Introduction
The rising global demand for energy, coupled with ambitious decarbonization targets, has catalyzed a significant shift towards more sustainable energy systems. As traditional energy sources increasingly fall out of favor owing to their environmental impacts, the spotlight has turned to more sustainable alternatives that promise not only reduced carbon footprints but also robust reliability and scalability [1, 2]. Among these, nuclear power is particularly promising. Unlike many renewable energy sources, which are often intermittent, such as solar and wind energy, nuclear power offers a steady and reliable flow of energy [3, 4]. Moreover, it does so without the direct emission of greenhouse gases, which are a major contributor to climate change [5]. The role of nuclear energy extends beyond simply providing electricity. It is increasingly regarded as a versatile player in the energy sector, capable of supporting various industrial processes through the generation of combined heat and power [6]. The multipurpose utility of nuclear energy is crucial in the broader context of creating more integrated and efficient energy systems. One of the most significant aspects of nuclear energy’s potential in the modern energy landscape is its ability to produce hydrogen [7].
Hydrogen is increasingly viewed as a critical element for transitioning to a sustainable energy future. It serves as a clean energy carrier, an effective solution for energy storage, and a valuable feedstock for numerous industrial processes [8-10]. Producing hydrogen through nuclear power not only satisfies the energy system’s need for low-carbon solutions but also aligns with global efforts to establish a more sustainable, reliable, and diversified energy supply chain [11].
To harness this potential effectively, advanced nuclear reactor technologies, such as Very High-Temperature Reactors (VHTR), Supercritical Water Reactors (SCWR), and Molten Salt Reactors (MSR), have been developed. These reactors are designed to provide the high-temperature heat necessary for efficient large-scale industrial applications, including hydrogen production [12]. The VHTR is notable for its use of helium as a coolant, which allows it to reach temperatures exceeding 1000 °C. Such high temperatures make VHTRs ideal for thermochemical hydrogen production, a process that can split water into hydrogen and oxygen at high efficiencies [13, 14]. Meanwhile, intermediate-temperature reactors, which operate at lower temperatures than VHTRs, can still play a pivotal role in hydrogen production through technologies such as Solid Oxide Electrolysis Cells (SOEC) [7, 15]. SOECs are a compelling technology for hydrogen production, capable of leveraging both electrical and thermal energy produced by nuclear reactors. These cells operate more efficiently at higher temperatures, which enhances their reaction kinetics, making them a promising option for sustainable hydrogen production [16]. In recognition of their potential, the European Union has funded numerous projects under the Hydrogen Joint Undertaking (FCH-JU) to advance SOEC technology and integrate it with existing energy systems [17, 18].
Research on SOECs and their integration with nuclear power has been ongoing for several years. In 2003, the Idaho National Laboratory initiated a significant project to explore the possibilities of hybrid nuclear energy systems incorporating SOECs [19, 20]. Various studies have examined system efficiencies under different operational conditions and system setups. For instance, Peters et al. [21] examined the efficiencies of SOEC systems when they were integrated with external heat sources. Their findings indicated that efficiencies could vary from 90% to 104%, depending on the configuration and operation of the system. Similarly, Milewski et al. [22] explored the integration of protonic and ionic SOECs with nuclear reactors, calculating the energy consumption for hydrogen production to be 38.83 and 37.55 kWh kg-1 respectively, which they found to be significantly efficient. Further studies, such as those by Fütterer et al. [23] within the European GEMINI+ project, have examined the coupling of high-temperature gas-cooled reactor (HTGR) power plants with SOECs. Their research suggested that extending the service life of SOECs could significantly enhance the feasibility and efficiency of such hybrid energy systems. Yalamati et al.[24] posited that the efficiency of SOECs depends on the nuclear heat source used. They suggested that utilizing both electricity and waste heat from nuclear power plants could elevate the hydrogen production efficiency of SOECs to as much as 60%. Moreover, Zhang et al. [25] calculated the thermo-hydrogen conversion efficiency for different coupling methods, finding when all the heat for SOECs is provided by a nuclear reactor, the highest thermo-hydrogen conversion efficiency is achieved with the nuclear reactor’s outlet temperature at 900 °C.
