Overall Water‐Splitting Electrocatalysts Based on 2D CoNi‐Metal‐Organic Frameworks and Its Derivative

Abstract

COMMUNICATION (1 of 8)composed of Co, Ni, and Fe have recently shown potentials with excellent catalytic properties, and great structural stabilities toward electrocatalytic OER and HER. [9][10][11][12][13] Active site availability and electronic conductivity are the key factors for electrocatalysts, which are determined by the surface species, morphology, and composition. Thus, tremendous effort has been put into the rational design of Co-, Ni-, and Fe-based catalysts and material interface to promote the reaction kinetics and improve the catalytic efficiency. [14,15] Recently, metal-organic frameworks (MOFs) have attracted great attention due to their flexible, porous structures, and tunable properties. [16,17] Direct exposure of metal nodes in the porous bulk structure to reaction environments makes MOFs a suitable catalyst candidate. Studies show that MOFs possess excellent electrocatalytic activities with high stability against chemical corrosion and bubbles' attack. [17][18][19][20][21] In addition, MOFs can serve as a template of porous carbon-metal structures with good structural stability. [22][23][24][25][26][27] Nevertheless, most MOF-based electrocatalysts show limited efficiencies due to low mass permeability and poor electrical conductivity. In a bulk MOF, the majority of active sites are located inside pores or channels, where the organic linkers may interfere and thus limit the accessibility. [28,29] To circumvent such shortcomings, thin 2D MOFs have been suggested to achieve much larger specific surface area with more active metal sites directly exposed to electrolytes. [30][31][32][33][34][35][36][37][38] Zhao et al. [31] reported that the unsaturated metal atoms on the ultrathin MOF surface could serve as the dominating active centers for OER. They also pointed out that the coupling between metal nodes significantly alters the catalytic activity. More recently, 2D MOFs were prepared by a dissolution-crystallization mechanism on the substrates [30] or selective removal of pillar organics from a 3D pillared-layer MOF. [38] Despite the huge potential, the synthesis of catalytically active 2D MOF with precise control of structure is still challenging, and the real active surface information remain unclear. Thus, the structure-activity relationships among morphology, electronic configuration, and catalytic performance of 2D MOFs still need more explorations.In this work, we report 2D CoNi bimetallic organic frameworks (CoNi-MOFs) directly grown as nanoplate array on a copper foil under hydrothermal conditions. Such CoNi-MOFs (Co:Ni = 1:1) demonstrate highly active OER catalysis, as manifested by a small overpotential of 265 mV at 10 mA cm −2 and Efficient electrocatalysts composed of non-precious elements are central to the development of overall water-splitting system. Herein, it is demonstrated that 2D CoNi-metal-organic framework (CoNi-MOF) array grown directly on a Cu substrate is a highly efficient and stable electrocatalyst for oxygen evolution reaction with a low overpotential (265 mV at 10 m...

Two‐Dimensional Metal–Organic Frameworks‐Based Electrocatalysts for Oxygen Evolution and Oxygen Reduction Reactions

“…The bimetallic 2D CoNi‐MOF nanoplate array with NDC as the organic ligand was grown directly on a copper foil (Cu substrate) by a simple hydrothermal process. [ 60 ] Different proportions of Co and Ni precursors were mixed with NDC to obtain different combinations of active sites (Co/Ni = 2:1, 1:1, and 1:2). SEM images showed petal‐like and cubic structures for Co‐MOFs and the Ni‐MOFs.…”

Metal‐organic frameworks‐derived novel nanostructured electrocatalysts for oxygen evolution reaction

“…When the ratio of Co and Ni appears to be 1:1, the thinnest 2D nanoplate arrays are formed in the MOF. Upon simple annealing treatment in the atmosphere of NH 3 , metallic nitrides’ hybrid nanoplate arrays on an amorphous carbon network (CoNiN@C) will be made available, demonstrating highly catalytic activity with a humble overpotential of 265 mV at 10 mA/cm 2 towards OER in alkaline media 92 . The impressive catalytic activity is attributed to the dominant (220) plane, which brings about the contraction and improved conductivity over the Z ‐axis, thus transporting the electrons from the substrate to the active catalytic centers effectively.…”

Recent Progress of Two‐Dimensional Metal‐Organic Frameworks and Their Derivatives for Oxygen Evolution Electrocatalysis

“…In contrast to pure 2D Co MOFs, 2D hybrid Co-based MOFs with metal heteroatoms (e. g. Fe, Ni), inheriting the controllable morphology and allowing for tailoring of the electronic structure, have demonstrated improved OER catalytic activity. [58,[76][77][78][79][80] For example, Lee et al [76] grew 2D CoNi-MOFs with different atom ratios of Co and Ni on Cu foil substrates using a hydrothermal procedure. The optimal material, CoNi (1 : 1)-MOF (thickness: 5.3 nm), showed a η of 265 mV at 10 mA cm À 2 , lower than that of pure Co MOF (341 mV).…”