Biogenic calcium carbonate forms the inorganic component of seashells, otoliths, and many marine skeletons, and its formation is directed by an ordered template of macromolecules. Classical nucleation theory considers crystal formation to occur from a critical nucleus formed by the assembly of ions from solution. Using cryotransmission electron microscopy, we found that template-directed calcium carbonate formation starts with the formation of prenucleation clusters. Their aggregation leads to the nucleation of amorphous nanoparticles in solution. These nanoparticles assemble at the template and, after reaching a critical size, develop dynamic crystalline domains, one of which is selectively stabilized by the template. Our findings have implications for template-directed mineral formation in biological as well as in synthetic systems.

The initial stages of template-controlled CaCO3 formation revealed by Cryo-TEM

Powered by renewable energy sources such as solar, marine, geothermal and wind, generation of storable hydrogen fuel through water electrolysis provides a promising path towards energy sustainability. However, state-of-the-art electrolysis requires support from associated processes such as desalination of water sources, further purification of desalinated water, and transportation of water, which often contribute financial and energy costs. One strategy to avoid these operations is to develop electrolysers that are capable of operating with impure water feeds directly. Here we review recent developments in electrode materials/catalysts for water electrolysis using low-grade and saline water, a significantly more abundant resource worldwide compared to potable water. We address the associated challenges in design of electrolysers, and discuss future potential approaches that may yield highly active and selective materials for water electrolysis in the presence of common impurities such as metal ions, chloride and bio-organisms. Production of hydrogen fuel by electrolysis of low-grade or saline water, as opposed to pure water, could have benefits in terms of resource availability and cost. This Review examines the challenges of this approach and how they can be addressed through catalyst and electrolyser design.

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Electrolysis of low-grade and saline surface water

The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-007233.pdf

First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method

Colloidal nanocrystals are nanometer-sized, solution-grown inorganic particles stabilized by a layer of surfactants attached to their surface. The inorganic cores exhibit useful properties controlled by composition as well as size and shape, while the surfactant coating ensures that these structures are easy to fabricate and process. It is this combination of features that makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. But their full potential can only be exploited if we achieve exquisite control over their composition, size, shape, crystal structure and surface properties. Here we review what is known about nanocrystal growth and outline strategies for controlling it.

Colloidal nanocrystal synthesis and the organic-inorganic interface

Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric
transportation market provided that major scientific advances including new materials and concepts are developed. Classical
positive electrodes for Li-ion technology operate mainly through an insertion–deinsertion redox process involving cationic
species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich
(Li1CxNiyCozMn(1

Reversible anionic redox chemistry inhigh-capacity layered-oxide electrodes

Seawater electrolysis is emerging as one of the most promising technologies for hydrogen and oxygen generation for spatially constrained offshore and mobile-maritime applications. Herein, we show t...

Selective Seawater Splitting Using Pyrochlore Electrocatalyst

Developing highly active oxygen evolution and reduction reaction (OER/ORR) bifunctional electrocatalysts is key to multiple technologies including regenerative fuel cells and metal-air batteries T

Oxidation State and Oxygen-Vacancy-Induced Work Function Controls Bifunctional Oxygen Electrocatalytic Activity

Ta–TiOx nanoparticles as radical scavengers to improve the durability of Fe–N–C oxygen reduction catalysts

Enhanced electrocatalytic activity of the oxygen evolution reaction (OER) can be achieved through modulation of the electronic structure of the electrocatalytic active sites. This modulation can also be achieved through stabilization of metastable or non-native polymorphs of the electrocatalyst. Non-native (NN) crystal structures differ in their discrete translational symmetry from the bulk native (N) crystal. The variable oxygen evolution reactivity in a basic medium of different polymorphs is demonstrated by synthesizing β/N-, γ/N-NN1-, r/NN1-, α/NN2-, and δ/NN3-MnO2 polymorphs of MnO2 which show different active site densities on the surface, XPS-derived oxidation state of Mn, and bulk electronic conductivity. The specific OER activity [activity per electrochemical surface area (ECSA)] of MnO2 is codependent on the oxidation state of Mn and electronic conductivity. A volcano-based relationship is observed for the specific OER activity of MnO2 polymorphs with the universal descriptor ΔGO* – ΔGHO*, compu...

Modulating Oxygen Evolution Reactivity in MnO 2 throughPolymorphic Engineering

Supports over which electrocatalysts are deposited play a crucial role in oxygen evolution reaction (OER) activity because they influence surface roughness, morphology, electronic structure and conductivity of electrocatalysts. In this context, we have designed a hybrid carbon support comprised of earth abundant metals as interlayer between Co3O4 electrocatalyst and carbon support. The present approach makes the electrode three dimensional with high porosity, provides low resistant parallel electron conduction pathways through metallic interlayer and modulates the electrocatalytic activity of Co3O4 by affecting its electronic structure. To rationalize the effect of metal interlayer, a range of non-noble earth abundant metals (e.g. Cu, Mo, Ti, Al) are explored in which Cu-modified carbon support results in maximum specific activity (i.e. activity per electrochemical surface area) for OER.While both electronegativity and conductivity of metal interlayer influence OER activity, the dominant controlling factor is conductivity in the explored systems. The specific activity of OER of electrodeposited Co3O4 is found to have a near-linear relationship with electrical conductivity with electron donor metals (e.g. Ti, Al) and another near-linear relationship having different intercept with electron acceptor metals (e.g. Cu, Mo, W). The above understanding can be useful in increasing OER activity of electrocatalysts through support-electrocatalyst interaction.

Sulay Saha

Papers

Selective Seawater Splitting Using Pyrochlore Electrocatalyst

Oxidation State and Oxygen-Vacancy-Induced Work Function Controls Bifunctional Oxygen Electrocatalytic Activity

Ta–TiOx nanoparticles as radical scavengers to improve the durability of Fe–N–C oxygen reduction catalysts

Modulating Oxygen Evolution Reactivity in MnO 2 throughPolymorphic Engineering

Enhanced Water Oxidation Activity of the Cobalt(II,III) Oxide Electrocatalyst on an Earth‐Abundant‐Metal‐Interlayered Hybrid Porous Carbon Support