Talks

Hydrogen


The Orkney Islands of Scotland have been selected for the development of a new Europeanwide hydrogen project, named BIG HIT (Building Innovative Green Hydrogen systems in an Isolated Territory: a pilot for Europe).
Started in May 2016, it is a five-year demonstration project involving 12 participants based across six EU countries and coordinated by the Aragon Hydrogen Foundation (FHA).
Within BIG HIT, the otherwise curtailed energy generated from tidal and wind turbines (on average more than 30% of the annual renewable output in Orkney) is being used to produce ‘green’ hydrogen from electrolysis, which is then transported across the Orkney islands and used as fuel for transport, heat and power community end-uses.




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Carbon Dioxide as Hydrogen Vector



Prof. Dr. Gabor Laurenczy (EPFL, CH)

Hydrogen is considered as one of the most promising energy carriers in the future. It is a storable form of chemical energy that could complement intermittent renewable energy sources. One of the disadvantages of hydrogen gas arises from its low density; and low temperature or high-pressure hydrogen storage methods have weight, safety and cost issues. Chemical storage systems,1 based on liquids - in particular formic acid and alcohols, are highly attractive hydrogen carriers as they can use carbon dioxide as H2 vector, and could be used in stationary power supply units, in hydrogen filling stations and directly as transportation fuels.2

Formic acid - containing 4.4 weight % of H2, that is 53 g hydrogen per liter - is suitable for H2 storage.3 We have shown that in aqueous solutions it can be selectively decomposed into CO-free (CO < 10 ppm) carbon dioxide and H2; an industrial prototype has been built. The reaction4 takes place under mild experimental conditions and it is able to generate high pressure H2. In the other hand, the chemical transformation of carbon dioxide into useful products becomes increasingly important as carbon dioxide levels in the atmosphere continue to rise as a consequence of human activities. The direct hydrogenation of carbon dioxide into formic acid5 can take place using a homogeneous ruthenium catalyst, in aqueous solution and in dimethyl-sulphoxide, without any additives.

The hydrogenation of carbon dioxide to formic acid and the disproportionation of formic acid into methanol can be realized in a homogeneous catalytic reaction6 at ambient temperatures and in aqueous, acidic solution. The formic acid yield is maximized in water without additives, while acidification results in complete (98%) and selective (96%) formic acid disproportionation into methanol.7

References
1M. Grasemann and G. Laurenczy, Energy Environ. Sci., 2012, 5, 8171–8181.
2A. Dalebrook, W. Gan, M. Grasemann, S. Moret, G. Laurenczy, Chem. Comm., 2013, 49, 8735-8751.
3 a)Céline Fellay, Paul J. Dyson, Gábor Laurenczy, Angew. Chem. Int. Ed., 2008, 47, 3966-3968;
b)Patents WO2008047312 and WO2014134742A1
4A. Boddien, D. Mellmann, F. Gaertner, R. Jackstell, H. Junge, P. J. Dyson, G. Laurenczy, R. Ludwig, M. Beller, Science 2011, 333, 1733-1736.
5 a)S. Moret, P. J. Dyson, G. Laurenczy, Nature Comm., 2014, 5, 4017; DOI: 10.1038/ncomms5017;
b)Patent EP2767530A1
6 a)K. Sordakis, A. Tsurusaki, M. Iguchi, H. Kawanami, Y. Himeda, G. Laurenczy, Chem. Eur. J. 2016, 22, 15605-15608;
b)Patent WO2017093782A1
7K. Sordakis, C. Tang, L. K. Vogt, H. Junge, P. J. Dyson, M. Beller, G. Laurenczy, Chemical Reviews, 2018, 118, 372-433; DOI: 10.1021/acs.chemrev.7b00182

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HyForm-PEMFC 1 kW demonstrator unit Results and perspectives



Dr. Nordahl Autissier (GRT, CH)

Formic acid is the simpliest Liquid Organic Hydrogen Carrier (LOHC). Following extensive laboratory research on catalyst and reactor design1, we decided to demonstrate the integration in real world conditions, combining the formic acid reformer with a Fuel cell power generation unit. Within the project, we successfully integrated (thermally and electrically) a reactor within a 1 kW fuel cell system

Fuel cell waste heat and post-combustion heat has been used to maintain and control fuel processing temperature. We obtained a stable hydrogen production at part-load and full load. Between 40% and 45% efficiency obtained from 400 to 950W electrical output. This world first system demonstrate the potential of the technology for applications for different fuel cell technologies, PEM and SOFCs. Providing a liquid fuel, formic acid can be reformed with low temperature heat, allowing simple, lightweight and self-pressurizing hydrogen fuel supply. This latter property allows to design efficient high pressure hydrogen filling stations.
Formic acid can bring benefits to a new hydrogen economy, offering a good opportunity to store2 at the same time hydrogen and heat in a liquid phase.

