We present a general purpose Pt-Pt density-functional tight-binding (DFTB) parameter for Pt clusters as well as bulk, using a genetic algorithm (GA) to automatize the parameterization effort. First we quantify the improvement possible by only optimizing the repulsive potential alone, and second we investigate the effect of improving the electronic parameter as well. During both parameterization efforts we employed our own training set and test sets, with one set containing ∼20,000 spin-polarized DFT structures. We analyze the performance of our two DFTB Pt-Pt parameter sets against density functional theory (DFT) as well as an earlier DFTB Pt-Pt parameters. Our study sheds light on the role of both repulsive and electronic parameters with regards to DFTB performance.

MXenes are a novel class of two dimensional materials, discovered by Barsoum and Gogotsi [M. Naguib, J. Come, B. Dyatkin, V. Presser, P. Taberna, P. Simon, M. W. Barsoum, and Y. Gogotsi, Electrochemistry Communications 16, 61-64 (2012); B. Anasori, M. R. Lukatskaya, and Y. Gogotsi, Nature Reviews Materials vol. 2, 16098 (2017)]. Their large specific surface area and the tunability of their physicochemical properties as a function of the transition metal and surface terminal group make them a unique design platform for various applications, a primary example of which is pseudocapacitive energy storage. However, there is still incomplete understanding of how the transition metal chemistry and stoichiometry, and the surface termination affect charge storage mechanisms in MXene. In this study, we have performed systematic first-principles calculations for bulk MXene and found that the atomic charge of the metal cations, which is related to their valence, decreases across the d-electron metal series. Electronic-structure indicators of performance are examined to understand the energy storage behavior, whereby charges are stored between the terminal groups and adsorbing cations. Importantly, we found that the differential Bader charges show good agreement with theoretical capacitances and are useful in predicting charge storage trends in MXene-based pseudocapacitors. Furthermore, we have performed first-principles and grand canonical Monte Carlo calculations for the slab systems, finding that the solvent plays a critical role in enhancing the pseudocapacitive response.

Numerous fabrication protocols are known to yield transition metal oxides with structures related to layered double hydroxides, but the effect of fabrication protocol on the uniformity of mixed-metal compositions remain largely unexplored. We have analysed the apparent solubility limits and the structural implications of iron ions in nickel hydroxide lattices for materials prepared by four different fabrication protocols. Opposing shifts in the (100) and (001) reflection in powder X-ray diffraction results revealed a contraction of the nickel lattice upon successful incorporation of iron, with Ni-M distances exhibiting an apparently linear decrease with respect to iron content. This feature revealed the amount of iron incorporated into nickel-based materials to be dependent on fabrication protocol, varying from apparently negligible concentrations to over fifty atomic percent. The dependency of structure on fabrication protocols provides a handle to improve fundamental understanding of catalytically relevant coordination environments.

Monolayer molecular electrodes composed of titanium oxide nanosheets (TiO2ns) or ruthenium oxide nanosheets (RuO2ns) were prepared and their activities in the oxygen reduction reaction (ORR) were evaluated to investigate the ORR active sites in oxide catalysts. In TiO2ns, the influence of physical distortion sites in the crystal structure formed by introducing oxygen vacancies was determined. The ORR activity of TiO2ns was improved by introducing physical distortion sites. In RuO2ns, the effects of both the type of crystal structure and electrochemical distortion sites arising from redox reactions on ORR performance were studied. The type of crystal structure had almost no effect on ORR activity. In contrast, electrochemical distortion sites were expected to behave as the ORR active sites because the on-set potential of the ORR was similar to the redox peak position for the RuO2ns. Thus, the distortion sites in oxide crystal structures may behave as the active sites in the ORR independent of the metal species.

In this study, a novel brick-like NiCo2O4 material was synthesized via a facile hydrothermal method. The as-prepared NiCo2O4 material possessed high porosity with the BET specific surface area of 58.33 m2/g, and its pore size distribution was in a range of 5-15 nm with a dominant pore diameter of 10.7 nm. The electrochemical performance of the NiCo2O4 was further investigated as anode material for lithium-ion battery. The NiCo2O4 anode possessed a high lithium storage capacity up to 2353.0 mAh/g at the current density of 100 mA/g. Even at the high rate of 1 A/g, a reversible capacity of ∼600 mAh/g was still retained, and an average discharge capacity of ∼1145 mAh/g could be recovered when the current density was reduced back to 150 mA/g. Due to the simple and cost-effective process, the NiCo2O4 bricks anode material shows great potential for further large-scale applications on the area of lithium-ion battery.

