Free energy difference to create the M-OH* intermediate of the oxygen evolution reaction by time-resolved optical spectroscopy.

Theoretical descriptors differentiate the catalytic activity of materials for the oxygen evolution reaction by the strength of oxygen binding in the reactive intermediate created upon electron transfer. Recently, time-resolved spectroscopy of a photo-electrochemically driven oxygen evolution reaction followed the vibrational and optical spectra of this intermediate, denoted M-OH*. However, these inherently kinetic experiments have not been connected to the relevant thermodynamic quantities. Here we discover that picosecond optical spectra of the Ti-OH* population on lightly doped SrTiO3 are ordered by the surface hydroxylation. A Langmuir isotherm as a function of pH extracts an effective equilibrium constant relatable to the free energy difference of the first oxygen evolution reaction step. Thus, time-resolved spectroscopy of the catalytic surface reveals both kinetic and energetic information of elementary reaction steps, which provides a critical new connection between theory and experiment by which to tailor the pathway of water oxidation and other surface reactions.

Coherent Acoustic Interferometry during the Photodriven Oxygen Evolution Reaction Associates Strain Fields with the Reactive Oxygen Intermediate (Ti-OH*).

The oxygen evolution reaction (OER) from water requires the formation of metastable, reactive oxygen intermediates to enable oxygen-oxygen bond formation. Conversely, such reactive intermediates could also structurally modify the catalyst. A descriptor for the overall catalytic activity, the first electron and proton transfer OER intermediate from water, (M-OH*), has been associated with significant distortions of the metal-oxygen bonds upon charge-trapping. Time-resolved spectroscopy of in situ, photodriven OER on transition metal oxide surfaces has characterized M-OH* for the charge trapping and the symmetry of the lattice distortions by optical and vibrational transitions, respectively, but had yet to detect an interfacial strain field arising from a surface coverage M-OH*. Here, we utilize picosecond, coherent acoustic interferometry to detect the uniaxial strain normal to the SrTiO3/aqueous interface directly caused by Ti-OH*. The spectral analysis applies a fairly general methodology for detecting a combination of the spatial extent, magnitude, and generation time of the interfacial strain through the coherent oscillations' phase. For lightly n-doped SrTiO3, we identify the strain generation time (1.31 ps), which occurs simultaneously with Ti-OH* formation, and a tensile strain of 0.06% (upper limit 0.6%). In addition to fully characterizing this intermediate across visible, mid-infrared, and now GHz-THz probes on SrTiO3, we show that strain fields occur with the creation of some M-OH*, which modifies design strategies for tuning catalytic activity and provides insight into photo-induced degradation so prevalent for OER. To that end, the work put forth here provides a unique methodology to characterize intermediate-induced interfacial strain across OER catalysts.

The electron-transfer intermediates of the oxygen evolution reaction (OER) as polarons by in situ spectroscopy.

The conversion of diffusive forms of energy (electrical and light) into short, compact chemical bonds by catalytic reactions regularly involves moving a carrier from an environment that favors delocalization to one that favors localization. While delocalization lowers the energy of the carrier through its kinetic energy, localization creates a polarization around the carrier that traps it in a potential energy minimum. The trapped carrier and its local distortion-termed a polaron in solids-can play a role as a highly reactive intermediate within energy-storing catalytic reactions but is rarely discussed as such. Here, we present this perspective of the polaron as a catalytic intermediate through recent in situ and time-resolved spectroscopic investigations of photo-triggered electrochemical reactions at material surfaces. The focus is on hole-trapping at metal-oxygen bonds, denoted M-OH*, in the context of the oxygen evolution reaction (OER) from water. The potential energy surface for the hole-polaron defines the structural distortions from the periodic lattice and the resulting "active" site of catalysis. This perspective will highlight how current and future time-resolved, multi-modal probes can use spectroscopic signatures of M-OH* polarons to obtain kinetic and structural information on the individual reaction steps of OER. A particular motivation is to provide the background needed for eventually relating this information to relevant catalytic descriptors by free energies. Finally, the formation of the O-O chemical bond from the consumption of M-OH*, required to release O2 and store energy in H2, will be discussed as the next target for experimental investigations.

Titanium elastic nailing in pediatric femoral diaphyseal fractures in the age group of 5-16 years - A short term study.

BACKGROUND: Management of femoral diaphyseal fracture in the age group of 5-16 years is controversial. The purpose of this study is to demonstrate the effectiveness of intramedullary fixation of femoral shaft fractures by using titanium elastic nailing system (TENS). MATERIALS AND METHODS: Between April 2011 and April 2014, 40 pediatric patients (31 boys, 9 girls) aged 5-16 years with diaphyseal femoral fractures were treated by retrograde TENS fixation. Fractures were classified according to system of Winquest and Hansen as Grade-I (n = 18), Grade-II (n = 10), Grade-III (n = 7) and compound fractures according to the Gustilo and Anderson's classification Grade-I (n = 3), Grade-II (n = 2). The final results were evaluated by using Flynn's criteria. RESULTS: The mean duration of follow-up was 21 months (range 3-39 months). All fractures were radiologically united with grade 3 callus formation at 8-10 weeks period (mean 9 weeks) and full weight bearing was possible in a mean time of 9.5 weeks. According to Flynn's criteria, excellent result was found in 33 patients (82.5%) and satisfactory in 7 patients (17.5%). Limb lengthening was noticed in 6 cases, varus mal-alignment was in 4 cases and rotational mal-alignment was seen in 3 cases. Peri-operative difficulties encountered were failure of closed reduction in 4 cases and cork screwing of nails in 2 cases. CONCLUSION: TENS is a safe and effective method for the treatment of pediatric femoral shaft fractures, because it is minimally invasive, relatively easy to use and shows very good functional and cosmetic results.