Long-term Performance Degradation Research Articles

Protic Ionic Liquids as Electrolytes for Metal-Hydride Batteries

Nowadays, the most popular and effective energy storage systems are Li-ion batteries, despite some limitations such as high cost, flammability, temperature restrictions, and use of critical raw material (e.g. Co) [1]. This raises the challenge of the demand for alternative systems. One potential alternative is the Ni-MH battery, which are recognized for their good cyclability, competitive energy density, low memory effect, wide range of operating temperatures, low cost, and environmental friendliness [1]. Their practical use, however, is constrained due to their low specific energy density, high self-discharge rate, and electrode ageing [2,3].This work is focused on the study of the negative electrode of the Ni-MH battery and its interaction with the electrolyte. The objective aims to improve the performance of the negative electrode of Ni-MH batteries by substituting the conventional water-based KOH 8.7 M electrolyte by a Protic Ionic Liquid (PIL) to overcome aforementioned drawbacks [4]. PILs can exchange a labile proton, thereby supporting the main redox reaction, hydrogenation, at the negative electrode of Ni-MH battery.Thus, a series of twelve PILs or their combinations were synthesized and tested in a half-cell configuration. The charge/discharge cycle tests were carried out. Results showed that Pyrrolidinium Acetate (PyrrAc), Ethanolammonium Acetate (EOAAc) mixed with g-butyrolactone (GBL), and Diethanolammonium Acetate (DEOAAc) exhibited promising performance in half-cell configuration (Table 1).PyrrAc was shown to be an optimal electrolyte and has been further studied in terms of long-term performance and system degradation. The morphology of the aged negative electrodes was observed by Scanning Electron Microscopy (SEM) (Fig. 1). For instance, after 7 cycles of charge/discharge, formation of cracks was observed in the electrode (Fig. 1 (right)) due to hydrogen ab/desorption.The utilization of PyrrAc as electrolyte resulted in no initial capacity loss and, moreover, exhibited an increase in capacity during the first cycles, which can be recognized as an activation of the electrode (similar to the one observed in aqueous electrolytes). In order to obtain a complete understanding of the electrode stability, the electrolytes after cycling as well as calendar corrosion were studied using Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES).[1] M.A. Hannan, M.M. Hoque, A. Mohamed, and A. Ayob, Renewable and Sustainable Energy Reviews, 69 (2017) 771–789.[2] B. Puga et al., ChemElectroChem, 2 (2015) 1321–1330.[3] J. Matsuda, Y. Nakamura, E. Akiba, J Alloys Compd, 509 (2011) 7498–7503.[4] T. Meng, K. H. Young, D. F. Wong, and J. Nei, Batteries, 3 (2017) 4. Figure 1

Enhancing Life Cycle Assessment for Reversible Ground-Coupled Heat Pump Systems through Dynamic Analysis

Ground-coupled heat pump (GCHP) systems can provide comfortable indoor environments, but also inevitably contribute to greenhouse gas emissions and other impacts on human health, ecosystems, and resources. Life cycle assessment (LCA) methodology has been widely adopted to estimate the environmental impacts associated with GCHP systems, with operational electricity consumption being the largest contributor among most categories. Given the data-intensive nature of LCA, operational electricity consumption should be prioritised to refine the accuracy of LCA results. Previous studies, however, have relied on static COP (Coefficient of Performance) and annual average data to obtain the environmental impacts and have disregarded the effect of long-term performance degradation caused by building thermal load imbalances. In this paper, to bridge this research gap, a dynamic operational environmental impact assessment (DOEIA) method was proposed to improve the precision of LCA results by incorporating higher temporal resolution data of electricity mix and real-time performance modelling of the reversible GCHP system. Impacts of different temporal resolutions (i.e. monthly, trimestral, and annual) on the accuracy of LCA results was examined and the operational performance degradation resulting from imbalanced building heating and cooling loads was considered. Results demonstrate that while performance degradation effects are evenly distributed across impact categories, gaps due to temporal resolutions vary significantly between different categories. Subsequent analysis of spatial variations in the latter further emphasises the importance of accounting for higher temporal resolutions. Finally, life cycle impact assessment (LCIA) results for reversible GCHP systems in different locations were obtained with the support of DOEIA method and the results underscore the necessity of a cleaner energy mix. The proposed DOEIA method can be applied to other energy systems for comparative analyses. It is replicable in other countries and regions and therefore is expected to provide methodological guidance for future decision-makers.

