Increase In Operating Temperature Research Articles

Permanent magnets with embedded phase changing material for electric motor thermal management

The magnetic performance of NdFeB permanent magnets rapidly decreases as their operation temperature increases. This limits the power output of electric motors as their internal temperature quickly increases with the power demand. This is particularly problematic for applications where high peak power is required for a short period of time, for example during automobile highway acceleration or during an airplane lift-off. With the advances in additive manufacturing, one can envision to fabricate more complex motor geometries and magnetic structures, without additional costs, allowing for enhanced functionalities such as better thermal management. In this context, this paper investigates the feasibility of using phase changing materials (PCMs) to mitigate the temperature rise in permanent magnets (PMs) fabricated by additive manufacturing. The potential of PCM and its relevance was validated by modeling the thermal response of an electric motor during a representative electric vehicle driving scenario. It was found that segmented magnets with embedded phase changing materials would allow to efficiently control temperature rise. To validate the simulation results, PM test pieces with and without embedded PCMs were fabricated using cold spray additive manufacturing and tested using a custom laser thermal cycling setup.

Corrosion resistance of multicomponent disilicate (Ho0.2Er0.2Tm0.2Yb0.2Lu0.2)2Si2O7 against CMAS and volcanic ash

With the increasing operating temperature of gas turbine engines, calcium-magnesium-aluminosilicate (CMAS) poses a serious threat on environmental barrier coatings (EBCs) applied on hot-sections of aero-engines. Here, we have synthesized a novel multicomponent disilicate—(Ho0.2Er0.2Tm0.2Yb0.2Lu0.2)2Si2O7 (brief to (5RE0.2)2Si2O7), and comparatively studied its performance in the presence of synthesized CMAS and natural volcanic ash at 1400ºC. In comparison with Yb2Si2O7, (5RE0.2)2Si2O7 has a shorter Si-O bond length and a larger RE-O bond length because of the larger average RE3+ radius. After CMAS corrosion, some apatite grains precipitate at the CMAS/(5RE0.2)2Si2O7 interface to develop a loose reaction layer, exhibiting a higher corrosion resistance than Yb2Si2O7. Meanwhile, the consumption of CaO and release of SiO2 during the chemical reaction process increase the viscosity of CMAS to some extent and thus weaken its infiltration propensity. For the volcanic ash case, it directly infiltrates into the interior of (5RE0.2)2Si2O7 along grain boundaries without any reaction due to the relatively low CaO content, exhibiting a more serious attacking behavior. In addition, (5RE0.2)2Si2O7 effectively increases the contact angle of molten volcanic ash due to its lower surface energy. These finds here provide a better understanding for the design and application of next-generation EBC material.

Efficiency enhancement of photovoltaic-thermoelectric generator hybrid module by heat dissipating technique

Exploring substantial solar irradiation and recuperating excess heat generated during photovoltaic energy conversion is a critical issue. The efficiency of photovoltaic systems (PV) is significantly depend on the increased operating temperatures encountered by solar radiation. One conceivable option for improving the conversion of solar energy is to integrate a photovoltaic (PV) panel with a thermal-electric generator (TEG) material module to create a hybrid system. This study proposed a parallel PV-TEG hybrid module that effectively harvests the maximum solar energy spectrum while maximizing the use of heat generated by the thermoelectric material to improve the overall system efficiency. The proposed module consists of a photovoltaic unit, thermoelectric material module and passive cooling of fluid channels. The aim of this work was to develop a PV-TEG hybrid system and create an energy simulation model in a MATLAB environment to analyze the model's performance under various operational conditions by applying both theoretical and experimental approaches. Findings showed considerable concurrence. At 13:00, when the PV surface temperature was 54 °C, the PV efficiency reached to its lowest value of 12.0 %. Nevertheless, the highest TEG efficiency recorded was 4.7 % at 12:00 h. The efficiency of the TEG module was significantly affected by weather conditions, inlet cooling water temperature, and fluid flow rate in comparison to both the PV efficiency and the thermal efficiency.

