A switchable pH-differential unitized regenerative fuel cell with high performance

Regenerative fuel cells are a potential candidate for future energy storage, but their applications are limited by the high cost and poor round-trip efficiency. Here we present a switchable pH-differential unitized regenerative fuel cell capable of addressing both the obstacles. Relying on a membraneless laminar flow-based design, pH environments in the cell are optimized independently for different electrode reactions and are switchable together with the cell process to ensure always favorable thermodynamics for each electrode reaction. Benefiting from the thermodynamic advantages of the switchable pH-differential arrangement, the cell allows water electrolysis at a voltage of 0.57 V, and a fuel cell open circuit voltage of 1.89 V, rendering round-trip efficiencies up to 74%. Under room conditions, operating the cell in fuel cell mode yields a power density of 1.3 W cm¯², which is the highest performance to date for laminar flow-based cells and is comparable to state-of-the-art polymer electrolyte membrane fuel cells

Effect of catalyst layer defects on local membrane degradation in polymer electrolyte fuel cells

© 2016 Elsevier B.V. All rights reserved. Aiming at durability issues of fuel cells, this research is dedicated to a novel experimental approach in the analysis of local membrane degradation phenomena in polymer electrolyte fuel cells, shedding light on the potential effects of manufacturing imperfections on this process. With a comprehensive review on historical failure analysis data from field operated fuel cells, local sources of iron oxide contaminants, catalyst layer cracks, and catalyst layer delamination are considered as potential candidates for initiating or accelerating the local membrane degradation phenomena. Customized membrane electrode assemblies with artificial defects are designed, fabricated, and subjected to membrane accelerated stress tests followed by extensive post-mortem analysis. The results reveal a significant accelerating effect of iron oxide contamination on the global chemical degradation of the membrane, but dismiss local traces of iron oxide as a potential stressor for local membrane degradation. Anode and cathode catalyst layer cracks are observed to have negligible impact on the membrane degradation phenomena. Notably however, distinct evidence is found that anode catalyst layer delamination can accelerate local membrane thinning, while cathode delamination has no apparent effect. Moreover, a substantial mitigating effect for platinum residuals on the site of delamination is observed

Use of Grooved Microchannels to Improve the Performance of Membrane-Less Fuel Cells

In this work, the fluid dynamics within a membrane-less microchannel fuel cell is analyzed computationally. The membrane-less design is a result of the laminar nature of the fluid flow at small Reynolds numbers, restricting the fuel and oxidant to the vicinity of the corresponding electrodes, without the need of a proton exchange membrane (PEM). However, the performance of such cells is limited by the slow diffusive mass transport near the electrodes, with a large fraction of the reactants leaving the channel without coming in contact with the catalytic surfaces, and thus not being used. We mitigate this problem through the introduction of channel surface modification consisting of angled grooves designed to create convective flows that direct the reactants toward the active surfaces. The grooved structures are optimized for maximum fuel utilization. Operation of this type of cells at Péclet numbers close to 2,500 leads to a performance doubling compared with unmodified cells. Moreover, this increase in efficiency is accompanied by a more uniform distribution of the current across the electrodes, reducing the possibility of hot spots being developed

Progression in the Morphology of Fuel Cell Membranes upon Conjoint Chemical and Mechanical Degradation

Ionomer membranes used to separate the electrodes in polymer electrolyte fuel cells are known to degrade both chemically and mechanically during regular fuel cell operation and may ultimately result in lifetime-limiting failure. The objective of the present work is to understand the effects of combined chemical and mechanical stresses on the mesoscale morphology of the membrane and its role in the overall degradation process. The mesoscale effects of sulfonic acid group loss and fluoride release on the phase segregated morphology of the membrane are analyzed using contrast-enhanced transmission electron microscopy and energy dispersive X-ray spectroscopy. The end-of-life ionic domain size of the ionomer is shown to be substantially enlarged compared to the pristine membrane state. Elemental mapping overlayed with the binary ionic and non-ionic morphology reveals mesoscopic void regions in the degraded material that are depleted of ionomer fluorine and carbon and considered susceptible to micro-crack initiation. A larger, severely degraded void region is also identified which contains evidence of hygrothermal stress induced localized ionomer crazing as a potential nucleation site for macroscopic fracture development. The synergetic effects of chemical and mechanical degradation on the progressive changes in the observed mesoscale morphology are discussed

New type of microengine using internal combustion of hydrogen and oxygen

Microsystems become part of everyday life but their application is restricted by lack of strong and fast motors (actuators) converting energy into motion. For example, widespread internal combustion engines cannot be scaled down because combustion reactions are quenched in a small space. Here we present an actuator with the dimensions 100x100x5 um^3 that is using internal combustion of hydrogen and oxygen as part of its working cycle. Water electrolysis driven by short voltage pulses creates an extra pressure of 0.5-4 bar for a time of 100-400 us in a chamber closed by a flexible membrane. When the pulses are switched off this pressure is released even faster allowing production of mechanical work in short cycles. We provide arguments that this unexpectedly fast pressure decrease is due to spontaneous combustion of the gases in the chamber. This actuator is the first step to truly microscopic combustion engines.Comment: Paper and Supplementary Information (to appear in Scientific Reports

