Federico Andres Viva

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a quasi-non-destructive technique capable of analyzing the outer monolayers of a solid sample and detecting all elements of the periodic table and their isotopes. Its ability to analyze the outer monolayers resides in sputtering the sample surface with a low-dose primary ion gun, which, in turn, imposes the use of a detector capable of counting a single ion at a time. Consequently, the detector saturates when more than one ion arrives at the same time hindering the use of TOF-SIMS for quantification purposes such as isotope ratio estimation. Even though a simple Poisson-based correction is usually implemented in TOF-SIMS acquisition software to compensate the detector saturation effects, this correction is only valid up to a certain extent and can be unnoticed by the inexperienced user. This tutorial describes a methodology based on different practices reported in the literature for dealing with the detector saturation effects and assessing the validity limits of Poisson-based correction when attempting to use TOF-SIMS data for quantification purposes. As a practical example, a dried lithium hydroxide solution was analyzed by TOF-SIMS with the aim of estimating the 6Li/7Li isotope ratio. The approach presented here can be used by new TOF-SIMS users on their own data for understanding the effects of detector saturation, determine the validity limits of Poisson-based correction, and take into account important considerations when treating the data for quantification purposes.

Solar technologies have emerged as a clean and sustainable source of energy towards the mitigation of climate change. In the last years, an increasing interest has been devoted to obtaining solar fuels such as hydrogen through photoelectrochemistry. In this framework, titanium dioxide is a sound and promising platform for photoelectrochemical water splitting; however, its performance is limited due to the sluggish oxygen evolution reaction (OER). In this work, a photoactive electrode was developed by combining ordered mesoporous TiO2 thin films with a cobalt oxo-phosphate OER catalyst (CoPi). We conducted a detailed structural and electrochemical characterization of the TiO2-CoPi nanocomposite. We compared the performance of dense and mesoporous TiO2 films on different substrates as photoelectrodes for water splitting. All studied photoelectrodes exhibit high stability, reproducibility and cycling durability, with consistent photocurrent densities. Controlled amounts of CoPi were deposited on this matrix. Low loadings resulted in a 20% increase in photocurrent, whereas higher loadings suppressed the photocurrent due to recombination with the TiO2 matrix or the underlying FTO. In this study, we demonstrate the importance of optimizing the co-catalyst loading based on the interactions between different components in a nanocomposite photoanode, with a focus on understanding the recombination pathways that appear when working with nanostructured semiconductors.

The development of sustainable materials capable of capturing and transforming solar energy into green chemical fuels has become of great interest in the last years. Several semiconductors have been studied for this application and the search for the ideal material continues. It is becoming increasingly evident that a single material will not be able to fully satisfy all the

Mesoporous carbons (MCs) with different pore sizes were synthesized and evaluated as a catalyst support for fuel cells. The MCs were obtained from resorcinol–formaldehyde precursors, polymerized in the presence of polydiallyldimethylammonium chloride (cationic polyelectrolyte) as a structuring agent and commercial silica (Sipernat® or Aerosil®) as the hard template. The MC obtained with Aerosil® shows a broad pore size distribution with a maximum at 21 nm. On the other hand, the MCs with Sipernat® show a bimodal pore size distribution, with a narrow peak centered at 5 nm and a broad peak with a maximum ca. 30 nm. All MCs present a high specific surface area (800–1000 m² g⁻¹) and total pore volume ranging from 1.36 to 1.69 cm³ g⁻¹. PtRu nanoparticles were deposited onto the MC support by an impregnation–reduction method with NaBH₄ at 80 °C in basic media. The electrochemical characterization reveals improved electrocatalysis towards the methanol oxidation for the catalyst deposited over the carbon with the highest total pore volume. This catalyst also presented the highest CO₂ conversion efficiency, ca. 80%, for the methanol oxidation as determined by differential electrochemical mass spectroscopy analysis. Moreover, the catalyst as a fuel cell anode showed the best performance, reaching a power density of 125 mW cm⁻² at 90 °C with methanol as fuel and dry O₂.

In this work, a comparative study between three carbon materials has been carried out to investigate the impact of the micro/mesoporous structure of the carbon substrate on their adsorption capabilities.