References:
1I. Youranov and al. , ACS Sustainable Chem. Eng. 2018, 6, 5, 6635-6643 .
2K. Sordakis, A. Dalebrook, G. Laurenczy, ChemCatChem, 2015, 7, 2332 – 2339.


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Synthetic Fuels


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SCCER Joint Activity
White Paper Perspectives of Power-to-X Technology in Switzerland



Dr. Tom Kober (Paul Scherrer Institut, CH)

Achieving stringent long-term climate change mitigation goals requires provision of clean fuels to endusers while intensifying the use of low carbon emissions sources (i.e. renewable energy). The growing share of intermittent renewable energy, such as wind and solar energy technologies, impose challenges related to the temporal and spatial grid balancing:

- Temporal balancing arises due to the inevitable mismatch between renewable electricity production and demand as a consequence of day/night cycles, weather effects and seasonal differences.
- Spatial balancing is necessary resulting from a possible mismatch between locations of electricity production and consumption.

Energy conversion technologies with storage, such as Power-to-Product (P2X) technologies, represent potential solutions for this multi-dimensional balancing challenge and to enhance the energy system’s flexibility. The term P2X refers to energy conversion technologies that produce synthetic gases, fuels or energy feedstock products using an electro-chemical conversion process. There is a variety of energy outputs that can be produced in P2X technologies, with methane produced in Powerto- Gas (PTG) systems being one of the most prominently discussed options. As such, P2X technology not only offers a possible flexibility solution for the electricity system, they can also connect the electricity sector with other sectors of the economy in a new way (e.g. the transport sector and industry). With the aim to derive a technical, economic and environmental assessment of Power-to-X technology with its systemic interdependencies, this research work specifically investigates the gas market, the mobility sector and the electricity market including the corresponding regulatory and innovation policy aspects. From the analysis we derive essential factors that can contribute to the successful implementation of this technology and to arrive at profitable business cases, as well as key energy market segments for P2X technology.

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The SCCER Joint Activity (JA) Coherent Energy Demonstrator Assessment (CEDA) consists of experts from Swiss Universities including a representative from HEPP. The main task of CEDA is to develop a new methodology to describe an energy demonstrator with technical parameters. The findings from all energy demonstrators of the involved partners including HEPP are used to develop this methodology. In the project end there is the chance to have consistent and comparable statements about all Swiss energy demonstrators to create credibility and trust in the technologies.


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Design Principles of Bipolar Electrochemical Co-Electrolysis Cells
for Efficient Reduction of Carbon Dioxide from Gas Phase at Low Temperature



Dr. Alexandra Pătru (Paul Scherrer Institut, CH)

The electrochemical reduction of carbon dioxide is a very attractive proposition for minimizing the level of atmospheric CO2, for reutilizing CO2 emissions from fossil fuel sources, and for storing energy when it is coupled to a renewable energy source such as wind or solar PV. In this process, carbon dioxide is converted to fuels or chemical feedstock, which, depending on the process efficiency, could be generated at a competitive price when compared with chemicals that are conventionally derived from petroleum1. Technically, CO2 reduction can be carried out in an electrochemical co-electrolyser device where two processes are coupled: CO2 reduction at the cathode side and water oxidation at the anode side. For this purpose, not only cathode catalyst materials with favorable electrokinetics towards CO2 reduction are necessary, but also highly rational device engineering, taking into account the constraints of unwanted side reactions, is required in order to achieve high performance in CO2 coelectrolysis.

