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We theoretically and experimentally show that, with water being adsorbed, the graphene oxide (GO) is converted to a spontaneously dynamic covalent material under ambient conditions, where the dominated epoxy and hydroxyl groups are mediated by water molecules to spontaneously break/reform their C–O bonds to achieve dynamic oxygen migration. This dynamic material presents structural adaptivity for response to biomolecule adsorption. Both density functional theory calculations and ab initio molecular dynamics simulations demonstrate that this spontaneously dynamic characteristics is attributed to the adsorption of water molecules, which sharply reduces the barriers of these oxygen migration reactions on GO to the level less than or comparable to the hydrogen bonding energy in liquid water. [ABSTRACT FROM AUTHOR]

Identifying the oxidation structure of two-dimensional interfaces is crucial to improve surface chemistry and electronic properties. Beyond graphene with only phenyl rings, a novel carbon-nitrogen material, C3N, presents an intrinsic heterogeneous surface morphology where each phenyl ring is encircled by six nitrogen atoms, yet its atomistic oxidation structure remains unclear. Here, combining a series of density functional theory calculations and ab initio molecular dynamics simulations, we demonstrate that thermodynamically favorable oxidation loci are confined to the phenyl ring, and kinetic transformations of oxidation structures are feasible along the phenyl ring, whereas those toward nitrogen atoms are proven to be extremely difficult. These results are attributed to the lower barrier of oxygen atom migration along the phenyl ring, while the significantly high barriers toward nitrogen atoms are due to the heterogeneous potential energy surface for oxygen–C3N interaction. This work highlights the significance of surface morphology on the characteristics of oxidation structure, offering insights into tunable electronic properties via confined interfacial oxidation. [ABSTRACT FROM AUTHOR]

[Display omitted] Water dissociation is of fundamental importance in scientific fields and has drawn considerable interest in diverse technological applications. However, the high activation barrier of breaking the O H bond within the water molecule has been identified as the bottleneck, even for the water adsorbed on the graphene oxide (GO). Herein, using the density functional theory calculations, we demonstrate that the water molecule can be spontaneously dissociated on GO supported by the (1 1 1) surface of the copper substrate (Copper-GO). This process involves a proton transferring from water to the interfacial oxygen group, and a hydroxide covalently bonding to GO. Compared to that on GO, the water dissociation barrier on Copper-GO is significantly decreased to be less than or comparable to thermal fluctuations. This is ascribed to the orbital-hybridizing interaction between copper substrate and GO, which enhances the reaction activity of interfacial oxygen groups along the basal plane of GO for water dissociation. Our work provides a novel strategy to access water dissociation via the substrate-enhanced reaction activity of interfacial oxygen groups on GO and indicates that the substrate can serve as an essential key to tuning the catalytic performance of various two-dimensional material devices. [ABSTRACT FROM AUTHOR]

Context : Previous theoretical studies have suggested that two-dimensional (2D) MBene materials might display adequate monatomic catalytic activity for the hydrogen evolution reaction (HER). Recently, a study reported the experimental synthesis of a 2D MBene (Mo4/3B2), re-defined as boridene, albeit no effort has been devoted to explore the single-atom catalytic activity for HER of this experimentally synthesized 2D material. Therefore, we herein investigate the single-atom HER performance of the boridene. Interestingly, with Mo defects mixed with single Au and Zn atoms shows excellent hydrogen evolution performance, and the change in the Gibbs free energy ( Δ G H ) value is close to 0 eV, which can even match the performance of Pt-based materials. Through analysis of the charge density difference and density of states, the mechanism affecting the HER performance is explained at the electronic level. This work provides a new direction for the use of the Mo4/3B2 monolayer two-dimensional materials in the field of single-atom catalysis for HER. Methods: This study used the DFT calculations in Vienna ab initio simulation package. The GGA-Perdew-Burke-Ernzerhof functional with DFT-D2 correction is used to describe the exchange–correlation interactions. The projection augmented wave is used with the plane wave cutoff of 500 eV. The convergences of energy and force are 10−5 eV and 0.01 eV/Å, respectively. A vacuum layer with a height of 20 Å is set in the Z direction. For geometry optimization, self-consistent, and DOS calculations, the k-point grids sampled in Brillouin zones are 3 × 3 × 1, 9 × 9 × 1, and 9 × 9 × 1, respectively. The AIMD simulation is performed in the canonical ensemble (NVT), and the temperature was maintained at 300 K by Nosé-Hoover thermostats with a time step of 2.0 fs. [ABSTRACT FROM AUTHOR]

