Cognitive engagement and academic performance of secondary school students on the Flipped Classroom model in distance education

O envolvimento cognitivo (EC) do aluno é um pré-requisito para uma aprendizagem significativa. Este texto analisa o EC do aluno numa proposta baseada no modelo Flipped Classroom (FC) na educação a distância (EaD). Implementou-se a proposta no ensino secundário português, através de um ciclo de investigação-ação, durante a pandemia Covid-19, com aulas assíncronas e síncronas divididas em atividades conduzidas pelo professor (ACP) e atividades centradas no aluno (ACA). Com o objetivo de compreender a influência do design das atividades no EC do aluno e o impacto da proposta nos desempenhos acadêmicos dos alunos, analisaram-se os discursos dos alunos, as percepções sobre a EaD e os testes de avaliação de conhecimentos. Os resultados mostraram níveis superiores de EC do aluno nas ACA, pois estas permitiram um papel mais ativo dos alunos na construção do conhecimento, uma maior facilitação da professora e aprendizagens com os pares. Os desempenhos acadêmicos dos alunos foram superiores na EaD comparativamente ao ensino presencial, o que pode estar associado aos indicadores de EC (autopercepções positivas, autoeficácia e compreensão dos conteúdos) identificados nas percepções dos alunos. Porém, a mesma análise também identificou vários aspetos que carecem de melhoria para potenciar o modelo FC na EaD.Cognitive engagement (CE) is a prerequisite for students’ meaningful learning. The present text analyses the student’s CE in a proposal based on the Flipped Classroom (FC) model, in distance education (DE). The proposal was implemented through an action-research cycle in Portuguese secondary schools during the Covid-19 pandemic. It combined asynchronous and synchronous lessons divided into teacher-led activities (TLA) and student-centred activities (SCA). To understand the influence of the design of the activities in the student’s CE and the impact of the proposal on the students’ academic performances, the students’ discourses, perceptions, and knowledge assessment tests were analysed. The results showed higher levels of student CE in ACA, as it allowed for a more active role for the students in knowledge construction, greater facilitation from the teacher and peer learning. The results of the students’ academic performance were higher in DE than in face-to-face teaching. This may be associated with the CE indicators (positive self-perceptions, self-efficacy, and content understanding) identified in the students’ perceptions. However, the same analysis also identified several aspects that need improvement to enhance the FC model in DE.Este trabalho é financiado pelo CIEd - Centro de Investigação em Educação, Instituto de Educação, Universidade do Minho, projetos UIDB/01661/2020 e UIDP/01661/2020, através de fundos nacionais da FCT/MCTES-PT. Também foi desenvolvido no âmbito do Programa de Doutoramento “Technology Enhanced Learning and Societal Challenges”, financiado pela Fundação para a Ciência e Tecnologia, FCT I. P. – Portugal, contrato # PD/BD/150424/2019

Three-dimensional modeling of PEMFC with contaminated anode fuel

A novel transient multi-dimensional non-isothermal multiphase model for simulating PEMFC was developed. A multiphase agglomerate catalyst model was considered for the cathode catalyst layer, while in the anode catalyst layer the effect of CO and CO2 presence was taken into consideration assuming two families of catalysts, Pt/C and Pt-Ru. The model predictions were compared to experimental data found in the literature and from an in-house PEMFC. The model was able to capture accurately the steady polarization curves of PEMFCs fed with hydrogen containing different amounts of CO and CO2. Moreover, the corresponding transient voltage was accurately simulated. The results indicated that even low CO concentration in the anode fuel, leads to a considerable degradation of the fuel cell output current density. Among the tested gas diffusion layers, the ones with the highest thickness showed worst performance of the PEMFC. Results showed, that high tortuosity and low contact angle (hydrophobicity) of the gas diffusion layer, decreases the performance of the PEMFC

The influence of impurities in high temperature polymer electrolyte membrane fuel cells performance

This work investigates the influence of carbon dioxide and non-reacted methanol, present in the reformate stream obtained via methanol steam reforming, in the performance of high temperature polymer electrolyte membrane fuel cells (HT-PEMFC), operating between 160 degrees C and 180 degrees C. The HT-PEMFC anode was fed with pure hydrogen, hydrogen balanced with carbon dioxide (75%/25% vol.) and synthetic reformate mixture, considering also vaporized methanol solution in the reformate content (up to 10% vol.). The synthetic reformate was feed during cycles of 420 min. The fuel cell was characterized based on the polarization curve and electrochemical impedance spectroscopy (EIS) analysis. Additionally, acid base titrations were performed to access the phosphoric acid content in different sections of the MEAs as well as scanning electron microscopy (SEM). A low impact in the fuel cell performance was observed when three cycles of synthetic reformate containing methanol solution were performed. When the number of cycles was increased, the performance of HT-PEMFC decreases and irreversible degradation of performance was observed. The cycles with synthetic reformate increased the ohmic resistance and high frequency resistance associated with anodic processes, but decreased the intermediate frequency resistance associated with cathodic processes. Additionally, by increasing the number of cycles, the phosphoric acid content of Celteca (R) MEAs and the thickness of the membrane decreased. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

A review on flow field design for proton exchange membrane fuel cells: Challenges to increase the active area for MW applications

