Monitoring Active Sites for Hydrogen Evolution Reaction at Model Carbon Surfaces

Carbon is ubiquitous as an electrode material in electrochemical energy conversion devices. If used as support material, the evolution of H2 is undesired on carbon. However, recently carbon-based materials are of high interest as economic and eco-conscious alternative to noble metal catalysts. The targeted design of improved carbon electrode materials requires atomic scale insight into the structure of the sites that catalyse H2 evolution. This work demonstrates that electrochemical scanning tunnelling microscopy under reaction conditions (n-EC-STM) can monitor active sites of highly oriented pyrolytic graphite for the hydrogen evolution reaction. With down to atomic resolution, the most active sites in acidic medium are pinpointed near edge sites and defects, whereas the basal planes remain inactive. Density functional theory calculations support these findings and reveal that only specific defects on graphite are active. Motivated by these results, the extensive usage of n-EC-STM on doped carbon-based materials is encouraged to locate their active sites and guide the synthesis of enhanced electrocatalysts.The authors thank Prof. Plamen Atanassov (University of California, Irvine, USA) and Dr. Jun Maruyama (Osaka Research Institute of Industrial Science and Technology, Japan) for fruitful discussion regarding some experimental results. RMK, RWH and ASB acknowledge the financial support from the German Research Foundation (DFG), in the framework of the projects BA 5795/4-1 and BA 5795/3-1, and under Germany's Excellence Strategy–EXC 2089/1–390776260, cluster of excellence ‘e-conversion’. ASB acknowledges the funding from the European Union's Horizon 2020 research and innovation programme under grant agreement HERMES No. 952184. FCV acknowledges financial support from Spanish MICIUN through RTI2018-095460-B-I00 and María de Maeztu (MDM-2017-0767) grants and a Ramón y Cajal research contract (RYC-2015-18996), and also from Generalitat de Catalunya (grants 2017SGR13 and XRQTC). The use of supercomputing facilities at SURFsara was sponsored by NWO Physical Sciences, with financial support from NWO

A trade-off between ligand and strain effects optimizes the oxygen reduction activity of Pt alloys

To optimize the performance of catalytic materials, it is paramount to elucidate the dependence of the chemical reactivity on the atomic arrangement of the catalyst surface. Therefore, identifying the nature of the active sites that provide optimal binding of reaction intermediates is the first step toward a rational catalyst design. In this work, we focus on the oxygen reduction reaction (ORR), an essential constituent of several energy provision and storage devices. Among the state-of-the-art ORR catalysts are platinum (Pt) and its alloys. The latter benefit from the so-called ligand and strain effects, which influence the electronic properties of the surface. Here, we “visualize” the active sites on Pt3Ni(111) in an acidic medium with a lateral resolution in the nanometer regime via an in-situ technique based on electrochemical scanning tunnelling microscopy. In contrast to pure Pt, where the active sites are located at concave sites close to steps, Pt3Ni(111) terraces contain the most active centres, while steps show activity to a comparable or lesser extent. We confirm the experimental findings by a model based on alloy- and strain-sensitive generalized coordination numbers. With this model, we are also able to assess both the composition and the geometric configuration of optimal catalytic active sites on various Pt alloy catalysts. In general, the interplay of ligand effects and lattice compression resulting from the alloying of Pt with 3d transition metals (Ti, Co, Ni, Cu) gradually increases the generalized coordination number of surface Pt atoms, thereby making (111) terraces highly active. This combination of theoretical and experimental tools provides clear strategies to design more efficient Pt alloy electrocatalysts for oxygen reduction.The authors cordially thank Mr Karl Eberle for his valuable assistance in the sample preparation and Mr Kun-Ting Song and Dr Batyr Garlyyev for helping with some of the electrochemical experiments. R. M. K., R. W. H., B. G. and A. S. B. acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG), in the framework of the project BA 5795/6-1. A. R. acknowledges funding by the DFG, project number 453903355. R. M. K., R. W. H., B. G., A. S. B., K. S., Y. B., J. V. B., and F. A. appreciate funding from the DFG through the Excellence Cluster “e-conversion”, EXC 2089/1-390776260. The grants RTI2018-095460-B-I00, María de Maeztu (MDM-2017-0767) and Ramón y Cajal (RYC-2015-18996) were funded by MCIN/AEI/10.13039/501100011033 and the European Union. This work was also partly funded by Generalitat de Catalunya 2017SGR13. The use of supercomputing facilities at SURFsara was sponsored by NWO Physical Sciences, with financial support from NWO. RMK, TOS and ASB acknowledge funding from the European Union's Horizon 2020 research and innovation programme under grant agreement HERMES No. 952184

Elucidation of structure–activity relations in proton electroreduction at Pd surfaces: Theoretical and experimental study

The structure–activity relationship is a cornerstone topic in catalysis, which lays the foundation for the design and functionalization of catalytic materials. Of particular interest is the catalysis of the hydrogen evolution reaction (HER) by palladium (Pd), which is envisioned to play a major role in realizing a hydrogen-based economy. Interestingly, experimentalists observed excess heat generation in such systems, which became known as the debated “cold fusion” phenomenon. Despite the considerable attention on this report, more fundamental knowledge, such as the impact of the formation of bulk Pd hydrides on the nature of active sites and the HER activity, remains largely unexplored. In this work, classical electrochemical experiments performed on model Pd(hkl) surfaces, “noise” electrochemical scanning tunneling microscopy (n-EC-STM), and density functional theory are combined to elucidate the nature of active sites for the HER. Results reveal an activity trend following Pd(111) > Pd(110) > Pd(100) and that the forma?tion of subsurface hydride layers causes morphological changes and strain, which affect the HER activity and the nature of active sites. These findings provide significant insights into the role of subsurface hydride formation on the structure–activity relations toward the design of efficient Pd-based nanocatalysts for the HER.</p

CEO compensation and performance in family firms

This study examines CEO compensation in family firms, with a particular focus on the effects exerted by governance characteristics such as ownership concentration, wedge between voting and cash-flow rights rights, and the presence of shareholder agreements. On a sample of Italian-listed companies over the period 1998-2002, we provide empirical evidence that family firms pay CEOs systematically more then other firms, and that the ownership structure exerts a significant effect on CEO compensation. In family firms, CEO pay is indeed positively affected by low ownership concentration, as well as a low wedge between voting and cash flow rights. Moreover, the presence of shareholders agreements has a moderating role on the level of CEO compensation. These effects are more pronounced in family than in non-family firms. The analysis of the relationship between excess compensation and future firm performance reveals that the higher compensation granted to the CEO by family firms is related to worse stock and accounting returns and could therefore be interpreted as a form of rent extraction. This result holds only for lower degrees of ownership concentration, higher wedge, and in absence of shareholder agreements, and supports the hypothesis that the prevalent agency conflict within Italian-listed family firms is between family owners and minority shareholders, instead of between shareholders and managers. The higher compensation granted to the CEO could be the premium for the loyalty of the CEO to the family and for allowing the family to extract private benefits of control