Most research has been focused on anode-supported and electrolyte-supported SOECs operating at temperatures above 750 °C, whereas the outlet temperature of the MSR is below 700 °C [26]. Considering that direct coupling offers significant advantages for large-scale hydrogen production, the outlet steam temperature of the nuclear reactor should exceed the operating temperature of the SOEC [25]. In this situation, acting as a high-temperature heat source, nuclear waste heat can be used for heating the SOEC module, gas preheating, and water vaporization processes [4]. To align with the outlet temperature of the MSR, the working temperature of the SOEC should be lowered to a medium temperature range, approximately 650 °C.
Although when SOEC operation is advantageous at high temperatures (>800 °C), it can introduce challenges [27]. One of the primary issues at these temperatures is the mutual diffusion of the components within the electrolysis cell. High temperatures can cause materials within the cell to intermingle at the molecular level, potentially leading to degradation of the cell’s structural integrity over time. This can result in a loss of efficiency and shorter operational lifespan of the cell. In addition, particle aggregation is a significant concern. At high temperatures, the particles within the cell materials can start to clump together, which can affect the cell performance by altering the material properties crucial for efficient operation. Another significant challenge is the selection of appropriate sealants. Sealants play a critical role in maintaining the integrity of SOECs by ensuring that the separate components of the cell are adequately sealed and do not leak. At high temperatures, finding materials that can withstand heat and maintain a robust seal is difficult. Many commonly used sealant materials either degrade or lose their sealing properties at high temperatures, posing a substantial challenge to maintenance of the overall effectiveness and safety of the system. In response to these high-temperature challenges, there has been a shift in focus towards developing intermediate-temperature SOECs (IT-SOECs) operating at approximately 650 °C. IT-SOECs offer a promising alternative that significantly mitigates the issues associated with high-temperature operations. Lower to medium temperatures impose reduced demands on connectors and seals in the fuel cell stack, aligning with the trend towards mid- to low-temperature transformation of SOEC [28].
Considering that the efficiency and return on investment of hybrid energy systems are constrained by the short service life of SOECs, investigating the long-term stability of SOECs at intermediate temperatures is crucial. The objective of this study is to reveal the alterations in the electrochemical behavior of the cell through stability tests on commercial Ni-YSZ|YSZ|GDC|LSC planar cells, specifically targeting electrolysis at 650 °C. Through the voltage-over-time curve and post-testing microscopic analysis, the degradation mechanisms within various components of the cell under intermediate temperatures were explored. Extensive research and development in this field highlight the synergy between nuclear power and hydrogen production as a beacon of hope for a more sustainable energy future. By leveraging advanced nuclear technologies and innovative hydrogen production methods, such as SOECs, we can move closer to achieving a low-carbon, high-efficiency energy system that not only meets global energy demands but also adheres to stringent environmental standards.
Experimental
Description of the hybrid energy system
The schematic depicted in Fig. 1 illustrates a nuclear-powered hydrogen production system in which the primary energy source is the MSR. In this system, the coolant salt heated in the MSR core is directed into a heat exchanger. This is a crucial step because the heat exchanger plays a pivotal role in transferring the immense thermal energy carried by the coolant salt to other parts of the system. Following the heat exchange process, thermal energy facilitates electricity generation via a turbine and generator setup. The electricity produced is then strategically distributed to serve two purposes. First, a portion of this electricity is fed into the electrical grid, contributing to the general power supply. Second, the remaining electricity is specifically allocated to power SOECs, which are tasked with the electrolysis of water, a key step in hydrogen production. Additionally, this electricity ensures the smooth functioning of various system components, including pumps, separators, and compressors, which are essential for maintaining operational continuity and system integrity of the system.
