Search

Magistritöö Metsamajanduse ja metsaökoloogia õppekaval Erinevates keskkondades ning raamistikes toimetavate maaomanike tegevuse võrdlemiseks kasutatakse standardiseeritud sertifikaate ja märgiseid. Eestis kasutatakse eelkõige puidu turustamisega seotud sertifikaate – FSC-d ja PEFC-d. Sertifikaadi omamine tagab kolmandatele osapooltele info selle kohta, et puidu päritolu on teada ja et seda metsa on majandatud jätkusuutlikult. Euroopa maaomanikud on loonud eraalgatusliku ja omaniku vabatahtlikkusel põhineva Wildlife Estates märgise, mis näitab, et maaomanik panustab aktiivselt oma tegevusega bioloogilise mitmekesisuse suurendamisse ning ökosüsteemide taastamisse. Magistritöö eesmärk on hinnata Wildlife Estates märgise hindamismetoodika sobivust Eesti kontekstis Järvselja Õppe- ja Katsemetskonna näitel. Antud töö põhjal saab vastata küsimusele, kas märgis sobib Eesti metsamajandusse. Magistritöös tuuakse välja märgise tugevused ja nõrkused. WE märgist võrreldakse PEFC ja FSC sertifikaatidega, et vastata küsimusele, miks Eesti maaomanikud peaksid WE märgist eelistama puidusertifikaatidele. Ühtlasi kaardistatakse märgise taotlemise motiive ning võimalikke arengusuundasid märgisega kaasnevate hüvede osas. Märgis pakub uudset lahendust eraloodushoiu edendamiseks, põhinedes omaniku vabatahtlikkusel ja vastutusel. Kuna märgise hindamismetoodikas on paljud kriteeriumid sellised, mida omanik on kohustatud täitma seadusandlusest tulenevalt, on omanikul paljudel juhtudel märgist võimalik lisameetmeid rakendamata taotleda. See on ka üks märgise tugevusi, mistõttu võib julgustada omanikke märgist taotlema. Märgise taotlemise motiivid põhinevad usaldusel, otsustamisvabadusel, teadmistel, rahaliste hüvede pakkumisel ja õiglusel. Usaldatavuse suurendamiseks peaks märgis tulevikus saavutama riiklikul või kohaliku omavalitsuse tasemel tunnustuse. Otsustusvabaduse tagab lepingu pikkus ja seotus. Märgist taotletakse viieks aastaks, mis tagab jätkusuutlikkuse ja samas annab uutele omanikele võimaluse näha, kas võrgustik pakub neile piisavalt hüvesid selleks, et loodushoidu panustada. Teadlikkuse suurendamise eelduseks on maaomanike vaheline tihe koostöö ja maaomandite kontrollitud avamine (avatud talude päev, matkarajad jne) ning publikatsioonides osalemine. Rahalisi hüvesid on võimaik siduda juba olemasolevate toetusmeetmetega. Looduskaitseliste piirangute leevendamine märgist omavate omanike kinnistutel suurendab omanike silmis õiglustunnet. Tulevikus peaksid omanikud ise näitama initsiatiivi märgise taotlemiseks. Standardized certificates and labels are used to compare the performance of landowners in different environments and frameworks. In particular, certificates related to the marketing and supply chain of timber are used in Estonia – FSC and PEFC. Having a certificate or label provides information to third parties that the origin of the timber is known and that the forest has been managed sustainably. European landowners have created a private and voluntary label called Wildlife Estates, which shows that landowners are actively contributing to increase biodiversity and to restore ecosystems. The aim of the master’s thesis is to analyze the suitability of the Wildlife Estates label evaluation methodology in the Estonian context on the example of the Järvselja Training and Experimental Forestry District. Based on this work, the question whether the label is suitable for Estonian forestry can be answered. The strengths and weaknesses of the label are also highlighted. The WE label is compared to PEFC and FSC certificates to answer the question of why Estonian landowners should prefer the WE label to timber certificates. The motives for applying for the label and possible developments in the benefits of the label are also mapped. The label offers an innovative solution for promoting private conservation, based on the voluntary and responsible nature of the owner. As many of the criteria in the label evaluation methodology are those that the owner is required to meet Under the legislation, in many cases the owner can apply for the label without taking further actions. This is also one of the strengths of the label, which is why owners can be encouraged to apply for the label. The motives for applying for the label are based on trust, freedom of choice, knowledge, the provision of financial benefits and justice. In order to increase credibility, the label should be recognized at national or local level. Freedom of decision is guaranteed by the length and connection of the contract. The label is applied for five years, which ensures sustainability and at the samet ime gives new owners the opportunity to see if the network offers them enough benefits to contribute to nature conservation. A prerequisite for raising awareness is cooperation between landowners and the controlled opening of land (open farm days, hiking trails etc) and participation in publications. Financial benefits can be linked to existing support measures. Easing nature conservation restrictions on the properties of the owners of the label increases the sense of justice. In the futuure, owners should take the initiative to apply for the label.