Exploring the mechanism of infrared emissivity control in YSZ-based ceramics doped with Yb2O3

Due to its exceptional thermal stability and high conductivity, Yttrium stabilized zirconia (YSZ) has become an essential material in the field of infrared camouflage. Although YSZ exhibits relatively low emissivity within the 3–5 μm wavelength range, the increasing operating temperatures of aircraft necessitate further reduction in infrared emissivity within this specific band, in accordance with the Wien displacement law. This study focuses on the preparation of ceramic samples of YSZ doped with varying concentrations of Yb2O3 through a high-temperature solid-state reaction. It aims to investigate the influence of different doping concentrations on the microstructure, crystal structure, and infrared radiation characteristics of YSZ ceramic blocks. The experimental results demonstrated that the addition of Yb2O3 induces changes in the grain size and phase content of YSZ. Notably, as the amount of Yb2O3 doping increases, the infrared emissivity of YSZ samples in the 3–5 μm wavelength range exhibits a pattern of initial decrease followed by an increase. Remarkably, at a doping amount of 3 % mol, YSZ ceramics demonstrated the lowest emissivity, with the average emissivity of the 3–5 μm wavelength range decreasing from 0.41 to 0.38.

Hydrogen blending with natural gas for combustion efficiency improvement toward decarbonisation of power plants

Abstract The 12th Malaysia Plan highlighted Malaysia’s commitment to reduce Greenhouse Gas (GHG) emissions by 45% based on Gross Domestic Product (GDP) in 2030 and reach net zero by 2050. To achieve this target, Malaysia has to decarbonise the energy sector as it is the primary emission source, contributing up to 75% of GHG emissions in Malaysia. Hydrogen fuel is getting much attention globally, and it has been said that it can be a new renewable energy source to replace fossil fuels. Hydrogen combustion is clean and only produces water and energy. However, several studies have identified that hydrogen combustion could produce NOx, which is more harmful to the environment than CO2. Studies on hydrogen application in the energy sector in Malaysia are limited, and the implementation of total hydrogen fuel in power plants may not happen shortly. Hence, a fundamental study was proposed on co-firing hydrogen and natural gas fuel. This study aimed to examine co-firing characteristics such as temperature, pressure, and air-to-fuel ratio on GHG emission and energy release to find the optimum natural gas-to-hydrogen ratio. The model was developed using Aspen Plus, and hydrogen-natural gas blend percentages varied from 0% to 30%. The findings showed that increased operating temperature led to higher NOx formation, while varying pressures did not impact the CO2 and NOx formation. The pure natural gas combustion system was more sensitive towards air-to-fuel ratio changes, and an increase in air-to-fuel ratio to 1.5 led to 160% higher NOx formation due to an increase in nitrogen content. The combustion of the hydrogen blend led to lower CO2 formation but higher NOx formation. Lastly, the energy released by the hydrogen blending system was lower due to the formation of water that absorbed the heat released by the combustion.

Liquid Cooling of Fuel Cell Powered Aircraft: The Effect of Coolants on Thermal Management

Abstract Electric propulsors powered by Proton Exchange Membrane Fuel Cells (PEMFCs) offer a net zero solution to aircraft propulsion. Heat generated by the PEMFCs can be transferred to atmospheric air via a liquid cooling system; however, the cooling system results in parasitic power and adds mass to the propulsion system, thereby affecting system specific power. The design of the cooling system is sensitive to the choice of liquid coolant and so informed coolant selection is required if associated parasitic power and mass are to be minimized. Two approaches to selection of coolants for PEMFC-powered aircraft are presented in this paper for operating temperatures in the range 80-200°C (this covers low, intermediate, and high temperature PEMFCs). The first approach uses a Figure of Merit (FoM) alongside minimum and maximum operating temperature requirements. The FoM supports the selection of coolants that minimize pumping power and mass while maximizing heat transfer rate. The second approach uses a cooling system model to select ȜPareto efficientȝ coolants. A hybrid-electric aircraft using a PEMFC stack is used as a representative case study for the two approaches. Hydrocarbon-based coolants are shown to be favorable for the case study considered here (aromatics for PEMFCs operating at <130°C and aliphatics for PEMFCs operating at >130°C). As the PEMFC operating temperature increases, the parasitic power and mass of the TMS decreases. Operating at elevated temperatures is therefore beneficial for liquid cooled PEMFC-powered aircraft. Nevertheless, there are diminishing performance gains at higher operating temperatures.

