In the initial stage of oxygen adsorption on Si(111) surfaces, a metastable molecular state is found which precedes dissociation and insertion of oxygen atoms in bridging positions between first- and second-layer silicon atoms. This precursor can be observed in conventional photoemission experiments at low coverages and—for optimum retention—at low substrate temperatures. Combining the results from several high-resolution electron spectroscopies such as x-ray photoemission (XPS), polarization- and photon-energy-dependent uv photoemission, x-ray-induced Auger spectroscopy, and near-edge x-ray absorption, we are able to characterize the precursor as a negatively charged molecular species chemisorbed in a bridge configuration between dangling bonds of the surface. Its decay and conversion into the stable dissociated state could be monitored by XPS up to room temperature, showing a thermally or electronically activated behavior. For the reaction of ${\mathrm{O}}_2$ with Si(111), a two-stage adsorption model is proposed. It explains a number of observations and features of oxygen adsorption on differently prepared Si(111) surfaces. The present model may be applicable to other semiconductor surfaces as well.

We present new experimental results from a comprehensive study of the chemisorption of oxygen on differently prepared Si(111) surfaces, using low-energy electron diffraction and high-resolution electron spectroscopies such as x-ray photoemission spectroscopy, x-ray-initiated Auger-electron spectroscopy, and polarization-dependent ultraviolet photoemission spectroscopy. In the monolayer regime two different states of oxygen have been observed: a molecular precursor and a stable dissociated configuration. The latter is the subject of this paper. Its electronic structure and local symmetry are compatible only with a bridge-bonded atom between Si atoms in the first and second layer, respectively, with relatively little influence on the dangling bonds. The presence of a second dissociated oxygen adsorbate, e.g., a diatomiclike monoxide, is excluded by our data. The coverage dependent O 1s and Si 2p data indicate that the observed satellite structures in the submonolayer regime are due to excitations rather than to chemically shifted peaks from atoms in different bonding situations.

The initial adsorption of oxygen on Si(111) surfaces proceeds via a molecular intermediate which is precursor to the stable dissociated adsorption state. This metastable precursor can only be observed under certain conditions; its conversion to the stable state depends on temperature, probe, surface structure, impurities, and oxygen coverage. The precursor is likely to be a peroxy-bridge configuration whereas the stable dissociated oxygen species forms short-bridge bonds between adjacent Si atoms.

A robust catalyst support is pivotal to Proton Exchange Membrane Fuel Cells (PEMFCs) to overcome challenges such as catalyst support corrosion, low catalyst utilization and overall capital cost. SiC is a promising candidate material which could be applied as a catalyst support in PEMFCs. SiC nanocrystals are here synthesized using nano-porous carbon black (Vulcan^® XC-72) as a template using two different reactions, which result in particle sizes in the ranges of 50–150 nm (SiC-SPR) and 25–35 nm (SiC-NS). Pt nano-catalysts of size 5–8 nm and 4–5 nm have successfully been uniformly deposited on the nanocrystals of SiC-SPR and SiC-NS by the polyol method. The SiC substrates are subjected to an acid treatment to introduce the surface groups, which help to anchor the Pt nano-catalysts. These SiC based catalysts have been found to have a higher electrochemical activity than commercially available Vulcan based catalysts (BASF & HISPEC). These promising results signal a new era of SiC based catalysts for fuel cell applications.

It is crucial but challenging to reduce the required noble‐metal loading without compromising the catalytic performance of oxygen evolution reaction (OER) catalysts. This study presents a highly active OER catalyst composed of IrO₂ with Ir rich surface (IrO₂@Ir) nanoparticles supported over nano TiN coated with TiO_xN_y (IrO₂@Ir/TiN). The present approach demonstrates superior OER catalysts with high activity through small, uniformly dispersed IrO₂@Ir nanoparticles, along with high durability owing to robust catalyst support and strong catalyst‐support interaction. The synthesized IrO₂@Ir/TiN with an Ir loading of 40 wt % exhibits a mass‐normalized OER activity of 637 Ag_Ir⁻¹, which is 2.4 times that of the unsupported commercial benchmark IrO₂ OER electrocatalyst. The fine nanoparticles and high activity enable significant (∼60 %) reduction in the Ir metal loading required to obtain equivalent OER performance. In addition, when evaluated through an accelerated stress test using potential cycling, the catalyst exhibits outstanding durability (79 % retention) compared to that of the commercial equivalent (66 % retention). The OER activity loss was attributed to the catalyst dissolution (30 % loss) and the catalyst particle growth (70 %), with no measurable loss due to the TiN support corrosion. The development of ultra‐fine IrO₂@Ir nanoparticles and robust ceramic catalyst support significantly improved the Ir utilization and open a new perspective for supported OER catalyst.