A new method for measuring membrane degradation in polymer electrolyte fuel cells (PEFCs) is proposed. The method is based on the detection of fluoride ions in effluent water from the cathode- and anode outlet of the PEFC using photometry (PM). The fluoride emission rate (FER) is an indicator of the membrane’s state of health (SoH) and can be used to measure the chemical membrane degradation. Commercial catalyst-coated membranes (CCMs) have been tested at 80 °C and 90 °C at 30% relative humidity (RH) to investigate the reliability of the developed method for fuel cell effluent samples. To verify the measurement, a mean-difference plot was created by measuring the same data with a fluorine selective electrode. The average difference was at ±0.13 nmol h−1 cm−2, which indicates good agreement between the two methods. These new findings imply that PM is a promising method for quick and simple assessment of membrane degradation in PEM technology.

In hydrogen energy systems, the polymer electrolyte fuel cell (PEFC) is an important component. The purpose of this study is to clarify the effect of separator thickness (s.t.) in PEFC on the distributions of mass such as H2, O2, H2O and current density when PEFC is operated at 363 K and 373 K. The relative humidity (RH) of supply gases also impacts the operation. The numerical simulation (using a 3D model) with COMSOL Multiphysics has been conducted to analyze the characteristics of PEFC. It has been observed that the molar concentration of H2 using s.t. of 2.0 mm is smaller compared with the thinner s.t. cases at the initial operation temperature of a cell (Tini) = 363 K and 373 K. The molar concentration of O2 using s.t. of 2.0 mm is smaller compared with the thinner s.t. cases at Tini = 373 K, as well as the case for the RH of supply gases at the anode of 40%RH and cathode of 40%RH (A40%RH/C40%RH) irrespective of Tini. Additionally, it has been clarified that the molar concentration of H2O maintains a low value along with the gas channel at Tini = 373 K using s.t. of 1.5 mm and 1.0 mm. Moreover, it has been clarified that the current density using s.t. of 2.0 mm is the highest among the different s.t. irrespective of Tini, which is the most remarkable in the case of A40%RH&C40%RH.

6 figures, 3 tables., Perfluorinated sulfonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membranes and ionomers in the catalytic layer of membrane-electrode assemblies (MEAs) because of their high protonic conductivity, σH, as well as chemical and thermal stability. The use of PFSA polymers with shorter side chains and lower equivalent weight (EW) than Nafion®, such as Aquivion® PFSA ionomers, is a valid approach to improve fuel cell performance and stability under drastic operative conditions such as those related to automotive applications. In this context, it is necessary to optimize the composition of the catalytic ink, according to the different ionomer characteristics. In this work, the influence of the ionomer amount in the catalytic layer was studied, considering the dispersing agent used to prepare the electrode (water or ethanol). Electrochemical studies were carried out in a single cell in the presence of H2-air, at intermediate temperatures (80–95 °C), low pressure, and reduced humidity ((50% RH). %). The best fuel cell performance was found for 26 wt.% Aquivion® at the electrodes using ethanol for the ink preparation, associated to a maximum catalyst utilization., This research was funded by the European Union’s Seventh Framework Programme (FP7/2007–2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant no 303452 (IMPACT).

Evaporative cooling is a promising concept to reduce the fuel cell system volume and mass significantly. This paper investigates the interactions between the fuel cell stack and the balance of plant in an evaporatively cooled polymer electrolyte fuel cell system (PEFCS). For this, a zero-dimensional PEFCS model, comprising the fuel cell stack, air compressor, charge air cooler, humidifier, hydrogen recirculation blower, condensing radiator and water separator has been developed and analyzed. Two evaporative cooling system architectures are compared to conventional, liquid cooling. Optimal operating conditions are determined by a numerical optimization of the net system power output. Main results show that evaporative cooling works on the system level over a wide range of operating conditions. The optimum system power and highest efficiencies are achieved at high temperatures (80–90 °C), low pressure (125–150 kPa) and a corresponding cathode stoichiometry between 1.5 and 3, allowing for a closed water loop at the same time. The air compressor shows an increased power demand, compared to conventional cooling and the exhaust gas condenser is identified as the one critical component for evaporative cooling. Its performance is key to an efficient operation and closed water loop at all ambient conditions., Journal of Power Sources, 542, ISSN:0378-7753, ISSN:1873-2755

The membrane-electrodes assembly (MEA) is the core of the Polymer Electrolyte Fuel Cell (PEFC). It consists of a membrane, catalytic (CL) and gas diffusion layers (GDL). In order to manufacture MEAs with suitable performance, a hot-pressing procedure is generally used. The relevant parameters are the temperature, pressure and time of hot-pressing. Such variables need to be adjusted as a function of the type of ionomer used in the catalytic layer and membrane. In this study, an evaluation of the temperature of hot-pressing was carried out and its influence on MEA electrochemical performance was assessed. In particular, preparation trials of MEAs were carried out with reinforced experimental membranes based on Aquivion® short-side-chain PFSA (by Solvay Specialty Polymers). The membranes were coupled to gas diffusion electrodes, and MEAs were manufactured using different temperatures for the hot-pressing procedure in order to evaluate their influence on the electrochemical performance of PEFCs, in the temperature range of 80–95 °C, with low relative humidity of the reactant gases. The electrochemical performance of the prepared MEAs was tested in a H2/Air 25 cm2 single cell in terms of polarization curves and accelerated stress test (AST).

