Ceria-Graphene Oxide Nanocomposite for Electro-oxidation of Urea: An Experimental and Theoretical Investigation

This study explores the potential of ceria-graphene oxide (CeO2-GO) nanocomposites as efficient electrocatalysts for urea electro-oxidation (UOR). This work combines experimental and theoretical investigations and characterization techniques confirm the successful formation of the CeO2 embedded on graphene oxide sheets. UOR activity was found to be dependent on both OH- and urea concentrations. The optimal UOR performance was achieved in a 0.1 M urea and 1.0 M KOH solution, as evidenced by the low Tafel slope of 60 mV/dec and high turnover frequency (TOF) of 1.690 s-1. DFT calculations revealed that the CeO2-GO nanocomposite exhibited strong urea adsorption due to its favorable bond lengths (Ce-O: 2.58 Å, O-H: 1.77 Å) and high adsorption energy (-1.05 eV). These findings revealed that the CeO2-GO nanocomposites are promising as efficient and durable electrocatalysts for urea conversion to valuable products like nitrogen and hydrogen gas, with potential applications in clean energy generation and ammonia synthesis.

Fine control for the preparation of ceria nanorods (111)

The morphologies and exposed surfaces of ceria nanocrystals are important factors in determining their performance. In order to establish a structure-property relationship for ceria nanomaterials, it is essential to have materials with well-defined morphologies and specific exposed facets. This is also crucial for acquiring high resolution ¹⁷O solid-state NMR spectra. In this study, we explore the synthesis conditions for preparing CeO₂ nanorods with exposed (111) facets. The effects of alkali concentration, hydrothermal temperature and time, cerium source and oxidation agent are investigated and optimal synthesis conditions are found. The resulting CeO₂ nanorods show very narrow ¹⁷O NMR peaks for the oxygen ions in the first, second and third layers, providing a foundation for future research on mechanisms involving ceria materials using ¹⁷O solid-state NMR spectroscopy.

Hydrogen assisted synthesis of branched nickel nanostructures: a combined theoretical and experimental study

The selective adsorption of small molecules over specific facets plays an important role in morphology controlled synthesis of metal nanocrystals. In the present work, hydrogen is found to be a good capping agent for direct synthesis of branched nickel nanocrystals, i.e., secondary branching (Ni-SB) nanoparticles and multipods (Ni-MP). Using ab initio thermodynamics and the Wulff construction principle, it has been found that: (i) in the presence of hydrogen (P_H2 = 6 bar), the facet structure stability follows the order of Ni(100) > Ni(111) > Ni(110), resulting in competitive over-growth along the 〈111〉 and 〈110〉 directions; (ii) with increasing hydrogen pressure, the Ni deposition rate over the crystal surface increases as a result of more Ni²⁺ reduction; the competition between deposition and surface diffusion, therefore, becomes the vital factor for the nanocrystal growth process; (iii) the diffusion energy barrier of a surface Ni atom on Ni(111) is lower than that on Ni(110), especially on hydrogen covered surfaces, indicating that the kinetic over-growth only along the 〈111〉 direction producing Ni-MP will be dominant under P_H2 = 14 bar; (iv) the ab initio based Wulff construction principle predicts the shapes and morphologies at different hydrogen pressures which is further confirmed with HRTEM results. Finally, compared with nickel nanoparticles (Ni-NP) synthesized in the absence of hydrogen, the hydrogen assisted branched Ni nanomaterials, especially the Ni-MP, show higher catalytic activities for hydrogenation reactions of acetophenone and nitrobenzene.

Adsorption of C2 gases over CeO2-based catalysts: synergism of cationic sites and anionic vacancies

Combined in situ DRIFTS and in silico DFT studies show the potential of Pd-substituted CeO₂ for the hydrogenation of C₂-gases.