Temperature-Driven Activated Sludge Bacterial Community Assembly and Carbon Transformation Potential: A Case Study of Industrial Plants in the Yangtze River Delta.

Temperature plays a critical role in the efficiency and stability of industrial wastewater treatment plants (WWTPs). This study focuses on the effects of temperature on activated sludge (AS) communities within the A2O process of 19 industrial WWTPs in the Yangtze River Delta, a key industrial region in China. The investigation aims to understand how temperature influences AS community composition, functional assembly, and carbon transformation processes, including CO2 emission potential. Our findings reveal that increased operating temperatures lead to a decrease in alpha diversity, simplifying community structure and increasing modularity. Dominant species become more prevalent, with significant decreases in the relative abundance of Chloroflexi and Actinobacteria, and increases in Bacteroidetes and Firmicutes. Moreover, higher temperatures enhance the overall carbon conversion potential of AS, particularly boosting CO2 absorption in anaerobic conditions as the potential for CO2 emission during glycolysis and TCA cycles grows and diminishes, respectively. The study highlights that temperature is a major factor affecting microbial community characteristics and CO2 fluxes, with more pronounced effects observed in anaerobic sludge. This study provides valuable insights for maintaining stable A2O system operations, understanding carbon footprints, and improving COD removal efficiency in industrial WWTPs.

Understanding the Temperature Effect on Carbon‐Carbon Coupling during CO2 and CO Electroreduction in Zero‐Gap Electrolyzers†

Comprehensive SummaryCu‐catalyzed electrochemical CO2 reduction reaction (CO2RR) and CO reduction reaction (CORR) are of great interest due to their potential to produce carbon‐neutral and value‐added multicarbon (C2+) chemicals. In practice, CO2RR and CORR are typically operated at industrially relevant current densities, making the process exothermal. Although the increased operation temperature is known to affect the performance of CO2RR and CORR, the relationship between temperatures and kinetic parameters was not clearly elaborated, particularly in zero‐gap reactors. In this study, we detail the effect of the temperature on Cu‐catalyzed CO2RR and CORR. Our electrochemical and operando spectroscopic studies show that high temperatures increase the activity of CO2RR to CO and CORR to C2H4 by enhancing the mass transfer of CO2 and CO. As the rates of these two processes are highly influenced by reactant diffusion, elevating the operating temperature results in high local CO2 and CO availability to accelerate product formation. Consequently, the *CO coverage in both cases increases at higher temperatures. However, under CO2RR conditions, *CO desorption is more favorable than carbon‐carbon (C—C) coupling thermodynamically at high temperatures, causing the reduction in the Faradaic efficiency (FE) of C2H4. In CORR, the high‐temperature‐augmented CO diffusion overcomes the unfavorable adsorption thermodynamics, increasing the probability of C—C coupling.

System Study Review of Electrical Machines under Specific Operating Conditions of Power Installations

The problem of life cycle vulnerability, predetermined by the development stages, operation and modernization of electrical machines due tosize and weight restrictions, dynamic electromagnetic and thermal overloads, possible flooding and changes in ventilation and cooling conditionsis considered. Reducing the weight and size of electric machines implies eliminating passive sections of magnetic circuits and optimizing the ratio of copper and steel. The desire to reduce weight and size indicators and increase energy density entails increased heat generation and temperature loads of structural elements. The increase in operatingtemperatures of modern machines indicates the need to develop mathematical models that account the response of electrical materials and structural elements to the combined thermal and magnetic fieldeffects. Such models are in demand to study the temperature dependence of insulating, magnetic and operating properties of electrical machines when establishing the requiredoperating moderestrictions in order to preserve and extend the life cycle. The criterion for making management decisions aimed at changing operating modes during operation can be maximum loads that limit exceeding the maximum permissible temperatures of the electrical insulationclass used, as well as critical values of induction determined by the temperature dependence of ferromagnetproperties that affect the performance characteristics of electrical machines. Further solution to the problem lies in the creation of digital twins containing complete mathematical and computer simulation models that describe processes in electrical machines, taking into account the temperature dependence of materialphysical properties of structural elements being subjected to thermal, magnetic and electric fields.

