Nanocarbon-Supported Electrocatalysts for the Alkaline Water Splitting and Fuel Cells

Electrocatalysts play a significant role in the processes of electrochemical energy conversion. This thesis focuses on the preparation of carbon-supported nanomaterials and their application as electrocatalysts for alkaline water electrocatalysis and fuel cell. A general synthetic route was developed, i.e., species intercalate into carbon layers of graphite forming graphite intercalation compound, followed by dispersion producing graphenide solution, which then as reduction agent reacts with different metal sources generating the final materials. The first metal precursor used was non-noble metal iron salt, which generated iron (oxide) nanoparticles finely dispersed on carbon layers in the final composite materials. Meanwhile, graphite starting materials differing in carbon layer size were utilized, which would diversify corresponding graphenide solutions, and further produce various nanomaterials. The characterization results showed that iron (oxide) nanoparticles varying in size were obtained, and the size was determined by the starting graphite material. It was found that they were electrocatalytically active for oxygen reactions. In particular, the one with small iron (oxide) nanoparticles showed excellent electrocatalytic activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Afterwards, the metal precursor was tuned from non-noble metal salt to noble metal salt. It was confirmed that carbon-supported Rh, Pt, and RhPt (oxide) nanoparticle composite materials were also successfully obtained from the reaction between graphenide solution and corresponding noble metal precursor. The electrochemical measurements showed that the prepared noble metal-based nanomaterials were quite effective for hydrogen evolution reaction (HER) electrocatalysis, and the Rh sample could also display excellent electrocatalytic property towards OER. Moreover, by this synthetic approach carbon-supported noble metal Pt and non-noble metal nickel (Ni) composite material was also prepared. Therefore, the utilization efficiency of noble metal could be improved. The prepared NiPt sample displayed a property close to benchmark HER electrocatalyst.

Sinus rhythm restoration with electrical cardioversion: acute effect of shock configuration and subsequent modifications in peripheral flow and sleep.

Atrial fibrillation (AF) is a widespread arrhythmia, associated with higher risk of stroke, sleep disorders and dementia. In some conditions, electrical cardioversion (ECV) represents the best choice for rhythm control. Nowadays, there is a growing interest in developing new devices for screening and monitoring of AF patients. We aimed to improve acute efficacy of ECV procedure and to explore the feasibility of the use of new wearable devices for monitoring in candidates to AF ECV. We compared antero-apical pads vs antero-posterior patches approach for AF ECV, and we elaborated a decision algorithm to improve acute efficacy. After, we evaluated the feasibility of the use of new wearable devices for monitoring of candidates to AF ECV. In particular, we analysed the effect of AF ECV on heart rate variability and vascular age parameters derived from PPG signals registered with Empatica (CE 1876/MDD 93/42/EEC), and on EEG pattern registered with Neurosteer (Israel). From December 2005 to September 2019, 492 patients were enrolled. We evaluated acute efficacy of the two approaches for AF ECV and we elaborated a decision algorithm based on body surface area, weight, and height. The decision algorithm improved first shock efficacy (93.2% vs. 87.2%, p=0.025). From 1st November 2021 to 1st April 2022, 24 patients were enrolled in PPEEG-AF pilot study. Considering vascular age parameters, a significant reduction in TPR and a wave was observed (p<0.001). Considering sleep patterns, a tendency to higher coherence was observed in registrations acquired during AF, or considering signals registered for each patient independently from AF. The new decision algorithm improved acute efficacy and reduced costs associated with adhesive patches. Significant modifications were observed on vascular age parameters measured before and after ECV, and a possible AF effect on sleep pattern was noticed. More data are necessary to confirm these preliminary results.

Kinetics of photogenerated carriers in nanostructured semiconductor heterojunctions for solar water splitting

This thesis aims to investigate the fundamental processes governing the performance of different types of photoelectrodes used in photoelectrochemical (PEC) applications, such as unbiased water splitting for hydrogen production. Unraveling the transport and recombination phenomena in nanostructured and surface-modified heterojunctions at a semiconductor/electrolyte interface is not trivial. To approach this task, the work presented here first focus on a hydrogen-terminated p-silicon photocathode in acetonitrile, considered as a standard reference for PEC studies. Steady-state and time-resolved excitation at long wavelength provided clear evidence of the formation of an inversion layer and revealed that the most optimal photovoltage and the longest electron-hole pair lifetime occurs when the reduction potential for the species in solution lies within the unfilled conduction band states. Understanding more complex systems is not as straight-forward and a complete characterization that combine time- and frequency-resolved techniques is needed. Intensity modulated photocurrent spectroscopy and transient absorption spectroscopy are used here on WO3/BiVO4 heterojunctions. By selectively probing the two layers of the heterojunction, the occurrence of interfacial recombination was identified. Then, the addition of Co-Fe based overlayers resulted in passivation of surface states and charge storage at the overlayer active sites, providing higher charge separation efficiency and suppression of recombination in time scales that go from picoseconds to seconds. Finally, the charge carrier kinetics of several different Cu(In,Ga)Se2 (CIGS)-based architectures used for water reduction was investigated. The efficiency of a CIGS photocathode is severely limited by charge transfer at the electrode/electrolyte interface compared to the same absorber layer used as a photovoltaic cell. A NiMo binary alloy deposited on the photocathode surface showed a remarkable enhancement in the transfer rate of electrons in solution. An external CIGS photovoltaic module assisting a NiMo dark cathode displayed optimal absorption and charge separation properties and a highly performing interface with the solution.