Despite significant advances in the fabrication and applications of graphene-like materials, it remains a challenge to prepare single-layered metallic materials, which have great potential applications in physics, chemistry and material science. Here we report the fabrication of poly(vinylpyrrolidone)-supported single-layered rhodium nanosheets using a facile solvothermal method. Atomic force microscope shows that the thickness of a rhodium nanosheet is o4 Å. Electron diffraction and X-ray absorption spectroscopy measurements suggest that the rhodium nanosheets are composed of planar single-atom-layered sheets of rhodium. Density functional theory studies reveal that the single-layered Rh nanosheet involves a d-bonding framework, which stabilizes the single-layered structure together with the poly(vinylpyrrolidone) ligands. The poly(vinylpyrrolidone)-supported single-layered rhodium nanosheet represents a class of metallic two-dimensional structures that might inspire further fundamental advances in physics, chemistry and material science.

The electrocatalytic reduction reaction of CO2 (CO2RR) is a promising strategy to promote the global carbon balance and combat global climate change. Herein, exclusive Bi-N4 sites on porous carbon networks can be achieved through thermal decomposition of a bismuth-based metal–organic framework (Bi-MOF) and dicyan­diamide (DCD) for CO2RR. Interestingly, in situ environmental transmission electron microscopy (ETEM) analysis not only directly shows the reduction from Bi-MOF into Bi nanoparticles (NPs) but also exhibits subsequent atomization of Bi NPs assisted by the NH3 released from the decomposition of DCD. Our catalyst exhibits high intrinsic CO2 reduction activity for CO conversion, with a high Faradaic efficiency (FECO up to 97%) and high turnover frequency of 5535 h–1 at a low overpotential of 0.39 V versus reversible hydrogen electrode. Further experiments and density functional theory results demonstrate that the single-atom Bi-N4 site is the dominating active center simultaneously for CO2 activation and the rapid formation of key intermediate COOH* with a low free energy barrier.

The local coordination environment of catalysts has been investigated for an extended period to obtain enhanced catalytic performance. Especially with the advancement of single-atom catalysts (SACs), research on the coordination environment has been advanced to the atomic level. The surrounding coordination atoms of central metal atoms play important roles in their catalytic activity, selectivity and stability. In recent years, remarkable improvements of the catalytic performance of SACs have been achieved by the tailoring of coordination atoms, coordination numbers and second-or higher-coordination shells, which provided new opportunities for the further development of SACs. In this review, the characterization of coordination environment, tailoring of the local coordination environment, and their related adjustable catalytic performance will be discussed. We hope this review will provide new insights on further research of SACs.

We report the formation of single-crystalline octahedral Au-Ag nanoframes by a modified galvanic replacement reaction. Upon sequential addition of AgNO(3), CuCl, and HAuCl(4) to octadecylamine solution, truncated polyhedral silver nanoparticles formed first and then changed into octahedral Au-Ag nanoframes, without requiring a conventional Ag removal step with additional oxidation etchant. The nanoframes have 12 sides, and all of the eight {111} faces are empty. The side grows along the [110] direction, and the diameter is less than 10 nm. The selective gold deposition on the high-energy (110) surface, the diffusion, and the selective redeposition of Au and Ag atoms are the key reasons for the formation of octahedral nanoframes.

Supported atomic clusters with uniform metal sites and definite low-nuclearity are intermediate states between single-atom catalysts (SACs) and nanoparticles in size. Benefiting from the presence of metal–metal bonds, supported atomic clusters can trigger synergistic effects among every metal atom, which contributes to achieving unique catalytic properties different from SACs and nanoparticles. However, the scalable and precise synthesis and atomic-level insights into the structure–properties relationship of supported atomic clusters is a great challenge. This perspective presents the latest progress of the synthesis of supported atomic clusters, highlights how the structure affects catalytic properties, and discusses the limitations as well as prospects.