Cell designs for the electrochemical reduction of CO2 from gas phase at low temperature were developed and investigated, and the critical elements for an efficient process were identified. Various types of polymeric membrane and ionomers were used to build membrane electrode assembly (MEA) adapted for CO2 reduction in gas phase: protonic and anion exchange membrane, bipolar membrane and a modified bipolar like membrane configuration. Configurations using anion exchange ionomer in the cathodic catalytic layer in contact with an anion exchange membrane allow for a great enhancement of the cathode reaction selectivity towards CO. However, a severe problem was identified when co-electrolysis is performed using only an anion exchange membrane: this type of membrane acts as a CO2 “pump” meaning that for each molecule of CO2 reduced at the cathode, one or two CO2 molecules are produced at the anode by oxidation of the carbonate/bicarbonate anion transported in the membrane. A bipolar membrane system was shown to soften this problem, but only a newly developed cell design was able to fully prevent the parasitic CO2 pumping. This new cell configuration made use of a standard Nafion® cation exchange membrane in combination with a modified cathode catalyst layer containing an additional thin film of alkaline ionomer coated on the cathode catalyst layer in order to prevent direct contact between the cathode catalyst and the acidic cation exchange membrane2. Using this cell configuration, the faradaic efficiency of an alkaline environment towards CO2 reduction is maintained, the parasitic CO2 pumping to the anode side is completely suppressed, and the overall cell voltage efficiency is highly improved due to the low ohmic resistance of the acidic membrane, i.e. at -100 mA/cm2, 2.8 V are needed in a full co-electrolyser system using the new developed cell design compared with 3.9 V when a commercial bipolar membrane is used.

References:
1 Durst, J.; Rudnev A.; Dutta, A.; Fu, Y.; Herranz, J.; Kaliginedi, V.; Kuzume, A.; Permyakova, A.A.; Paratcha, Y.; Broekmann, P.; Schmidt, T.J. Chim Int J Chem 2015;69:769–76.
2Pătru, A.; Binninger, T.; Pribyl, B.; Schmidt, T.J. Co-electrolysis cell design for efficient CO2

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Batteries


Lithium-ion batteries enabled the success of portable electronics and find increasingly application in electric vehicles and in centralized and decentralized stationary storage for the temporal and spatial balancing of energy supply and demand. Worldwide efforts to scale production volumes for lithium-ion batteries have led to a significant cost reduction over recent years, but also result in increasing challenges in the supply of raw materials, in particular cobalt, which is already classified as critical by the European commission.1
Within SCCER HaE, we are investigating cathode materials for next-generation lithium-ion batteries. Our research focuses on nickel-rich layered oxides with reduced cobalt content. Increasing the nickel content in layered oxides offers significantly improved lithium storage capacity, but at the price of reduced cycling stability. Employing sacrificial electrolyte additives, we were able to demonstrate a NMC811/graphite full cell with a capacity retention of >90% after 200 cycles.2

To improve operational safety and reduced cell production costs, we are also developing concepts to replace the liquid electrolytes based on highly-flammable organic solvents in lithium- and sodium-ion batteries by non-flammable aqueous electrolytes. The major disadvantage of water as electrolyte solvent is its intrinsically narrow electrochemical stability window (thermodynamically only 1.23 V) limiting maximum cell voltage and consequently the batteries energy density. We recently discovered an aqueous sodium-ion electrolyte system with a much wider electrochemical stability window of 2.6 V 3 enabling us to demonstrate a NaTi2(PO4)3/Na3(VOPO4)2F full cell with 85% capacity retention after 500 cycles.4
We are also developing solid-state electrolytes for all-solid-state batteries based on closoborate salts. We were able to stabilize a highly ionically conducting phase at room temperature using anion mixing reaching ionic conductivities on the order of 1 mS/cm at room temperature.5 This achievement further enabled us to assemble an all-solid-state battery with a sodium metal anode and a NaCrO2 cathode delivering a capacity retention of 85% after 250 cycles bringing this class of materials to a technology readiness level comparable to other current all-solid-state battery concepts.6
We are also investigating ionic transport in Na-β’’-Al2O3 ceramics, an archetypical ion conductor, commercially employed as solid-state electrolytes in high-temperature sodium-nickel-chloride and sodium-sulfur batteries, but also promising for applications in future all-solid-state batteries. Although already discovered in the 1960s, Na-β’’-alumina ceramics are challenging to prepare with the desired composition, phase content, and microstructure. These parameters have a direct impact on the ion conductivity, which varies by a factor of 100 at a given temperature when comparing different studies. We developed a comprehensive model identifying the dominant factors governing ion transport in these materials.7

