We propose a model which describes the frequency shift $\left(\Delta {\omega }_{\mathit{SM}}\right)$ of the stretching mode (SM) of $\mathrm{Si}\mathrm{H}$ monohydrides (MH’s) when incorporated in hydrogenated amorphous silicon $(a\text{−}\mathrm{Si}:\mathrm{H})$ with respect to the unscreened MH SM at $\sim 2099\pm 2{\mathrm{cm}}^{-1}$. The model is based on an effective medium approximation of the dielectric using multiple Lorentz-Lorenz dielectrics, corresponding to a host dielectric with MH’s embedded in cavities, separately. The $\Delta {\omega }_{\mathit{SM}}$ as derived in this model correctly predicts all bulk MH-SM positions in $a\text{−}\mathrm{Si}:\mathrm{H}$ films and relates it directly to the nanostructure of the MH bulk configurations.

The plasma chemistry of an argon/hydrogen expanding thermal arc plasma in interaction with silane injected downstream is analyzed using mass spectrometry. The dissociation mechanism and the consumption of silane are related to the ion and atomic hydrogen fluence emanating from the arc source. It is argued that as a function of hydrogen admixture in the arc, which has a profound decreasing effect on the ion-electron fluence emanating from the arc source, the dissociation mechanism of silane shifts from ion-electron induced dissociation towards atomic hydrogen induced dissociation. The latter case, the hydrogen abstraction of silane, leads to a dominance of the silyl $({\mathrm{SiH}}_{\mathrm{3}})$ radical whereas the ion-electron induced dissociation mechanism leads to ${\mathrm{SiH}}_x$ $\text{(x<3)}$ radicals. In the pure argon case, the consumption of silane is high and approximately two silane molecules are consumed per argon ion-electron pair. It is shown that this is caused by consecutive reactions of radicals ${\mathrm{SiH}}_x$ $\text{(x<3)}$ with silane. Almost independent of the plasma conditions used, approximately one ${\mathrm{H}}_{\mathrm{2}}$ is produced per consumed ${\mathrm{SiH}}_{\mathrm{4}}$ molecule. Disilane production is observed which roughly scales with the remaining silane density. Possible production mechanisms for both observations are discussed.

The development of efficient and stable earth-abundant water oxidation catalysts is vital for economically feasible water-splitting systems. Cobalt phosphate (CoPi)-based catalysts belong to the relevant class of nonprecious electrocatalysts studied for the oxygen evolution reaction (OER). In this work, an in-depth investigation of the electrochemical activation of CoPi-based electrocatalysts by cyclic voltammetry (CV) is presented. Atomic layer deposition (ALD) is adopted because it enables the synthesis of CoPi films with cobalt-to-phosphorous ratios between 1.4 and 1.9. It is shown that the pristine chemical composition of the CoPi film strongly influences its OER activity in the early stages of the activation process as well as after prolonged exposure to the electrolyte. The best performing CoPi catalyst, displaying a current density of 3.9 mA cm^–2 at 1.8 V versus reversible hydrogen electrode and a Tafel slope of 155 mV/dec at pH 8.0, is selected for an in-depth study of the evolution of its electrochemical properties, chemical composition, and electrochemical active surface area (ECSA) during the activation process. Upon the increase of the number of CV cycles, the OER performance increases, in parallel with the development of a noncatalytic wave in the CV scan, which points out to the reversible oxidation of Co²⁺ species to Co³⁺ species. X-ray photoelectron spectroscopy and Rutherford backscattering measurements indicate that phosphorous progressively leaches out the CoPi film bulk upon prolonged exposure to the electrolyte. In parallel, the ECSA of the films increases by up to a factor of 40, depending on the initial stoichiometry. The ECSA of the activated CoPi films shows a universal linear correlation with the OER activity for the whole range of CoPi chemical composition. It can be concluded that the adoption of ALD in CoPi-based electrocatalysis enables, next to the well-established control over film growth and properties, to disclose the mechanisms behind the CoPi electrocatalyst activation.

Heterogeneous catalysts coupled with non-thermal plasmas (NTP) are known to achieve reaction yields that exceed the contributions of the individual components. Rationalization of the enhancing potential of catalysts, however, remains challenging because the background contributions from NTP or catalysts are often non-negligible. Here, we first demonstrate platinum (Pt)-catalyzed nitrogen (N₂) oxidation in a radio frequency plasma afterglow at conditions at which neither catalyst nor plasma alone produces significant concentrations of nitric oxide (NO). We then develop reactor models based on reduced NTP- and surface-microkinetic mechanisms to identify the features of each that lead to the synergy between NTP and Pt. At experimental conditions, NTP and thermal catalytic NO production are suppressed by radical reactions and high N₂ dissociation barrier, respectively. Pt catalyzes NTP-generated radicals and vibrationally excited molecules to produce NO. The model construction further illustrates that the optimization of productivity and energy efficiency involves tuning of plasma species, catalysts properties, and the reactor configurations to couple plasma and catalysts. These results provide unambiguous evidence of synergism between plasma and catalyst, the origins of that synergy for N₂ oxidation, and a modeling approach to guide material selection and system optimization.