Metal oxide semiconductors with surface homojunctions characteristic of continuous band bending and well-defined epitaxial interfaces show amazing potential for photocatalytic applications. Herein, a new concept of facet junctions is proposed and validated according to the synergy between the co-exposed crystal facets of shape-tailored anatase TiO₂ single crystals. By considering the atomic and electronic interactions between the co-exposed facets, our density functional theory calculations reveal the existence of type-II band alignment between the co-exposed {001} and {101} facets. This band alignment results in in situ construction of a facet junction to allow built-in facet-mediated carrier transfer. The self-constructed {101}/{001} facet junction, due to the effective carrier separation between different exposed facets, exhibits a significantly enhanced quantum efficiency and catalytic performance in photochemical hydrogen generation compared to TiO₂ poly-crystals. These findings open a new horizon of facet junction-engineered nano-catalysts for more robust and efficient energy and environmental applications.

With crystal structure prediction using a genetic algorithm method, we propose a novel two-dimensional (2D) carbon allotrope with relatively low energy, which is composed of tetragonal and heptagonal carbon rings, named thgraphene. The robust thermodynamic, dynamic, and mechanic stability of thgraphene signify the high possibility for experimental synthesis. As a metallic 2D carbon material, thgraphene is proved to be an efficient bifunctional electrocatalyst for hydrogen and oxygen evolution reactions (HER and OER), with low overpotentials of 0.14 V and 0.46 V, respectively. Moreover, the HER/OER catalytic activities can be further tuned close to the ideal values by applying a certain amount of strain. Also, we find that thgraphene is a promising anode material for potassium-ion batteries due to its excellent ductility (Poisson’s ratio ∼ 0.39), ultra-low diffusion barrier (0.06 eV), high theoretical specific capacity (744 mA h g⁻¹), and moderate average open-circuit voltage (0.30 V). Our findings highlight a new 2D carbon allotrope as a bifunctional HER/OER electrocatalyst and potassium-ion anode material.

Precise spatial control of the spin propagation channels is of fundamental and practical importance in future graphene-based spintronic devices. Here we use first-principles calculations to show that when narrow zigzag graphene nanoribbons are connected to form junctions or superlattices, properly placed square-shaped carbon tetragons not only serve as effective bundles of the two incoming spin edge channels, but also act as definitive topological spin switches for the two outgoing channels. The nanoribbon segments are largely drawn from different acene molecules. We further show that such spin switches can lift the degeneracy between the two spin propagation channels, which enables tunability of different magnetic states upon charge doping. Preliminary experimental supports for the realization of such tetragons connecting nanoribbon segments are also presented.