The Influence of Elastic Strain on Catalytic Activity in the Hydrogen Evolution Reaction.

Understanding the role of elastic strain in modifying catalytic reaction rates is crucial for catalyst design, but experimentally, this effect is often coupled with a ligand effect. To isolate the strain effect, we have investigated the influence of externally applied elastic strain on the catalytic activity of metal films in the hydrogen evolution reaction (HER). We show that elastic strain tunes the catalytic activity in a controlled and predictable way. Both theory and experiment show strain controls reactivity in a controlled manner consistent with the qualitative predictions of the HER volcano plot and the d-band theory: Ni and Pt's activities were accelerated by compression, while Cu's activity was accelerated by tension. By isolating the elastic strain effect from the ligand effect, this study provides a greater insight into the role of elastic strain in controlling electrocatalytic activity.

Improvement in hydrogen desorption from ß- and γ-MgH2 upon transition-metal doping.

A thorough study of the structural, electronic, and hydrogen-desorption properties of ß- and γ-MgH2 phases substituted by selected transition metals (TMs) is performed through first-principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125 % in both the hydrides. This insertion of TMs causes a variation in the cell volumes of ß- and γ-MgH2 . The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation-energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both ß- and γ-MgH2 and cause destabilization by weakening the MgH bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from ß- and γ-MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis.

Elastic strain effects on catalysis of a PdCuSi metallic glass thin film.

The influence of strain on catalytic activity has previously been examined directly by calculations and indirectly by experiments. The origin of the phenomenon has been attributed to strain-induced changes in the catalyst electronic structure. By employing a Pd-based metallic glass film capable of large elastic strains, we provide direct experimental evidence for catalytic activity being differently influenced by mechanically applied uniaxial tensile and compressive strains. We demonstrate the effect on the oxygen reduction reaction with cyclic voltammetry (CV) curves at different strain levels and compare X-ray photoelectron spectrometry (XPS) results for unstrained and strained (in uniaxial tension) specimens to confirm valence electron band shifts. The experimental findings are complemented by electronic structure calculations on single crystal Pd, as well as alloys with Cu and Si. The CV and XPS shifts observed in the experiments are consistent in both direction and magnitude to those predicted by theory for single crystal Pd.

Cluster-Mediated Crossed Bilayer Precision Assemblies of 1D Nanowires.

Highly organized crossed bilayer assemblies of nanowires (NWs) are made using directed hydrogen bonding between the protecting ligand shells of atomically precise cluster molecules anchored on NWs. Layers of quantum clusters remain sandwiched between two neighboring NWs at a defined distance, dictated by the core-size of the cluster, while the orientation of the ligands in space dictates the interlayer geometry.