An efficient and robust Co-free BaFeO3-based oxygen electrode for protonic ceramic electrochemical cells

Protonic ceramic electrochemical cells (PCECs) are promising devices for sustainable energy conversion and storage with high efficiency and low cost. However, the application of PCECs is limited by the scarcity of oxygen electrode materials with excellent oxygen reduction/evolution reaction (ORR/OER) activity and robust durability. In this investigation, perovskite oxide with specific non-stoichiometric ratios, namely Ba0.9Sr0.05La0.05Fe0.8Zn0.1Y0.1O3 (BSLFZY) are synthesized using a sol-gel method, and electrochemically evaluated as oxygen electrodes for PCECs. The structural and chemical stability of the synthesized material is explored and analyzed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations. Surface catalytic activity is assessed using X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), and oxygen temperature-programmed desorption techniques (O2-TPD). Additionally, the electronic conductivity results demonstrate the suitability of BSLFZY for application in PCECs. The electrochemical performance of the material is estimated using a homemade Ni-BZCYYb/BZCYYb cell with a BSLFZY oxygen electrode. Electrochemical impedance spectra within a specific temperature range are analyzed using the distribution of relaxation times (DRT) method. The results offer valuable insights into the underlying reasons for long-term electrochemical performance degradation in fuel cell (FC) mode. These results present the potential of BSLFZY for practical applications in PCECs, highlighting its excellent electrochemical performance and durability.

Thermal Sprayed Protective Coatings for Bipolar Plates of Hydrogen Fuel Cells and Water Electrolysis Cells

As one core component in hydrogen fuel cells and water electrolysis cells, bipolar plates (BPs) perform multiple important functions, such as separating the fuel and oxidant flow, providing mechanical support, conducting electricity and heat, connecting the cell units into a stack, etc. On the path toward commercialization, the manufacturing costs of bipolar plates have to be substantially reduced by adopting low-cost and easy-to-process metallic materials (e.g., stainless steel, aluminum or copper). However, these materials are susceptible to electrochemical corrosion under harsh operating conditions, resulting in long-term performance degradation. By means of advanced thermal spraying technologies, protective coatings can be prepared on bipolar plates so as to inhibit oxidation and corrosion. This paper reviews several typical thermal spraying technologies, including atmospheric plasma spraying (APS), vacuum plasma spraying (VPS) and high-velocity oxygen fuel (HVOF) spraying for preparing coatings of bipolar plates, particularly emphasizing the effect of spraying processes on coating effectiveness. The performance of coatings relies not only on the materials as selected or designed but also on the composition and microstructure practically obtained in the spraying process. The temperature and velocity of in-flight particles have a significant impact on coating quality; therefore, precise control over these factors is demanded.

Use of condition-based valuation approach to evaluate the maintenance decision of pavement assets: a case study of Yunnan Province in China

Pavements are critical components of highway assets, but accurately estimating their value can be challenging due to the lack of connection between valuation and long-term service performance degradation. To address this issue, the replacement cost and condition-based valuation methods were introduced using the Yunnan province highway in China as an example, which divided pavement into four performance states based on service stages. The rationality of maintenance decisions and the impact of preventive maintenance investment on life cycle assessments were also considered. The results indicate that there are issues of irrational allocation of maintenance funds of the highway in Yunnan province, and a higher proportion of preventive maintenance investment is required. Moreover, it is recommended to balance the maintenance funds for bridge and tunnel engineering in the following year, focusing on bridge engineering with a rapid decline in the newness rate. The implementation of preventive maintenance has a positive correlation with the replacement cost and newness rate of the road sections. Through comparison, it was found that the road surface renewal rate in 2019 was lower than that in 2018, and some highway management departments in certain regions need to adjust their preventive maintenance strategies. Overall, the condition-based pavement asset valuation method comprehensively considers each stage of pavement operation and can serve as an effective tool for evaluating pavement asset depreciation. This research finding can promote the sustainable development of road infrastructure.