Ultrasensitive and highly selective NO2 gas sensing of porous MXene nanoribbon assemblies

Nitrogen dioxide (NO2), a potential source for acid rain and photochemical smog, is known to harm human health, plant growth and crop yield, and the environment. Therefore, designing a room temperature operable NO2 gas sensor with exceptional sensitivity and selectivity is extremely important. Herein, we report that Ti3C2Tx MXene (Tx = –OH, –O, –F, etc.) nanoribbons containing inbuilt anatase TiO2 on their surfaces achieve highly sensitive detection of NO2 gas at room temperature with negligible cross-responses to other gas analytes. The MXene nanoribbons' ability to form porous gas sensor film facilitates the efficient diffusion of gas molecules and the sufficient utilization of surface-active sites, leading to a high response of −87.5 % to 50 ppm NO2 gas exposure with a response time of 9.2 s at room temperature. Signifying the low concentration NO2 detection abilities, MXene nanoribbons displayed a response of −4.4 % towards 500 ppb NO2 exposure. MXene nanoribbons' NO2 gas sensing ability is carrier gas dependent and declines monotonically as operating temperature increases. In addition, the performance comparison experiments conducted at 50 ppm NO2 gas exposure suggest that the MXene nanoribbons' response is 14.3, 1.6, and 45.3 times higher than the responses of multilayer MXene, MXene-TiO2 nanoplate, and MXene-TiO2 nanoparticle structures, respectively. The explicit selectivity and high sensitivity of MXene nanoribbons toward NO2 gas are expected to provide exciting opportunities for personal safety and environmental monitoring.

The paradigm of magnetic molecule in quantum matter: Slow molecular spin relaxation

The quantum nature of single-ion magnets, single-molecule magnets, and single-chain magnets has been manifested among other phenomena by magnetic hysteresis due to slow spin relaxation, competing with fast quantum tunneling at low temperatures. Slow spin relaxation, described by Arrhenius-type law with the effective barrier energies Ueff = 50 cm–1, was discovered 3 decades ago in paramagnetic Mn12-acetate complex of oxy-bridged mixed-valence manganese ions, below the blocking temperature TB = 3 K. In contrast to common magnetic materials, it is governed primarily by magnetic anisotropy, set by zero-splitting of spin states of a magnetic ion in a field of ligands, and spin-lattice coupling. The emerging studies on the border of coordination chemistry, physics of spin systems with reduced dimensionality, and nanotechnologies, were performed in search of routes for enhancement of Ueff and TB characteristics, in line with increase of operation temperature and quantum correlation time, mandatory for quantum applications. The best results with TB ∼ 80 K and Ueff ∼ 1261 cm–1, were obtained for DyIII single-ion magnet, so far. Numerous excellent research and review articles address particular activities behind this achievement. It follows, that present challenges are dictated by the rational development of novel, smart magnetic molecules, featured by butterfly cores, cyano-bridges, 2D metal-organic frameworks, and metal-free graphene nanoclusters, as well as stable free radicals, magnetized by spare electrons. These species are briefly considered here with respect to the unique experience of international collaborative activity, established by Prof. Juan Bartolomé.

Correlating long-term performance and aging behaviour of building integrated PV modules

Because building-integrated photovoltaic (BIPV) modules are fully integrated into a building envelope, the back of the module can be exposed to little or no ventilation, resulting in increased operating temperatures. As the temperature increases, the performance of the modules decreases, and the durability of the module and its polymeric components (e.g., encapsulant and backsheet) may be impacted. Over the years, three different PV test stands were monitored in Canobbio (southern Switzerland) in different configurations: open-rack, BIPV partially-ventilated and BIPV insulated (non-ventilated) to investigate the effect of the operating temperatures on the long-term energy performance of the different BIPV module types. In this study, the PV modules installed in these test stands were thoroughly examined by: (i) evaluating the long-term performance of the modules, and (ii) establishing a correlation between the electrical performance and changes in the properties of the polymers used in the laminate. In general, we observe that: (i) for some bill of materials (BOM), the higher thermal stress of BIPV configurations can accelerate the degradation, particularly of the encapsulant, leading to current losses attributed to the polymer (discolouration); (ii) in some cases, the higher thermomechanical stress can lead to a higher rate of damaged cells and cell interconnects, resulting in fill factor losses; (iii) on the other hand, a careful selection of the BOM and system design (with adequate rear ventilation) may mitigate the issues related to higher thermal and thermomechanical stresses.