In this study, we investigated the influence of the Catalyst-Layer (CL) structure on Polymer Electrolyte Fuel Cell (PEFC) performance using an inkjet coating printer, and we especially focused on the CL thickness and the electrode area. In order to evaluate the influence of CL thickness, we prepared four Membrane Electrode Assemblies (MEAs), which have one, four, five and six CLs, respectively, and evaluated it by an overpotential analysis. As a result, the overpotentials of an activation and a diffusion increased with the increase of thickness of CL. From Energy Dispersive X-ray spectroscopy (EDX) analysis, because platinum twines most ionomers and precipitates, the CL separates into a layer of platinum with a big grain aggregate ionomer and the mixing layer of platinum and ionomer during the catalyst ink drying process. Consequently, the activation overpotential increased because the three-phase interface was not able to be formed sufficiently. The gas diffusivity of the multilayer catalyst electrode was worse than that of a single layer MEA. The influence of the electrode area was examined by two MEAs with 1 and 9 cm2 of electrode area. As a result, the diffusion overpotential of 9 cm2 MEA was worse than 1 cm2 MEA. The generated condensate was multiplied and moved to the downstream side, and thereafter it caused the flooding/plugging phenomena.

Bakalaureusetöö Metsanduse õppekaval Siinses bakalaureusetöös uuriti Eesti erametsa ettevõtete ja ühistute hinnanguid metsamajandamise sertiftitseerimisele. Töö aluseks on 28 sertifitseeritud metsandusettevõtte ja metsaühistu antud vastused, kelle esindajad vastasid 2019.aastal kaheksale küsimusele QuestionPro keskkonnas. Küsimustiku eeskujuks on Rumeenias läbiviidud uuringu küsimused, mis on kohandatud Eesti tingimustele. Põhilised põhjused, miks sooviti/soovitakse omada sertifikaati, oli kolm: puiduturu regulatsioonide ja majanduslike eeliste pärast ning maine tõstmiseks. Metsandusettevõtete ja metsaühistute hinnangul on põhiliseks takistavaks asjaoluks sertifitseerimisel mahukas dokumentatsioon ja bürokraatia. Uurimusest selgub, et sertifitseeritud ettevõtete ja ühistute põhiprobleemiks on soovitud tulu mitte realiseerumine, mida võib seletada nii tegevusala, turul valitseva nõudluse, kui ka alles hiljutise sertifitseerimisega. In this Bachelor's thesis, the assessments of Estonian private forest companies and cooperatives on forest management certification were studied. The work is based on the answers given by 28 certified forestry companies and forest associations, whose representatives answered eight questions in 2019 in the QuestionPro environment. The example of the questionnaire is from the survey conducted in Romania, which was adapted to Estonian conditions. There were three main reasons for wanting to have a certificate: for the regulations and economic benefits of the timber market, and for raising reputation. According to forestry companies and forest associations, the main obstacle of certification is extensive documentation and bureaucracy. The study shows that the main problem of certified companies and cooperatives is they haven’t gotten the desired income, which can be explained by the industry, the prevailing demand in the market, as well as the recent certification.

Polymer electrolyte fuel cells (PEFCs) have shown a great potential to be used in several applications, e.g., portable, mobile and stationary systems. Each of the mentioned applications demands from PEFCs different operating conditions to perform in the best possible manner. Knowing in detail the behavior of their internal components will help to improve the mechanical and thermal properties of the different constitutive layers. The objective of this research is to analyze in detail the behavior of the internal resistances of a PEFC, using the impedance spectroscopy technique. A single cell is evaluated in a broad range of current densities, i.e., from 0.2 to 2.0 A.cm–2, to evaluate the resistances that cause loss of performance. The analyzed resistances correspond to the ohmic, charge transfer and mass transport resistance. The results were obtained after the interpretation of the data taking from Nyquist diagrams, and they were analyzed considering high and low conditions of relative humidity (RH). The obtained results showed that the ohmic resistance (attributed to membrane Nafion® 212), is independent of the load applied for fully humidified conditions, with a value of 0.0725 Ω.cm2. On the other hand, it is strongly dependent on low humidification conditions, with values between [0.198–0.132] Ω.cm2, for current density of [0.2–2.0] A.cm–2, respectively. It was also found that the charge transfer resistance decreases with respect to the applied load until a saturation value, and further it represents the major participation to the total resistance of the cell. The charge transfer resistance represents around 50–75% of the total resistance in conditions of high RH, and among 30–65% for conditions of low RH. In addition, it was found that the mass transport resistance appears early at low RH and triples for full humidification conditions. (Less)