Effects of basalt fiber reinforced polymer minibars on the flexural behavior of pre-cracked UHPC after chloride induced corrosion

Ultra-high performance concrete (UHPC) exhibits high shrinkage, which results in a severe risk of cracking in practice, leading to the risk of long-term mechanical performance degradation caused by steel fiber corrosion in harsh environment. This study aims to use basalt fiber reinforced polymer (BFRP) minibars to improve the long-term flexural behavior of UHPC. UHPC reinforced with 3 % BFRP minibars and 3 % steel fibers were pretreated for initial crack and cured in chloride solution for various dry-wet cycles, respectively. The long-term tensile behavior of BFRP minibar and steel fiber, and long-term flexural behavior of UHPC with BFRP minibars and steel fibers were systematically tested and evaluated before and after corrosion, respectively. According to the test results, compared to steel fiber, BFRP minibar showed a much better chloride resistance, leading to a great improvement in long-term flexural behavior of UHPC after chloride induced corrosion. When the initial crack width was less than 0.1 mm, two kinds of UHPC showed the ideal residual flexural behavior rate after a 150-cycle corrosion, which exceeded 95 %, owing to the self-healing of initial crack caused by the further hydration of unreacted binders in UHPC matrix. When the initial crack width was near 0.2 mm and 0.3 mm, after a 150-cycle corrosion, the flexural strength of UHPC with BFRP minibars was decreased by 10.94 % and 12.99 %, the decrease rate was 59.72 % and 52.24 % lower than UHPC with steel fibers in same environment, respectively. The similar changes in toughness and stiffness were found too. It indicated that using BFRP minibars to reinforce UHPC effectively alleviated the risk of decrease in mechanical properties of pre-cracked UHPC caused by steel fiber corrosion under harsh environment.

Self-Healing Sulfonated Poly(ether ether ketone)-Based Polymer Electrolyte Membrane for Direct Methanol Fuel Cells: Effect of Solvent Content.

Proton exchange membranes (PEMs) with superior characteristics are needed to advance fuel cell technology. Nafion, the most used PEM in direct methanol fuel cells (DMFCs), has excellent proton conductivity but suffers from high methanol permeability and long-term performance degradation. Thus, this study aimed to create a healable PEM with improved durability and methanol barrier properties by combining sulfonated poly(ether ether ketone) (SPEEK) and poly-vinyl alcohol (PVA). The effect of changing the N,N-dimethylacetamide (DMAc) solvent concentration during membrane casting was investigated. Lower DMAc concentrations improved water absorption and, thus, membrane proton conductivity, but methanol permeability increased correspondingly. For the best trade-off between these two characteristics, the blend membrane with a 10 wt% DMAc solvent (SP10) exhibited the highest selectivity. SP10 also showed a remarkable self-healing capacity by regaining 88% of its pre-damage methanol-blocking efficiency. The ability to self-heal decreased with the increasing solvent concentration because of the increased crosslinking density and structure compactness, which reduced chain mobility. Optimizing the solvent concentration during membrane preparation is therefore an important factor in improving membrane performance in DMFCs. With its exceptional methanol barrier and self-healing characteristics, the pioneering SPEEK/PVA blend membrane may contribute to efficient and durable fuel cell systems.

Analysis of wind time-varying performance of reinforced concrete electric pole under Marine atmospheric environment