As a reaction to climate change, several countries have set decarbonization plans, in which hydrogen and fuel cells play a central role. Due to its distinctive features, PEMFC is considered a promising technology to decarbonise heavy-duty transport including applications requiring MW-power. Hence, development of high-power stacks, i.e., stacks with significantly increased flow field area is required. This implies possible issues such as uneven distribution of reactants, heat and water management. Consequently, adequate flow field designs are crucial to tackle these issues and ensure stable PEMFC operation at high power. Flow fields have been investigated across PEMFC literature. However, considerations how to develop an effective flow field with a large active area are missing. This work aims to fill this gap by, (i) listing challenges to develop a flow field with an active area >1000 cm2 (ii) analysing most powerful PEMFC stacks on the market and (iii) reviewing the literature regarding flow field, while providing a critical analysis of the information gathered and identifying promising patterns and optimization routes. The aim is to encourage further investigation on scalable flow field designs and push PEMFC closer towards MW-applications. It was found that, despite the unprecedented scale of the active area, most of the issues identified can be addressed through adequate flow field design. Moreover, PEMFC stacks available on the marked still fall short of the MW-range, delivering typically around 100 kW. Based on literature several factors affecting flow field design are identified. Eventually, a specific flow field for MW-applications was proposed

Synergetic integration of a methanol steam reforming cell with a high temperature polymer electrolyte fuel cell

In this work an integrated unit, combining a methanol steam-reforming cell (MSR-C) and a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) was operated at the same temperature (453 K, 463 K and 473 K) allowing thermal integration and increasing the system efficiency of the combined system. A novel bipolar plate made of aluminium Gold plated was built, featuring the fuel cell anode flow field in one side and the reformer flow field on the other. The combined unit (MSR-C/HT-PEMFC) was assembled using Celtec® P2200N MEAs and commercial reforming catalyst CuO/ZnO/Al2O3 (BASF RP60). The water/ methanol vaporisation originates oscillations in the vapour flowrate; reducing these oscillations increase the methanol conversion from 93% to 96%. The MSR-C/HT-PEMFC showed a remarkable high performance at 453 K. The integrated unit was operated during ca. 700 h at constant at 0.2 A cm�2, fed alternately with hydrogen and reformate at 453 K and 463 K. Despite the high operating temperature, the HT-PEMFC showed a good stability, with an electric potential difference decreasing rate at 453 K of ca. 100 mV h�1. Electrochemical impedance spectroscopy (EIS) analysis revealed an overall increase of the ohmic resistances and charge transfer resistances of the electrodes; this fact was assigned to phosphoric acid losses from the electrodes and membrane and catalyst particle size growth

Heat and fuel coupled operation of a high temperature polymer electrolyte fuel cell with a heat exchanger methanol steam reformer

In this work a methanol steam reforming (MSR) reactor has been operated thermally coupled to a high temperature polymer electrolyte fuel cell stack (HT-PEMFC) utilizing its waste heat. The operating temperature of the coupled system was 180 C which is significantly lower than the conventional operating temperature of the MSR process which is around 250 C. A newly designed heat exchanger reformer has been developed by VTT (Technical Research Center of Finland LTD) and was equipped with commercially available CuO/ZnO/Al2O3 (BASF RP-60) catalyst. The liquid cooled, 165 cm2, 12-cell stack used for the measurements was supplied by Serenergy A/S. The off-heat from the electrochemical fuel cell reaction was transferred to the reforming reactor using triethylene glycol (TEG) as heat transfer fluid. The system was operated up to 0.4 A cm2 generating an electrical power output of 427Wel. A total stack waste heat utilization of 86.4% was achieved. It has been shown that it is possible to transfer sufficient heat from the fuel cell stack to the liquid circuit in order to provide the needed amount for vaporizing and reforming of the methanol-water-mixture. Furthermore a set of recommendations is given for future system design considerations

CuO/ZnO/Ga2O3 catalyst for low temperature MSR reaction: Synthesis, characterization and kinetic model

Highly active catalysts for the methanol steam reforming (MSR) capable of operating efficiently at the same temperature of high temperature polymer electrolyte membrane fuel cells (HTPMFCs) devices are strongly desired. A novel CuO/ZnO/Ga2O3 catalyst was synthesized by co-precipitation method and characterized by ICP-AES, N2-physisorption, SEM-EDX and XRD. This catalyst showed a catalytic activity 2.2 times higher than commercial CuO/ZnO/Al2O3 catalysts at 453 K Two kinetic models one empirical and one mechanistic were applied to describe the methanol steam reforming reaction over one of the most promising catalyst family. (c) 2017 Elsevier B.V

Modelling of a high-temperature polymer electrolyte membrane fuel cell integrated with a methanol steam reformer cell

A 3-dimensional non-isothermal simulator comprising a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) and a methanol steam-reforming cell (MSR-C) was developed in Fluent (Ansys). The simulator takes into account most of the significant physical processes, including the electrochemical reactions and carbon monoxide poisoning effect on the electro-catalytic activity of the FC; it also considers the methanol steam reforming (MSR), water gas shift (WGS) and methanol decomposition (MD) reactions in the MSR-C. The developed model for the integrated MSR-C/HT-PEMFC unit was simulated between 443 K and 473 K and validated with experimental results reported in the literature, showing always a very good agreement. The thermal sustainability of the MSR-C/HT-PEMFC unit was assessed, and the role of the thermal insulation and air intake (cathode) stoichiometry in the thermal equilibrium of the device were analysed. A novel integrated MSR-C/HT-PEM stack with ten cells was proposed and simulated, showing a performance above the reported in the literature for similar devices. The results indicated that the proposed stack operates at currents between 4.5 A (0.1 A cm2) and 54 A (1.2 A cm2) without any external heat source. To minimize the degradation of the components the stack should adapt the operating temperature to the current density. © 2017 Elsevier Lt