Development of innovative materials used in electrochemical devices for the renewable production of hydrogen and electricity

One of the most important challenges for our society is providing powerful devices for renewable energy production. Many technologies based on renewable energy sources have been developed, which represent a clean energy sources that have a much lower environmental impact than conventional energy technologies. Nowadays, many researches focus their attention on the development of renewable energy from solar, water, organic matter and biomass, which represent abundant and renewable energy sources. This research is mainly focused on the development of promising electrode materials and their potential application on emerging technologies such as artificial photosynthesis and microbial fuel cell (MFC). According to desired proprieties of functional materials, this research was focused on two main materials: (1) TiO2 for the development of electrodes for the water splitting reaction due to its demonstrated application potential as photocatalyst material and (2) carbon-based materials for the development of electrodes for MFC. In the first part of the investigation, different TiO2 nanostructures have been studied including: synthesis, characterization and test of TiO2-based materials with the aim of improving the limiting factors of the photocatalytic reaction: charge recombination and separation/migration processes. The photo-catalytic properties of different TiO2 nanostructures were evaluated including: TiO2 nanoparticles (NPs) film, TiO2 nanotubes (NTs) and ZnO@TiO2 core-shell structures. Photo-electrochemical activity measurements and electrochemical impedance spectroscopy analysis showed an improvement in charge collection efficiency of 1D-nanostructures, related to a more efficient electron transport in the materials. The efficient application of both the TiO2 NTs and the ZnO@TiO2 core-shell photoanodes opens important perspectives, not only in the water splitting application field, but also for other photo-catalytic applications (e.g. photovoltaic cells, degradation of organic substances), due to their chemical stability, easiness of preparation and improved transport properties. Additionally, in order to improve the photo-catalytic activity of TiO2 NPs, PANI/TiO2 composite film was synthesized. PANI/TiO2 composite film was successfully applied as anode material for the PEC water splitting reaction showing a significant increase in the photocatalytic activity of TiO2 NPs composite film essentially attributed to the efficient separation of the generated electron and hole pairs. To date, no cost-effective materials system satisfies all of the technical requirements for practical hydrogen production under zero-bias conditions. For this propose, to promote the sustainability of the process, the bias require to conduct PEC water splitting reaction could be powered by MFC systems in which many efforts have been done to improve power and electricity generation as is explained below. In this work, different strategies were also applied in order to improve the performance of anode materials for MFCs. The investigation of commercial carbon-based materials demonstrated that these materials, normally used for other ends are suitable electrodes for MFC and their use could reduce MFC costs and improve the energy sustainability of the process. In addition, to enhance power generation in MFC by using low-cost and commercial carbon-based materials, nitric acid activation (C-HNO3) and PANI deposition (C-PANI) were performed on commercial carbon felt (C-FELT) in order to increase the performance of MFC. Electrochemical determinations performed in batch-mode MFC reveled a strong reduction of the activation losses contribution and an important decrease of the internal resistance of the cell using C-HNO3 and C-PANI of about 2.3 and 4.4 times, respectively, with respect to C-FELT. Additionally, with the aim of solvent different MFC operational problems such as: biofouling, low surface area and large-scale MFC, an innovative three-dimensional material effectively developed and used as anode electrode. The conductive carbon-coated Berl saddles (C-SADDLES) were successfully used as anode electrode in batch-mode MFC. Electrochemical results suggested that C-SADDLES offer a low-cost solution to satisfy either electrical or bioreactor requirements, increasing the reliability of the MFC processes, and seems to be a valid candidate for scaled-up systems and for continuous mode application of MFC technology. In addition, the electrochemical performance and continuous energy production of the most promising materials obtained during this work were evaluated under continuous operation MFC in a long-term evaluation test. Remarkable results were obtained for continuous MFCs systems operated with three different anode materials: C-FELT, C-PANI and C-SADDLES. From polarization curves, the maximum power generation was obtained using C-SADDLES (102 mW•m-2) with respect to C-FELT (93 mW•m-2) and C-PANI (65 mW•m-2) after three months of operation. The highest amount of electrical energy was produced by C-PANI (1803 J) with respect to C-FELT (1664 J) and C-SADDLES (1674 J). However, it is worth to note that PANI activity was reduced during time by the operating conditions inside the anode chamber. In order to demonstrate the wide application potential MFC, this work reports on merging heterogeneous contributions and combining the advantages from three separate fields in a system which enables the ultra-low-power monitoring of a microbial fuel cell voltage status and enables pressure monitoring features of the internal conditions of a cell. The solution is conceived to provide an efficient energy source, harvesting wastewater, integrating energy management and health monitoring capabilities to sensor nodes which are not connected to the energy grid. Finally, this work presented a general concept of the integration of both devices into a hybrid device by interfacing PEC and MFC devices (denoted as PEC-MFC), which is proposed to generate electricity and hydrogen using as external bias the potential produce by microbial fuel cel