Made available in DSpace on 2022-05-01T05:29:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-10-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Certification programs may include market access benefits for those business that have certified voluntarily, but there are also other consequences, such as the ban on the use of certain chemical pesticides imposed by the Forest Stewardship Council (FSC) that can negatively affect integrated pest management. The Programme for the Endorsement of Forest Certification (PEFC) was created in response to FSC standards and includes national certification schemes such as the Responsible Wood (RW), previously known as the Australian Forestry Standard (AFS). The objective of this study was to evaluate the impacts of FSC and RW/PEFC certification on practices of integrated pest management from the perspective of Australian forest growers. Questionnaires were emailed to all organizations in Australia with forest plantations certified by FSC and/or RW/PEFC. The questionnaire addressed the importance of forest pest groups, pest control techniques, chemical pesticides (insecticides and herbicides) in derogation; the advantages and disadvantages of integrated pest management related to the certification; and satisfaction with certification in relation to pest management. The two insecticides in derogation were considered unnecessary by most of Australian growers. FSC promoted more changes in integrated pest management than RW. Half the FSC-certified companies stated that they had greater costs associated with integrated pest management to adequately meet certification. RW-certified growers were more satisfied than FSC-certified ones, but both groups stated that they would maintain certification in a scenario without further insecticide derogation. The main changes in pest management for FSC-certified companies were with preventive techniques that reduce the use and dependence on insecticides. The environmental and social side of FSC prevailed in these changes. Raising certification rigor can increase costs, making certification impracticable, forcing companies to adopt less restrictive schemes or simply not certify. Instituto de Ciências Agrárias Universidade Federal de Minas Gerais, Av. Universitária, 1000, Universitário Departamento de Entomologia/BIOAGRO Universidade Federal de Viçosa Departamento de Engenharia Florestal Universidade Federal de Viçosa Departamento de Proteção Vegetal Universidade Estadual Paulista “Júlio de Mesquita Filho” Forest Industries Research Centre Faculty of Arts Business and Law University of the Sunshine Coast, 90 Sippy Downs Dr Departamento de Proteção Vegetal Universidade Estadual Paulista “Júlio de Mesquita Filho” CAPES: BEX 11710/13-6

Water management represents one of the main challenges in the design and operation of Polymer Electrolyte Fuel Cells (PEFCs). Besides performance, the water level also affects the durability of the cell. Understanding the degradation processes is of vital importance for extending durability of PEFCs by suitable mitigation strategies. In this work, the degradation processes related to operation with fully- and non-humidified gas streams were locally studied. The differences were analyzed using in-situ diagnostic tools, such as segmented cell for local current density measurements, during a 300 h test operating under constant conditions, in combination with local post-test analysis, i.e. SEM/EDX and XPS. The results showed the deep impact of the RH on homogeneity during the degradation process due to the fact that different water distribution influences the chemical environment. Under non-humidified gas streams, the cathode inlet region exhibited increased degradation, whereas with fully humidified gases the bottom of the cell had the higher performance losses. The degradation and the degree of reversibility produced by Pt dissolution, PTFE defluorination, and contaminants such as silicon (Si) and nickel (Ni) were locally evaluated

6 Figuras, 4 Tablas, The large-scale application of polymer electrolyte membrane fuel cells (PEMFCs) requires a reduction of the costs and an improvement in performance and stability. Particularly, the automotive market needs the PEMFC works under harsh conditions (high temperature, low relative humidity, etc.), maintaining a good performance level and low degradation. These operating conditions permit to mitigate the constraints concerning the thermal and water management allowing both a simplification and a volume reduction of the system inside the car with a strong impact on costs and reliability. However, PEMFCs require the development of the components such as catalysts, ionomers and membranes with a proper stability. In this work, PtCo/KB and Pt/KB electrocatalysts were investigated with the aim of verifying the performance and stability, coupling them with an innovative reinforced Aquivion® membrane. An optimization of the catalytic ink composition was carried out, according to the different ionomers characteristics to be used in the catalytic layer in order to reduce the degradation level. The stability is assessed by considering the variations of the performance and electrochemical parameters, such as electrochemical surface area (ECSA) and mass activity (jm), at the beginning and end of accelerated stress test procedures., The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant no 303452 (IMPACT).