Bearing capacity calculation model of concrete electric pole considering concrete long-term performance degradation and steel corrosion is established. The horizontal bearing capacity and wind resistance of typical concrete electric pole under Marine atmospheric environment are analyzed with service time. The effects of concrete protective layer thickness, stirrup diameter and strength coefficient on the long-term wind resistance of electric pole are discussed. It is found that with the increase of service time, the shear strength of the concrete pole deteriorates faster than that of the flexural strength, and the failure mode changes from bending failure to shear failure. The wind resistance of the pole after long service can be improved by increasing the thickness of the protective layer, adopting larger diameter stirrup and higher strength coefficient. The bearing capacity calculation model of concrete electric pole considering concrete long-term performance degradation and steel corrosion is established. The horizontal bearing capacity and wind resistance of typical concrete electric pole under Marine atmospheric environment are analyzed with service time. The effects of concrete protective layer thickness, stirrup diameter and strength coefficient on the long-term wind resistance of electric pole are discussed. It is found that with the increase of service time, the shear strength of the concrete pole deteriorates faster than that of the flexural strength, and the failure mode changes from bending failure to shear failure. The wind resistance of the pole after long service can be improved by increasing the thickness of the protective layer, adopting larger diameter stirrup and higher strength coefficient.

Optimization of Extrinsic Impact Factors for Improving Performance and Mitigating Performance Degradation of LSCF-SDC/YSZ/Ni-YSZ Cells Under Solid Oxide Electrolysis Operation

Long-term solid oxide electrolysis operation (SOEC) testing was performed to study the performance and performance degradation of LSCF-SDC/YSZ/Ni-YSZ cells under temperatures of 750 oC, 800 oC, and 850 oC, current density of 0.5A/cm2 and 1.0A/cm2, and H2/H2O ratio of 1:1, 1:3, and 2:1. Operational temperature, current density, and H2/H2O ratio played important roles in the cells’ performance and performance degradation. These factors were correlated and should be balanced and/or optimized to maximize overall lifetime performance. LSCF-SDC cells showed better performance and less performance degradation under higher temperature. Electrochemical impedance spectroscopy (EIS) data showed polarization resistance was significantly lower for the cell operated at higher temperature. Therefore, SOEC operation may need relatively higher temperature to be activated. Long-term SOEC testing under different current density showed better performance and less performance degradation at 0.5A/cm2, 850 oC, and 1:1 of H2/H2O ratio. H2/H2O ratio in the functional layer of the cell also played an important role. The cell showed best performance and less performance degradation under 1:1 of H2/H2O ratio. EIS data showed the polarization resistance was significantly lower under 1:1 of H2/H2O ratio. H2/H2O ratio needs to be optimized for different operational temperature and current density. Overdosed steam may react with Ni causing Ni movement in the H2 electrode, adding to cell degradation. Transmission electron microscopy (TEM) studies identified the formation of the (CoFe)Ox along the SDC grain boundaries, which could impact both the SDC conductivity and the LSCF catalytic activity due to the loss of the transition metals in the LSCF. TEM analysis of the H2 electrode identified a large number of NiO clusters relocated into the original pore region, seemingly formed during Ni migration. This NiO formation in the H2 electrode during SOEC operation is another cause of long-term performance degradation.

A simplified ANN-based evaluation method for creep sensitive girder bridge identification at preliminary design stage

Excessive deflection which exceeded expectations has been identified as one of the main problems contributing to long-term performance degradation of long-span girder bridges. Although the 3D refined finite element model of the full bridge can improve the prediction accuracy of long-term creep deformation, there is still a lack of efficient creep-sensitive structural judgment methods in the preliminary design stage. This study was thus intended to develop a new evaluation method and model to identify the possibility of excessive deflection will occur by utilizing simple structural design parameters, which contributed to new understandings of the creep deformation of bridge structural level. A finite element model database established by 20 long-span prestressed concrete girder bridges with actual project backgrounds was used for providing training, testing, and validation sample datasets for the artificial neural networks (ANN). The Back Propagation (BP) model was chosen for creating mappings among variables and results and solving complex problems with a fairly accurate prediction even without sufficient information. The indicator of deflection-span ratio difference between creep models was proposed as the key analysis factor. A case study was conducted to validate the effectiveness of the ANN model. The mean absolute error (MAE) between the results of the ANN model and FE analysis was 6.25%, which indicated a high consistency. The analysis of bridge design parameters using the ANN model revealed that it had a high risk of excessive deformation, which was consistent with the conclusion of the actual situation. Multiparameter sensitivity analysis results from the model also suggest that the side-span ratio, the main span, and the deflection caused by the pavement are the most three significant impacts compared to different input variables in this model. Based on the results, it can be concluded that the performance of the ANN-based technique can predict possible excessive creep problems in advance.

