit quite strong binding with reaction intermediates and thus compromised activity due to the scaling relations. Involving weakly bonded ligands downshifts the d-band center, which narrows the band gap, and optimizes the adsorption of these intermediates. For example, the activity of the oxygen evolution reaction (OER) can be greatly promoted by ≈5.7 times over a NiCo layered double hydroxide (LDH) after a terephthalic acid (TPA)-induced conversion process, arising from the reduced energy barrier of the deprotonation of OH* to O*. Impressively, the proposed ligand-induced conversion strategy is applicable to a series of 3d-block metal (hydro)oxides, including NiFe2 O4 , NiCo2 O4 , and NiZn LDH, providing a general structural upgrading scheme for existing high-performance electrocatalytic systems.