Pt SAC, [3] Au SAC, [4] and Co SAC, [5] have been reported. A few strategies have thus been proposed to fabricate metal SACs, including wet impregnation, [6] metal (hydr) oxides@polymer core−shell strategy, [7] atomic layer deposition, [8] and photochemical strategy. [6] However, the construction of metal SACs remains challenging because of the high surface energy of single atoms. Thus, to further promote the wide application of metal SACs, it is urgent to develop new, advanced, and universal synthetic methodology.Metal-organic frameworks (MOFs), are a unique type of porous materials with ultrahigh porosity, tunable pore sizes, and wellcharacterized crystalline architectures. [9] MOFs are composed of metal ions and organic linkers, serving as excellent templates for the preparation of composite materials with functional species, such as nitrogen-doped carbon and transition metal carbides/nitrides. [10] Recently, MOFs have been employed as templates to fabricate SACs, through adding metal precursors into the synthetic solution of MOFs. It was proposed that the metal precursors were trapped in the cage of the resultant MOF, anchored to the functional group, or incorporated as In the present study, a highly efficient strategy is reported using open framework platforms with abundant chelating ligands to fabricate a series of stable metal single-atom catalysts (SACs). Here, the metal ions are initially anchored onto the active bipyridine sites through postsynthetic modification, followed by pyrolysis and acid leaching. The resulting single metal atoms are uniformly distributed on a nitrogen-doped carbon (N-C) matrix. Interestingly, each metal atom is found to be coordinated with five N atoms, in contrast to the average coordination number of four as previously reported. The as-prepared Fe SAC/N-C catalyst exhibits excellent oxygen reduction reaction (ORR) activity (with a half-wave potential of 0.89 V), outstanding stability, and good methanol tolerance. The density functional calculations reveal that the coordinated pyridine can favorably modulate the interaction strength of oxygen on the Fe ion and thus improve the ORR activity. More importantly, it is demonstrated that this strategy can be successfully extended to the preparation of other transition metal SACs, simply by altering the metal precursors used in the metalation step.
Single-Atom CatalystsMetal single-atom catalysts (SACs) with atomically distributed active metal centers have emerged as a new research frontier in the catalytic community because of their maximum atom efficiency and high selectivity in a wide variety of catalytic reactions. [1] To date, quite a few metal SACs, such as Fe SAC, [2] The ORCID identification number(s) for the author(s) of this article can be found under https://doi.