The exchanged heat is utilized for heating the SOEC module, gas preheating, and water vaporization processes, all of which are essential in the hydrogen production pathway. Notably, the gas produced by the SOEC still possesses a high heat value, which is subsequently released to processes such as water vaporization through another heat exchanger, a step that is simplified in the diagram. The repurposing of waste heat significantly enhances the thermal efficiency of the system.
In the system shown in Fig. 1, the heating of the SOEC module, water vaporization, and gas superheating are powered by waste heat from the MSR. Within this framework, only the electricity required for the operation of the SOEC for water electrolysis (Pele) and the power needed to run other components, such as pumps and compressors (Pother), are supplied by the electricity generated by the MSR. This design effectively utilizes the thermal energy of the MSR for process heating, thereby optimizing the energy efficiency of the system by repurposing waste heat for critical thermal processes, while relying on the MSR-generated electricity for operations that require it. This integrated approach enhances the overall energy efficiency and sustainability of the hydrogen production process, and the corresponding efficiency is calculated as Eq. (1) [25]:
The cell and the test system
In this study, the examination was carried out on commercial fuel electrode-supported cells, with detailed specifics on cell preparation documented in preceding articles [16]. As presented in Fig. 2, a detailed exploration of the cell cross-sectional microstructure was performed using scanning electron microscopy (SEM), providing a comprehensive understanding of the material interfaces and layer continuity, which are essential for optimizing cell performance. At the bottom is a support layer for the fuel electrode, typically comprising approximately 400 μm of Ni/3YSZ (yttria-stabilized zirconia). The substantial thickness of approximately 400 μm ensures mechanical robustness, allowing the cell to withstand the stresses encountered during operation at elevated temperatures and the dynamic conditions of electrolysis. This support layer is complemented by an active fuel electrode layer, featuring a Ni/8YSZ composition with a thickness of approximately 12 μm. A thinner active fuel electrode layer is tailored for enhanced catalytic activity and increased ionic conductivity, which are crucial for the electrolysis process. An in-depth analysis further reveals the presence of a 3 μm electrolyte layer, the very thin electrolyte is critical for maintaining high ionic conductivity while ensuring minimal electronic leakage. The thinness of the layer substantially reduces the ohmic losses, which ensures the attainment of high current densities at the relatively lower operational temperature of 650 °C. This is followed by a 3 μm gadolinium-doped ceria (GDC) barrier layer, which plays an integral role in mitigating chemical reactivity and inter-diffusion issues between the YSZ electrolyte and the
To align with the outlet temperature of the molten salt nuclear reactor, which is below 700 °C [26], the operating temperature of the SOEC was reduced to approximately 650 °C. Consequently, in this study, we placed the electrolysis cell in a furnace set to 650 °C to simulate the coupling of the SOEC with the MSR. The electrochemical performance of the cell was evaluated using a custom-designed integrated testing station. As shown in Fig. 3, this setup was meticulously engineered to provide a highly controlled environment, essential for achieving reproducible and precise electrochemical measurements. The gas supply system is critical because it manages the feed gases of both electrodes (typically hydrogen, steam, and air) involved in the electrolysis process. The precision in controlling these gas flows was achieved using high-quality mass flow controllers, which are essential for maintaining the desired gas compositions and ratios. The gas composition for the fuel electrode in our experiments was 80% steam and 20% hydrogen. Specifically, the flow rates were 230 ml min-1 for steam and 58 ml min-1 for hydrogen, with hydrogen serving as a protective gas to prevent Ni oxidation. On the oxygen electrode side, pure air was supplied at a flow rate of 1152 ml min-1. The core of the testing station is its ability to perform various electrochemical tests, such as Electrochemical Impedance Spectroscopy (EIS), current-voltage (I-V) measurements, and durability testing. These tests are instrumental in evaluating cell performance under different operational conditions. In addition, accurate temperature control via a thermal management system is indispensable. The design of this testing system ensures the reliability and reproducibility of the electrolysis process, as detailed in previous studies [16].