Single transition‐metal atom coordinated graphite carbon nitride, including the metal atom doped g‐C3N4 system, displays catalytic activity comparable to that of the noble metal Pt catalyst with outstanding performance. Herein, we investigate the single atom catalytic performance of g‐C3N3 embedded by a single transition metal atom (M−C3N3; M=Mn, Fe, Co, Ni, Cu, Rh, Pd, Ag, and Pt) for hydrogen evolution reaction (HER) using density functional theory (DFT) calculations. The results indicate that all the M−C3N3 catalysts are thermally and dynamically stable systems. By comparing the Gibbs free energies, we found that the Rh−C3N3 catalyst exhibits the best HER electrocatalytic performance among the investigated systems. Subsequently, analysis of electronic structure indicates that the Rh−C3N3 system displays a metallic behavior, which is a beneficial feature for an adequate HER electrocatalyst. Finally, the charge density difference of the Rh−C3N3 structure further supports the rationality of our results. This study provides a new candidate of low‐cost, high‐performance, and highly active non‐noble metal electrocatalysts. [ABSTRACT FROM AUTHOR]

Recent experiments have shown the coexistence of both large unoxidized and oxidized regions on graphene oxide (GO), but the underlying mechanism for the formation of the GO atomic structure remains unknown. Now, using density functional calculations, 52 oxidation pathways for local pyrene structures on GO were identified, and a kinetic profile for graphene oxidation with a high correlation between oxidation loci was proposed, which is different from the conventional view, which entails a random distribution of oxidation loci. The high correlation is an essential nature of graphene oxidation processes and can be attributed to three crucial effects: 1) breaking of delocalized π bonds, 2) steric hindrance, and 3) hydrogen-bond formation. This high correlation leads to the coexistence of both large unoxidized and oxidized regions on GO. Interestingly, even in oxidized regions on GO, some small areas of sp2-hybridized domains, similar to 'islands', can persist because of steric effects. [ABSTRACT FROM AUTHOR]

• The anion plays a crucial function in controlling the GO interlayer spacing. • The ion bridge is chiefly responsible for the reducing of the GO interlayer spacing. • The ion bridge is composed of one anion sandwiched by two cations. • The effect of the number of ion bridges on the GO interlayer spacing is investigated. Interlayer spacing of graphene oxide (GO) membranes can be precisely controlled using cations, which has been extensively used in nanofiltration membrane. However, no report definitely discloses the specific performance of anion in treating GO membrane, although cations and anions naturally coexist in aqueous solution. Subjectively, anion might have weak/reverse effect in maintaining the interlayer of negatively charged GO, which is yet confirmed by no evidence. In this work, combining molecular dynamics simulations and density functional theory calculations, we have discovered a long-time unexplored effect that anion can also sustain the GO membrane interlayer — specifically, two types of ion bridges (confined within two neighboring GO sheets), one composed of one anion intercalated into two cations and the other composed of two anions sandwiched by two cations, can effectively and stably fix the interlayer spacing of GO membrane. Our calculations revealed that the ion bridges greatly enhance the interaction between two neighboring GO sheets, making them highly stabilize in aqueous solution. Moreover, free energy calculations and density functional theory calculations further confirm the critical role of ion bridge in controlling the interlayer spacing of GO membrane. Our findings highlight, for the first time, the undiscovered control of GO membrane interlayer with anions via forming an ingenious ion bridge, rather than the preconceived weak/reverse effect of anions, which could inspire the future application of anions (and ion bridge) in membrane design. [ABSTRACT FROM AUTHOR]