Oxophilicity

About: Oxophilicity is a research topic. Over the lifetime, 151 publications have been published within this topic receiving 3277 citations.

Pt–Ru catalyzed hydrogen oxidation in alkaline media: oxophilic effect or electronic effect?

Abstract: A current challenge to alkaline polymer electrolyte fuel cells (APEFCs) is the unexpectedly sluggish kinetics of the hydrogen oxidation reaction (HOR). A recently proposed resolution is to enhance the oxophilicity of the catalyst, so as to remove the Had intermediate through the reaction with OHad, but this approach is questioned by other researchers. Here we report a clear and convincing test on this problem. By using PtRu/C as the HOR catalyst for the APEFC, the peak power density is boosted to 1.0 W cm−2, in comparison to 0.6 W cm−2 when using Pt/C as the anode catalyst. Such a remarkable improvement, however, can hardly be explained as an oxophilic effect, because, as monitored by CO stripping, reactive hydroxyl species can generate on certain sites of the Pt surface at more negative potentials than on the PtRu surface in KOH solution. Rather, the incorporation of Ru has posed an electronic effect on weakening the Pt–Had interaction, as revealed by the voltammetric behavior and from density-functional calculations, which thus benefits the oxidative desorption of Had, the rate determining step of HOR in alkaline media. These findings further our fundamental understanding of the HOR catalysis, and cast new light on the exploration of better catalysts for APEFCs.

A Quantitative Scale of Oxophilicity and Thiophilicity.

Abstract: Oxophilicity and thiophilicity are widely used concepts with no quantitative definition. In this paper, a simple, generic scale is developed that solves issues with reference states and system dependencies and captures empirically known tendencies toward oxygen. This enables a detailed analysis of the fundamental causes of oxophilicity. Notably, the notion that oxophilicity relates to Lewis acid hardness is invalid. Rather, oxophilicity correlates only modestly and inversely with absolute hardness and more strongly with electronegativity and effective nuclear charge. Since oxygen is highly electronegative, ionic bonding is stronger to metals of low electronegativity. Left-side d-block elements with low effective nuclear charges and electronegativities are thus highly oxophilic, and the f-block elements, not because of their hardness, which is normal, but as a result of the small ionization energies of their outermost valence electrons, can easily transfer electrons to fulfill the electron demands of oxyge...

CO2 Electroreduction Performance of Transition Metal Dimers Supported on Graphene: A Theoretical Study

Abstract: Graphene-based materials are being hotly pursued for energy and environment applications. Inspired by the recent experimental synthesis of Fe2 dimer supported on graphene (He, Z.; He, K.; Robertson, A. W.; Kirkland, A. I.; Kim, D.; Ihm, J.; Yoon, E.; Lee, G.-D.; Warner, J. H. Nano Lett. 2014, 14, 3766–3772), here using large-scale screening-based density functional theory and microkinetics modeling, we have identified that some transition metal dimers (Cu2, CuMn, and CuNi), when supported on graphene with adjacent single vacancies (labeled as XY@2SV), perform better in CO2 electroreduction with reduced overpotental and enhanced current density. Specifically, Cu2@2SV is catalytically active toward CO production, similar to Au electrodes but distinct from bulk Cu; MnCu@2SV is selective toward CH4 generation, while NiCu@2SV promotes CH3OH production because of the difference in oxophilicity between incorporated Mn and Ni. The advantages of the outstanding selectivity of products, the high dispersity of spati...

Density functional theory studies on the mechanism of the reduction of CO2 to CO catalyzed by copper(I) boryl complexes

Abstract: The detailed reaction mechanism for the reduction of CO2 to CO catalyzed by (NHC)Cu(boryl) complexes (NHC = N-heterocyclic carbene) was studied with the aid of DFT by calculating the relevant intermediates and transition state structures Our DFT calculations show that the reaction occurs through CO2 insertion into the Cu−B bond to give a Cu−OC(O)−boryl species (ie, containing Cu−O and C−B bonds), and subsequent boryl migration from C to O, followed by σ-bond metathesis between pinB−Bpin (B2pin2, pin = pinacolate = OCMe2CMe2O) and (NHC)Cu(OBpin) The overall reaction is exergonic by 380 kcal/mol It is the nucleophilicity of the Cu−B bond, a function of the very strong σ-donor properties of the boryl ligand, rather than the oxophilicity of boron, which determines the direction of the CO2 insertion process The boryl migration from C to O, which releases the product CO, is the rate-determining step and involves the “vacant” orbital orbital on boron The (NHC)Cu(boryl) complexes show unique activity in t

The role of ruthenium in improving the kinetics of hydrogen oxidation and evolution reactions of platinum

Abstract: Modifying Pt surfaces by foreign metals with a higher oxophilicity is a promising approach to improve the kinetics of hydrogen evolution and oxidation reactions. The role of foreign metals, however, is not fully understood. Here we study Ru-modified Pt as a model system to understand the underlying mechanisms in activity improvement through combining in situ infrared spectroscopy and theoretical calculations. In an alkaline solution, the hydrogen evolution and oxidation reaction activity of Ru-modified Pt is proportional to the Ru coverage due to the strain and electronic effects of the Pt substrate, which lower the energy barrier of the rate-determining Volmer step; these are the governing reasons for the improved catalytic activities. This work not only deepens our understanding of hydrogen electrocatalysis mechanisms, but also provides guidelines for the rational design of advanced electrocatalysts. Modifying Pt surfaces with highly oxophilic metals can increase the hydrogen evolution and oxidation performance in alkaline media, but the underlying mechanism remains elusive. Now, it is demonstrated that the activity improvement of Ru-modified Pt mainly originates from the strain and electronic effects rather than an alternative bifunctional mechanism.