In-Plane Porous Graphene: A Promising Anode Material with High Ion Mobility and Energy Storage for Rubidium-Ion Batteries.

Rubidium-ion batteries (RIBs) have received a lot of attention in the quantum field because of their fast release and reversible advantages as alkali sources. However, the anode material of RIBs still follows graphite, whose layer spacing can greatly restrict the diffusion and storage capability of Rb-ions, posing a significant barrier to RIB development. Herein, using first-principles calculations, the potential performance of three kinds of in-plane porous graphene with pore sizes of 5.88 Å (HG588), 10.39 Å (HG1039), and 14.20 Å (HG1420) as anode materials for RIBs was explored. The results indicate that HG1039 appears to be an appropriate anode material for RIBs. HG1039 has excellent thermodynamic stability and a volume expansion of <25% during charge and discharge. The theoretical capacity of HG1039 is up to 1810 mA h g-1, which is ∼5 times higher than that of the existing graphite-based lithium-ion batteries. Importantly, not only HG1039 enables the diffusion of Rb-ions at the three-dimensional level but also the electrode-electrolyte interface formed by HG1039 and Rb-ß-Al2O3 facilitates the arrangement and transfer of Rb-ions. In addition, HG1039 is metallic, and its outstanding ionic conductivity (diffusion energy barrier of only 0.04 eV) and electronic conductivity indicates superior rate capability. These characteristics make HG1039 an appealing anode material for RIBs.

Monolayer H-MoS2 with high ion mobility as a promising anode for rubidium (cesium)-ion batteries.

Secondary ion batteries rely on two-dimensional (2D) electrode materials with high energy density and outstanding rate capability. Rb- and Cs-ion batteries (RIBs and CIBs) are late-model batteries. Herein, using first-principles calculations, the potential performance of H-MoS2 as a 2D electrode candidate in RIBs and CIBs has been investigated. The M-top site on 2D H-MoS2 possesses the most stable metal atom binding sites, and after adsorbing Rb and Cs atoms, its Fermi level goes up to the conduction band, indicating a semiconductor-to-metal transition. The maximal theoretical capacities of RIBs and CIBs are 372.05 (comparable to those of commercial graphite-based LIBs) and 223.23 mA h g-1, respectively, due to the strong adsorption capability of H-MoS2 for Rb and Cs ions. Noticeably, the diffusion barriers of Rb and Cs on H-MoS2 are 0.037 and 0.036 eV, respectively. Such a low diffusion barrier gives MoS2-based RIBs and CIBs high rate capability. In addition, H-MoS2 also has the characteristics of suitable open-circuit voltage, low expansion, good cycle stability, low cost, and easy experimental realization. These results indicate that MoS2-based RIBs and CIBs are innovative batteries with great potential, and may provide opportunities for cross-application of energy storage and multiple disciplines.

Two-Dimensional Lateral Heterostructures of Triphosphides: AlP3-GaP3 as a Promising Photocatalyst for Water Splitting.

Photocatalytic water splitting to produce hydrogen is a potential means of achieving scalable and economically feasible solar hydrogen production. Two-dimensional (2D) triphosphides are 2D materials with potential applications in photovoltaics and optoelectronics. Here, we theoretically investigated 56 systems in total, including seven monolayer XP3 (X = Al, Ga, Ge, As, In, Sn, and Sb) and their combined vertical and lateral heterostructures. We found that the lateral heterostructure AlP3-GaP3 should be a promising photocatalyst for water splitting, through a quadruple screening process combining free energy calculations. It is fascinating that AlP3-GaP3 ingeniously combines all the desired features for photocatalytic water-splitting reactions, including a nearly direct band gap (1.43 eV), perfect band edge position, high STH efficiency (16.89%), broad light absorption region of sunlight, ultrahigh carrier mobility (20,000 cm2 V-1 s-1), low exciton binding energy (0.33 eV), and excellent stability in a water environment. Moreover, through Gibbs free energy calculations, the active sites and possible reaction pathways of the overall water-splitting reaction by AlP3-GaP3 were also confirmed. Our work offers a strategy for the design and fabrication of novel lateral heterostructures for a high-performance photocatalyst in water-splitting reactions.

A promising photocatalyst for water-splitting reactions with a stable sandwiched P4O2/black phosphorus heterostructure and high solar-to-hydrogen efficiency.

Black phosphorus (BP) is a promising two-dimensional (2D) semiconductor, because of its tunable band gap and high hole mobility; however, its easy degradation under atmospheric conditions largely limits its application in photocatalytic water-splitting reactions. To overcome this disadvantage, we proposed a strategy for designing sandwiched P4O2-encapsulated BP (P4O2/BP) 2D materials, considering the automatic formation and high stability of P4O2 in air. We systematically considered five different packing models involving twenty sandwiched P4O2/BP systems using first-principles calculations. Through the triple screening process of 20 sandwiched P4O2/BP systems, we found that the O-1-P system with intrinsic electric field ingeniously combines all the desired features for photocatalytic water-splitting reactions, including small direct band gap (1.34 eV), low exciton binding energy, high hole mobility and ultrahigh solar-to-hydrogen efficiency as high as 22.77%. Through Gibbs free energy calculations, the active sites and possible reaction pathways of full water-splitting reactions were also confirmed. Our work offers useful guidance for designing and fabricating stable 2D materials with high performance for application in photocatalytic water-splitting reactions.

Few-Layer P4O2: A Promising Photocatalyst for Water Splitting.

Photocatalytic water splitting by a two-dimensional material is a promising technology for producing clean and renewable energy. Development of this field requires candidate materials with desirable optoelectronic properties. Here, we present a detailed theoretical investigation of the atomic and electronic structure of few-layer P4O2 systems to predict their optoelectronic properties. We predict that the three-layer P4O2 with normal packing (α-3), ingeniously combining all desired optoelectronic features, is an ideal candidate for photocatalytic water splitting. It fascinatingly bears nearly a direct band gap (1.40 eV), appropriate band edge position, high solar-to-hydrogen efficiency (17.15%), high sunlight absorption efficiency, and ultrahigh carrier mobility (21 460 cm2 V-1 s-1) at room temperature. These results make three-layer P4O2 a promising candidate for photocatalytic water splitting.

(111) Facets-Oriented Au-Decorated Carbon Nitride Nanoplatelets for Visible-Light-Driven Overall Water Splitting.

Development of a simple and stable photocatalyst for overall water splitting is a promising avenue for solar energy conversion. Here, carbon nitride (CN) nanosheet panels decorated with in situ-formed (111) facets-oriented Au nanoparticles (AuNPs) have been prepared by vapor-deposition polymerization followed by an easy immersion technique. Benefiting from the enhanced visible light absorption, the surface plasmon resonance effect of AuNPs, rapid transportation and separation of charge carriers, as well as better-aligned valence band levels, the as-obtained photocatalyst shows effective overall water splitting with stoichiometric H2 and O2 evolution even without any sacrificial agent, distinct from the half-reaction of Pt-decorated CN. This work opens up a brand-new route for facet self-selective growth of metal on two-dimensional conjugated carbon nitride materials, which has been demonstrated to be effective for artificial photosynthesis applications.