Ni/GDC Fuel Electrode for Low-Temperature SOFC and its Aging Behavior Under Accelerated Stress

The microstructural integrity of Ni-based fuel electrodes is important for long-term solid oxide fuel cell (SOFC) operation. Degradation due to microstructural changes such as Ni-agglomeration, coarsening, and densification must be prevented by an appropriate microstructure. Here, the performance of four types of nickel-ceria-based fuel electrodes, which differ concerning layer sequence and manufacturing processes, was evaluated by electrochemical impedance spectroscopy at the nominal operating temperature of 600 °C. Electrodes produced through screen-printed GDC exhibited an acceptable polarization resistance (0.260 Ωcm2), whereas electrodes with an additional printed Ni/GDC layer demonstrated inferior performance (0.550 Ωcm2). Electrodes formed through infiltration of GDC into the printed GDC-layer displayed unreproducible performance values ranging from 0.16 to 1.20 Ωcm2 despite similar processing. Conversely, electrodes with an extra layer of GDC infiltrated into the Ni-backbone exhibited good performance (0.195 Ωcm2) and stability. Accelerated degradation tests under OCV at increased operating temperatures of 700 and 900 °C were performed on the sample based on a GDC infiltrated Ni-backbone that performed best among reproducible samples. The polarization resistance at 600 °C recorded at the beginning and the end of life increased by up to 100%. Microstructural analysis of the electrodes at different aging states revealed strong microstructural changes of fine-infiltrated GDC structures and Ni agglomeration at higher operating temperature.

Experimental investigation on the heat transfer performance of pulsating heat pipe with self-rewetting Fe3O4-nanofluid

This paper conducted an experimental study on the heat transfer performance of pulsating heat pipe (PHP) under three different working fluids: ultrapure water, n-butanol self-rewetting fluid (SRWF), and self-rewetting Fe3O4-nanofluid (SRNF). The effects of filling ratio (FR), heating power, and magnetic field are studied. The results mainly show that the PHP with SRNF under a magnetic field, the start-up time increases, the evaporation section operating temperature increases, and the thermal performance decreases as the filling ratio increases. Increasing the FR, applying SRWF and SRNF can effectively increase the dry-out limit of PHP. At FR = 50 %, the overall thermal performance of PHP is best. In 10–130W, the thermal resistance of the SRWF and the SRNF with/without magnetic field is reduced by 14.5 %–27.8 %, 27.6 %–47.9 %, and 4.2 %–24.8 %, respectively, compared with that of ultrapure water. Similarly, compared without a magnetic field, the thermal resistance of SRNF with a magnetic field is reduced by 14.0 %–35.1 %. At FR = 50 %, the heat transfer performance of SRNF-PHP is best with a magnetic field. When the input power is 130W, the effective heat transfer coefficient keff is 5967.6 W/m∙ K, approximately 13.92 times greater than copper.

Thermal design of operating parameter for reliable AlSi7Mg selective laser melting

Gas turbines require high power density for applications like aircraft and future mobility. Increasing operating temperature, particularly turbine inlet temperature, boosts performance. However, conventional cooling methods limit this increase. Selective laser melting (SLM) offers a promising avenue for realizing advanced cooling configurations beyond conventional fabrication techniques. However, unexpected defects in the final product can occur, making pre-fabrication quality estimation difficult. This necessitates thermal analysis during SLM and design guidelines for suitable fabrication. This study investigates the thermal design guidelines for AlSi7Mg alloy using SLM for high-heat-flux applications. Simulations explored melt pool size dependence on operating parameters like laser power and scan speed. Comparisons with experimental results revealed diverse heat transfer modes under different operating conditions. Finally, a normalized enthalpy factor, integrating operating parameters like scan speed and laser power, was proposed for thermal design in SLM processes for high-heat-flux applications.