Comparison of photocatalytic and transport properties of TiO2 and ZnO nanostructures for solar-driven water splitting

Titanium dioxide (TiO2) and zinc oxide (ZnO) nanostructures have been widely used as photo-catalysts due to their low-cost, high surface area, robustness, abundance and non-toxicity. In this work, four TiO2 and ZnO - based nanostructures, i.e. TiO2 nanoparticles (TiO2 NPs), TiO2 nanotubes (TiO2 NTs), ZnO nanowires (ZnO NWs) and ZnO@TiO2 core-shell structures, specifically prepared with a fixed thickness of about 1.5 μm, are compared for the solar-driven water splitting reaction, under AM1.5G simulated sunlight. A complete characterization of these photo-electrodes in their structural and photo-electrochemical properties was carried out. Both TiO2 NPs and NTs showed photo-current saturation reaching 0.02 and 0.12 mA/cm2, respectively, for potential values of about 0.3 and 0.6 V vs. RHE. In contrast, the ZnO NWs and the ZnO@TiO2 core-shell samples evidence a linear increase of the photocurrent with the applied potential, reaching 0.45 and 0.63 mA/cm2 at 1.7 V vs. RHE, respectively. However, under concentrated light conditions, the TiO2 NTs demonstrate a higher increase of the performance with respect to the ZnO@TiO2 core-shells. Such material dependent behaviours are discussed in relation with the different charge transport mechanisms and interfacial reaction kinetics, which were investigated through electrochemical impedance spectroscopy. The role of key parameters such as electronic properties, specific surface area and photo-catalytic activity on the performance of these materials are discussed. Moreover, proper optimization strategies are analyzed in view of increasing the efficiency of the best performing TiO2 and ZnO - based nanostructures, toward their practical application in a solar water splitting device

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTIC‐HF: baseline characteristics and comparison with contemporary clinical trials

Aims: The safety and efficacy of the novel selective cardiac myosin activator, omecamtiv mecarbil, in patients with heart failure with reduced ejection fraction (HFrEF) is tested in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTIC‐HF) trial. Here we describe the baseline characteristics of participants in GALACTIC‐HF and how these compare with other contemporary trials. Methods and Results: Adults with established HFrEF, New York Heart Association functional class (NYHA) ≥ II, EF ≤35%, elevated natriuretic peptides and either current hospitalization for HF or history of hospitalization/ emergency department visit for HF within a year were randomized to either placebo or omecamtiv mecarbil (pharmacokinetic‐guided dosing: 25, 37.5 or 50 mg bid). 8256 patients [male (79%), non‐white (22%), mean age 65 years] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NT‐proBNP 1971 pg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTIC‐HF randomized patients representative of recent HF registries and trials with substantial numbers of patients also having characteristics understudied in previous trials including more from North America (n = 1386), enrolled as inpatients (n = 2084), systolic blood pressure &lt; 100 mmHg (n = 1127), estimated glomerular filtration rate &lt; 30 mL/min/1.73 m2 (n = 528), and treated with sacubitril‐valsartan at baseline (n = 1594). Conclusions: GALACTIC‐HF enrolled a well‐treated, high‐risk population from both inpatient and outpatient settings, which will provide a definitive evaluation of the efficacy and safety of this novel therapy, as well as informing its potential future implementation

