Morphology and reactivity of size-selected titanium oxide nanoclusters on Au(111).

The morphology and reactivity of mass-selected titania clusters, Ti3O6 and Ti3O5, deposited onto Au(111) were studied by scanning tunneling microscopy and temperature programmed desorption. Despite differing by only one oxygen atom, the stoichiometric Ti3O6 and the sub-stoichiometric ("reduced") Ti3O5 clusters exhibit very different structures and preferred binding sites. The Ti3O6 clusters bind at step edges and form small assemblies (2-4 clusters) on Au terraces, while the "reduced" Ti3O5 clusters form much larger fractal-like assemblies that can extend across step boundaries. Annealing the Ti3O5,6/Au(111) systems to higher temperatures causes changes in the size-distributions of cluster assemblies, but does not lead to the formation of TiOx nanoislands for temperatures ≤700 K. Reactivity studies show that the reduced Ti3O5 cluster has higher activity than Ti3O6 for 2-propanol dehydration, although both clusters exhibit substantial activity for dehydrogenation to acetone. Calculations using DFT+U suggest that the differences in aggregate morphology and reactivity are associated with the number of undercoordinated Ti3c sites in the supported clusters

3D Honeycomb‐Like Structured Graphene and Its High Efficiency as a Counter‐Electrode Catalyst for Dye‐Sensitized Solar Cells

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99676/1/9210_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/99676/2/anie_201303497_sm_miscellaneous_information.pd

Visible light-driven H2 production over highly dispersed Ruthenia on Rutile TiO2 nanorods

The immobilization of miniscule quantities of RuO2 (~0.1%) onto one-dimensional (1D) TiO2 nanorods (NRs) allows H2 evolution from water under visible light irradiation. Rod-like rutile TiO2 structures, exposing preferentially (110) surfaces, are shown to be critical for the deposition of RuO2 to enable photocatalytic activity in the visible region. The superior performance is rationalized on the basis of fundamental experimental studies and theoretical calculations, demonstrating that RuO2(110) grown as 1D nanowires on rutile TiO2(110), which occurs only at extremely low loads of RuO2, leads to the formation of a heterointerface that efficiently adsorbs visible light. The surface defects, band gap narrowing, visible photoresponse, and favorable upward band bending at the heterointerface drastically facilitate the transfer and separation of photogenerated charge carriers.Peer ReviewedPostprint (published version

The conversion of CO2 to methanol on orthorhombic β-Mo2C and Cu/β-Mo2C catalysts: mechanism for admetal induced change in the selectivity and activity

The conversion of CO2 into methanol catalyzed by β-Mo2C and Cu/β-Mo2C surfaces has been investigated by means of a combined experimental and theoretical study. Experiments have shown the direct activation and dissociation of the CO2 molecule on bare β-Mo2C, whereas on Cu/β-Mo2C, CO2 must be assisted by hydrogen for its conversion. Methane and CO are the main products on the clean surface and methanol production is lower. However, the deposition of Cu clusters avoids methane formation and increases methanol production even above that corresponding to a model of the technical catalyst. DFT calculations on surface models of both possible C- and Mo-terminations, corroborate the experimental observations. Calculations for the clean Mo-terminated surface reveal the existence of two possible routes for methane production (C + 4H → CH4; CH3O + 3H → CH4 + H2O) which are competitive with methanol synthesis, displaying slightly lower energy barriers. On the other hand, a model for Cu deposited clusters on the Mo- terminated surface points towards a new route for methanol and CO production avoiding methane formation. The new route is a direct consequence of the generation of a Mo2C-Cu interface. The present experimental and theoretical results entail the interesting catalytic properties of Mo2C as an active support of metallic nanoparticles, and also illustrate how the deposition of a metal can drastically change the activity and selectivity of a carbide substrate for CO2 hydrogenation

3D Honeycomb‐Like Structured Graphene and Its High Efficiency as a Counter‐Electrode Catalyst for Dye‐Sensitized Solar Cells

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99684/1/ange_201303497_sm_miscellaneous_information.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/99684/2/9380_ftp.pd

