An open-source zero-gradient cell hardware to improve and accelerate durability testing of PEM fuel cells

The design of an open zero-gradient hardware is proposed in this work. The hardware is thought for characterizing single Polymer Electrolyte Membrane Fuel Cells (PEMFCs), specifically Membrane Electrode Assemblies (MEAs), with a focus on transport application. The objective of the proposed design is to minimize both operation and degradation heterogeneities over the cell active area in order to evaluate material properties only. It is indeed specifically intended to quantify the PEMFC materials performance without accounting for any interdependency between the layers of the MEA and the cell hardware design (e.g. heating/cooling system and flow field features). This is granted by combining high stoichiometry ratios of the gas reactants and limited pressure drops: they indeed keep uniform operating conditions (concentration in the gas phase, relative humidity, pressure and temperature), as verified by the electrochemical and operational characterization. With such characteristics, accurate information about both the performance and the degradation of the MEA materials can be provided. This tool is powerful for assessing the ranking in terms of performance and durability of different PEMFCs, as well as for application in the field of the materials local diagnostics

Revealing the critical role of low voltage excursions in enhancing PEM fuel cell catalyst degradation by automotive hydrogen/air potential cycling experiments

The durability of Polymer Electrolyte Membrane Fuel Cells under dynamic operation still needs to be improved. To understand the automotive voltage cycling-induced catalyst degradation, the loss of the electrochemically active surface area (ECSA) is investigated through an experimental campaign on Membrane Electrode Assemblies. Ad-hoc hydrogen/air accelerated protocols were designed to evaluate the voltage profile impact in a range relevant for both automotive and heavy duty transport application (<0.90 V). Besides the well-known aging dependence on the upper potential limit, this work evidences the critical role of the short-stops, characterized by low voltage transients. Effort was spent in studying this procedure parameters (voltage level, duration, scan rate, humidification). The accelerated ECSA loss is due to Pt nanoparticles coarsening as proved by transmission electron microscopy and is suspected dominated by Pt cathodic dissolution, incentivized during excursions towards very low potentials (<0.4 V). These findings help the development of system mitigation strategies

Dynamic modeling of polymer electrolyte membrane fuel cells under real-world automotive driving cycle with experimental validation on segmented single cell

A 1+1D transient non-isothermal and multiphase polymer electrolyte membrane fuel cell model is developed. The model is validated on experimental data gathered on a segmented single cell and representative of a real-world automotive driving cycle, derived from the stack protocol defined in the ID-FAST H2020 project. During Low-Power operation, cell voltage response is mainly controlled by platinum oxide and water dynamics: the low hydration significantly affects cathode inlet performance. Throughout High-Power operation, instead, voltage transients are ascribable to local mass-transport related phenomena: in particular, liquid water accumulation along the channel strongly decreases the efficiency of cathode outlet region. Finally, the effect of relative humidity at cathode channel inlet is investigated: an increase in the humidification of the air inlet stream from 30% to 50% leads to a better proton conductivity and, therefore, to a significant enhancement of the performance of cathode inlet regions, which also means a slight improvement in the average stack efficiency from 62.2% to 62.8%. Lowering RH of the air-inlet stream from 30% to 15%, a worsening of proton conductivity is observed, which exacerbates performance heterogeneities and leads to a reduction of the average stack efficiency from 62.2% to 61.5%, consistently with experimental results

Transformative social innovation in developing and emerging ecosystems: a configurational examination

Despite the literature on social innovation (SI) in ecosystems growing considerably in recent years, what makes an ecosystem a facilitator for transformative SI remains unexamined, particularly indeveloping and emerging countries. Our research aims to fill this literature gap by determining which combination of characteristics-stemming from stakeholder theory and knowledge management-turns local smallholder coffee farmers in developing and emerging producing countries into autonomous and empowered partners and catalysts for spreading SI initiatives locally. We adopt a configurational approach using fuzzy-set qualitative comparative analysis of 18 SI projects that coffee MNEs, nongovernmental organizations, and institutions have undertaken to favor such an egalitarian value co-creation with local stakeholders. We demonstrate that stakeholder empowerment, cooperative strategic posturing, knowledge transfer, and local knowledge exchange are necessary conditions within the ecosystem to create local autonomy as an antecedent for transformative SI. The novelty in our approach lies in proposing a shift from a pure firm-centric perspective based on stakeholder dependence to a more participatory relational perspective that entails lower-power stakeholders' interdependence and collaboration for autonomous decision-making, thereby advancing fresh thinking on stakeholder and knowledge management applied to SI in developing and emerging contexts. We also propose practical suggestions to deal with stakeholder power's imbalances, which might limit the ecosystems' adaptation toward transformative SI