Design of All‐Oxide Multilayers with High‐Temperature Stability Toward Future Thermophotovoltaic Applications

AbstractThermophotovoltaic (TPV) technology converts heat into electricity using thermal radiation. Increasing operating temperature is a highly effective approach to improving the efficiency of TPV systems. However, most reported TPV selective emitters degrade rapidly via. oxidation as operating temperatures increase. To address this issue, replacing nanostructured oxide‐metal films with oxide–oxide films is a promising way to greatly limit oxidation, even under high‐temperature conditions. This study introduces new all‐oxide photonic crystal designs for high‐temperature stable TPV systems, overcoming limitations of metal phases and offering promising material choices. The designs utilize both yttria‐stabilized zirconia (YSZ)/MgO and CeO2/MgO combinations with a multilayer structure and stable high‐quality growth. Both designsexhibit positive optical dielectric constants with tunable reflectivity, measured via optical characterization. Thermal stability testing using in situ heating X‐ray diffraction (XRD) suggests high‐temperature stability (up to 1000 °C) of both YSZ/MgO and CeO2/MgO systems. The results demonstrate a new and promising approach to improve the high‐temperature stability of TPV systems, which can be extended to a wide range of material selection and potential designs.

Electrocatalysts for High Temperature (100-200 ºC) and Pressure (45 bar) Alkaline Electrolysis

Electrolytic hydrogen production is key in transitioning to a sustainable energy system, as it enables the production of sustainable fuels and chemicals from renewable electricity sources and a means to address their intermittent nature at the same time. Amongst the main electrolysis technologies, Alkaline Electrolysis (AE) is the most suitable for the hundreds of GW capacity that is required, as it relies only on abundant, low-cost materials, and has a proven record of reliability and scalability. However, AE suffers from poor efficiency and productivity. Increasing operating temperature and pressure offers a means to overcome this limitation [1, 2]. Nevertheless, electrodes with good long-term stability in the hot corrosive alkaline environment are required. Here, we report the performance of Co3O4 and NiMoOx coated nickel foam (NF) electrodes for the anode and cathode, respectively. The electrodes are tested from room temperature to 150 ºC at 45 bar pressure in 45 wt.% KOH. The Co3O4 coated NF (Co3O4/NF) anode performance is compared to that of commercial pristine NF and Inconel coated NF (Inconel/NF) electrodes. At room temperature the Inconel/NF electrode outperforms both the pristine NF as well as the Co3O4/NF electrodes. At 150 ºC and 45 bar pressure, the Co3O4/NF and Inconel/NF electrode perform quite similar. During the 108 h long-term stability test at 150 ºC and 45 bar, the Co3O4/NF electrode remains stable requiring an overpotential of ~185 mV at 500 mA.cm-2, whereas the overpotential of the Inconel/NF electrode increased from 178 mV to 209 mV after 84 h of operation at the same conditions. The structural and chemical evolution of these electrodes was explored by post-mortem scanning electron microscopy (SEM) in comparison to the fresh electrodes. The NiMoOx coated NF (NiMoOx/NF) cathode showed a low and stable overpotential (~130 mV) at the same conditions, similar to a precious metal coated nickel perforated plate electrode (~125 mV). References C. Chatzichristodoulou, F. Allebrod, and M. B. Mogensen, J. Electrochem. Soc., 163, F3036–F3040 (2016).F. Allebrod, C. Chatzichristodoulou, and M. B. Mogensen, J. Power Sources, 229, 22–31 (2013).

(Invited) Chemical and Microstructural Reaction Paths in High-Temperature Alloys in Contact to Molten Salts

Molten salts for thermal energy storage applications have gained attention in recent years. Simultaneously, demands on salt melts are also getting higher: higher thermal stability, availability, and economic feasibility.Maybe the most crucial factor, however, is the possibility to match a suitable containment material for salt melts. By increasing operation temperature, material degradation processes commonly accelerate beyond tolerable thresholds. These thresholds are referring to material integrity, strength, and local attack.It turns out that every salt melt hereby reacts along characteristic pathways influencing alloys’ surface chemistry and underlying microstructures to very deep levels.High-temperature alloys depend on their carefully balanced elemental compositions. During this presentation, we will explore how subtle salt-induced compositional shifts have a large and rapid influence on microstructural properties in alloys and thereby on their performance assessment.

