Sensing water accumulation and transport in proton exchange membrane fuel cells with terahertz radiation

Fuel cells are like batteries in the sense that they are electrochemical cells whose main components are two electrodes (anode and cathode) and an electrolyte material. They differ from most batteries as they require a continuous stream of fuel and oxidant, generating electricity and heat for as long as these are supplied. Perfluorinated sulfonic-acid ionomers such as Nafion are the most common proton exchange membrane material (solid electrolyte) whose structure underpins its unique water and chemical/mechanical stability properties. Pure hydrogen and air are typically used as the fuel and oxidant, respectively, and by-products are water and waste heat. Due to their high efficiency, low temperature operation and capacity to quickly vary their output to meet shifting demands, these fuel cells are attractive to the automobile industry, although they can also be used for stationary power production. Water management is a prominent issue in proton exchange membrane fuel cell technology. Strategies in this topic must maintain a delicate balance between adequate hydration levels in the Nafion proton electrolyte membrane to maximise proton conductivity, and minimal flooding, which hinders mass transport to active sites. The complex nature of water transport in these fuel cells can be investigated via in situ or ex situ diagnostics with visualisation techniques such as neutron imaging or optical diagnostics. Despite the wealth of information provided by these techniques, they suffer from issues such as limited availability, excessive cost, limited sensitivity, and penetration depth. Terahertz radiation has been growing in popularity for contactless and non-destructive testing across various industrial sectors, including pharmaceutical coating analysis, defect identification, and gas pipeline monitoring. The ability of terahertz waves to penetrate through dielectric materials such as plastics or ceramics combined with strong attenuation by liquid water provides the necessary contrast to image water presence in proton exchange membrane fuel cells and their components. Motivated by the recent commercial availability of a compact terahertz source and video-rate terahertz camera, a simple terahertz imaging system in transmission geometry was realised. First, as a first step towards flooding inspection in an operating fuel cell, the feasibility of the imaging system for visualising and quantifying liquid water during an ambient air desorption process for Nafion membranes of a wide range of thicknesses – NRE-212 (50 µm), N-115 (127µm), N-117 (180 µm) and N-1110 (254 µm) was investigated. It was demonstrated that the imaging system was able to quantify liquid water in the 25-500 µm thickness range, estimate membrane weight change related to liquid water desorption, which correlated well against simultaneous gravimetric analysis and visualise the room temperature liquid water desorption process of a partially hydrated Nafion N-117 membrane. Further work consisted in imaging water build-up inside an operating proton exchange membrane fuel cell using the terahertz imaging system, combined with high-resolution optical imaging. Using a custom-built, laboratory-scale, terahertz, and optically transparent fuel cell, two-phase flow phenomena of water accumulation and transport, such as membrane hydration, main droplet occurrence, water pool formation, growth, and eventual flush out by gases were imaged. Results of the terahertz agree with simultaneous optical imaging and electrochemical readings. To demonstrate the potential used of the proposed imaging modality, the effect of air gas flow rates on flooding was demonstrated

Quantitative video-rate hydration imaging of Nafion proton exchange membranes with terahertz radiation

Nafion membranes are considered as the industry standard electrolyte material for proton exchange membrane fuel cells. These membranes require adequate hydration in order to reach a high proton conductivity. The relatively high sensitivity of terahertz radiation to liquid water enables contrast to be observed for inspecting water presence in Nafion electrolyte membranes. Utilising a commercially available terahertz source and camera, this paper investigates the feasibility of a compact terahertz imaging system for visualising and quantifying liquid water during an ambient air desorption process for Nafion membranes of a wide range of thicknesses – NRE-212 (50 μm), N-115 (127 μm), N-117 (180 μm) and N-1110 (254 μm). We demonstrate that the terahertz imaging system is able to quantify liquid water in the 25–500 μm thickness range, estimate membrane weight change related to liquid water desorption, which correlated well against simultaneous gravimetric analysis and visualise the room temperature liquid water desorption process of a partially hydrated Nafion N-117 membrane

Extracting the dielectric relaxation of water in thin Nafion membranes by terahertz spectroscopy

Terahertz time domain spectroscopy (THz-TDS) has been demonstrated to be capable of quantifying water uptake and retention properties of Nafion proton exchange membranes (PEMs). With a growing interest in thinner membranes, we analysis thin membranes to reveal its water uptake and retention propertie

Quantification of water states in thin proton exchange membrane manufacturing using terahertz time-domain spectroscopy

Water states in proton exchange membranes have previously been extracted using terahertz time-domain spectroscopy (THz-TDS) for thick Nafion membranes. In this work, we have developed a parametric based algorithm for data analysis and applied it to thin industrially relevant membranes (13-70μm), processed under different conditions, producing results consistent with conventional gravimetric analysis and prior demonstrations. This therefore opens up opportunities for rapid membrane investigations and understanding

Graphene-based External Optoelectronic Terahertz Modulators for High Speed Wireless Communications

The realization of terahertz external amplitude modulators with a carrier frequency of 0.8 THz is presented for application in the next generation near-field wireless communications

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): study protocol for a randomized controlled trial

BACKGROUND: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). METHODS/DESIGN: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH2O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure 6430 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. DISCUSSION: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration metho

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt

Investigations on the impact of the introduction of the Aloe vera into the hydrogel matrix on cytotoxic and hydrophilic properties of these systems considered as potential wound dressings

In the paper, synthesis of chitosan-based hydrogels modified with Aloe vera juice is presented. The novelty of the research was a combination of hydrogel materials with properties beneficial in viewpoint of their use as modern wound dressings and Aloe vera juice supporting the wound healing process. Hydrogels have been obtained via UV radiation. The impact of the amount of the crosslinking agent as well as the introduction of the Aloe vera juice into the hydrogel matrix has been determined. Performed measurements involved analysis of the swelling ability, characteristics of the surface roughness, determining the release profile of Aloe vera and the contact angles of hydrogels. Furthermore, the analysis of the dehydration process of the polymer membrane, investigations on the cytotoxicity of hydrogels via MTT reduction assay and the neutral red uptake assay as well as the studies on the pro-inflammatory activity have also been performed. It was proved that the addition of Aloe vera juice improves the hydrophilic properties of the materials (e.g. contact angle changed from 82.5° to 73.0°). Next, the use of 25% more of the crosslinker resulted even in the increase of the contact angle by 86%. Modified hydrogels showed higher swelling properties even by 15% than unmodified materials. Furthermore, obtained hydrogels show an ability to release Aloe vera – after 5 h approx. 80% of this additive has been released in an acidic environment. Tested materials do not exhibit cytotoxic properties, the addition of Aloe vera results in an improvement of the viability of L929 murine fibroblasts and, importantly, these materials show lower pro-inflammatory activity than the positive control. Performed investigations allow to state that obtained materials show a great application potential

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.13Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt