Single sublattice endotaxial phase separation driven by charge frustration in a complex oxide.

Complex transition-metal oxides are important functional materials in areas such as energy and information storage. The cubic ABO3 perovskite is an archetypal example of this class, formed by the occupation of small octahedral B-sites within an AO3 network defined by larger A cations. We show that introduction of chemically mismatched octahedral cations into a cubic perovskite oxide parent phase modifies structure and composition beyond the unit cell length scale on the B sublattice alone. This affords an endotaxial nanocomposite of two cubic perovskite phases with distinct properties. These locally B-site cation-ordered and -disordered phases share a single AO3 network and have enhanced stability against the formation of a competing hexagonal structure over the single-phase parent. Synergic integration of the distinct properties of these phases by the coherent interfaces of the composite produces solid oxide fuel cell cathode performance superior to that expected from the component phases in isolation.

Computationally assisted identification of functional inorganic materials.

The design of complex inorganic materials is a challenge because of the diversity of their potential structures. We present a method for the computational identification of materials containing multiple atom types in multiple geometries by ranking candidate structures assembled from extended modules containing chemically realistic atomic environments. Many existing functional materials can be described in this way, and their properties are often determined by the chemistry and electronic structure of their constituent modules. To demonstrate the approach, we isolated the oxide Y(2.24)Ba(2.28)Ca(3.48)Fe(7.44)Cu(0.56)O21, with a largest unit cell dimension of over 60 angstroms and 148 atoms in the unit cell, by using a combination of this method and experimental work and show that it has the properties necessary to function as a solid oxide fuel-cell cathode.

Quantized electron-transfer pathways at nanoparticle-redox centre hybrids.

Hexanethiolate gold monolayer-protected clusters (C6-MPCs) with an average core diameter of 1.8 nm and a capacitance of 0.6 aF are synthesised by a two-phase method. These clusters are functionalised with (6-ferrocenyl)-1-hexanethiol by a place exchange reaction at different molar ratios. The average number of ferrocene centres per cluster determined by (1)H NMR is ten, seven and four. Differential pulse voltammetry and cyclic voltammetry measurements for cluster solutions in 0.1 M TBAPF(6)/Tol:AN (2:1) clearly show the response of the Fc(+)/Fc redox couple and of quantized double layer (QDL) charging events of the gold core. A transition from single to multiple electron-transfer response for the redox couple is observed as the number of ferrocene units per cluster is increased. The distances between the redox moieties are estimated considering a homogeneous distribution of the redox sites on the nanoparticle ligand shell. In all the cases, the inter-ferrocene average separation is too large to observe self-exchange reactions and the most likely electron-transfer pathway is by fast rotational diffusion. The oxidation of the ferrocene groups results in an electrostatic switching-off of electron transfers between the electrode and the nanoparticle core.

Single atom hot-spots at Au-Pd nanoalloys for electrocatalytic H2O2 production.

A novel strategy to direct the oxygen reduction reaction to preferentially produce H(2)O(2) is formulated and evaluated. The approach combines the inertness of Au nanoparticles toward oxidation, with the improved O(2) sticking probability of isolated transition metal "guest" atoms embedded in the Au "host". DFT modeling was employed to screen for the best alloy candidates. Modeling indicates that isolated alloying atoms of Pd, Pt, or Rh placed within the Au surface should enhance the H(2)O(2) production relative to pure Au. Consequently, Au(1-x)Pd(x) nanoalloys with variable Pd content supported on Vulcan XC-72 were prepared to investigate the predicted selectivity toward H(2)O(2) production for Au alloyed with Pd. It is demonstrated that increasing the Pd concentration to 8% leads to an increase of the electrocatalytic H(2)O(2) production selectivity up to nearly 95%, when the nanoparticles are placed in an environment compatible with that of a proton exchange membrane. Further increase of Pd content leads to a drop in H(2)O(2) selectivity, to below 10% for x = 0.5. It is proposed that the enhancement in H(2)O(2) selectivity is caused by the presence of individual surface Pd atoms surrounded by gold, whereas surface ensembles of contiguous Pd atoms support H(2)O formation. The results are discussed in the context of exergonic electrocatalytic H(2)O(2) synthesis in Polymer Electrolyte Fuel Cells for the simultaneous cogeneration of chemicals and electricity, the latter a credit to production costs.

In situ preparation of network forming gold nanoparticles in agarose hydrogels.

Gold nanoparticles are obtained by reduction of a Au(iii) precursor within an agarose hydrogel where they form percolating networks upon partial dehydration and shrinkage of the gel.