A comparative study of the performance of commercial carbon felt and the innovative carbon-coated Berl saddles as anode electrode in MFC

Microbial Fuel Cell (MFC) is a prospective technology that allows oxidizing organic and inorganic matter to generate current by the activity of bacteria with a high potential as portable remote energy generation. To render MFC as a cost-effective and energy sustainable technology, low-cost conductive materials can be employed as support for bacterial growth and proliferation. For this reason, in this work we performed a comparative study of the performance between commercial carbon felt and the innovative carbon-coated Berl saddles (C-Berl saddles) developed in our labs used as anode electrode in MFC. Both the experiments were conducted simultaneously using the same MFC configuration in continuous mode for more than 3 months at room temperature (22 ± 2 °C). In the anodic chamber, a mixed microbial population naturally present in sea water was employed as active microorganisms and sodium acetate (1 g.L-1 per day) with buffer solution was continuously fed as substrate. In the cathodic chamber, carbon felt was used as electrode material and potassium ferricyanide with buffer solution as an electron acceptor. A complete characterization of anodic solution was carried out with continuous measurement of pH, conductivity and redox potential. Electrochemical characterization were performed as a follow: (i) polarization curves including: Linear Sweet Voltammetry, Current Interrupt and Electrochemical Impedance Spectroscopy using a multi-channel VSP potentiostat by BioLogic and (ii) current and voltage under an external resistance of 1000 Ω using a Data Acquisition Unit by Agilent 34972A. Results showed that C-Berl saddles performed better than carbon felt showing an average maximum power density of 90 mW.m-2 and 60 mW.m-2 , respectively. In addition, from current vs. time data both cells were produced a comparable quantity of energy, linked to the good biocompatibility, conductibility and high mechanical stretching of electrode materials. Furthermore, C-Berl saddles helped to reduce the biofouling and favored the growth of biofilm as anode material for scaling-up MFC

Streamlining of commercial Berl saddles: A new material to improve the performance of microbial fuel cells

Microbial fuel cell (MFC) is an upcoming technology that allows oxidizing organic matter to generate current by microorganism's activity. To render MFCs a cost-effective and energy sustainable technology, low-cost materials can be employed as support for bacteria growth and proliferation. With this purpose in mind, ceramic Berl saddles were opportunely covered by a thin and conductive carbon layer, thus obtaining an innovative low-cost anode material able to efficiently recover the electrons released by bacteria metabolisms. The conductive layer was obtained by using a-D-glucose deposition process within the following steps: impregnation, caramelization, and pyrolysis. In this way, a homogenous coating of polycrystalline graphitic carbon was successfully obtained and characterized by several methods. The carbon-coated Berl saddles were then tested as anode material in a two-compartment MFC prototype, in batch mode and using Saccharomyces cerevisiae as active microorganisms. The MFC performances were evaluated using electrochemical techniques. The carbon-coated Berl saddles showed a maximum power density of 130 mW m2 (29.6 mA L1) which is about 2e3 times higher than the values reported in literature by using commercial anode materials. In particular, we have carefully estimated the production and process costs of these carbon-coated Berl saddles used in our MFC prototype, obtaining a value comparable to the commercial carbon felt employed in the same MFC apparatus. All these results confirm that our innovative carbon-coated Berl saddles not only satisfy the electrical requirements, but also favor an optimal bacteria adhesion and can be produced as a low-cost anode for scaling-up MF

One Dimensional Core-Shell ZnO/TiO2 Nanowire Arrays for Visible Light Driven Photoelectrochemical Water Splitting

