Ligand Modulation of Active Sites to Promote Electrocatalytic Oxygen Evolution

Abstract

kinetics in anodic electrode, that is, the four-electron coupled oxygen evolution reaction (OER). [1][2][3] At present, the benchmark OER catalysts are noble metalbased oxides such as IrO 2 and RuO 2 ; however, they are limited by scarcity and expensive cost. [4][5][6] Given this fact, the relatively inexpensive and performancepromising transition metal-based catalysts such as Fe/Co/Ni oxohydroxide and oxides are attracting increasing attention. [7][8][9][10][11][12] Ligand-modulation of Fe/Co/Ni-based metal-organic frameworks (MOFs) and hydroxides have demonstrated great potential in OER. [13][14][15][16][17] Through ligand modulation, the crystalline structure and mass/charge transfer behaviors of catalysts could be effectively modified, and enhanced OER performance could be achieved. For example, by a ligand-competition amorphization pathway, Yu et al. [18] reported a nanorod@nanosheet core-shell structured amorphous OER catalyst, consisting of a Fe-rich MOF core, a Co-rich MOF shell, and an amorphous Co(OH) 2 nanosheet outer layer. Taking advantage of the 3D amorphous architecture, the obtained OER catalyst demonstrates a small overpotential of 249 mV at 10 mA cm -2 . Hou et al. [19] reported the construction of N-doped carbon nanosheet networks with abundant active sites and enhanced charge transfer for OER using the complexes of ZIF-8 and layered double hydroxides as the precursors. Regardless of the research progress, understanding the intrinsic active sites of OER catalyst as well as the structure-performance correlation is still challenging.Herein, we report a 2-methylimidazole (MI) modulated cobalt-iron oxyhydroxide OER catalyst, (Fe,Co)OOH/MI, with low crystallinity and nanosheet structure. The low-crystalline nanosheet structure maximizes the exposure of active sites and facilitates the mass transfer process, while the MI modulation optimizes the electronic configuration of the catalyst. Specifically, the coordination of MI with (Fe,Co)OOH reduces the orbital overlap between Fe/Co 3d and O 2p, which weakens the adsorption to oxygen-containing intermediates and thus facilitates the unfavorable O 2 desorption. As expected, the (Fe,Co) OOH/MI demonstrates ultralow overpotentials of 230/290 mV at 10/100 mA cm -2 and affords more than 155-h durability with negligible decay in OER. Rationally designed catalystshold the key to address the sluggish kinetics of oxygen evolution reaction (OER). However, engineering the active sites of such catalysts still faces grand challenges. This study proposes a feasible ligand modulation strategy to boost the OER catalytic activity of cobalt-iron oxyhydroxide ((Fe,Co)OOH). The 2-methylimidazole (MI) ligand coordination on (Fe,Co)OOH reduces the orbital overlap between the Fe/Co 3d and O 2p, which weakens the adsorption to oxygen-containing intermediates and thus facilitates the unfavorable O 2 desorption. As a result, the MI ligand modulated (Fe,Co)OOH achieves an excellent OER performance with low overpotentials (230/290 mV at 10/100 mA cm -2 ) and excellent durability (...

Molecule-Enhanced Electrocatalysis of Sustainable Oxygen Evolution Using Organoselenium Functionalized Metal–Organic Nanosheets

“…Porous coordination polymers (PCPs) or metal–organic frameworks (MOFs) are architected from the self-assembly of metal ions/clusters and organic ligands, − which possess highly tunable structures, high specific surface areas, and abundantly accessible metal sites, enabling them to be attractive catalysts for both performance upgrades and mechanism studies. − In particular, ultrathin two-dimensional (2D) PCP nanosheets are promising electrocatalysts due to their more exposed catalytic active sites and superior electrical conductivity. − Recently, many investigations have confirmed that structural reconstruction can also occur in nanoscale PCPs to form more highly active species during the OER process. − However, the main attention is focused on MASs to date, and the role of organic ligands in electrocatalysis is usually ignored. − Hence, the quantitative correlation between the organic species, especially those containing heteroatoms, and OER activity remains enigmatic.…”

Freestanding Cactus-Like Dual-Phase Bimetallic Metal–Organic Framework as a High-Efficiency Electrocatalyst for Water Oxidation

“…To improve the poor electronic conductivity, a feasible and highly efficient strategy is directly growing MOF catalysts on a conductive substrate. ,, Catalysts directly grown on a conductive substrate such as nickel foam (NF) and carbon cloth avoid the utilization of nonconductive binders that bury partial metal sites as well as enhance the electronic conductivity due to seamless contact between the catalyst and substrate. , Meanwhile, the mechanical stability will be pronouncedly promoted because self-supported electrocatalysts with strong binding force are less sensitive to the fast release of gas bubbles at high current density …”

Regulating the coordination environment of a metal–organic framework for an efficient electrocatalytic oxygen evolution reaction

“…[34][35][36][37][38][39] However, in the structure of MOFs, the metal nodes are surrounded by organic linking groups, 40 which limits their catalytic activity and conductivity; 41 thereby, it is vital to construct these structures with a rational design. [42][43][44][45] In terms of macrostructure control, 46 Lou et al typically construct a unique core-shell structure through chemical etching methods and other methods, 47 which could provide a larger catalytic interface area, 48 thereby significantly improving the electrocatalytic performance. 49 Li et al used carbonization to precisely regulate Hofmann-type MOFs into different forms (including nanosheets, nanoflowers, 50 nanotubes and aggregates), which OER catalytic performance far exceeds that of commercial RuO 2 catalysts.…”