Effects of climate change on long-term building heating performance of medium-deep borehole heat exchanger coupled heat pump

The medium-deep borehole heat exchanger (MDBHE) coupled heat pump (HP) is a promising building heating solution for carbon reduction. Existing studies claim that the MDBHE-HP suffers a bottleneck challenge of long-term heating performance degradation because of the heating extraction attenuation of the MDBHE, which largely hinders the practical applications of the MDBHE-HP. This study innovatively proposes and justifies that climate change positively compromises the heating extraction attenuation of the MDBHE and significantly improves the long-term building heating performance of the MDBHE-HP. Climate change reduces the building heating load, which mitigates the heating extraction attenuation of the MDBHE, thereby reducing the unmet level of the building heating load. The mitigated heating extraction attenuation enhances the coefficient of performance of the MDBHE-HP, thereby reducing the heating energy consumption. Case studies of 30-year operation in the severe cold and cold zones of China with different geological conditions show that while the heating extraction attenuation of the MDBHE increases the heating energy consumption by 5.0% – 8.7%, climate change reduces the heating energy consumption by 9.2% – 17.0%. Moreover, climate change reduces the unmet level of the building heating load by 70.5% – 100%. Therefore, the positive effects of climate change on the long-term building heating performance of MDBHE-HP should be considered, which contributes to promoting the practical applications of the MDBHE-HP for low-carbon building heating.

The Aging Behavior and Life Prediction of CFRP Rods under a Hygrothermal Environment.

Carbon fiber-reinforced polymer (CFRP) composites have been widely used in civil engineering structures due to their excellent mechanical and durability properties. The harsh service environment of civil engineering leads to significant degradation of the thermal and mechanical performances of CFRP, which then reduces its service reliability, service safety, and life. Research on the durability of CFRP is urgently needed to understand the long-term performance degradation mechanism. In the present study, the hygrothermal aging behavior of CFRP rods was investigated experimentally through immersion in distilled water for 360 days. The water absorption and diffusion behavior, the evolution rules of short beam shear strength (SBSS), and dynamic thermal mechanical properties were obtained to investigate the hygrothermal resistance of CFRP rods. The research results show that the water absorption behavior conforms to Fick's model. The ingression of water molecules leads to a significant decrease in SBSS and glass transition temperature (Tg). This is attributed to the plasticization effect of the resin matrix and interfacial debonding. Furthermore, the Arrhenius equation was used to predict the long-term life of SBSS in the actual service environment based on the time-temperature equivalence theory, obtaining a stable strength retention of SBSS of 72.78%, which was meaningful to provide a design guideline for the long-term durability of CFRP rods.

Multi-Contaminant Getter for Trace Airborne Contaminant Capture in Elevated Temperature Electrochemical Systems

Electrode poisoning in high temperature electrochemical systems from trace levels of airborne contaminants remains a critical issue, contributing to long-term irreversible performance degradation. The intrinsic and extrinsic presence of gas phase Cr, Si, B, and SOx, species in air have been reported to form detrimental secondary compounds and microstructural changes at the electrode/electrolyte interface, consuming electrochemically active sites. Herein, a novel contaminant capture method is reported that uses low-cost getter materials based on alkaline-earth metals. The getters, in benchtop transpiration tests, demonstrated the desired ability to form thermodynamically stable reaction products and reducing the gaseous contaminant partial pressures by several orders of magnitude. Consumption of the contaminants in the getter preserves the performance of solid oxide cells. The presented results have demonstrated the feasibility of the use of getter materials under operating conditions typical to elevated-temperature electrochemical systems.

