Reducing the energy consumption of a hydrogen evolution reaction (HER) at a platinum (Pt) electrode is important for the hydrogen economy. Herein, we report the loading of alpha- or beta-nickel hydroxide (α- or β-Ni­(OH)2) nanostructures on the surface of a Pt electrode to improve its catalytic activity and stability for HER in alkaline electrolytes. Both experimental and theoretical studies reveal that β-Ni­(OH)2 is a better co-catalyst of Pt than α-Ni­(OH)2 for promoting the HER, attributed to the higher water dissociation ability of β-Ni­(OH)2, as well as the stronger interactions between β-Ni­(OH)2 and the Pt electrode. Particularly, the overpotential of the HER in 0.1 M KOH at 10 mA cm–2 is decreased from 278 mV at the Pt electrode to 92 mV at the β-Ni­(OH)2/Pt electrode, and the Tafel slope decreased from 62 to 42 mV dec–1, correspondingly. The performance of the β-Ni­(OH)2/Pt catalytic electrode surpasses that of most of the previously reported electrodes for the same purpose.

The discovery of stable two-dimensional (2D) semiconductors with exotic electronic properties is crucial to the future electronic technologies. Using the first-principles calculations, we predict the monolayered Silicon- and Germanium-monopnictides as a new class of semiconductors owning excellent dynamical and thermal stabilities, prominent anisotropy, and high possibility of experimental exfoliation. These semiconductors, including the monolayered SiP, SiAs, GeP, and GeAs, possess wide bandgaps of 2.08-2.64 eV obtained by hybrid functional calculation. Under small uniaxial strains (-2 to 3%), dramatic modulations of their band structures are observed, and furthermore, all the 2D monolayers (MLs) can be transformed between indirect and direct semiconductors. The monolayered GeAs and SiP exhibits extraordinary optical absorption in the range of visible and ultraviolet (UV) light spectra, respectively. The exfoliation energies of these monolayers are comparable to graphene, implying a strong probability of successful fabrication by mechanical exfoliation. These intriguing properties of the monolayered silicon- and germanium-monopnictides, combined with their highly stable structures, offer tremendous opportunities for electronic and optoelectronic devices working under UV-visible spectrum.

No abstract

Catalysts based on earth-abundant non-noble metals are interesting candidates for alkaline water electrolysis in sustainable hydrogen economies. However, such catalysts often suffer from high overpotential and sluggish kinetics in both the hydrogen and oxygen evolution reactions (HER and OER). In this study, a hybrid catalyst made of iron-doped cobalt phosphide (Fe-CoP) nanowire arrays and Ni(OH) 2 nanosheets is introduced that displays strong electronic interactions at the interface, which significantly improves the interfacial reactivity of reactants and/or intermediates with the hybrid catalyst surface. The combined experimental and theoretical study further confirms that the hybrid catalyst promotes the sluggish rate-limiting steps in both the HER and OER. Full water electrolysis is thus enabled to take place at such a low cell voltage as 1.52 V to reach the current density of 10 mA cm −2 along with superior durability and high conversion efficiency.

Polar interactions such as electrostatic forces and hydrogen bonds play an essential role in biological molecular recognition. On a protein surface, polar interactions occur mostly in a hydrophobic environment because nonpolar amino acid residues cover ~75% of the protein surface. We report that ionic interactions on a hydrophobic surface are modulated by their subnanoscale distance to the surface. We developed a series of ionic head groups-appended self-assembled monolayers with C2, C6, C8, and C12 space-filling alkyl chains, which capture a dendritic guest via the formation of multiple salt bridges. The guest release upon protonolysis is progressively suppressed when its distance from the background hydrophobe changes from 1.2 (C2) to 0.2 (C12) nanometers, with an increase in salt bridge strength of ~3.9 kilocalories per mole.

No abstract

Searching for new van der Waals (vdW) heterostructure with novel electronic and optical properties is of great interest and importance for the next generation of devices. By using first-principles calculations, we show that the electronic and optical properties of the arsenene/CN vdW heterostructure can be effectively modulated by applying vertical strain and external electric field. Our results suggest that this heterostructure has an intrinsic type-II band alignment with an indirect bandgap of 0.16 eV, facilitating the separation of photogenerated electron-hole pairs. The bandgap in the heterostructure can be tuned from 0-0.35 eV via the strain, experiencing an indirect-to-direct bandgap transition. Moreover, the bandgap of the heterostructure varies linearly with respect to a moderate external electric field, and the semiconductor-to-metal transition can be realized in the presence of a strong electric field. The calculated band alignment and the optical absorption reveal that the arsenene/CN heterostructure could present excellent light-harvesting performance. Our designed vdW heterostructure is expected to have great potential applications in nanoelectronic devices and photovoltaics.

First-principles total energy calculations are performed to investigate the formation and structures of Pt clusters on graphene. It is found that the formation energy of Pt on graphene increases with increasing Pt coverage. The structures of the absorbed Pt are that it is at the bridge site for a single Pt atom absorption, but form a dimerized cluster when two atoms are absorbed on graphene. For three- and four-Pt-atom absorption, linear and tetrahedral structures form, respectively, and the three-dimensional tetrahedral Pt(4) cluster is most stable in all the configurations investigated. There is a strong interatomic interaction among Pt atoms and so they tend to form clusters. While no magnetic behavior is expected after a single Pt atom is absorbed on graphene, the absorption of tetrahedral Pt(4) leads to Fermi level shifting to the valence band and the spin waves of C atoms in graphene become asymmetric and so they exhibit magnetism. The magnetic properties can thus be tuned by Pt absorption on graphene. The ultimate aim is to apply it in catalytic activity and electronic devices.