Heptanuclear brucite disk with cyanide bridges in a cocrystal and tracking its pyrolysis to an efficient oxygen evolution electrode - zeng's paper

The development of efficient oxygen evolution reaction (OER) catalysts is still lacking in exploration of the mechanism of controlled pyrolysis of precursors among new material platforms. Here, a novel Co-based coordination molecular cluster has been first introduced as precursor to obtain metallic cobalt core shelled by N-doped carbon (Co@NC) structure which operates as an oxygen evolution electrode. Specifically, a new cocrystal compound, [CoII 7(l3-CN)6(mmimp)6] [CoIICl3N(CN)2]3CH3OH (Co7+1, mmimp = 2-methoxy-6-((methylimino)-methyl)phenol), was isolated consisting of Brucite disks of cobalt where the usual bridging l3-OH is replaced by l3-CN produced by the in-situ decomposition of dicyanamide (NC-N-CN). The cobalt atoms are bonded through the nitrogen atom of the cyanide. Remarkably, time dependent thermogravimetric-mass spectrometry (TG-MS) analysis was utilized to track its pyrolysis process. It allowed us to propose a possible formation process of the Co@NC structure from Co7+1. Interestingly, an extremely superior OER electrode is optimized for Co@NC-600 having the lowest overpotential of 257 mV at 10 mA/cm2 in 1 mol/L KOH solution. The present study pins down the importance of clusters of transition metals on realizing distinct nanostructures operating as highly efficient OER electrocatalyst.