On the thermodynamics of hydrogen adsorption over Pt(111) in 0.05M NaOH.

The reasons for the sluggish kinetics of the hydrogen adsorption reaction in alkaline media remain a question still to be solved. This information is important to achieve a complete understanding of the mechanistic details that could lead to the production of key catalytic materials necessary for the development of a future hydrogen economy. For a better understanding of this reaction, it is important to acquire information about the thermodynamic parameters characteristic of the different steps in the reaction. Among these, the hydrogen adsorption is a key step in the process of hydrogen evolution. Although some debate still remains about the difference between adsorbed hydrogen in the underpotential deposition (UPD) region and at the overpotential deposition region, there is no doubt that understanding the former can help in the understanding of the latter. Making use of charge density measurements, we report on this paper a thermodynamic study of the hydrogen UPD process on Pt(111) in 0.05M NaOH over the range of temperatures from 283 ≤ T/K ≤ 313. The coulometric features corresponding to HUPD allow for the calculation of the hydrogen coverage and a fit to a Generalized Frumkin isotherm. From these values, different thermodynamic functions for the UPD reaction have been calculated: ΔGads, ΔSads, ΔHads, and the Pt-H bond energy. From extrapolation, a value of ΔSads ◦=-7.5±4Jmol-1K-1 was found, which is very close to 0, much lower than previously reported measurements both in acid and in alkaline solutions. Such value has an effect on the enthalpy and bond energy calculations, the latter having a decreasing tendency with pH and coverage. This tendency is completely different from the acidic systems and implies that the change in the thermodynamic functions due to the formation of the double layer and the reorganization of interfacial water has a strong influence on the process in high pH solutions.

Activation Energy of Hydrogen Adsorption on Pt(111) in Alkaline Media: An Impedance Spectroscopy Study at Variable Temperatures.

The hydrogen evolution reaction is one of the most studied processes in electrochemistry, and platinum is by far the best catalyst for this reaction. Despite the importance of this reaction on platinum, detailed and accurate kinetic measurements of the steps that lead to the main reaction are still lacking, particularly because of the fast rate of the reaction. Hydrogen adsorption on Pt(111) has been taken as a benchmark system in a large number of computational studies, but reliable experimental data to compare with the computational studies is very scarce. To gain further knowledge on this matter, a temperature study of the hydrogen adsorption reaction has been carried out to obtain kinetic information for this process on Pt(111) in alkaline solution. This was achieved by measuring electrochemical impedance spectra and cyclic voltammograms in the range of 278 ≤ T ≤ 318 (K) to obtain the corresponding surface coverage by adsorbed species and the faradaic charge transfer resistance. From this data, the standard rate constant has been extracted with a kinetic model assuming a Frumkin-type isotherm, resulting in values of 2.60 × 10-7 ≤ k0 ≤ 1.68 × 10-6 (s-1). The Arrehnius plot gives an activation energy of 32 kJ mol-1. Comparisons are made with values calculated by computational methods and reported values for the overall HER, giving a reference frame to support future studies on hydrogen catalysis.

Pt-grown carbon nanofibers for detection of hydrogen peroxide.

Removal of left-over catalyst particles from carbon nanomaterials is a significant scientific and technological problem. Here, we present the physical and electrochemical study of application-specific carbon nanofibers grown from Pt-catalyst layers. The use of Pt catalyst removes the requirement for any cleaning procedure as the remaining catalyst particles have a specific role in the end-application. Despite the relatively small amount of Pt in the samples (7.0 ± 0.2%), they show electrochemical features closely resembling those of polycrystalline Pt. In O2-containing environment, the material shows two separate linear ranges for hydrogen peroxide reduction: 1-100 µM and 100-1000 µM with sensitivities of 0.432 µA µM-1 cm-2 and 0.257 µA µM-1 cm-2, respectively, with a 0.21 µM limit of detection. In deaerated solution, there is only one linear range with sensitivity 0.244 µA µM-1 cm-2 and 0.22 µM limit of detection. We suggest that the high sensitivity between 1 µM and 100 µM in solutions where O2 is present is due to oxygen reduction reaction occurring on the CNFs producing a small additional cathodic contribution to the measured current. This has important implications when Pt-containing sensors are utilized to detect hydrogen peroxide reduction in biological, O2-containing environment.

Olfactory bulb implantation and methylprednisolone administration in the treatment of spinal cord injury in rats.

Estimate the effects of methylprednisolone (MP) administration and olfactory bulb (OB) implantation independently and in combination after a spinal trauma model in Wistar rats, evaluated with BBB scale and CBS with remark of inclined plane test and Tarlov scale. Thirty adult rats were divided into six different groups, evaluated before trauma, one day post-surgery and weekly up to six weeks post-lesion. Group A (control); group B (sham) laminectomy without lesion; group C (SCI) lesion only; group D (MP) SCI and MP; group E (OB) SCI and OB implantation; group F (MP/OB) SCI and both therapeutics. Intragroup data at three weeks showed evident significance in groups D, E and F for Tarlov (p=0.001) and BBB (p<0.01); groups C, D, E and F for CBS (p<0.05); and only group D with inclined plane (p<0.05). On the sixth week differences were present in groups C, D, E, and F for Tarlov, BBB and CBS (p<0.001); and C and F for inclined plane (p<0.05). For intergroup analysis any treatment showed differences with Tarlov scale; for BBB and inclined plane, statistical differences were evident in groups E and F; and for CBS only in group F (p<0.05). Real effects of MP are obtained at immediate follow-up, without notorious augmentation after time. OB improvement is achieved only after weeks. None of these therapies used independently achieve a constant and sustained improvement. Combined treatments were more effective and reached higher functional levels for longer periods of time.