Tailored (La0.2Pr0.2Nd0.2Tb0.2Dy0.2)2Ce2O7 as a Highly Active and Stable Nanocatalyst for the Oxygen Evolution Reaction.

Designing highly active and robust catalysts for the oxygen evolution reaction is key to improving the overall efficiency of the water splitting reaction. It has been previously demonstrated that evaporation induced self-assembly (EISA) can be used to synthesize highly porous and high surface area cerate-based fluorite nanocatalysts, and that substitution of Ce with 50% rare earth (RE) cations significantly improves electrocatalyst activity. Herein, the defect structure of the best performing nanocatalyst in the series are further explored, Nd2Ce2O7, with a combination of neutron diffraction and neutron pair distribution function analysis. It is found that Nd3 + cation substitution for Ce in the CeO2 fluorite lattice introduces higher levels of oxygen Frenkel defects and induces a partially reduced RE1.5Ce1.5O5 + x phase with oxygen vacancy ordering. Significantly, it is demonstrated that the concentration of oxygen Frenkel defects and improved electrocatalytic activity can be further enhanced by increasing the compositional complexity (number of RE cations involved) in the substitution. The resulting novel compositionally-complex fluorite- (La0.2Pr0.2Nd0.2Tb0.2Dy0.2)2Ce2O7 is shown to display a low OER overpotential of 210 mV at a current density of 10 mAcm-2 in 1M KOH, and excellent cycling stability. It is suggested that increasing the compositional complexity of fluorite nanocatalysts expands the ability to tailor catalyst design.

Imidazolatic-Framework Bimetal Electrocatalysts with a Mixed-Valence Surface Anchored on an rGO Matrix for Oxygen Reduction, Water Splitting, and Dye Degradation.

This paper presents a simple strategy for manufacturing bifunctional electrocatalysts-graphene nanosheets (GNS) coated with an ultrafine NiCo-MOF as nanocomposites (denoted NiCo-MOF@GNS) having a N-doped defect-rich and abundant cavity structure through one-pool treatment of metal-organic frameworks (MOFs). The precursors included N-doped dodecahedron-like graphene nanosheets (GNS), in which the NiCo-MOF was encompassed within the inner cavities of the GNS (NiCo-MOF@GNS) at the end or middle portion of the tubular furnace with several graphene layers. Volatile imidazolate N x species were trapped by the NiCo-MOF nanosheets during the pyrolysis process, simultaneously inserting N atoms into the carbon matrix to achieve the defect-rich porous nanosheets and the abundantly porous cavity structure. With high durability, the as-prepared nanomaterials displayed simultaneously improved performance in the oxygen reduction reaction (ORR), the oxygen evolution reaction (OER), and photocatalysis. In particular, our material NiCo-MOF@GNS-700 exhibited excellent electrocatalytic activity, including a half-wave potential of 0.83 V (E ORR, 1/2), a low operating voltage of 1.53 V (E OER, 10) at 10 mA cm-2, a potential difference (ΔE) of 1.02 V between E OER, 10 and E ORR, 1/2 in 0.1 M KOH, and a low band gap of 2.61 eV. This remarkable behavior was due to the structure of the defect-rich porous carbon nanosheets and the synergistic impact of the NPs in the NiCo-MOF, the N-doped carbon, and NiCo-N x . Furthermore, the hollow structure enhanced the conductivity and stability. This useful archetypal template allows the construction of effective and stable bifunctional electrocatalysts, with potential for practical viability for energy conversion and storage.

Effect of Ligand Polarity on the Internal Dipoles and Ferroelectric Distortion in BaTiO3 Nanocubes.

Surface adsorbates and surrounding matrix species have been demonstrated to affect the properties of nanoscale ferroelectrics and nanoscale ferroelectric composites; potentially counteracting performance losses that can occur in small particle sizes. In this work, the effects of nonpolar oleic acid (OA) and polar tetrafluoroborate (BF4 - ) ligand capping on the surface of various sizes of BaTiO3 nanocubes have been investigated with combined neutron diffraction and neutron pair distribution function (PDF), density functional theory (DFT), and ab initio molecular dynamics (AIMD) methods. The low real space PDF region provides an unobstructed view of rhombohedral (split short and long) Ti-O distances in BaTiO3 nanocubes, mimicking the well-established order-disorder local structure found in bulk BaTiO3 . Interestingly, the intermediate-range order in nanocubes is found to be orthorhombic, rather than tetragonal. It is concluded that polar ligands adsorbed at BaTiO3 surfaces stabilize the correlation length scale of local rhombohedral distortions in ferroelectric nanoparticles relative to nonpolar ligands.

Controlled Synthesis of Highly Crystallized Mesoporous Mn2 O3 and Mn3 O4 by Using Anionic Surfactants.

Mesostructured manganese oxide (Mn3 O4 ) is prepared by a soft-templating method employing sodium dodecyl sulfate (SDS) as a structure-directing agent. By removing the template from the as-prepared mesostructured Mn3 O4 by extraction or calcination, we successfully synthesized highly crystallized mesoporous Mn3 O4 or Mn2 O3 , respectively, with different crystalline structures.