Nanocrystalline platinum with different morphologies is synthesized via electrochemical deposition technique. The nucleation mechanism and its structural effect over the electrodeposited Pt on carbon electrodes have been systematically studied. Powder X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy are employed to study nucleation, oxidation states, and Pt structure growth on a carbon electrode. This study reports significant development of Pt metal nanoparticles with different morphologies such as a sphere, flower, core-flower, and rod-like structure directly fabricated on carbon electrode while tuning the deposition parameters such as current density, time, temperature, pH during the deposition process. The proposed electrochemical route represents a superior fabrication procedure for large-scale electrode fabrication compared to a conventional method for preparing membrane electrode assemblies for fuel cell stacks.

In the polymer electrolyte fuel cell (PEFC), the electrolyte membranes are chemically deteriorated by H 2 O 2 which are reacted during operation. Also, the electrolyte membranes are suffered a cyclic stress caused by starting and shut-down operation. Because, during the operation of a PEFC, a water elongates the electrolyte membranes, and during the stoppage operation, the membranes are contracted under waterless condition. For accumulation of these chemically and/or mechanically damage, quality of the membranes are gradually worsened. In this study, to study a degradation distribution on the electrolyte membranes, a perforating testing machine was newly developed. By using this testing machine, we can make a “degradation map” for visualizing a degree of degradation in the cell of a PEFC.

Composite membranes based on sulphonated Polyetheretherketone (sPEEK) and 5,10,15,20-tetra(4-pyridyl)porphyrin (TPyP) were developed for portable applications. A sulphonation degree of 65% and different loadings (0-5wt%) of TPyP porphyrin were used. Spectroscopic studies (UV-Vis and fluorescence emission), ionic exchange capacity, water uptake, structural and morphological analyses were carried out. A good interaction between the filler and the polymer was found, probably due to specific supramolecular interactions among the nitrogenous atoms present in the periphery of the porphyrin ring and sulphonic groups of polymer. The membrane with the lowest loading (~1wt%) of TPyP, shows slightly lower water uptake and unaltered ? values than the reference membrane, resulting in quite unaltered proton conductivity also in anhydrous conditions. Electrochemical tests were performed in a PEFC 25cm2 single cell at room temperature and anhydrous hydrogen/humidified air. A power density of 93mW/cm2 was found in anhydrous conditions for sample with the lowest loading of TPyP.

Analyzing the fluid behavior in complex porous media like gas diffusion layers (GDLs) in polymer electrolyte fuel cells (PEFCs) can be accurately done using the lattice Boltzmann method (LBM). This article shows the data obtained from a study in which diffusion parameters such as porosity, gas phase tortuosity and diffusibility are computed considering simulated porous media [1]. The data were computed when a water drop obstacle is placed inside the GDL domain and the size of the water-drop is varied. Additionally, figures showing the evolution of the flow velocity field are presented alongside graphics that presents the change in local and bulk porosity for each obstacle size. Finally, there is a detailed method explanation concerning the implementation of the lattice Boltzmann method and a general description of computational codes for the domain and obstacle generation as well as the boundary conditions simulation. Data and processes in this article can be exploited in new attempts to solve real case problems in complex mesoscale media. Keywords: Gas diffusion layer, PEFC, Gas-phase tortuosity, Diffusibility, Water-droplet

Perfluorinated sulphonic acid (PFSA) polymers such as Nafion® are widely used for both electrolyte membrane and ionomer in the catalytic layer because of their high proton conductivity (σH) as well as chemical and thermal stability. When PFSA polymers alternative to Nafion® with a different EW are used, it is necessary to optimize the composition of the catalytic ink, considering the different ionomer characteristics. Moreover, fuel cell operating conditions play an important role regarding the catalytic layer optimization. In this work, the influence of ionomer amount in the catalytic layer was evaluated. The electrochemical studies were carried out in a single cell in H2–O2 at intermediate temperatures (80 °C–130 °C) by using a fumapem® F-950 membrane as an electrolyte. A hydro-alcoholic dispersion of fumion® F was also used as an ionomer in the electrode catalytic structure with an amount ranging from 30 to 60%. Under operating conditions finalised to automotive applications (intermediate temperature, low relative humidity and low pressure of gases) an improvement of performance in terms of maximum power density was obtained by using optimized ionomer content.

Understanding the freezing mechanism of liquid water within polymer electrolyte fuel cells (PEFC) is crucial for its commercialization for mass market. Although various publications investigated the cold start capability of PEFCs, contradictory behaviors during cold starts at freezing temperatures have been published in literature. Interestingly, differences can be mainly identified between large and small size fuel cells: the latter have a significantly higher cold start capability than large size fuel cells. In order to understand the influence of different active areas, we present measurements of cold starts performed with cells sizes of 1 and 50 cm2 using the same materials, including a large count of experiments (>200) on the 1 cm2 cells to perform statistical analysis. The cold start capability is strongly reduced with an increasing size of the active area, and the operating times changes from stochastic values for small cells to reproducible values for large cells. Both effects can be explained by the higher probability of the aggregate state transition from super-cooled water to ice in large cells. Consequently this paper highlights the implications of downscaling PEFCs to draw conclusions for technical relevant cold-starts., Journal of the Electrochemical Society, 162 (10), ISSN:0013-4651, ISSN:1945-7111

