Recent years have witnessed an explosive increase in the exploration of single atom catalysts (SACs) because of their high catalytic activity, selectivity, and maximal atom utilization. In this work, we systemically investigated the adsorption and dissociation of O₂ molecules on a series of transition metals anchored on nitrogen-doped graphene as SACs by using density functional theory (DFT) calculations, aiming at screening highly efficient nanocatalysts toward the oxygen reduction reaction (ORR). Our calculations demonstrated that Ag, W, Re, and Os single atoms cannot be stably anchored on nitrogen-doped graphene. Furthermore, physical adsorption is observed between O₂ molecules and Ni, Cu, Pd, Pt, and Au SACs, thus leading to catalytic inactivation. In contrast, O₂ molecules can obtain more charges from Cr, Mn, Mo, and Tc SACs with the side-on absorption configuration than from the rest of the SACs with the end-on configuration, thus being beneficial to the dissociation of O₂. By overall consideration of the reaction energy, energy barrier, and free energy, Mn SACs should be the optimal graphene-supported nonprecious metal SACs for the ORR. These results are helpful for comprehensive understanding of the interaction between O₂ molecules and transition metal single atoms on graphene-based supports and provide new insights into design and application of cost-effective transition metal SACs.

We explored the electrocatalytic mechanisms of N₂ conversion into ammonia on six MB (M = Sc, Ti, V, Cr, Mo, and W) monolayers and screened out three MB monolayers (VB, CrB, and MoB monolayers) with high electrocatalytic activity for the NRR.

With the rapid development of rechargeable lithium-ion batteries, the search for highly efficient electrode materials has become an ever-growing need for high power density and fast charge–discharge rate to meet the future challenges of energy storage. Two-dimensional MXenes exhibit good electrical and electrochemical properties and are very attractive candidates for anode materials. In this article, we addressed ordered double-metal pristine TiVC and functionalized TiVCT₂ (T = O, S, F, or OH) MXenes and investigated their electrochemical properties by using density functional theory calculations. Our results reveal that these ordered MXenes all exhibit metallic characteristics with high electronic conductivity. The diffusion barrier of a Li ion is only 15 meV on the Ti surface and 14 meV on the V surface of the pristine TiVC monolayer. However, functional group terminations markedly increase the Li ion diffusion barrier on TiVC monolayers. Among all the group functionalized TiVCT₂ monolayers, the TiVCS₂ monolayer exhibits the lowest diffusion barrier of a Li ion (0.191 eV on the Ti surface and 0.186 eV on the V surface). Furthermore, the open circuit voltages of Li ions on both TiVC and TiVCS₂ monolayers fall in the range of 0–1.0 V, which may prevent the dendrite formation of alkali metals in the charge/discharge process. Therefore, ordered pristine TiVC and functionalized TiVCS₂ monolayers should be promising candidates as anode materials for lithium-ion batteries.

Emerging as a new family of two-dimensional materials, transition-metal borides, namely MBenes, are expected to possess outstanding physical and chemical properties owing to their layered structures analogous to MXenes. Here, we explore the electrochemical properties of ScB and TiB monolayers as anode materials for lithium- and sodium-ion batteries by density-functional theory calculations. Our results reveal that Li/Na ions can be stably adsorbed on surfaces of both monolayers with moderate adsorption energy, rapid charge/discharge rate, higher storage capacity, and much lower diffusion energy barrier (0.108 eV for Li ion on ScB, 0.105 eV for Li ion on TiB, 0.072 eV for Na ion on ScB, and 0.063 eV for Na ion on TiB) as compared with other MBene monolayers currently reported. Meanwhile, the open-circuit voltages all fall in the range of 0–1 V for Li/Na ion on the monolayers, which may effectively suppress the formation of Li/Na dendrite on anodes during the charge/discharge process. Besides, at room temperature, Li adatoms could be adsorbed on the monolayers more stably than Na adatoms. Our work demonstrates that ScB and TiB monolayers should be promising two-dimensional anode materials for lithium-ion batteries and are less suitable for sodium-ion batteries. These results advance our understanding on the electrochemical performances of MBenes and provide important insights into the design and development of high-performance electrode materials for metal-ion batteries.