Highly Efficient Hybrid Ni/Nitrogenated Graphene Electrocatalysts for Hydrogen Evolution Reaction.

Two nickel/nitrogenated graphene hybrid electrodes (Ni-NrGO NH3 and Ni-NrGO APTES ) were synthesized, and their catalytic activity with respect to the hydrogen evolution reaction (HER) in alkaline media was analyzed. Incorporation of nitrogen to the carbon structure in graphene oxide (GO) or reduced GO (rGO) flakes in aqueous solutions was carried out based on two different configurations. NrGO NH 3 particles were obtained by a hydrothermal method using ammonium hydroxide as the precursor, and NGO APTES particles were obtained by silanization (APTES functionalization) of GO sheets. Aqueous dispersions containing NrGO NH 3 and NGO APTES particles were added to the traditional nickel Watts plating bath in order to prepare the Ni-NrGO NH 3 and Ni-NrGO APTES catalysts, respectively. Nickel substrates were coated with the hybrid nickel electrodeposits and used as electrodes for hydrogen production. The Ni-NrGO catalysts show a higher activity than the conventional nickel electrodeposited electrodes, particularly the ones containing APTES molecules because they allow obtaining a hydrogen current density 130% higher than conventional Ni-plated electrodes with a Watts bath in the absence of additives. In addition, both catalysts show a low deactivation rate during the ageing treatment, which is a sign of a longer midlife for the catalyst. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were used for examination of the catalytic efficiency of hybrid Ni-NrGO electrodes for HER in KOH solution. High values of exchange current densities, 8.53 × 10-4 and 2.53 × 10-5 mA cm-2 for HER in alkaline solutions on Ni-NrGO NH 3 and Ni-NrGO APTES electrodes, respectively, were obtained.

A spectroscopic sensing platform for MARCKS protein monolayers.

We developed a highly sensitive silicon platform, suitable to assess the molecular organization of protein samples. Prototype platforms were obtained using different electrochemical protocols for the electrodeposition of Ag-nanoparticles onto the hydrogenated silicon surface. A platform with high Surface Enhanced Raman Scattering efficiency was selected based on the surface coverage and the number density of particles size distribution. The performance of the platform was determined by studying the interaction of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS) protein with the substrate according to its molecular organization. The chemical and structural characteristics of MARCKS molecules were examined under two configurations: i) a disordered distribution given by a MARCKS solution drop deposited onto the platform and, ii) a compact monolayer transferred to the platform by the Langmuir-Blodgett method. Raman spectra show vibrational bands of Phenylalanine and Lysine residues specific for the protein effector domain, and evidence the presence of alpha helix structure in both configurations. Moreover, we distinguished the supramolecular order between the compact monolayer and random molecular distribution. The platforms containing Ag-nanoparticles are suitable for studies of protein structure and interactions, advancing a methodological strategy for our long term goal, which is to explore the interaction of proteins with model membranes.

Synergy between graphene and Au nanoparticles (heterojunction) towards quenching, improving Raman signal, and UV light sensing.

Here, we developed a simple method for obtaining a heterojunction composed of graphene (G) and surfactant-coated Au nanoparticles (NPs) to measure film conductivity and surface enhanced Raman scattering (SERS). Monolayer G is obtained by chemical vapor deposition (CVD) and transferred via poly(methyl methacrylate) (PMMA) to microfabricated Au electrodes, glass, and silicon. Post-synthesis treatments of G with PMMA and ozone (O3) showed 1 and 6 orders of magnitude decrease in film conductivity, respectively. The heterojunction formation with Au NPs had no major effect on G conductivity. In this work is demonstrated that G quenches more than 90% of the combined photoluminescence and fluorescence of Au NPs and Rhodamine B (RhB), respectively. Signal quenching permitted quantitative analysis of SERS of RhB on various substrates including as-transferred graphene, oxidized graphene (OG), and the heterojunction. While G is mainly responsible for quenching photoluminescence and fluorescence, ∼3 orders of magnitude increase SERS activity for RhB was accomplished by the heterojunction. Finally, we wanted to correlate changes in film current during UV light sensing experiments. We found striking differences in the sensing profiles at different UV energies.

Spectroscopic investigation of the adsorption and oxidation of thiourea on polycrystalline Au and Au(111) in acidic media.

In the present paper, a systematic electrochemical investigation on thiourea (TU) electrooxidation was developed on polycrystalline and (111) single-crystal gold electrodes in 0.1 M perchloric acid. The combination of cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry techniques have allowed the nature of the species formed during the electroadsorption and electrooxidation of TU to be established. FTIRS experiments were performed in D2O to clean up the region of the H2O bending around 1600 cm(-1). It was concluded that TU adsorbs tilted on the surface in the 0.05-0.40 VRHE potential range. A dual-path reaction mechanism was evidenced in the oxidation process. The first pathway takes place from adsorbed TU at E > 0.40 VRHE and implies the formation of [Au(I)-(TU)2]+, which is oxidized to NH2CN and S0 at E > 0.80 VRHE. In a following oxidation step at E > 1.20 V, N2, CO2, and HSO4-/SO4(2-) were produced. The second parallel reaction occurs from TU in solution at E > 0.50 VRHE to form (TU)2(2+). All these species were characterized from the spectroscopic experiments. Similar results were obtained for both surfaces.