Surface‐Adsorbed Carboxylate Ligands on Layered Double Hydroxides/Metal–Organic Frameworks Promote the Electrocatalytic Oxygen Evolution Reaction

Abstract

Metal-organic frameworks (MOFs) with carboxylate ligands as co-catalysts are very e cient for oxygen evolution reaction (OER). However, the role of local adsorbed carboxylate ligands around the in situ transformed metal (oxy)hydroxides during OER is often overlooked. Here we reveal the extraordinary role and mechanism of surface adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for OER catalytic activity enhancement. The results of X-ray photoelectron spectroscopy (XPS), synchrotron X-ray absorption spectroscopy and theoretical calculations show that the carboxylic groups around metal (oxy)hydroxides can e ciently induce the interfacial electron redistribution, facilitate abundant high-valence state of nickel species with partial distorted octahedral structure, and optimize the d-band center together with the bene cial Gibbs free energy of intermediate. Furthermore, the results of in-situ Raman and FI-IR spectra rstly reveal that the surface adsorbed carboxylate ligands as Lewis base can promote the sluggish OER kinetics by accelerating proton transfer and facilitating adsorption/ activation/dissociation of hydroxyl ions (OH − ). Our ndings will offer unique insights into the reason for disclosing the origin of excellent electrocatalytic activity for MOF/NiFe-LDHs catalysts.

Electronic Modulation Caused by Interfacial Ni‐O‐M (M=Ru, Ir, Pd) Bonding for Accelerating Hydrogen Evolution Kinetics

“…[5] As shown in Figure 4 d, the DG H* of Ru@Ni-MOF-Ru site (À0.13 eV) and Ru@Ni-MOF-Ni site (À0.18 eV) is much closer to the thermoneutral value than that of pure Ni-MOF (À0.40 eV) and Ru NPs (À0.32 eV), indicating smaller between Ni 2+ and O 2À . [43,44] A weaker interaction is generated through p-donation as the M-O bridge is formed in M@Ni-MOF (Figure 5 e). In addition, considering the sequence of ionic electronegativity, [45,46] the electron cloud around the M is transferred to Ni because of the formation of Ni-O-M bond in M@Ni-MOF, confirmed by the experimental and theoretical results.…”

Nonmetallic Active Sites on Nickel Phosphide in Oxygen Evolution Reaction

“…We found that the transferred charge is strongly correlated with adsorption energy, i.e., larger charge transfers between OH or O and adsorption sites are correlated with lower adsorption energy in the corresponding adsorption structure. The larger transferred charge indicates low charge transfer resistance between the adsorption site and the OH and O groups, which can promote the adsorption of these groups, thus showing excellent performance [ 71 , 72 , 73 ].…”

Electronic Modulation Caused by Interfacial Ni‐O‐M (M=Ru, Ir, Pd) Bonding for Accelerating Hydrogen Evolution Kinetics

“…Additionally, the adsorption free energy of H* (DG H* ) is a key factor to decide the HER activity, while DG H* with a value close to zero means feasible H adsorption and H 2 desorption. [5] As shown in Figure 4 [43,44] A weaker interaction is generated through p-donation as the M-O bridge is formed in M@Ni-MOF (Figure 5 e). In addition, considering the sequence of ionic electronegativity, [45,46] the electron cloud around the M is transferred to Ni because of the formation of Ni-O-M bond in M@Ni-MOF, confirmed by the experimental and theoretical results.…”

“…[5] As shown in Figure 4 between Ni 2+ and O 2À . [43,44] A weaker interaction is generated through p-donation as the M-O bridge is formed in M@Ni-MOF (Figure 5 e). In addition, considering the sequence of ionic electronegativity, [45,46] the electron cloud around the M is transferred to Ni because of the formation of Ni-O-M bond in M@Ni-MOF, confirmed by the experimental and theoretical results.…”