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.

Near- and Long-Range Electronic Modulation of Single Metal Sites to Boost CO2 Electrocatalytic Reduction.

Tuning the electronic structure of the active center is effective to improve the intrinsic activity of single-atom catalysts but the realization of precise regulation remains challenging. Herein, a strategy of "synergistically near- and long-range regulation" is reported to effectively modulate the electronic structure of single-atom sites. ZnN4 sites decorated with axial sulfur ligand in the first coordination and surrounded phosphorus atoms in the carbon matrix are successfully constructed in the hollow carbon supports (ZnN4 S1 /P-HC). ZnN4 S1 /P-HC exhibits excellent performance for CO2 reduction reaction (CO2 RR) with a Faraday efficiency of CO close to 100%. The coupling of the CO2 RR with thermodynamically favorable hydrazine oxidation reaction to replace oxygen evolution reaction in a two-electrode electrolyzer can greatly lower the cell voltage by 0.92 V at a current density of 5 mA cm-2 , theoretically saving 46% of energy consumption. Theoretical calculation reveals that the near-range regulation with axial thiophene-S ligand and long-range regulation with neighboring P atoms can synergistically lead to the increase of electron localization around the Zn sites, which strengthens the adsorption of *COOH intermediate and therefore boosts the CO2 RR.