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We have examined the potential energy hypersurfaces for the carbon-rich phases of carbon nitride, CN and C 3 N, and discovered low-energy structures different from those reported previously. Trends in the preferred local bonding environments have been analyzed as a function of nitrogen content. For each composition, several structures with similar energies were found, but they have very different equilibrium volumes; the structure produced during synthesis will strongly depend on the preparation conditions. When low densities are favored, conjugated planar-ring structures with sp 2 hybridized carbon are most likely to be formed. These structures are similar to those suggested as potential photocatalytic materials. At high pressures, the preferred structures contain three-coordinate nitrogen and sp 3 hybridized carbon, including the ␤-InS structure, which we predict to be the thermodynamically preferred structure for CN under positive hydrostatic pressures. This structure has a moderately high bulk modulus with a lower formation energy than ␤-C 3 N 4 and so should be more easily synthesized.

The development of new insertion electrodes in sodium-ion batteries requires an in-depth understanding of the relationship between electrochemical performance and the structural evolution during cycling. To date in situ synchrotron X-ray and neutron diffraction methods appear to be the only probes of in situ electrode evolution at high rates, a critical condition for battery development. Here, the structural evolution of the recently synthesized O3-phase of Na 2/3 Fe 2/3 Mn 1/3 O 2 is reported under relatively high current rates. The evolution of the phases, their lattice parameters, and phase fractions, and the sodium content in the crystal structure as a function of the charge/discharge process are shown. It is found that the O3-phase persists throughout the charge/discharge cycle but undergoes a series of two-phase and solid-solution transitions subtly modifying the sodium content and atomic positions but keeping the overall space-group symmetry (structural motif ). In addition, for the fi rst time, evidence of a structurally characterized region is shown that undergoes two-phase and solid-solution phase transitions simultaneously. The Mn/Fe-O bond lengths, c lattice parameter evolution, and the distance between the Mn/FeO 6 layers are shown to concertedly change in a favorable manner for Na + insertion/extraction. The exceptional electrochemical performance of this electrode can be related in part to the electrode maintaining the O3-phase throughout the charge/discharge process.

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Here, we demonstrate that structural defects can induce catalytic reactivity in simple metal oxides to deliver cost-effective alternatives to noble metal group catalysts. We detail a strategy for introducing multiple defect sites in a binary TiO2–SiO2 composite to invoke synergism for oxygen activation. Hydrogenation and UV light pretreatment were applied to generate two distinct and adjacent defect sites, Ti3+ and silica-based nonbridging oxygen hole centers (NBOHC)which work in unison to activate oxygen and oxidize formic acid under ambient conditions without light. The hydrogenation step was found to be crucial for rupturing Ti–O–Si bonds while first-principles calculations indicated that Si-doped TiO2 lowered the energy barrier for oxygen activation and formic acid dehydrogenation on the defect sites. Activity lost during the reaction was recoverable by catalyst reillumination. Defective metal oxides represent an appealing prospect in the pursuit of simple and readily accessible catalyst materials.

In this study, we utilize scalable, flame spray synthesis to develop defective ZnO nanomaterials for the concurrent generation of H 2 and CO during electrochemical CO 2 reduction reactions (CO 2 RR). The designed ZnO achieved a H 2 /CO ratio of ~1 with a large current density (j) of 40 mA cm -2 during longterm continuous reaction at a cell voltage of 2.6 V. Through in-situ atomic pair distribution function analysis, we explored the remarkable stability of our ZnO structures, addressing the knowledge gap in understanding the dynamics of oxide catalysts during CO 2 RR. Through optimization of synthesis conditions, ZnO facets were modulated which were shown to affect reaction selectivity, in agreement with theoretical calculations. These findings and insights on synthetic manipulation of active sites in defective metal-oxides can be used as guidelines to develop active catalysts for syngas production for renewable power-to-X to generate a range of fuels and chemicals.