References:
1 http://ec.europa.eu/growth/sectors/raw-materials/specific-interest/critical.
2 Vidal Laveda J., Low J. E., Stilp E., Dilger S., Battaglia C., submitted.
3 Duchêne L., Kühnel R.-S., Rentsch D., Remhof A., Hagemann H., Battaglia C., Chem. Comm., 2017, 53, 4195.
4 Duchêne L., Kühnel R.-S., Stilp E., Cuervo Reyes E., Remhof A., Hagemann H., Battaglia C., Energy Environ. Science, 2017, 10, 2609.
5 Kühnel R.-S., Reber D., Battaglia C., ACS Energy Lett., 2017, 2, 2017.
6 Reber D., Kühnel R.-S., Battaglia C., submitted.
7 Bay M.-C. Heinz M. V. F., Figi R., Schreiner C., Basso D., Zanon N. Vogt U. F., Battaglia C., submitted.


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Heat


Thermal energy storage and the components therefore are essential in a large field of applications. In residential building applications – for example – their size i.e. volume and the efficiency is a cost driver. In solar thermal energy use the storage units are important components, because they bridge the time between diurnal conversion and demand. In case of a sensible (water) heat storage, the stratification within the tank is of key importance for the efficiency of the system. Existing recommendations for the design of storage tanks which have a good temperature stratification are generalized to any storage size. The feed flow deflection relation is identified as a relevant variable. If this deflection relation is less than 0.12 for horizontal inlet into the tank and less than 0.5 for inlet via an upward or downward elbow pipe pointing towards the top or bottom of the tank, the unintended deflection of the entering fluid stream into local vertical flows is low and an existing storage stratification is effectively maintained1.

To increase storage density and therefore reduce storage volume an ice storage allows the storing of solar heat in a compact volume for the later use as source for a heat pump that provides heat for a building – or as a sink in a cooling system. As an example a novel ice storage with 2m3 water volume is described which contains heat exchanger plates for extracting the latent heat. A numerical model for the heat exchanger plates that was implemented into the Polysun system simulation software will be presented. The model allows the numerical simulation of an ice storages according a field installation with heat exchanger plates. The field installation will be used for the validation of the system template. The core elements of the developed model are the heat transfer values (𝑈𝑈𝐴𝐴𝑖𝑖) between the brine inside the heat exchangers plates and the water inside the storage2. The UA-values limit the maximum power that can be extracted from or injected to the storage (ice or fluid) and thus, have a large influence on the simulation results. Sensible heating, sensible cooling as well as icing are treated individually as they all inflict different physical dynamics in the fluid on small scales that effect the overall heat (power and energy) balance. In all states, the UAvalues are derived from general heat transfer correlations. In the model all UA-values represent the values associated to one control volume (1 knot), while the heat exchanger has a fixed number of control volumes 12 - of 12 knots - and the water volume is modelled as 1 knot. As a further step in decreasing thermal energy storage volume an absorption desorption seasonal thermal energy storage system – a thermo-chemical storage could be applied. Such a closed sorption heat storage based on water vapour absorption in aqueous slat solutions theoretically achieves a significantly higher volumetric energy density compared to conventional hot water or ice storage systems. To this purpose, the development of an absorber-desorber unit - a prototype designed for a power output of 10 kW – is presented. In this work, the influence of two main parameters on the exchanged power is evidenced. Furthermore, a comparison with the results of the initial numerical model used to design the heat and mass exchanger is carried out. Physical explanations of the diverging results encountered during the absorption process as well as an improved heat transfer coefficient model for the desorption process are proposed3.

References:
1Battaglia, M.; Haller, M. Y. Stratification in large thermal storage tanks. Eurosun 2018, September 10 – 13, Rapperswil, Switzerland.
2Philippen, D.; Battaglia M.; CarbonellD.; Thissen B.; Kunath L. Validation of an ice storage model and its integration into a solar-ice system. Eurosun 2018, September 10 – 13, Rapperswil, Switzerland.
3Daguenet-Frick, X.; Gantenbein, P.; Müller, J.; Fumey B.; Werber, R. Seasonal thermochemical energy storage: comparison of the experimental results with the modelling of the falling film tube bundle heat and mass exchanger unit. Renewable Energy 110 (2017) 162-173.


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