Multi-Step Wind Power Forecasting with Stacked Temporal Convolutional Network (S-TCN)

Nowadays, wind power generation has become vital thanks to its advantages in cost, ecological friendliness, enormousness, and sustainability. However, the erratic and intermittent nature of this energy poses significant operational and management difficulties for power systems. Currently, the methods of wind power forecasting (WPF) are various and numerous. An accurate forecasting method of WPF can help system dispatchers plan unit commitment and reduce the risk of the unreliability of electricity supply. In order to improve the accuracy of short-term prediction for wind power and address the multi-step ahead forecasting, this research presents a Stacked Temporal Convolutional Network (S-TCN) model. By using dilated causal convolutions and residual connections, the suggested solution addresses the issue of long-term dependencies and performance degradation of deep convolutional models in sequence prediction. The simulation outcomes demonstrate that the S-TCN model’s training procedure is extremely stable and has a powerful capacity for generalization. Besides, the performance of the proposed model shows a higher forecasting accuracy compared to other existing neural networks like the Vanilla Long Short-Term Memory model or the Bidirectional Long Short-Term Memory model.

Insights on designing non-PGM catalyst layers at low humidity

Non-precious group metal (non-PGM) catalysts offer the opportunity to significantly reduce fuel cell costs. However, owing to its low volumetric activity, non-PGM electrodes are made an order of magnitude thicker than platinum-based electrodes. Thicker electrodes increase transport losses making it critical to optimize electrode composition. In most studies, non-PGM electrodes are tested with fully humidified O2/air to maximize the proton conductivity. However, the fully humidified inlet gas makes non-PGM electrodes more prone to water flooding which can cause long-term performance degradation. In the present study, a single-phase, non-isothermal model was used to investigate the structure-performance relationships of the non-PGM electrodes operated at low relative humidity. Our modeling study reveals that high porosity is not necessarily required for non-PGM electrodes operating at low relative humidity. Instead, high solid and electrolyte phase volume fractions are desired. Our proposed strategy is to reduce the thickness of the non-PGM electrode while keeping the mass loading of the non-PGM catalyst consistent.

Applied current on the suppression of strontium segregation in Sr2Fe1.5Mo0.5O6-δ electrode for improved oxygen evolution reaction

Strontium surface segregation is the main issue that causes long-term performance degradation in strontium-containing electrodes for solid oxide electrolysis cells. In this research, we effectively suppress strontium segregation by applying an anodic current that drives the segregated strontium back to the perovskite lattice and mitigate electrode performance degradation. By monitoring the impedance of Sr2Fe1.5Mo0.5O6-δ (SFM) air electrode under open circuit voltage at high temperature with changing current densities over time, the degradation caused by strontium segregation is verified. The applied current successfully prevent the polarization resistance from increasing is observed. The cell with 0.8 A/cm2 of the applied current increase only 3% of polarization resistance as compared to the cell without applied current after testing at 800 ℃ for 24 h. The atomic ratio of strontium on the SFM electrode surface shows lower strontium content after undergoing applied current, which means that the strontium is indeed migrated back to perovskite lattice under the applied current and result in slower degradation of the SFM electrode.

Transient Multi-Physics Modeling and Performance Degradation Evaluation of Direct Internal Reforming Solid Oxide Fuel Cell Focusing on Carbon Deposition Effect

The performance degradation issue caused by carbon deposition has limited the commercial application of natural-gas-fueled solid oxide fuel cells. Most previous corresponding studies are based on thermodynamic equilibrium analyses, while long-term transient evaluation work is lacking. Therefore, a transient multi-physics numerical model is developed in present work. The corresponding long-term performance degradation evaluation is then conducted. The results show that, for a direct internal reforming solid oxide fuel cell, the increase in carbon deposition and deterioration of performance degradation were concentrated in the first 180 days of steady−state operation and slowed down at the later stage. The electrode inlet rapidly developed a high concentration of carbon deposition after 180 days of steady−state operation. The deposited carbon deteriorated the gas transport and decayed reaction activity within the porous electrode, eventually inducing a deactivation zone with 0 current density at the inlet. Key measures to inhibit carbon deposition should be implemented within the first 180 days of operation, and the pre-reformed operation of natural gas is encouraged for natural-gas-fueled solid oxide fuel cells.

