Oxygen storage/release (OSC) capacity is an important feature common to all three-way catalysts to combat harmful exhaust emissions. To understand the mechanism of improved OSC for doped CeO2, we undertook the structural investigation by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-TPR (temperature-programmed hydrogen reduction) and density functional theoretical (DFT) calculations of transition-metal-, noble-metal-, and rare-earth (RE)-ion-substituted ceria. In this report, we present the relationship between the OSC and structural changes induced by the dopant ion in CeO2. Transition metal and noble metal ion substitution in ceria greatly enhances the reducibility of Ce1−x M x O2−δ (M = Mn, Fe, Co, Ni, Cu, Pd, Pt, Ru), whereas rare-earth-ion-substituted Ce1−x A x O2−δ (A = La, Y) have very little effect in improving the OSC. Our simulated optimized structure shows deviation in cation−oxygen bond length from ideal bond length of 2.34 Å (for CeO2). For example, our theoretical calculation for Ce28Mn4O62 structure shows that Mn−O bonds are in 4 + 2 coordination with average bond lengths of 2.0 and 3.06 Å respectively. Although the four short Mn−O bond lengths spans the bond distance region of Mn2O3, the other two Mn−O bonds are moved to longer distances. The dopant transition and noble metal ions also affects Ce coordination shell and results in the formation of longer Ce−O bonds as well. Thus longer cation−oxygen bonds for both dopant and host ions results in enhanced synergistic reduction of the solid solution. With Pd ion substitution in Ce1−x M x O2−δ (M = Mn Fe, Co, Ni, Cu) further enhancement in OSC is observed in H2−TPR. This effect is reflected in our model calculations by the presence of still longer bonds compared to the model without Pd ion doping. The synergistic effect is therefore due to enhanced reducibility of both dopant and host ion induced due to structural distortion of fluorite lattice in presence of dopant ion. For RE ions (RE = Y, La), our calculations show very little deviation of bonds lengths from ideal fluorite structure. The absence of longer Y−O/La−O and Ce−O bonds make the structure much less susceptible to reduction.

Both nanocolumnar and dense germanium thin films, synthesized by evaporative deposition, were tested as a potential anode material for sodium-ion batteries. The reversible capacity of the nanocolumnar films was found to be 430 mAh/g, which is higher than the theoretical capacity of 369 mAh/g. The nanocolumnar films retained 88% of their initial capacity after 100 cycles at C/5, whereas the dense films began to deteriorate after ∼15 cycles. Additionally, the nanocolumnar films were stable at charge/discharge rates up to 27C (10 A/g). The diffusion coefficient for sodium in germanium was estimated, from impedance analysis of the dense films, to be ∼10 −13 cm 2 s −1 . Modeling of diffusion in the sodium-germanium system predicts that sodium diffusion in the near-surface layers of the material is significantly faster than in the bulk. These results show that small feature sizes are critical for rapid, reversible electrochemical sodiation of germanium.

Sn0.9Cu0.1 nanoparticles were synthesized via a surfactant-assisted wet chemistry method, which were then investigated as an anode material for ambient temperature rechargeable sodium ion batteries. The Sn0.9Cu0.1 nanoparticle-based electrodes exhibited a stable capacity of greater than 420 mA h g(-1) at 0.2 C rate, retaining 97% of their maximum observed capacity after 100 cycles of sodium insertion/deinsertion. Their performance is considerably superior to electrodes made with either Sn nanoparticles or Sn microparticles.

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Flourite-type nanocrystalline Ce0.9Fe0.1O2−δ and Ce0.89Fe0.1Pd0.01O2−δ solid solutions have been synthesized by solution combustion method, which show higher oxygen storage/release property (OSC) compared to CeO2 and Ce0.8Zr0.2O2. Temperature programmed reduction and XPS study reveal that the presence of Pd ion in Ce0.9Fe0.1O2−δ facilitates complete reduction of Fe3+ to Fe2+ state and partial reduction of Ce4+ to Ce3+ state at temperatures as low as 105 °C compared to 400 °C for monometal-ionic Ce0.9Fe0.1O2−δ. Fe3+ ion is reduced to Fe2+ and not to Fe0 due to favorable redox potential for Ce4+ + Fe2+ → Ce3+ + Fe3+ reaction. Using first-principles density functional theory calculation we determine M−O (M = Pd, Fe, Ce) bond lengths, and find that bond lengths vary from shorter (2.16 Å) to longer (2.9 Å) bond distances compared to mean Ce−O bond distance of 2.34 Å for CeO2. Using these results in bond valence analysis, we show that oxygen with bond valences as low as −1.55 are created, leading to activation of lattice oxygen in the bimetal ionic catalyst. Temperatures of CO oxidation and NO reduction by CO/H2 are lower with the bimetal-ionic Ce0.89Fe0.1Pd0.01O2−δ catalyst compared to monometal-ionic Ce0.9Fe0.1O2−δ and Ce0.99Pd0.01O2−δ catalysts. From XPS studies of Pd impregnated on CeO2 and Fe2O3 oxides, we show that the synergism leading to low temperature activation of lattice oxygen in bimetal-ionic catalyst Ce0.89Fe0.1Pd0.01O2−δ is due to low-temperature reduction of Pd2+ to Pd0, followed by Pd0 + 2Fe3+ → Pd2+ + 2Fe2+, Pd0 + 2Ce4+ → Pd2+ + 2Ce3+ redox reaction.