Holli

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Improvements in the fundamental understanding of electrocatalysis have started to revolutionize the development of electrochemical interfaces for the efficient conversion of chemical energy into electricity, as well as for the utilization of electrons to produce new chemicals that then can be re-used in energy conversion systems. Here, some facets of the role of trace level of impurities (from 10⁻⁷ to 10⁻⁶ M) in electrocatalysis of the oxygen reduction reaction, hydrogen oxidation and evolution reactions, and CO oxidation reactions are explored on well-characterized platinum single crystal surfaces and high surface area materials in alkaline and acidic environments. Of particular interest is the effect of anions (e.g., Cl⁻, \( {\text{NO}}_{ 3}^{ - } \) ) and cations (i.e., Cu²⁺) present in the supporting electrolytes as well as surface defects (i.e., ad-islands) that are present on metal surfaces. The examples presented are chosen to demonstrate that a small level of impurities may play a crucial role in governing the reactivity of electrochemical interfaces.

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This paper studies simple kinetic models for proton-coupled electron transfer reactions, and demonstrates that for reactions in which proton and electron do not transfer simultaneously, pH dependence of the overall reaction rate is expected. In particular, if the current is evaluated on the reversible hydrogen scale, this may lead to volcano-type activity relations as a function of pH. In case that an acid–base equilibrium is part of the mechanism, the optimal pH occurs close to the pK_a of this equilibrium.

Article

Hydrogen evolution technologies for a future carbon-free energy economy require efficient catalysts which can be implemented on a large scale. Here, the authors prepare a composite electrode from readily available elements, whereby a metal-organic framework boosts catalytic performance by enabling rapid proton transport.

Nature Communications doi: 10.1038/ncomms9304

Authors: Idan Hod, Pravas Deria, Wojciech Bury, Joseph E. Mondloch, Chung-Wei Kung, Monica So, Matthew D. Sampson, Aaron W. Peters, Cliff P. Kubiak, Omar K. Farha, Joseph T. Hupp

Article

A future carbon-free energy economy requires an efficient photocatalytic route to hydrogen generation. Here, the authors employ surface modification techniques to raise the performance of an unassisted solar water splitting device to achieve exceptional performances.

Nature Communications doi: 10.1038/ncomms9286

Authors: Matthias M. May, Hans-Joachim Lewerenz, David Lackner, Frank Dimroth, Thomas Hannappel

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In situ EPR spectroscopy proved to be a versatile tool to identify active sites for photocatalytic hydrogen generation in modified Y₂Ti₂O₇ and CsTaWO₆ catalysts of pyrochlore structure, in which the metal cations are located in two different positions A and B. It was found that the B-sites exclusively occupied by titanium (Y₂Ti₂O₇) and tantalum/tungsten (CsTaWO₆) act as electron traps on the surface. From these sites, electron transfer to the co-catalysts proceeds. Thus, the B-sites are responsible for photocatalytic water reduction.

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In the context of homogeneous catalysis, open-shell systems are often quite challenging to characterize. Nuclear magnetic resonance (NMR) spectroscopy is the most frequently applied tool to characterize organometallic compounds, but NMR spectra are usually broad, difficult to interpret and often futile for the study of paramagnetic compounds. As such, electron paramagnetic resonance (EPR) has proven itself as a useful spectroscopic technique to characterize paramagnetic complexes and reactive intermediates. EPR spectroscopy is a particularly useful tool to investigate their electronic structures, which is fundamental to understand their reactivity. This paper describes some selected examples of studies where EPR spectroscopy has been useful for the characterization of open-shell organometallic complexes. The paper concentrates in particular on systems where EPR spectroscopy has proven useful to understand catalytic reaction mechanisms involving paramagnetic organometallic catalysts. The expediency of EPR spectroscopy in the study of organometallic chemistry and homogenous catalysis is contextualized in the introductory Sect. 1. Section 2 of the review focusses on examples of C–C and C–N bond formation reactions, with an emphasis on catalytic reactions where ligand/substrate non-innocence plays an important role. Both carbon and nitrogen centered radicals have been shown to play an important role in these reactions. A few selected examples of catalytic alcohol oxidation proceeding via related N-centered ligand radicals are included in this section as well. Section 3 covers examples of the use of EPR spectroscopy to study important commercial ethylene oligomerization and polymerization processes. In Sect. 4 the use of EPR spectroscopy to understand the mechanisms of Atom Transfer Radical Polymerization is discussed. While this review focusses predominantly on the application of EPR spectroscopy in mechanistic studies of C–C and C–N bond formation reactions mediated by organometallic catalysts, a few selected examples describing the application of EPR spectroscopy in other catalytic reactions such as water splitting, photo-catalysis, photo-redox-catalysis and related reactions in which metal initiated (free) radical formation plays a role are included as well. EPR spectroscopic investigation in this area of research are dominated by EPR spectroscopic studies in isotropic solution, including spin trapping experiments. These reactions are highlighted in Sect. 5. EPR spectroscopic studies have proven useful to discern the correct oxidation states of the active catalysts and also to determine the effective concentrations of the active species. EPR is definitely a spectroscopic technique that is indispensable in understanding the reactivity of paramagnetic complexes and in conjunction with other advanced techniques such as X-ray absorption spectroscopy and pulsed laser polymerization it will continue to be a very practical tool.

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Article

The efficiency of a single-junction photovoltaic cell is constrained by the Shockley-Queisser limit. Here, the authors adopt a triple-junction configuration which relaxes material and current-matching constraints, providing a generic strategy for advancing the efficiency roadmap of photovoltaic technologies.

Nature Communications doi: 10.1038/ncomms8730

Authors: Fei Guo, Ning Li, Frank W. Fecher, Nicola Gasparini, Cesar Omar Ramirez Quiroz, Carina Bronnbauer, Yi Hou, Vuk V. Radmilović, Velimir R. Radmilović, Erdmann Spiecker, Karen Forberich, Christoph J. Brabec

Why we are teaching science wrong, and how to make it right

Nature 523, 7560 (2015). http://www.nature.com/doifinder/10.1038/523272a

Author: M. Mitchell Waldrop

Active problem-solving confers a deeper understanding of science than does a standard lecture. But some university lecturers are reluctant to change tack.

Lifelong learning: Science professors need leadership training

Nature 523, 7560 (2015). doi:10.1038/523279a

Authors: Charles E. Leiserson & Chuck McVinney

To drive discovery, scientists heading up research teams large and small need to learn how people operate, argue Charles E. Leiserson and Chuck McVinney.