COF-C₄N Nanosheets with uniformly anchored single metal sites for electrocatalytic OER: From theoretical screening to target synthesis

COF-C₄N, an effective oxygen evolution reaction (OER) electrocatalyst with a low overpotential, has ideal N-edge cavities for anchoring transition metal (TM) sites to achieve single atom catalysts (SACs) with higher OER activity. To screen out the optimal TM, two descriptors for characterizing the OER activities are proposed based on systematic density-functional theory calculations for two different classes of COF, TM-COF-C₄N and TM-Aza-CMP. Among them, Co-COF-C₄N and Ni-COF-C₄N are theoretically suggested to be highly active and low-cost OER SACs for target synthesis. Followed by a series of structural characterizations (PXRD, XPS, FT-IR, EXAFS, ICP, TEM and SEM) as well as OER performance measurement, it is confirmed that Co-COF-C₄N exhibits excellent OER activity with an overpotential of 280 mV at 10 mA cm⁻², more active than most of previously reported OER electrocatalysts. The molecular mechanism underlying the high activity is explored.