Homogeneous Distribution of Pt₁₆(C₄O₄SH₅)₂₆ Clusters in ZIF-67 for Efficient Hydrogen Generation and Oxygen Reduction

In recent years, based on the high catalytic activities of metal nanoclusters (MNCs) and the unique porous structure of metal-organic frameworks (MOFs), much work has focused on MOF-confined small MNCs for catalysis applications. However, the commonly used "ship-in-boat" approach is unfeasible for precisely controlling the size and composition of the formed MNCs and meanwhile often causes structural distortion/degradation. On the other hand, the "bottle-around-ship" method usually has the disadvantages that MOFs show uncontrollable self-nucleation outside the MNCs and the stabilizers on the surface of MNCs may greatly reduce their catalytic activities. In this work, monodispersed Pt₁₆(C₄O₄SH₅)₂₆ clusters (Pt₁₆(MSA)₂₆) were first prepared and used as a precursor for the synthesis of Pt(MSA)@ZIF-67 via the typical Co-carboxylate type of linkage at the interface under ambient atmosphere. After encapsulating the Pt clusters in ZIF-67, the protecting ligands were removed under 300 °C to get surface-clean Pt₁₆ clusters confined in ZIF-67 (Pt@ZIF-67). The obtained Pt@ZIF-67 exhibited high catalytic activity for the hydrolysis of ammonia borane that was superior to that of most of the reported noble-metal catalysts. Meanwhile, by annealing the Pt(MSA)@ZIF-67 at 800 °C to form highly conductive graphitic carbon-coated Pt NCs and Co nanoparticles (NPs) (Pt/Co@NC), the obtained composite showed high catalytic activity for the oxygen reduction reaction (ORR). The formed Pt/Co@NC showed 9.6 times higher ORR mass activity (at 0.8 V) than Pt/C. This work provides a strategy to fabricate highly dispersed and stable metal clusters confined in the porous matrix for catalysis and shows that highly porous MOFs have promising catalysis applications by combining them with other active components.