Ultrasmall Co@Co(OH)2 Nanoclusters Embedded in N-Enriched Mesoporous Carbon Networks as Efficient Electrocatalysts for Water Oxidation.

Metal nanoclusters (NCs, size ≤2 nm) are emerging materials in catalysis owing to their unique catalytic and electronic properties such as high surface/volume ratio, high redox potential, plethora of surface active sites, and dynamic behavior on a suitable support during catalysis. Herein, in situ growth of ultrasmall and robust Co@β-Co(OH)2 NCs (≈2 nm) hosted in a honeycomb-like 3D N-enriched carbon network was developed for water-oxidation catalysis with extremely small onset potential (1.44 V). Overpotentials of 220 and 270 mV were required to achieve a current density of 10 mA cm-2 and 100 mA cm-2 , respectively, in alkaline medium (1 m KOH). More promisingly, at η10 =240 mV, the prolonged oxygen evolution process (>130 h) with faradaic efficiency >95 % at a reaction rate of 22 s-1 at 1.46 V further substantiated the key role of the ultrasmall supported NCs, which outperformed the benchmark electrocatalysts (RuO2 /IrO2 ) and NCs reported so far. It is anticipated that the high redox potential of NCs with regeneratable active sites and their concerted synergistic effects with the N-enriched porous/flexible carbon network are inherently worth considering to enhance the mass/charge transport owing to the nanoscale interfacial collaboration across the electrode/electrolyte boundary, thereby efficiently energizing the sluggish/challenging oxygen evolution process.