Interface Problems in Solid Oxide Electrolysis Cells

In this talk, I introduce topics, that I have been working on, in solid oxide electrolysis cells involving complicated interfacial structures and dynamics of interfaces. Then I will focus on my recent work on nickel (Ni) particle migration in electrodes consisting of Ni, yttria-stabilized zirconia (YSZ), and pores during the operation of oxygen-ion conducting solid oxide electrolysis cells (o-SOECs) and Faraday efficiency in proton-conducting solid oxide electrolysis cells (p-SOECs) under electrolysis operations. SOECs can have a significant impact on climate change over the next decade and beyond, in applications such as balancing renewable grid electricity via electrolytic fuel production. However, long-term performance degradation remains a key issue that may limit further implementation of O-SOECs, and the dependency of operation conditions on Faraday efficiency in P-SOECs has been under debate. In particular, in Ni/YSZ/pore electrode of O-SOEC, a phase-field model is proposed that employs the Ni-YSZ 3D microstructure as the initial condition and large-scale numerical simulation is implemented that predicts the directional Ni migration. The results are thus directly comparable to experimental observations. Quantitative predictions of the evolution of the Ni/YSZ/pore system's microstructures due to Ni particles' migration are studied through theoretical analysis and data analysis. In P-SOECs, an electrochemical model is proposed to study the dependency of Faraday efficiency on operation conditions for P-SOECs with yttrium-doped barium zirconates (BZY) and co-doping barium zirconate-cerate oxides with ytterbium and yttrium (BCZYYb) as electrolytes respectively. Our numerical predictions are verified by experimental results obtained in INL. An optimal structure of electrolyte is proposed to boost the Faraday efficiency in P-SOECs.

Degradation prediction of proton exchange membrane fuel cell stack using semi-empirical and data-driven methods

Degradation prediction of proton exchange membrane fuel cell (PEMFC) stack is of great significance for improving the rest useful life. In this study, a PEMFC system including a stack of 300 cells and subsystems has been tested under semi-steady operations for about 931 h. Then, two different models are respectively established based on semi-empirical method and data-driven method to investigate the degradation of stack performance. It is found that the root mean square error (RMSE) of the semi-empirical model in predicting the stack voltage is around 1.0 V, while the predicted voltage has no local dynamic characteristics, which can only reflect the overall degradation trend of stack performance. The RMSE of short-term voltage degradation predicted by the DDM can be less than 1.0 V, and the predicted voltage has accurate local variation characteristics. However, for the long-term prediction, the error will accumulate with the iterations and the deviation of the predicted voltage begins to fluctuate gradually, and the RMSE for the long-term predictions can increase to 1.63 V. Based on the above characteristics of the two models, a hybrid prediction model is further developed. The prediction results of the semi-empirical model are used to modify the input of the data-driven model, which can effectively improve the oscillation of prediction results of the data-driven model during the long-term degradation. It is found that the hybrid model has good error distribution (RSEM = 0.8144 V, R2 = 0.8258) and local performance dynamic characteristics which can be used to predict the process of long-term stack performance degradation.

The effect of humidity control on all-thin-film electrochromic devices and their superior sustainable recoverability

In this paper, the all-thin-film electrochromic devices (ECDs) with well-designed structure of glass/ITO/NiOx/Ta2O5/WO3/ITO are fabricated by e-beam evaporation method. In particular, the ECDs are placed in the different-humidity environment to absorb water as the electrolyte. We reported for the first time about the influence of humidity during humidification process on electrochromic performance of the ECDs. The research results demonstrate that the humidity has a significant influence on transmittance modulation and coloration efficiency (CE) of the as-prepared ECDs. The ECD humidified at 50-60% humidity environment shows optimal electrochromic performance containing large optical transmittance modulation (69.1% at 633 nm) and high coloration efficiency (90.74 cm2·C−1 at 633 nm). Furthermore, a novel mechanism, water-decreasing-induced degradation, is proposed to explain the degradation of the ECDs with water as electrolyte during repeated electrochemical cycle. Encouragingly, their electrochromic performance has a significant recovery when the degraded ECDs are humidified again. Importantly, the recovery process can be repeated many times. This means that the electrochromic performance of this ECD is recoverable, and their long-term performance degradation can be successfully avoided. Our results will open avenues for designing and developing superior electrochromic devices.