Photo-electrochemical (PEC) water-splitting offers a promising way for clean, low-cost and environmentally friendly production of H2 by solar energy. Wide-band-gap semiconductor materials such as zinc oxide (ZnO) and titanium dioxide (TiO2) have attracted considerable research interest in the past few decades as photocatalysts due to their unique properties: abundance, low cost and possibility to create nanostructures to improve their transport properties. In addition, ZnO nanowires (NWs) is one of the semiconductors with a high electronic mobility (1000 cm2Vs-1), which gives rise to fast electron transport and lower recombination of charge carriers. However, due to their large band gaps, they are active only under UV irradiation, and ZnO has the drawback of a low photo-corrosion resistance in aqueous media, that reduces their practical application. In this work, we present for the first time a fast and low-cost synthesis procedure for preparation of TiO2/ZnO core-shell heterostructures, in order to combine the merit of these two materials and improve their photocatalytic performances, with high efficiency and durability. In a first step, ZnO NWs were grown on glass electrodes covered with a Fluorine-doped Tin Oxide (FTO) conductive film by hydrothermal route. Subsequently, a shell of TiO2 nanoparticles was deposited in the ZnO NWs by in-situ sol-gel synthesis in a non-acidic solution. The resulting core-shell TiO2-ZnO structures were annealed in Air or N2 flow at 450oC and characterized by X-ray diffraction (Philips X’Pert, Cu Kα, λ = 1.54059 Å), Energy Dispersive Spectroscopy (EDS), Field Emission Scanning Electron Microscopy (FESEM, ZEISS Auriga) and Transmission Electron Microscopy (TEM, FEI Tecnai F20ST operating at 200 kV), clearly showing the formation of a crystalline anatase TiO2 shell completely covering the crystalline structures of wurtzite ZnO NWs, with a thickness dependent on the impregnation time in the titania synthesis bath. Moreover, optical properties and the surface properties of the TiO2/ZnO heterojunction have been further investigated by UV-Vis spectra and X-ray Photoelectron Spectroscopy (XPS), that evidence an increase of absorbance over the entire visible light region and a reduction of the band gap, with respect to the pristine ZnONWs treated under the same annealing conditions. PEC activity, action spectra and carriers dynamics of the samples were studied in NaOH (0.1M) electrolyte, using the prepared materials as working electrode, a Pt foil as counter electrode and a Ag/AgCl reference electrode, under dark and simulated solar light irradiation (using a 450W Xe lamp with a AM 1.5 filter) and employing monochromatic light in all the UV-Visible range

Optimization of 1D ZnO@TiO2Core–Shell Nanostructures for Enhanced Photoelectrochemical Water Splitting under Solar Light Illumination

A fast and low-cost sol-gel synthesis used to deposit a shell of TiO 2 anatase onto an array of vertically aligned ZnO nanowires (NWs) is reported in this paper. The influence of the annealing atmosphere (air or N 2) and of the NWs preannealing process, before TiO2 deposition, on both the physicochemical characteristics and photoelectrochemical (PEC) performance of the resulting heterostructure, was studied. The efficient application of the ZnO@TiO2 core-shells for the PEC water-splitting reaction, under simulated solar light illumination (AM 1.5G) solar light illumination in basic media, is here reported for the first time. This application has had a dual function: to enhance the photoactivity of pristine ZnO NWs and to increase the photodegradation stability, because of the protective role of the TiO2 shell. It was found that an air treatment induces a better charge separation and a lower carrier recombination, which in turn are responsible for an improvement in the PEC performance with respect to N2-treated core-shell materials. Finally, a photocurrent of 0.40 mA/cm2 at 1.23 V versus RHE (2.2 times with respect to the pristine ZnO NWs) was obtained. This achievement can be regarded as a valuable result, considering similar nanostructured electrodes reported in the literature for this application. © 2014 American Chemical Society