Tuning the reversible chemisorption of hydroxyl ions to promote the electrocatalysis on ultrathin metal-organic framework nanosheets

Interfacial engineering to alter the configuration of active sites in heterogeneous catalysts is a potential strategy for activity enhancement, but it remains unelucidated for metal-organic frameworks (MOFs). Here, we demonstrate that the surface of two-dimensional Co-based MOF is modified by decorating Ag quantum dots (QDs) simply through in-situ reduction of Ag⁺ ions. Toward oxygen evolution reaction (OER), it reveals that the catalysis is mediated by the reversible redox of Co sites between Co³⁺ and Co⁴⁺ states coupling with transfer of OH⁻ ions. The decoration of Ag QDs decreases the redox potential of Co sites, and thus effectively decreases the overpotential of OER. The TOFs of Co sites are increased by 77 times to reach 5.4 s⁻¹ at an overpotential of 0.35 V. We attribute the activity enhancement to the tuning of the coupling process between Co sites and OH⁻ ions during the redox of Co sites by Ag QDs decoration based on Pourbaix analysis.