Mechanochemical-tuning size dependence of iridium single atom and nanocluster towards highly selective ammonium production

The electrochemical nitrate reduction reaction (NO3RR) is an effec-tive pathway to achieving sustainable NH3 production. However, both the experimental investigations and the detailed mechanism are still lacking in terms of the size effect of nanocatalysts during NO3RR, especially at the near atomic scale. Herein, we demonstrate a facile mechanochemical strategy to precisely immobilize Ir single -atom catalysts (SACs) or nanoclusters on spinel Co3O4. Compared with the conventional pyrolysis method, the established mechano-chemical strategy can realize ultrafast (10 min) and mild synthesis at ambient temperature, avoiding hard-to-control agglomeration at high pyrolysis temperature. The results reveal that the atomic -scale Ir SAC-Co3O4 can significantly boost NO3RR activity compared with nanocluster-scale Ir NC-Co3O4 by effectively enhancing the charge transfer and decreasing the energy barrier. Therefore, the present study not only provides new opportunities to fabricate nanocatalysts with controllable size but also gives new insights into the NO3RR mechanism on the basis of the size effect.