Development of graphene oxide/nafion polymeric membranes toward the improvement of direct methanol fuel cell membranes

Nowadays the direct methanol fuel cell (DMFC) technology attracts a lot of interest because it represents a low temperature, high efficiency power source that can be advantageously used for mobile and portable applications and thus, it can be a valid alternative to the use of lithium battery technology. The DMFC is an electrochemical system that produces energy by oxidizing the liquid fuel (a mixture of water and methanol) without auxiliary devices. The use of DMFC has several advantages: easy fuel storage, low cost of methanol, operation at low temperature and pressure, small system size and low weight. However, several issues hinder the spreading of this technology. Firstly, the fuel cell membrane is generally composed by Nafion, a perfluorosulfonic polymer. Such membrane is prone to allow the passage of methanol, the so called cross-over, that strongly reduces DMFC performance. Furthermore, high cost and limited operating temperature range represent a strong limit to the commercialization of that technology. Research activities are focused on developing new polymer electrolyte membrane (PEM) materials aiming at overcoming the crossover. Among several types of material, graphene oxide (GO) has been considered as a promising element that offers great results in terms of water uptake and mechanical properties. Several authors have reported that GO contributes to reduce methanol permeability because it acts as a barrier, due to its higher tortuosity, while proton conductivity shows an opposite trend. In addition, it is well known that temperature, methanol concentration as well as flow rate affect proton conductivity and methanol crossover and, consequently, DMFC performance. It is therefore necessary to investigate what are the best conditions to make better use of this innovative material. The objective of this study is to assess the potential of GO in improving DMFC performance. To this end, several composite Nafion/GO membranes with different GO loading were manufactured using casting method. The internship at the School of Chemical Engineering at the University of Birmingham, allowed me to learn the methodology to prepare and characterize polymeric membranes. The composite membranes demonstrated higher mechanical strength, enhanced water uptake but lower proton conductivity than recast Nafion. Once the optimum loading was estimated, the performance of the DMFC, in a passive configuration, was analysed through the analysis of the polarization and power curves. It was revealed that the DMFC performance was enhanced by increasing the temperature. The DMFC performance increases when using GO membranes when increasing methanol concentration and flow rate. However, it is necessary to use the appropriate range of methanol concentration and anode flow rate. Extending the anode flow rate and methanol concentration has a dual effect: increasing the flow of the reactant allows to obtain higher performance despite enhancing the methanol crossover and losses. At one point, the loss will be no longer counterbalanced, and performance starts decreasing. Comparing the results with those of recast Nafion, it was demonstrated that by utilising GO-Nafion composite membranes, an increase in the maximum power density, open circuit condition and operating range, at all operating conditions, can be achieved. So, the detriment of proton conductivity was counterbalanced by the reduction of fuel cell crossover

Design and experimental set-up of hydrogen based microgrid: characterization of components and control system development

In this study, the implementation of a hydrogen microgrid is investigated, considering the integration of H2 production, storage, and energy conversion to feed a typical end-user. A remote control system has been realized through LabVIEW software, allowing to monitor real-time all the devices and analyze their performances. The integrated system is composed of a PEM electrolyzer (325 W), a storage system based on metal hydrides (two tanks, 54 g of hydrogen each, 1.08 wt%) and an energy converter (PEM Fuel Cell stack, 200 W). A programmable electronic load was used to set a power demand throughout the year, simulating an end-user. Data collected from each component of the micro-grid were used to characterize the energetic performance of the devices, focusing on the H2 production via electrolyzer, charging cycles of the H2 storage system, and energy conversion efficiency of the FC stack. Finally, the global efficiency of the microgrid is computed. Even though the system is realized in laboratory scale, this circumstance will not invalidate the significance of the configuration due to modularity of all the technologies that can be easily scaled up to realistic scales

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Analysis of the NOx Emissions Deriving From Hydrogen/Air Combustion in a Swirling Non-Premixed Annular Micro-Combustor

