Bond energy | EPFL Graph Search

In chemistry, bond energy (BE), also called the mean bond enthalpy or average bond enthalpy is a measure of bond strength in a chemical bond. IUPAC defines bond energy as the average value of the gas-phase bond-dissociation energy (usually at a temperature of 298.15 K) for all bonds of the same type within the same chemical species. The bond dissociation energy (enthalpy) is also referred to as bond disruption energy, bond energy, bond strength, or binding energy (abbreviation: BDE, BE, or D). It is defined as the standard enthalpy change of the following fission: R - X → R + X. The BDE, denoted by Dº(R - X), is usually derived by the thermochemical equation, : \begin{array}{lcl} \mathrm{D^\circ(R-}X) \ = \Delta H^\circ_f\mathrm{(R)} + \Delta H^\circ_f(X) - \Delta H^\circ_f(\mathrm{R}X)
\end{array} The enthalpy of formation ΔHfº of a large number of atoms, free radicals, ions, clusters and compounds is available from the websites of NIST, NASA, CODATA, and IUPAC. Mo

State-to-state studies of intramolecular dynamics and unimolecular reactions

Thomas Rizzo

Double-resonance vibrational overtone excitation spectra of small molecules, in combination with laser-induced fluorescence product detection, provide information on both their energetics and intramolecular energy redistribution dynamics. Application of this approach to measure OH stretch overtone spectra of HOOH and NH2OH near their dissociation threshold provides estimates of the O-O and N-O bond energies of 17051.8 +/- 4 cm(-1) and 21 620 +/- 20 cm(-1) respectively. In symmetrical molecules, such as HOOH, the double-resonance excitation technique allows us to prepare molecules in either pure OH stretch overtone levels or combination levels in which the excitation energy is divided between two identical OH stretch oscillators. Comparison of the resulting vibrational overtone linewidths indicates no clear difference between the pure OH stretch and the local-local combination levels. However, comparison of the energy transfer rates from pure OH stretch vibrations and those in which one quantum of energy is put in a low frequency mode reveals faster rates from the latter. This observation clearly indicates that coupling strengths depend markedly on the vibrational character of the coupling partner and not simply on the total energy. Comparison of the OH stretch overtone spectra of the structurally similar molecules HOOH, NH2OH, and CH3OH reveal similar rates of vibrational energy redistribution, despite the difference in the density of states in these molecules. This observation reinforces the notion that energy flow between the OH stretch and dark background states is not statistical but rather is controlled by coupling to a small subset of background states.

1997

Synthesis and Application of Transition Metal Oxides as Oxygen Evolution Catalysts

Laurent Liardet

Nowadays, mankind is facing an important energy challenge. Depletion in fossil fuels reserves and increasing energy demand, coupled with the problematic greenhouse effect induced by massive anthropogenic release of carbon dioxide into the atmosphere, are driving forces for the development of renewable and carbon-free energy technologies. Hydrogen gas is considered as the energy carrier of the future and is expected to replace fossil fuels in order to create a Hydrogen Economy. Hydrogen is viable for decarbonization of our society only if it is produced from sustainable and renewable energies. Water splitting, the redox reaction producing hydrogen and oxygen gas by reducing and oxidizing water, respectively, is a promising technique to produce clean hydrogen. However, the kinetics of the oxidative half-reaction, namely the oxygen evolution reaction (OER), are slow and catalysts are required in order to increase the global efficiency of water splitting. Moreover, in order to perform water splitting at large scale, catalysts based on Earth-abundant elements should be developed. This thesis focuses on the development of transition metal oxides catalysts, by different synthesis techniques, for electrochemical and photoelectrochemical oxygen evolution. Chapter 2 focuses on the atomic layer deposition (ALD) of different cobalt-based metal oxides and the development of procedures to fabricate bi- and trimetallic oxides catalysts. Cobalt vanadium oxide (CoVOx), cobalt iron oxide (CoFeOx) as well as cobalt vanadium iron oxide (CoVFeOx) are deposited by ALD and evaluated for OER. The ALD deposition method allowed us to apply these material on high-surface area nickel foam substrates. Among them, CoFeOx shows the highest catalytic activity for water oxidation and can compete with state-of-the art electrocatalysts for OER in alkaline solution. In Chapter 3, we focused on developing a photoelectrodeposition method to deposit CoFeOx on nanocauliflower hematite photoanodes. This photoelectrodeposition method allowed the deposition of an ultrathin, amorphous and optically transparent CoFeOx layer that induced a large cathodic shift of the photocurrent onset potential of hematite and a high enhancement of the photocurrent at 1.0 V vs RHE. Additionally, the reason of the improvement of the onset potential was explored in detail in order to differentiate between possible activity enhancement effects such as an increase of charge transfer kinetics, a reduction of surface recombination, a modification of the flat band potential or an increase of the photovoltage. We concluded that CoFeOx improved the OER efficiency of nanocauliflower hematite photoanodes by purely enhancing the kinetics of water oxidation. Chapter 4 details the development of a hydrothermal route to fabricate CoVOx. On the basis of a volcano plot that correlates the OER activity to the M-OH bond strength of metal oxides, CoVOx was predicted to be a highly active electrocatalyst that could compete with the most active OER electrocatalysts in alkaline solution. After characterization, this hydrothermally synthesized cobalt vanadium oxide was seen to be amorphous and provided high catalytic activity towards OER. This chapter, in addition to increasing the library of OER electrocatalysts, demonstrates the usefulness of M-OH bond strength as a simple descriptor for experimental development of OER catalysts.

EPFL2019

Evaluation of Thin Film Indium Bonding at Wafer Level

Danick Briand, Nico de Rooij, Yves Pétremand, Rahel Strässle

needed. By an optimized patterning of the evaporated indium film and the lid, surface hermetic bonding on wafer level is reached without exceeding 140 °C in any step of the procedure. Different designs of the indium metallization and lid were tested to improve bond strength while keeping the same bonding parameters. By depositing an adhesion layer of CrAu on the lid, the bond strength can be increased by 30 % compared to the one of indium to glass bonding. Another way to increase bond strength by 40 % is to profile one bonding surface in such a way that the indium oxide breaks at multiple places within the deposited area. Hermeticity is proven for all different designs.

Elsevier Science, Reg Sales Off, Customer Support Dept, 655 Ave Of The Americas, New York, Ny 10010 Usa2011

Synthesis and Application of Transition Metal Oxides as Oxygen Evolution Catalysts

Laurent Liardet

EPFL2019