Activity and Stability of High-Surface-Area Nickel-Based Catalysts for the Alkaline Hydrogen Evolution Reaction Under Industrially Relevant Conditions

Alkaline water electrolysis (AWE) is at a stage of high technological maturity, and modern pressurized designs have mitigated the weaknesses of now-outdated atmospheric electrolyzers. For instance, pressurized systems now deliver high hydrogen outputs and can efficiently adjust to rapid changes in power loads. These improvements were, in part, made possible through significant reductions to internal ohmic losses coming from improved gas separators, shorter distances between electrodes, and increased operating temperatures.From an industrial point of view, the critical parameter to optimize is the full stack voltage. The stack voltage is tightly bound to the individual cell voltage and can thus be lowered by employing more efficient electrocatalysts. However, reducing the cell voltage by raising the temperature of operation—thereby improving both reaction kinetics and the conductivity of the KOH electrolyte—can be of similar or even higher importance (e.g., ca. 4.5 mV/˚C, Figure 1) [1]. Therefore, stability under operation at elevated temperatures must be considered when evaluating novel hydrogen and oxygen evolution reaction catalysts for AWE. Else, a novel catalyst risks becoming the bottleneck in the pursuit of higher operating temperatures, limiting its applicability for large-scale electrolysis [2]. Many assessments of novel AWE catalysts are still carried out at room temperature in diluted electrolytes and at low current densities [3]. In the harsher conditions of an electrolyzer, catalysts experience higher dissolution rates and are subject to higher mechanical stress from, for instance, the aggressive bubble evolution. This gap hinders the transfer of catalyst developments from academia to industrial research laboratories and, ultimately, to practical applications.In this work, we attempted to narrow that gap by conducting electrochemical measurements under more application-oriented conditions (i.e., 80-120 °C and 8-11 M KOH). We evaluated the HER activity and the robustness of high-surface-area electrodes produced through controlled leaching of bimetallic nickel-based alloys. A parametric study of the overpotential and robustness as a function of electrochemically active surface area was enabled by varying the synthesis parameters of a Raney-type preparation. Direct coupling to renewable energy sources requires the electrolyzer to frequently and rapidly shut off and on. This intermittent operation induces additional stress on the electrodes as the catalysts transition through different redox states, which is often overlooked in AWE electrocatalyst research. To track redox, compositional, and morphological changes, we used ex situ X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy. At the same time, the dissolution and redeposition of ionic species were monitored using inductively coupled plasma mass spectrometry. By matching the characterization data with the evolution of the overpotential until complete deactivation, we gained an understanding of the degradation mechanisms in high-surface-area nickel-based electrodes. These results shed light on the challenges and prospects of this promising class of electrocatalysts for alkaline HER under industrial conditions.Acknowledgement:This work is partly funded by the Innovation Fund Denmark (IFD) under File No. 1044-00162B.

(Invited) High Performing Fuel Cell Stack and Systems

PowerCellGroup has worked in the field of fuel cell systems and fuel cell stacks for more than 25 years. The development of both systems and stacks have gone hand in hand and have been important to reach the targets for both.The fuel cell stack currently offered to the market has been developed during the last 10 years. Starting out with focus on passenger vehicles to achieve the requirements on power density. The second step the development was tailored to meet the demands from heavy-duty usage, that requires high efficiency at high power output and longer durability as well as increased operating temperature. This second stage unlocked the usage of fuel cell in more applications like, stationary high-power generation, off-rad machinery and lately the aviation sector.The later years the implementation of hydrogen and fuel cell on the market have accelerated and more commercial usage putting larger requirement on higher power, longer durability, higher operating temperatures etc. For example, how to install several MW into marine vessels.The third phase that we are now entering is to take the fuel cell to the next level, to the sky. Improving power density towards 5-6 kW/kg, operating temperature up to 120°C, and larger stack sizes 300 kW scalable to about 1 MW this to meet the higher power demand by aircraft. PowerCell is on a good track in all these aspects to be ready for the future. In this talk will be about how we constantly improving and challenging the fuel cell system and fuel cell stacks to be used in commercial operation.