An Ideal Electrode Material, 3D Surface-Microporous Graphene for Supercapacitors with Ultrahigh Areal Capacitance

© 2017 American Chemical Society. The efficient charge accumulation of an ideal supercapacitor electrode requires abundant micropores and its fast electrolyte-ions transport prefers meso/macropores. However, current electrode materials cannot meet both requirements, resulting in poor performance. Herein, we creatively constructed three-dimensional cabbage-coral-like graphene as an ideal electrode material, in which meso/macro channels are formed by graphene walls and rich micropores are incorporated in the surface layer of the graphene walls. The unique 3D graphene material can achieve a high gravimetric capacitance of 200 F/g with aqueous electrolyte, 3 times larger than that of commercially used activated carbon (70.8 F/g). Furthermore, it can reach an ultrahigh areal capacitance of 1.28 F/cm2 and excellent rate capability (83.5% from 0.5 to 10 A/g) as well as high cycling stability (86.2% retention after 5000 cycles). The excellent electric double-layer performance of the 3D graphene electrode can be attributed to the fast electrolyte ion transport in the meso/macro channels and the rapid and reversible charge adsorption with negligible transport distance in the surface micropores

Design and Synthesis of 3D Potassium-Ion Pre-Intercalated Graphene for Supercapacitors

In this paper, a novel material - 3D potassium-ion preintercalated graphene - was designed and synthesized via one step using a new reaction between K and CO. Furthermore, this material exhibited excellent performance as electrodes for aqueous symmetrical supercapacitors. When the electrode was scaled up from 3.0 to 8.0 mg/cm2, negligible capacitance degradation was observed, leading to a very high areal capacitance of 1.50 F/cm2 at 1 A/g. Furthermore, even if a large operating temperature of -15 or 55 °C was employed, its excellent electrochemical performance remained with specific capacitances of 208 F/g at 55 °C, 184 F/g at 25 °C, and 98 F/g at -15 °C. This could be attributed to 3D structure and K+ preintercalation of the material, which provides rich active sites for electric double-layer formation, lower ion transport resistance, and shorter diffusion distance

Direct conversion of CO2 to meso/macro-porous frameworks of surface-microporous graphene for efficient asymmetrical supercapacitors

CO2 conversion to useful materials is the most attractive approach to control its content in the atmosphere. An ideal electrode material for supercapacitors should possess suitable meso/macro-pores as electrolyte reservoirs and rich micro-pores as places for the adsorption of electrolyte ions. Herein, we designed and synthesized such an ideal material, meso/macro-porous frameworks of surface-microporous graphene (MFSMG), from CO2via its one-step exothermic reaction with potassium. Furthermore, the MFSMG electrode exhibited a high gravimetric capacitance of 178 F g-1 at 0.2 A g-1 in 2 M KOH and retained 85% capacitance after increasing current density by 50 times. The combination of the MFSMG electrode and the activated carbon (AC) electrode constructed an asymmetrical AC//MFSMG capacitor, leading to a high capacitance of 242.4 F g-1 for MFSMG and 97.4 F g-1 for AC. With the extended potential, the asymmetrical capacitor achieved an improved energy density of 9.43 W h kg-1 and a power density of 3504 W kg-1. This work provides a novel solution to solve the CO2 issue and creates an efficient electrode material for supercapacitors

3D graphene from CO2 and K as an excellent counter electrode for dye-sensitized solar cells

Copyright © 2017 John Wiley & Sons, Ltd. 3D graphene, which was synthesized directly from CO2 via its exothermic reaction with liquid K, exhibited excellent performance as a counter electrode for a dye-sensitized solar cell (DSSC). The DSSC has achieved a high power conversion efficiency of 8.25%, which is 10 times larger than that (0.74%) of a DSSC with a counter electrode of the regular graphene synthesized via chemical exfoliation of graphite. The efficiency is even higher than that (7.73%) of a dye-sensitized solar cell with an expensive standard Pt counter electrode. This work provides a novel approach to utilize a greenhouse gas for DSSCs