The cell and the test system
Experimental assessments involved current-voltage polarization curves to explore the initial performance of the cell. The fuel electrode was supplied with a steam content of 80%, while the operating temperature was varied between 600, 650, 700, and 750 °C to investigate the temperature’s impact on SOEC performance. Stability testing over prolonged periods is crucial for understanding the operational viability of SOEC in specific applications. Subsequently, a current density of -0.5 A cm-2 was applied to the cell at a temperature of 650 °C to explore its stability. The steam content was maintained at 80%, and this steam partial pressure was considered to increase the cell voltage and gas diffusion impedance [29, 30].
To gain insights into the degradation mechanism of the electrolysis cell, post-test characterization was performed. Scanning electron microscopy (SEM, Carl Zeiss, Germany) and energy dispersive spectrometry (EDS, Zeiss Merlin Compact, Germany) were employed to analyze the microstructure and composition of the cell denoted as “aging cell", which was subjected to a stability test for 1800 h. SEM analysis provided detailed insights into the morphological changes that occurred during long-term operation. EDS analysis further complemented these findings by revealing compositional shifts, such as the depletion of active elements and the formation of secondary phases, which could negatively affect the electrochemical performance of the cell. A reference electrolysis cell from the same production batch, subjected only to reduction, served as a comparison point. The reference cell maintained its original microstructural and compositional integrity during cycling. Comparing the aging cell with the reference specimen allowed for a clearer understanding of the degradation processes, thereby highlighting the extent of degradation in the aged cell.
Results and discussion
Initial performance and evolution of the cell
The initial experiments, conducted through current-voltage (I-V) polarization tests, as depicted in Fig. 4a, provided crucial data on the electrochemical behavior of the SOEC under operational conditions. These tests serve to establish a baseline from which the durability and long-term stability of the cells can be assessed. The current-voltage (I-V) polarization curves were tested under a steam flow rate of 230 ml min-1 at the fuel electrode and 1152 ml min-1 of air at the air electrode. The cell’s performance varied across a temperature range from 600 °C to 750 °C, demonstrating an inverse relationship between temperature and the open circuit voltage, coherent with the predictions from the Nernst equation, which could be formulated as [31]:
At higher temperatures of 750 °C and 700 °C, the I-V curves showed current limitations, where the voltage increased disproportionately relative to the current density, indicating non-linear characteristics. This behavior, specifically the turning points at a steam conversion of 48.48%, is likely due to concentration polarization caused by limitations in gas diffusion [31]. At these higher operational temperatures, the kinetic processes may be enhanced, but the physical transport of reactants to the three-phase boundary (TPB) becomes a limiting factor.
Although the electrolysis cell could attain a higher electrolysis current density and hydrogen production efficiency at elevated temperatures. In this study, a temperature of 650 °C was chosen to align with the temperature range associated with nuclear reactor outlet temperatures. At 650 °C, the I-V curve showed a linear relationship, suggesting an adequate gas supply for efficient electrolysis.
Figure 4b shows the Electrochemical Impedance Spectroscopy (EIS) results at different temperatures and provides critical insights into how temperature affects the cell efficiency. The data show that lower temperatures increase both the Ohmic and Polarization impedances within the electrolysis cell. This is attributed to the pronounced effects of temperature on oxygen ion transport kinetics within the electrolyte, the catalytic effectiveness of nickel (Ni), and the charge transfer dynamics at the TPB [32, 33]. Temperature significantly influences the mobility of oxygen ions in the electrolyte. Lower temperatures tend to slow down the kinetics, leading to higher impedance as the ionic conductivity decreases at lower temperatures. Furthermore, Nickel, which is commonly used as a fuel electrode material in SOECs, exhibits decreased catalytic activity at lower temperatures. This reduction in activity impairs the overall efficiency of the electrochemical reactions, particularly the hydrogen evolution reaction. The TPB, where the electrolyte, electrode, and gas phase meet, is crucial for effective charge transfer. At lower temperatures, the charge transfer dynamics are hindered, contributing to an increase in the polarization impedance.
