Defect Engineered Metal-Organic Framework with Accelerated Structural Transformation for Efficient Oxygen Evolution Reaction.

Metal-organic frameworks (MOFs) have been increasingly applied in oxygen evolution reaction (OER), and the surface of MOFs usually undergoes structural transformation to form metal oxyhydroxides to serve as catalytically active sites. However, the controllable regulation of the reconstruction process of MOFs remains as a great challenge. Here we report a defect engineering strategy to facilitate the structural transformation of MOFs to metal oxyhydroxides during OER with enhanced activity. Defective MOFs (denoted as NiFc'x Fc1-x ) with abundant unsaturated metal sites are constructed by mixing ligands of 1,1'-ferrocene dicarboxylic acid (Fc') and defective ferrocene carboxylic acid (Fc). NiFc'x Fc1-x series are more prone to be transformed to metal oxyhydroxides compared with the non-defective MOFs (NiFc'). Moreover, the as-formed metal oxyhydroxides derived from defective MOFs contain more oxygen vacancies. NiFc'Fc grown on nickel foam exhibits excellent OER catalytic activity with an overpotential of 213 mV at the current density of 100 mA cm-2 , superior to that of undefective NiFc'. Experimental results and theoretical calculations suggest that the abundant oxygen vacancies in the derived metal oxyhydroxides facilitate the adsorption of oxygen-containing intermediates on active centers, thus significantly improving the OER activity.

Hierarchically Ordered Macro-Mesoporous Electrocatalyst with Hydrophilic Surface for Efficient Oxygen Reduction Reaction.

Metal-organic frameworks (MOFs) offer versatile templates/precursors to prepare supported metal catalysts. However, the afforded catalysts usually exhibit microporous structures and unsuitable wettability, which will restrict the accessibility of active sites in liquid-phase reactions. Herein, an etching-functionalization strategy is developed for the construction of a tannic-acid-functionalized MOF with a unique hollow-wall and 3D-ordered macroporous (H-3DOM) structure. The functional MOF can be further employed as an ideal precursor for the synthesis of cobalt supported on oxygen/nitrogen-co-doped carbon composites with H-3DOM structures, and hydrophilic surface. The H-3DOM structure can improve the external surface area to maximize the exposure of active sites. Moreover, the oxygen-containing functional groups can enhance the surface wettability to guarantee the external active sites to be more electrochemically accessible in aqueous electrolyte. Benefitting from these outstanding characteristics, H-3DOM-Co/ONC exhibits high electrocatalytic activity in the oxygen reduction reaction, superior to its counterparts without the hierarchically ordered structure and surface functionalization.