Carbon nanomaterials are consistently providing new excitement over their properties and potential applications, but many of these material have yet to fully live up to their expectations commercially. The barrier to adoption often exists as a result of complex processing, fragility of the as-produced material, or difficulty scaling beyond laboratory quantities. This work provides a new approach for utilizing fibrous carbon nanomaterials to advance the technology toward new applications and industrial utility. This is accomplished by creating tailored device architectures through in-situ integration of activated carbon powder using carbon nanofiber deposition. The resulting hybrid materials and components can serve in diverse applications, with each instance able to be fine-tuned through a combination of processing parameters. The applications of such materials are anticipated to directly serve current carbon-based technology in filtration, energy storage and delivery, and thermal management, but the concepts are not limited to current carbon applications.

Colloidal gold-palladium (Au-Pd) bimetallic nanoparticles were used as catalysts to study the ethanol (EtOH) photo-oxidation cycle, with an emphasis towards driving carbon-carbon (C-C) bond cleavage at low temperatures. Au-Pd bimetallic alloy and core-shell nanoparticles were prepared to synergistically couple a plasmonic absorber (Au) with a catalytic metal (Pd) with composite optical and catalytic properties tailored towards promoting photocatalytic oxidation. Catalysts utilizing metals that exhibit localized surface plasmon resonance (SPR) can be harnessed for light-driven enhancement for small molecule oxidation via augmented photocarrier generation/separation and photothermal conversion. The coupling of Au to Pd in an alloy or core-shell nanostructure maintains SPR-induced charge separation, mitigates the poisoning effects on Pd, and allows for improved EtOH oxidation. The Au-Pd nanoparticles were coupled to semiconducting titanium dioxide photocatalysts to probe their effects on plasmonically-assisted photocatalytic oxidation of EtOH. Complete oxidation of EtOH to CO2 under solar simulated-light irradiation was confirmed by monitoring the yield of gaseous products. Bimetallics provide a pathway for driving desired photocatalytic and photoelectrochemical reactions with superior catalytic activity and selectivity.

In this paper, a novel NiFe-LDH@ZnO composite was prepared by using a facile two-step process upon nickel foam (NF) substrate. The morphologies and chemical compositions of the samples were characterized by SEM, EDS, XRD and XPS. Photocatalytic degradation of Rhodamine B dye was tested with the samples NiFe-LDH@ZnO@NF, ZnO@NF and NiFe-LDH under the same conditions. The experimental results revealed that the NiFe-LDH@ZnO@NF composite exhibited excellent photocatalytic performance, i.e., 1.4 and 2.5 times higher than that of pure ZnO and NiFe-LDH, respectively. The reason was that the NiFe-LDH@ZnO@NF composite provided a possibility to effectively inhibit the recombination of the photogenerated electron-hole pairs, and therefore enhanced the photocatalytic efficiency. This composite is expected to have potential applications in wastewater treatment field.

Ultraviolet light-emitting diodes (UVLEDs) with phosphor materials have considerable advantages over traditional illumination devices. Doping with rare earth ions can modify the optical spectrum of phosphor materials, but rare earths are very expensive. Thus, replacing rare earths with a common material would provide a great potential for the wide application in the future. In this study, we discovered that a novel type of semiconductor nanometre powder, namely manganese cobalt nickel copper oxide (MCNC), is able to emit blue-green wavelength spectrum when exited by 365-400nmUVLED. In addition, MCNC shows less attenuation of luminescence efficiency than other UVLED phosphor materials doped with rare earths with temperature increase. It is thus concluded that MCNC is a promising low-cost material to replace rare earths to adjust the optical spectrum wavelength of UVLED. This is the first time that nano-scale MCNC is reported to possess the property to change the optical spectrum wavelength of UVLED. This provides a new mechanical and nanometer phosphor material without rare earth doping to shift the wavelength spectrum.