Density Functional Theory (DFT) has proven to be an invaluable and effective tool for identifying highly active electrocatalysts for the oxygen evolution reaction (OER). Herein we take a computational approach in order to first identify a series of rare-earth pyrochlore oxides based on Ir and Ru as potential OER catalysts. The DFT-based phase diagrams, Pourbaix diagrams (E vs. pH), projected density of states (PDOS), and band energy diagrams were used to identify prospective OER catalysts based on rare earth Ir and Ru pyrochlores. The predicted materials were synthesized using the sprayfreeze freeze-drying approach to afford nanoparticulate oxides conforming to the pyrochlore structural type A 2 B 2 O 7 where A = Nd, Gd, or Yb and B = Ir or Ru. In agreement with the computed Pourbaix diagrams, the materials were found to be moderately stable under OER conditions. All prepared materials show higher stability as compared to the benchmark IrO 2 catalyst and the OER mass activity of Yb 2 Ir 2 O 7 and the ruthenate pyrochlores (Nd 2 Ru 2 O 7 , Gd 2 Ru 2 O 7 , and Yb 2 Ru 2 O 7) were also found to exceed that of the benchmark IrO 2 catalyst. We find that the OER activity of each pyrochlore series Page 1 of 40 ACS Paragon Plus Environment ACS Applied Materials & Interfaces 2 (i.e. iridate or ruthenate) generally improves as the size of the A-site cation decreases, indicating that maintaining control over the local structure can be used to influence the electrocatalytic properties.

Luminescent organometallic platinum(II) compounds are of interest as phosphors for organic light emitting devices. Their emissive properties can be tuned by variation of the ligands or by specific electron-withdrawing or electron-donating substituents. Different ancillary ligands can have a profound impact on the emission color and emission efficiency of these complexes. We studied the influence of sterically hindered, aryl-substituted β-diketonates on the emission properties of C^C* cyclometalated complexes, employing the unsubstituted methyl-phenyl-imidazolium ligand. The quantum yield was significantly enhanced by changing the auxiliary ligand from acetylacetonate, where the corresponding platinum(II) complex shows only a very weak emission, to mesityl (mes) or duryl (dur) substituted acetylacetonates. The new complexes show very efficient emission with quantum yields >70% in the sky-blue spectral region (480 nm) and short decay times (<3 μs).

Anodic oxygen evolution has gained significant prominence in electrochemical research in the last decade in connection with renewable electricity storage. With water being the only available fossil free source of hydrogen, which is deemed the primary storage medium, the water electrolysis optimization is one of the biggest challenges of today's electrochemistry. A development of novel OER catalysts is motivated to increase the feasibility of the current OER catalysts in terms of activity, stability and price. This review summarizes the most recent synthetic approaches in OER catalyst synthesis for acid and alkaline electrolyzers stressing the structural aspects of the proposed catalysts. The reported novel catalyst approaches are aligned with existing theoretical and experiment based descriptors for rational of oxygen evolution activity improvement.

A combination of operando small- and wide-angle X-ray scattering is here presented to provide insights into the changes in mean particle sizes and phase fractions in fuel cell catalyst layers during accelerated stress tests (ASTs). As a fuel cell catalyst, a bimodal Pt/C catalyst was chosen that consists of two distinguishable particle size populations. The presence of the two different sizes should favor and uncover electrochemical Ostwald ripening as a degradation mechanism, that is, the growth of larger particles in the Pt/C catalyst at the expense of the smaller particles via the formation of ionic metal species. However, instead of electrochemical Ostwald ripening, the results point toward classical Ostwald ripening via the local diffusion of metal atoms on the support. Furthermore, the grazing incidence mode provides insights into the catalyst layer depth-dependent degradation. Although the larger particles show the same particle size changes close to the electrolyte–catalyst interface and within the catalyst layer, the smaller Pt nanoparticles exhibit a slightly decreased size at the electrolyte–catalyst interface. During the AST, both size populations increase in size, independent of the depth. Their phase fraction, that is, the ratio of smaller- to larger-size population, however, exhibits a depth-dependent behavior. Although at the electrolyte–catalyst interface, the phase fraction of the smaller-size population decreases, it increases in the inner catalyst layer. The results of a depth-dependent degradation suggest that employing a depth-dependent catalyst design can be used for future improvement of catalyst stability.