Degradation of lithium-ion batteries under automotive-like conditions: aging tests, capacity loss and q-OCP interpretation

Battery electric vehicles are spreading worldwide as a relevant solution for the decarbonization of the transportation sector, ensuring high volume and weight-based energy density, high efficiency and low cost. Nevertheless, batteries are known to age in a rather complex and conditions-dependent way. This work aims at investigating battery aging resulting from close-to-real world conditions, highlighting single stressors role. Hence, aiming at representativeness for automotive application, an extensive literature review is performed, identifying a wide set of representative conditions together with their specific variations to be investigated. Realistic driving schedules like WLTP is identified and continuously applied in cycling on commercial samples, investigating the capacity loss from a q-OCP perspective with an equilibrium model. In general, loss of lithium inventory is detected as the main degradation parameter, likely related to SEI growth. Recharge C-rate and load profile appear as poorly-affecting degradation, while a dominant role is associated with operating temperature. Interestingly, temperature and cycling-related degradation appears to be independent and their effects can be effectively superimposed. Loss of active positive electrode material seems particularly affected by cycling depth of discharge, likely having mechanical origin as particle cracking

New Insights on the Photochromism of 2-(2‘,4‘-Dinitrobenzyl)pyridine

The photochromic behavior of 2-(2‘,4‘-dinitrobenzyl)pyridine (α-DNBP) has been followed in poly(methyl methacrylate) (PMMA) films and benzene solutions to clarify the behavior of a precursor state, previously identified in studies on crystalline α-DNBP at low temperatures. In PMMA films, photolysis at temperatures ≤50 K led to the concurrent formation of a NH tautomer and a colorless intermediate, which was stable for several hours. On irradiation at low temperatures and warming the sample, the colorless intermediate was seen to react to produce the NH tautomer in a higher yield than that found in the direct photolysis. Further information on this intermediate has come from flash photolysis studies in benzene solution, in which a new transient absorption has been observed at 335 nm and assigned to this species. This decays within a few microseconds at room temperature to form an OH tautomer, which then interconverts to the NH tautomer. The precursor state is not quenched by oxygen or naphthalene. From consideration of the kinetic and spectral data, it is suggested that this new species corresponds to a nonrelaxed tautomeric form of the OH state of α-DNBP

Buckling of built-up columns of pultruded fiber-reinforced polymer C-sections

This paper presents the test results of an experimental investigation to evaluate the buckling behavior of built-up columns of pultruded profiles, subjected to axial compression. Specimens are assembled by using four (off the shelf) channel shaped profiles of E-glass fiber-reinforced polymer (FRP), having similar detailing to strut members in a large FRP structure that was executed in 2009 to start the restoration of the Santa Maria Paganica church in L’Aquila, Italy. This church had partially collapsed walls and no roof after the April 6, 2009, earthquake of 6.3 magnitude. A total of six columns are characterized with two different configurations for the bolted connections joining the channel sections into a built-up strut. Test results are discussed and a comparison is made with closed-form equation predictions for flexural buckling resistance, with buckling resistance values established from both eigenvalue and geometric nonlinear finite element analyses. Results show that there is a significant role played by the end loading condition, the composite action, and imperfections. Simple closed-form equations overestimate the flexural buckling strength, whereas the resistance provided by the nonlinear analysis provides a reasonably reliable numerical approach to establishing the actual buckling behavior

Dramatic mitigation of capacity decay and volume variation in vanadium redox flow batteries through modified preparation of electrolytes

Electrolyte imbalance caused by the undesired vanadium-ions cross-over and water transport through the membrane is one of the main critical issues of vanadium redox flow batteries, leading to battery capacity loss and electrolytes volume variation. In this work, the evolution of discharged capacity and electrolyte volume variation were firstly investigated adopting commercial electrolyte for hundreds of charge-discharge cycles in vanadium redox flow batteries employing different membranes, varying thickness and equivalent weight. Subsequently, with the support of a 1D physics-based model, the origin of the main phenomena regulating capacity decay and volume variation has been identified and different modifications in the preparation of electrolytes have been proposed. Electrolytes characterized by an equal proton concentration between the two tanks at the beginning of cycling operation turned out to limit capacity decay, while increasing electrolyte proton concentration was effective also in the mitigation of volume variation. The most promising electrolyte preparation combined the effect of high proton concentration and null osmotic pressure gradient between the two tanks: compared to commercial electrolyte this preparation reduced the capacity decay from 47.7% to 20.9%, increased the coulombic efficiency from 96.2% to 98.9% and the energy one from 79.9% to 83.4%, and also implied a negligible volume variation during cycles. The effectiveness of this electrolyte preparation has been verified with different membranes, increasing the range of validity of the results, that could be thus applied in a real system regardless of the adopted membrane