Spatially resolved imaging of inhomogeneous charge transfer behavior in polymorphous molybdenum oxide. II. Correlation of localized coloration/insertion properties using spectroelectrochemical microscopy

A newly developed spectroelectrochemical imaging approach for directly assessing lithium ion insertion energetics and kinetics in mixed-phase, polymorphous MoO3 is reported. Two variants of spectroelectrochemical microscopy were used to monitor insertion dynamics and to follow electrochemically induced phase transformations at specifically identified structural and compositional domains. Cyclovoltoabsorptometric (dOD/dE) measurements carried out in LiClO4/propylene carbonate solutions reveal that the lithium insertion is nonuniform and can be directly correlated with phase-segregated domains comprising alpha-MoO3, beta-MoO3, and intermixed alpha-/beta-MoO3. Lithium insertion is found to proceed by a staging process where each phase displays energetically distinct insertion behaviors. Chronoabsorptometric imaging measurements allow for the simultaneous estimation of lithium diffusion coefficients, ionic conductivities, and lithium capacities at isolated phases within the polymorphous material. The lithium diffusion coefficient and ionic conductivity is largest for domains comprising intermixed alpha-/beta-MoO3, whereas it is smallest at domains consisting of beta-MoO3. The higher diffusion coefficient observed for intermixed alpha-/beta-MoO3 domains is most likely due to larger thermodynamic enhancement factors for the mixed phase domains than for domains consisting of either alpha-MoO3 or beta-MoO3. Estimation of capacity values within each uniquely identified domain reveals that the lithium insertion capacity is about 4 times greater in alpha-MoO3 than in beta-MoO3. The discrepancies between the lithium insertion capacities can be rationalized in terms of lattice oxygen defects, which effectively reduce the number of available lithium insertion sites in beta-MoO3 as compared to alpha-MoO3.     

Adsorption state and morphology of anthraquinone-2-carboxylic acid deposited from solution onto the atomically-smooth native oxide surface of Al(111) films studied by infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy.

The adsorption state and morphology of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.02 - 1.00 mg ml(-1)) onto atomically-smooth native oxide surfaces of Al(111) films were investigated by infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The atomically-smooth oxide surfaces were prepared by vacuum evaporation of Al on mica substrates at 350 degrees C, followed by oxidation in an oxygen-dc glow discharge at room temperature. It was found that AQ-2-COOH is adsorbed on the film surfaces in both the neutral and ionized state, where the amount of the neutral molecules increases with increasing concentration. This molecule is adsorbed as both a uniform nanometer-scale film, and as micrometer-sized particles with heights ranging from 10 to 200 nm above the film surface. The volumes of the particles of deposited AQ-2-COOH increased with increasing concentration. It is concluded that the particles are microcrystallites of neutral AQ-2-COOH and that the thin uniform film results from AQ-2-COOH anion formation on the film surfaces. A comparison of the results obtained by use of these surface analytical techniques clearly shows the features and advantages of these tools.