The article discusses the issues of effectiveness of the FSC (Forest Stewardship Council) and PEFC (Programme for the Endorsement of Forest Certification) certification systems in relation to enterprises and the level to which the systems which present sustainability as a part of their ethos are accepted by consumers. The justifiability and topicality of this issue result from the increasingly strong interest in sustainability of the society as a whole as well as from the long-term vision of sector policies with respect to meeting the objectives of sustainable development. The increasing demand for natural resources exerts pressure on our planet. Sustainability is hence essential for our future and has long been in the centre of the European project. Its economic, social and environmental aspects which form the common objective of society have been acknowledged in EU agreements. A principal document of a global nature is the 2030 UN Agenda for Development, a sustainability programme which has the sustainability of forest ecosystems established in its Goal 15: Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss. Visions, direction and goals of sustainable development have also been stipulated in the Paris Agreement on climate change (COP21), in the Addis Ababa action programme and in The Future We Want declaration, namely in its Chapter II, which appeals to enterprises and industries for developing strategies which would contribute to sustainable development. This study aims to analyse and assess the justifiability of the existence of certification systems in relation to processing operators and end consumers in the Czech Republic. From the results of the study, it can be concluded that, despite the strong representation of selected certification systems in the Czech Republic, their effectiveness in economic, social and environmental terms is not perceived exclusively positive by businesses and consumers. info:eu-repo/semantics/openAccess

To overcome the fundamental disadvantages of conventional cathodes for polymer electrolyte fuel cells (PEFCs), such as dissolution and migration of platinum-based catalysts and consumption of the carbon catalyst-support, a substantially novel gas-diffusion cathode has been proposed. The electrode was made of a porous oxide catalyst, which was coated on the inner and outer surfaces of a macro-porous titanium sheet substrate, using neither a platinum catalyst nor carbon catalyst-support. The suitability of this cathode for PEFCs, tested using a highly porous iridium oxide strongly coated on the macro-porous titanium sheet substrate, was confirmed by successful power generation. The gas-diffusion electrode functioned not only as the cathode but also as an anode of a PEFC., Article, ELECTROCHIMICA ACTA. 105:224-229 (2013)

Proton transport properties of a partially protonated poly(aspartic acid)/sodium polyaspartate (P-Asp) were investigated. A remarkable enhancement of proton conductivity has been achieved in the thin film. Proton conductivity of 60-nm-thick thin film prepared on MgO(100) substrate was 3.4 × 10(-3) S cm(-1) at 298 K. The electrical conductivity of the oriented thin film was 1 order of magnitude higher than the bulk specimen, and the activation energies for the proton conductivity were 0.34 eV for the oriented thin film and 0.65 eV for the pelletized sample, respectively. This enhancement of the proton transport is attributable to the highly oriented structure on MgO(100) substrate. This result proposes great potential for a new strategy to produce a highly proton-conductive material using the concept of an oriented thin film structure without strong acid groups.

This paper describes the use of an in situ analytical technique based on simultaneous displacement and resistance measurement of gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs), when exposed to varying compaction pressure. In terms of the losses within fuel cells, the ohmic loss makes up a significant portion. Of this loss, the contact resistance between the GDL and the bipolar plate (BPP) is an important constituent. By analysing the change in thickness and ohmic resistance of GDLs under compression, important mechanical and electrical properties are obtained. Derived parameters such as the ‘displacement factor’ are used to characterise a representative range of commercial GDLs. Increasing compaction pressure leads to a non-linear decrease in resistance for all GDLs. For Toray paper, compaction becomes more irreversible with pressure with no elastic region observed. Different GDLs have different intrinsic resistance; however, all GDLs of the same class share a common compaction profile (change in resistance with pressure). Cyclic compression of Toray GDL leads to progressive improvement in resistance and reduction in thickness that stabilises after ∼10 cycles.

The durability of polymer exchange membrane (PEM) fuel cells, under a wide range of operational conditions, has been attracting intensive attention, as durability is one of the largest barriers for commercialization of this promising technology. In the present work, membrane electrode assembly (MEA) degradation of a four-cell stack with Nafion membranes of different thicknesses, including N117, N115, NR212, and NR211, was carried out for 1000 h under idle conditions. By means of several on-line electrochemical measurements, the performance of the individual cells was analyzed at different times during the degradation process. The results indicate that the cells with thinner membranes have a lower open circuit voltage (OCV) due to the higher fuel crossover. Before degradation, the thickness of the membranes correlates with performance of the cell. However, with the advancement of degradation, the performance of cells with thinner membranes degraded much faster than those with thicker membranes, especially after 800 h of operation. The fast performance degradation for thinner membranes is evident by a dramatic increase in hydrogen crossover indicating membrane thinning or pinhole formation.

