There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2

http://pubs.acs.org/doi/pdf/10.1021/cr1002326

Solar Water Splitting Cells

Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.

http://nanotubes.rutgers.edu/PDFs/nchem_TMDs_2013.pdf

The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets

We present a method for calculating the stability of reaction intermediates of electrochemical processes on the basis of electronic structure calculations. We used that method in combination with detailed density functional calculations to develop a detailed description of the free-energy landscape of the electrochemical oxygen reduction reaction over Pt(111) as a function of applied bias. This allowed us to identify the origin of the overpotential found for this reaction. Adsorbed oxygen and hydroxyl are found to be very stable intermediates at potentials close to equilibrium, and the calculated rate constant for the activated proton/electron transfer to adsorbed oxygen or hydroxyl can account quantitatively for the observed kinetics. On the basis of a database of calculated oxygen and hydroxyl adsorption energies, the trends in the oxygen reduction rate for a large number of different transition and noble metals can be accounted for. Alternative reaction mechanisms involving proton/electron transfer to ...

/pdf/origin-of-the-overpotential-for-oxygen-reduction-at-a-fuel-jdt5gxiyj8.pdf

Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode

As a promising catalyst for methanol synthesis from CO2 hydrogenation, In2O3 has attracted considerable interest due to its high methanol selectivity. Understanding the structure–activity relations...

Relations between Surface Oxygen Vacancies and Activity of Methanol Formation from CO2 Hydrogenation over In2O3 Surfaces

Surfaces that efficiently catalyse the oxygen reduction reaction (ORR) are highly desirable for applications in energy utilization. Here, we computationally investigate the ORR on hexagonal boron nitride (h-BN) supported on Ni, Cu, and Co. We find a significant influence of the metal on the reaction energetics. In particular, h-BN/Cu is predicted to catalyse the ORR with a low overpotential, while on the other substrates the reaction is impeded by the formation of too stable surface hydroxyl species. Our results highlight trends in the reactivity of these heterostructures and may guide further rational design of O2-activating catalysts based on supported h-BN.

A systematic study of metal-supported boron nitride materials for the oxygen reduction reaction.

A simple explanation for the acceleration of reactions by catalysts is that they speed up the rate-determining step. However, many reactions of practical importance are complex, multistep processes, and assessing the role that each step may play in controlling the overall rate of the reaction is not trivial. In a recent paper, Stegelmann et al. ( 1 ) have introduced a useful concept for characterizing such reactions: the general degree of rate control. Identifying the elementary steps that exert the greatest control on the overall rate of a chemical reaction offers the possibility of finding an appropriate catalyst or improving existing ones.

https://science.sciencemag.org/content/sci/324/5935/1655.full.pdf

Rate Control and Reaction Engineering

Rhodium (Rh) catalysts are among the major candidates for syngas conversion to higher oxygenates (C2+oxy), with manganese (Mn) as a commonly used promoter for enhancing the activity and selectivity toward C2+oxy. In this study, we use atomic layer deposition (ALD) to controllably modify Rh catalysts with MnO, by depositing manganese oxide as a support layer or an overlayer, in order to identify the function of the Mn promoter. We also compare the ALD-modified catalysts with those prepared by coimpregnation. An ultrathin MnO support layer shows the most effective enhancement for C2+oxy production. Transmission electron microscopy, temperature-programmed reduction, and diffuse reflectance infrared Fourier transform spectroscopy characterization indicates that formation of Rh–MnO interface sites is responsible for the observed activity and selectivity improvements, while ruling out Rh nanoparticle size and alloy or mixed oxide formation as significant contributors. MnO overlayers on Rh appear to suffer from ...

Rh-MnO Interface Sites Formed by Atomic Layer Deposition Promote Syngas Conversion to Higher Oxygenates

The interaction of nitric oxide, NO, with the stepped Pd(211) surface is studied using density functional theory slab calculations. Calculated chemisorption energies and geometries reveal that surface sites are not populated in a sequential manner as the NO coverage is increased. This comes about through mutual NO interactions that reorganize the adsorbates during the adsorption. The finding of nonsequential site population allows a reinterpretation of existing experimental data.

/pdf/adsorbate-reorganization-at-steps-no-on-pd-211-19hd6ftbqt.pdf

Jens K. Nørskov

Papers

Relations between Surface Oxygen Vacancies and Activity of Methanol Formation from CO2 Hydrogenation over In2O3 Surfaces

A systematic study of metal-supported boron nitride materials for the oxygen reduction reaction.

Rate Control and Reaction Engineering

Rh-MnO Interface Sites Formed by Atomic Layer Deposition Promote Syngas Conversion to Higher Oxygenates

Adsorbate Reorganization at Steps: NO on Pd(211)