The effects of electrode and catalyst selection on microfluidic fuel cell performance

A fuel cell can be best defined as an electrochemical converter of fuel and oxidant of chemical energy to electrical energy. The important components of micro fuel cells are the electrodes and catalysts because the kinetics and rates of the electrochemical reactions depend on their materials. All fuel cells consist of two electrodes: the anode, where fuel oxidation takes place, and the cathode, which is used to reduce the oxidants. The present review article highlights the use of a range of electrodes made up of different materials, a variety of catalysts that have been used in previous studies, and their fabrication materials and approaches. In this article, electrodes and catalysts are classified into two types based on the design approach applied to produce the micro fuel cell: micro fuel cell design and conventional assembly design. Most previous studies on fuel cells have demonstrated that the construction and position of the electrodes play crucial roles in improving the performance of micro fuel cells

Paper-based enzymatic microfluidic fuel cell: From a two-stream flow device to a single-stream lateral flow strip

This work presents a first approach towards the development of a cost-effective enzymatic paper-based glucose/O2 microfluidic fuel cell in which fluid transport is based on capillary action. A first fuel cell configuration consists of a Y-shaped paper device with the fuel and the oxidant flowing in parallel over carbon paper electrodes modified with bioelectrocatalytic enzymes. The anode consists of a ferrocenium-based polyethyleneimine polymer linked to glucose oxidase (GOx/Fc-C6-LPEI), while the cathode contains a mixture of laccase, anthracene-modified multiwall carbon nanotubes, and tetrabutylammonium bromide-modified Nafion (MWCNTs/laccase/TBAB-Nafion). Subsequently, the Y-shaped configuration is improved to use a single solution containing both, the anolyte and the catholyte. Thus, the electrolytes pHs of the fuel and the oxidant solutions are adapted to an intermediate pH of 5.5. Finally, the fuel cell is run with this single solution obtaining a maximum open circuit of 0.55 ± 0.04 V and a maximum current and power density of 225 ± 17 μA cm−2 and 24 ± 5 μW cm−2, respectively. Hence, a power source closer to a commercial application (similar to conventional lateral flow test strips) is developed and successfully operated. This system can be used to supply the energy required to power microelectronics demanding low power consumption.F. Javier del Campo acknowledges funding from the Spanish Ministry of Economy through the DADDi2 project (TEC2013-48506-C3). Juan Pablo Esquivel would like to thank the support from Marie Curie International Outgoing Fellowship (APPOCS-328144) within the 7th European Community Framework Programme. Shelley D. Minteer and Fabien Giroud would like to thank the National Science Foundation (CHE-1057597) for funding. Neus Sabaté acknowledges funding from the European H2020 Framework Programme (Grant Agreement 648518 - SUPERCELL - ERC 2014 CoG).Peer reviewe

Modelling of redox flow battery electrode processes at a range of length scales : a review

In this article, the different approaches reported in the literature for modelling electrode processes in redox flow batteries (RFBs) are reviewed. RFB models vary widely in terms of computational complexity, research scalability and accuracy of predictions. Development of RFB models have been quite slow in the past, but in recent years researchers have reported on a range of modelling approaches for RFB system optimisation. Flow and transport processes, and their influence on electron transfer kinetics, play an important role in the performance of RFBs. Macro-scale modelling, typically based on a continuum approach for porous electrode modelling, have been used to investigate current distribution, to optimise cell design and to support techno-economic analyses. Microscale models have also been developed to investigate the transport properties within porous electrode materials. These microscale models exploit experimental tomographic techniques to characterise three-dimensional structures of different electrode materials. New insights into the effect of the electrode structure on transport processes are being provided from these new approaches. Modelling flow, transport, electrical and electrochemical processes within the electrode structure is a developing area of research, and there are significant variations in the model requirements for different redox systems, in particular for multiphase chemistries (gas–liquid, solid–liquid, etc.) and for aqueous and non-aqueous solvents. Further development is essential to better understand the kinetic and mass transport phenomena in the porous electrodes, and multiscale approaches are also needed to enable optimisation across the relevent length scales

Good advice need not be expensive! : About personalised energy advising in an increasingly digitised society