Degradation processes in PEFC lead to insufficient life-time which is one of the crucial problems hindering mass market penetration of fuel cells. The degradation rate depends strongly on the operating conditions, of fuel cells and in addition the operating conditions can vary significantly along the flow path. Therefore, at DLR the degradation processes are investigated with locally resolved in-situ methods which are combined with locally resolved ex-situ characterizations. The combination of the in-situ and ex-situ methods allows to quantify and to identify the degradation processes. Based on the locally resolved investigations the relation of the degradations processes with the operating conditions and consequently the identification of the causes and effects of degradation processes is discussed for electrodes and gas diffusion layers.

A fuel cell microgrid with photovoltaics effectively reduces greenhouse gas emission. A system operation optimization technique with photovoltaics and unstable power is important. In this paper, the optimal operation algorithm of this compound microgrid is developed using numerical weather information (NWI) that is freely available. A GA (genetic algorithm) was developed to minimize system fuel consumption. Furthermore, the relation between the NWI error characteristics and the operation results of the system was clarified. As a result, the optimized operation algorithm using NWI reduced the energy cost of the system.

In this contribution a simplified, isothermal, two-phase, one-dimensional model for the calculation of the cathodic gas flow along the flow field channels of a polymer electrolyte fuel cell (PEFC) is presented. The composition of the humidified oxidant gas, average gas velocity, pressure drop, and other quantities can be calculated for any gas distributor structures with one channel. Thereby, the model requires several input parameters which have to be determined solely by experiment and pre-defined operation conditions, e.g. the water content of the feed gas, local current densities, and gas flow rates. In contrast to other models, the cross-section reduction has been taken into account which results from the penetration of the gas diffusion layer into the flow field channels due to the mounting pressure. Beyond this, the model needs no fit-parameters for further adjustment. For close examination of the factors limiting the performance of a PEFC, the DLR has developed several techniques for measuring the current density distribution with spatial resolution. In order to investigate the origin of the corresponding effects, one of these techniques has been improved by implementing the model of the cathodic gas flow as an on-line feature. The combination of a spatially resolved measurement technique with a real-time simulation gives a better understanding of the local processes within the cell and represents a helpful tool for the development of fuel cell components as well as for the optimization of the operating conditions. Exemplarily, the presentation the results for a 25 cm 2 serpentine flow field at different operation modes are shown in this paper.

In order to optimize the electrode composition and performance of Polymer Fuel Cells and to reduce the production cost of membrane electrode assemblies (MEAs), different MEAs using different catalyst powders, carbon supported and unsupported catalysts with different proton conducting electrolyte powder (Nafion) content were produced by using a dry powder spraying technique developed at German Aerospace Research Center (DLR, Deutsches Zentrum fuer Luft- und Raumfahrt). The electrochemical characterization was performed by recording current–voltage curves and electrochemical impedance spectra (EIS) in the galvanostatic mode of operation at 500 mA cm −2 . The evaluation of the measured impedance spectra with an adequate equivalent circuit shows that the cathode of the fuel cell is very sensitive to the electrode composition whereas the contribution of the anode is very small and invariant to the electrode composition. Furthermore, it could be shown for the first time using electrolyte powder in the electrodes that the charge transfer of the cathode decreasing monotonically with increasing electrolyte content in the cathode. These findings suggest that with increasing electrolyte content in the electrodes, in particular in the cathode, the utilization degree of the catalyst increasing linearly with increasing electrolyte content in the electrode.

This paper deals with a two-dimensional model of a preferential oxidation (PROX) reactor to be used in a beta 5 kWe hydrogen generator, named HYGen II, to integrate with polymer electrolyte fuel cells (PEFCs) for residential applications. The reactor geometrical configuration developed is a single-stage multi-tube configuration, in which a cocurrent air flow in the interspace is aimed at improving heat transfer and consequently controlling the temperature of the reactor. The aim of the model is to investigate the process performance of the reactor in order to enhance optimization and control of the PROX unit. The model concerns chemical kinetics and heat and mass transfer phenomena in the reactor. The model plays a key role in overcoming the issues of system design, by evaluating the temperature and the gas concentration profiles in the reactor. The CO removal from simulated reformate was examined with varying inlet temperature. Simulation results showed the strong dependence of the overall performance upon the reactor geometrical configuration.

Stainless steels are one of the most promising materials as bipolar plates for polymer electrolyte membrane fuel cells(PEFCs). In use of stainless steel bipolar plates, however, corrosion and corrosion induced degradation of cell performance are anticipated. In the present study, corrosion behavior of SUS 304 and 310S stainless steels was investigated through polarization tests in the simulated PEFC envtronment(0.05M Na2SO4(pH2.3)+2ppmF solution at 353K), contact resistance measurement between steels and carbon diffusion layer and cell operation.XPS analysis was also carried out to compare the steel surfaces after polarization measurements and cell operation. The results indicated that passive current density for SUS 3lOS stainless steel in the simulated PEFC environments was lower than that for SUS 304 stainless steel, as expected from higher Cr content. Longer polarization of these steels decreased the passive current density but increased contact resistance due to thickening of the passive film.The cell voltage drops after 3.6 x lO^6 s operation were 14 mV for graphite, 22 mV for SUS 310S and 46 mV for SUS 304 steel. Apparent corrosion was recognaized for SUS 304 stainless steel served for cathode.

