Unveiling the Aggregation of M−N−C Single Atoms into Highly Efficient MOOH Nanoclusters during Alkaline Water Oxidation

M-N-C-type single-atom catalysts (SACs) are highly efficient for the electrocatalytic oxygen evolution reaction (OER). And the isolated metal atoms are usually considered real active sites. However, the oxidative structural evolution of coordinated N during the OER will probably damage the structure of M-N-C, hence resulting in a completely different reaction mechanism. Here, we reveal the aggregation of M-N-C materials during the alkaline OER. Taking Ni-N-C as an example, multiple characterizations show that the coordinated N on the surface of Ni-N-C is almost completely dissolved in the form of NO