”Nu är goda råd dyra”, heter det sedan gammalt i en svensk krissituation. I denna licentiatavhandling, vars rubrik kopplar till talesättet, behandlas svensk energirådgivnings utveckling och framtid. Forskning visar att i ett alltmer digitaliserat samhälle behöver energirådgivningen utvecklas för att bättre nå målgrupperna - hushåll, småföretag och organisationer. Digitala tjänster ger många möjligheter, men den viktiga personliga kontakten med energirådgivaren går inte att ersätta fullt ut. Med hjälp av fokusgrupper, intervjuer och samtal med energirådgivare, villaägare och enskilda experter har kunnat konstateras att den personligt genomförda rådgivningstjänsten är efterfrågad, angelägen och framgångsrik när byte av värmesystem, större ombyggnationer eller nybyggnationer är aktuellt. Att pröva idéer och lösningar, helst i hemmamiljön inför en ombyggnad, är uppskattad rådgivning. I samtalet, där inte enbart tekniska detaljer och lönsamhet diskuteras, kan alla i hushållet engageras. Energirådgivningen kan bli mer framgångsrik, men då krävs ett större kommunalt engagemang och en tydligare samverkan med andra statliga styrmedel. Hållbara råd kan alla få i Sverige idag och de goda råden är gratis! Med hjälp av dessa kan kanske kriser undvikas…Att använda energin effektivare än vad som görs idag inom både industri, transporter och byggnader är en väg till ett mer hållbart samhälle. Den rika delen av världen har här ett speciellt ansvar. I Sverige har den kommunala energirådgivningen under närmare fyrtio år varit ett av statens styrmedel för att på olika sätt bistå lokala beslutsfattare att effektivisera energianvändningen, men också öka andelen förnybar energi i systemet. Denna licentiatavhandling har studerat energirådgivningen under tidsperioden, men också dokumenterat och analyserat rådgivningen ur ett samhällsperspektiv. Forskning visar att i ett alltmer digitaliserat samhälle behöver energirådgivningen utvecklas för att bättre nå målgrupperna - hushåll, småföretag och organisationer. Internet är idag den vanligaste sökvägen för de som önskar information kring energirelaterade frågor. Digitala tjänster ger många möjligheter, men den viktiga personliga kontakten med energirådgivare går inte att ersätta fullt ut. I studien har fokusgrupper, intervjuer och samtal med energirådgivare, villaägare och enskilda experter genomförts och analyserats. Resultat visar att den personligt genomförda rådgivningstjänsten är efterfrågad, angelägen och framgångsrik när byte av värmesystem, större ombyggnationer eller nybyggnationer är aktuellt. Studien visar också att personliga samtal med energirådgivare är värdefullt för att pröva idéer och lösningar som är hämtade från internet samt att hemmet är den lämpligaste platsen för framgångsrik rådgivning. I denna situation är rådgivarens sociala kompetens central. Kvinnors synpunkter och erfarenheter har ofta gått förlorade. Vidare har ett för stort fokus lagts på tekniska detaljer och lönsamhet, medan många beslut tas av miljöskäl eller sociala orsaker som upplevd ökad komfort. Energirådgivningen kan bli mer framgångsrik, men då krävs ett större kommunalt engagemang och en tydligare samverkan med andra statliga styrmedel.Improving the efficiency of energy use across all the sectors – industrial, transport and households – is one of the many necessary approaches to be adopted to ensure sustainable development. The countries of the developing world have to play a key role in such a transition. In Sweden, for close to half a century now, the municipal energy-advising function has been a governmental instrument to support decision-makers in bringing about systemic changes to improve energy efficiency on the one hand and the share of renewable energy in the mix, on the other.  This licentiate thesis has its focus on this function over the said time-period. It has also documented and analysed the energy-advising function from a social perspective. The research shows that in an increasingly-digitalised society, energy-advising must be developed further to be able to reach and impact different categories of energy users – households, small and medium scale enterprises and organisations – more effectively. The Internet happens to be the first resort of most people seeking information on energy-related issues, these days. Digital services do offer a range of possibilities but cannot substitute for the much-needed personal contact, which is provided by the energy-advising function. In this thesis, focus groups, interviews and conversations with energy advisers, homeowners and experts have been availed of, and subsequently analysed. The results also show that personal energy advice is actually popular, indispensable and effective, where replacement of interior heating systems, refurbishment or new building constructions are concerned. This research also shows that interactions with energy advisers are useful to test and verify the suitability of ideas and solutions obtained from the Internet. Besides, the home in which these solutions may eventually be tried out, is the perfect place for having such conversations. In this context, the social skills of the energy adviser assume paramount importance. It has been noticed that the viewpoints and experiences of women in households have often been ignored.  Further, the focus on finding solutions has sometimes been narrowed down to the technical and economic aspects, while at other times, decisions have been based on environmental or social factors like maintenance of comfort levels. In order to make the energy advising function more effective and avail of what it has to offer for the journey towards greater sustainability, it needs to be given the importance it deserves by the municipalities and there is also a need of stronger interplay among the other governmental instruments.Bo och leva energieffektivt. Kommunal energirådgivning som medspelare i människors varda