The objective of this paper is to analyse the thermal performances and emission levels of a swirling non-premixed annular micro-combustor. A three-dimensional simulation of the internal flow in an annular combustion chamber fuelled by hydrogen/air in non-premixed conditions was carried out through Ansys Fluent 2020 R2. A detailed mechanism involving many species and reactions was required to represent the complexity of the combustion process. A 19-reactions and 9 species mechanism was deemed to be appropriate to predict the combustion characteristics with great accuracy and limited processing resources. The reaction mechanism was implemented in Fluent through Chemkin. This model was then compared with the built-in model of the chemical kinetics, which involves just one reaction. The results showed that the 19-reactions model is more accurate to reproduce the centerline temperature distribution than the default simpler model: the 1-reaction model differs by 230 K compared to the experimental data, while the 19-reactions one only by 80 K. The comparison between the velocity of the mixture inside the combustor with and without combustion was also carried out, providing an estimate of the influence of temperature on the flow field. Finally, to meet the emission limits established by the European Commission in 2015, the thermal NOx and NOx derived by NNH were examined on both the outlet and the centerline of the combustor. The study reveals great potential of hydrogen mixtures in reducing emissions and provides insights on the cooling requirements to guarantee wall materials reliability

Synthesis of methanol from a chemical looping syngas for the decarbonization of the power sector

One promising pathway for carbon capture and utilization is represented by the coupling of chemical looping cycles with liquid fuel synthesis processes. Methanol is an interesting fuel for gas turbines engines, due to its potential reduction of NOX and particulate emissions along with the absence of SO2 emissions. In this work, methanol production from the syngas generated by a three-reactors chemical looping process is investigated by mass and energy balances. The cycle is composed by a reducer reactor, where Fe2O3 is reduced to FeO by the injection of a reducing agent; an oxidizer reactor, where FeO reacts with CO2 and H2O to produce a syngas; an air reactor, where Fe3O4 is regenerated to Fe2O3 by ambient air. The produced syngas is then sent to a methanol synthesis plant. Several syngas compositions deriving from different CO2/(H2O+ CO2) molar fractions (1–3) at the oxidizer inlet are taken into account. The resulting methanol flow rates are almost equal in all investigated configurations (about 0.35 t/h). From an energy standpoint, the required electric power is greater for higher hydrogen mole fractions in the syngas. However, the case with 75% H2 content is characterized by the greatest methanol yield (⁠12.6%⁠), carbon efficiency (⁠23%⁠) and a high feed/recirculation ratio (⁠0.80⁠), thus representing the most indicated configuration among the investigated ones. Finally, by burning methanol in a gas turbine, the total CO2 emissions are halved with respect to the case without the system (if the CO2 associated with biogenic carbon in the reducer reactor is considered as net-zero)

Integration of Floating Photovoltaic Panels with an Italian Hydroelectric Power Plant

The potential of applying a floating PV (FPV) system in an Italian context (namely, Cecita dam and Mucone hydroelectric power plants) is studied. The additional PV energy production, as well as the effect of non-evaporated water on the productivity of the hydropower plant, is analyzed by varying the basin surface coverage. The simulations highlight that the amount of additional hydroelectricity is quite small if compared to the non-FPV system, reaching about 3.56% for 25% basin surface coverage. However, the annual PV energy production is noticeable even at low coverage values. The expected gain in electricity production in the case of 25% basin surface coverage with the FPV plant rises to 391% of that of the actual hydropower plant. This gain becomes even larger if a vertical axis tracking system is installed and the increase is about 436%. The economic analysis confirms that the production costs (USD/kWh) of FPV systems are comparable to those of land-based PV (LBPV) plants, becoming smaller in the case that a tracking system is installed. In particular, the best solution is the one with 15% coverage of the lake. In this case, the levelized cost of electricity for the LBPVs is 0.030 USD/kWh and for the FVPs, with and without tracking, it is equal to 0.032 and 0.029 USD/kWh, respectively

Effects of pre‐operative isolation on postoperative pulmonary complications after elective surgery: an international prospective cohort study

We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05-1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4-7 days or >= 8 days of 1.25 (1.04-1.48), p = 0.015 and 1.31 (1.11-1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care