Modulating Oxygen Reduction Behaviors on Nickel Single-Atom Catalysts to Probe the Electrochemiluminescence Mechanism at the Atomic Level.

Luminol-dissolved O2 electrochemiluminescence (ECL)-sensing platforms have been widely developed for sensitive and reliable detection, while their actual ECL mechanisms are still in controversy due to the involved multiple reactive oxygen species (ROS). Different from the structural complexity of nanomaterials, well-defined single-atom catalysts (SACs) as coreaction accelerators will provide great prospects for investigating the ECL mechanism at the atomic level. Herein, two carbon-supported nickel SACs with the active centers of Ni-N4 (Ni-N4/C) and Ni-N2O2 (Ni-N2O2/C) were synthesized as efficient coreaction accelerators to enhance the ECL signals of a luminol-dissolved O2 system. By modulating the surrounding environment of the center metal atoms, their corresponding oxygen reduction behaviors can be well controlled to selectively produce intermediate ROS, giving a great chance to study the following ECL process. According to the experimental and calculated results, the superoxide radical (O2•-) acts as the main radical for the ECL reaction and the Ni-N4/C catalyst with the four-electron pathway to activate dissolved O2 is preferential to enhance ECL emission.