This paper explores the behaviour of a dynamically operated fuel cell system regarding to an automotive application, examining the air supply and their interaction with the fuel cell stacks. The dynamic limits of stack operation are also discussed. Finally, the paper provides a description of the test facility used in these investigations. The research of dynamically operated fuel cell stacks shows that in order to achieve high energy efficiency, a power-dependent modulation of the pressure and flow rate of the air supply is necessary. A test facility designed for energy management and power train research (up to 42 kW) was used for the experiment. A number of 11.5 kW fuel cell stacks was examined experimentally with respect to performance in interaction with the air supply in stationary and dynamic operation. The stacks were tested individually and in parallel. All of them were operated “dead-end” on the hydrogen side. Experimental results varying the parameters and load curves applied to the air supply system are given in the paper. The results show different dynamic behaviours between the stacks and a substantial difference in efficiency and dynamic response of the fuel cell system operated with different strategies. The results of different operating strategies for fuel cell systems, with respect to the interaction between the fuel cell stack and the air supply and in their dependency on air mass flow and pressure level are presented. The examinations were done with the test facility using real current demand profile of the experimental car HyLite ® from zero to full load and the New European Drive Cycle (NEDC).

To date, the available equipment for characterising the microstructure of membrane electrode assembly (MEA) is still not well developed. For example, applying the normal scanning electron microscope (SEM) only provides information on the dry structure of MEAs. This paper presents a microstructure analysis method of MEAs in proton exchange membrane fuel cells (PEMFC). The microstructure analysis in this paper utilises the environmental scanning electron microscope (ESEM), which shows its advantage on the sample microstructure analysis in wet mode. When water is present, the characteristics of the MEA, especially the hydrophobic and/or hydrophilic properties, are distinguishable on the ESEM images. With proper temperature and pressure control, the water distribution within both the membrane and the catalyst layer can be viewed by ESEM. Based on ESEM measurement and mercury porosity measurement, the distributions of hydrophobic and hydrophilic pores in MEA have been analyzed. By means of ESEM and energy dispersive X-ray (EDX), a degraded MEA is characterized. The microstructure change of the degraded MEA has been discussed. The results provide helpful information for the understanding of MEAs in PEMFC.

The functional group p -benzensulfonic acid ( pb -SO 3 H) was chemically attached to the surfaces of two different carbon supports, XC72 and BP2000, to improve carbon support corrosion resistance. An accelerated durability test (ADT) utilizing a rotating disk electrode (RDE) system was used to study the corrosion of Pt catalysts using these two carbon supports, Pt/FXC72-SO 3 H and Pt/FBP2000-SO 3 H, under simulated fuel cell conditions. The results showed that the functional group pb -SO 3 H can effectively reduce the performance decay of these catalysts by enhancing the corrosion resistance of the carbon support and promoting the stability of the Pt nanoparticles. The ECASA and ORR current measurements of these catalysts indicate that the effects of the functional group ( pb -SO 3 H) on improving carbon corrosion resistance were more significant for the BP2000 than for the XC72. TME imaging revealed that the size of the Pt nanoparticles was significantly reduced and the particle distribution was improved in a polymer electrolyte fuel cell (PEFC).

The most common method used to characterise the electrochemical performance of fuel cells is the recording of current/voltage U(i) curves. Separation of electrochemical and ohmic contributions to the U(i) characteristics requires additional experimental techniques like electrochemical impedance spectroscopy (EIS). The application of EIS is an approach to determine parameters which have proved to be indispensable for the characterisation and development of all types of fuel cell electrodes and electrolyte electrode assemblies. In addition to EIS semi-empirical approaches based on simplified mathematical models can be used to fit experimental U(i) curves. By varying the operating conditions of the fuel cell and by the simulation of the measured EIS with an appropriate equivalent circuit, it is possible to split the cell impedance into electrode impedances and electrolyte resistance. Integration in the current density domain of the individual impedance elements enables the calculation of the individual overpotentials in the fuel cell (PEFC) and the assignment of voltage loss to the different processes. In case of using a three electrode cell configuration with a reference electrode, one can directly determine the corresponding overvoltage. For the evaluation of the measured impedance spectra the porous electrode model of Gohr [3] was used. This porous electrode model includes different impedance contributions like impedance of the interface porous layer/pore, interface porous layer/electrolyte, interface porous layer/bulk, impedance of the porous layer and impedance of the pores filled by electrolyte.