The specific values reported, such as the Ohmic impedance of 0.22 Ω and polarization impedance of 0.14 Ω at 650 °C highlight the more favorable conditions at this temperature compared to lower temperatures like 600 °C, where a significantly increased impedance arc is noted for the charge transfer reaction at the fuel electrode. This suggests that 650 °C may be more suitable for long-term stability research of the cell, as it provides better conductivity and catalytic activity at the temperature window for coupling SOEC with MSR, minimizing the losses associated with impedance, and enhancing overall cell performance.
The long-term stability of Solid Oxide Electrolysis Cells (SOECs) is crucial for their practical application, particularly in coupling with nuclear energy systems for hydrogen production. Figure 5 presents the voltage-time (V-T) curve of the SOEC operating in the galvanostatic mode, offering insights into its performance and degradation behavior over an extended period. The stability test was conducted at -8 A (-0.5 A cm-2) and 650 °C, with the same atmosphere as the initial performance test. The electrolysis cell demonstrated stable operation in the SOEC mode for more than 1800 h. The V-T curve can be divided into three distinct phases, each characterized by a different degradation rate. During the initial 90 h, the curve fitting of voltage versus time yielded a slope of approximately -3.604 × 10-5, indicating a degradation rate of -3.42% kh-1 over this period. The negative slope indicates a decrease in degradation, suggesting an activation process in which the cell components stabilize and improve their performance [33]. In the following phase, spanning from 90 h to 1120 h, the voltage of the electrolysis cell increased from 1.101 V to 1.136 V, representing a linear degradation rate of approximately 3.58% kh-1. This phase is marked by a rapid decay process, reflecting a period of significant degradation, as reported by Wang et al. [16, 34]. Throughout the steady decay period from 1120 h to 1818 h, the voltage of the electrolysis cell continued to increase, although at a slower rate than that in the previous phase. The average degradation rate during this phase was calculated to be 2.14% kh-1. The reduction in the slope of the voltage curve indicates a transition to a more stable degradation phase. This steady decay period aligns with the patterns reported in Ref. [35], characterized by a slower, more consistent rate of degradation. Consequently, the long-term stability exhibited by the SOEC in this study suggests substantial potential for its use in coupling with nuclear energy systems for water electrolysis applications. The relatively low degradation rates, especially during the steady decay phase, indicate that SOECs can maintain their efficiency over extended periods, making them suitable for continuous hydrogen production applications.
Post-test analysis of cells
In studies of SOEC operating at intermediate temperatures, one critical aspect is understanding the factors contributing to cell degradation. To this end, SEM and EDS were employed to analyze the microstructure and elemental distribution of the tested cells. This approach enabled a comprehensive examination of both the physical and chemical changes occurring in the fuel electrode over time. Figure 6 presents cross-sectional SEM images, depicting the morphology of the SOEC before and after stability testing. In contrast to the blocky structure of Ni-YSZ shown in Fig. 6a, significant microstructural changes were observed in the Ni-YSZ layer after long-term testing (Fig. 6b). Within the Ni-YSZ functional layer of the post-testing fuel electrode, numerous particles with a diameter of approximately 100 nm were observed near the electrolyte interface. The presence of these particles indicates significant microstructural alterations that could impact the overall performance and stability of SOECs [36, 37]. Additionally, the SEM images highlighted the presence of microcracks and voids between the electrolyte layer and the GDC barrier. These defects can impede ionic conductivity and exacerbate degradation processes, leading to a further decline in cell efficiency [38]. Furthermore, the dense layer found between the electrolyte layer and GDC barrier layer may be indicative of secondary phase formation, possibly resulting from interactions between the electrode materials and electrolyte. These phases could contribute to degradation by introducing additional resistive interfaces within the cell, thus impacting the overall electrochemical performance [39].
Further analysis was conducted on the Ni-YSZ fuel electrode of the cell after long-term stability testing, as shown in Fig. 7. The SEM and EDS results of the Ni-YSZ fuel electrode showed no obvious Ni migration during this process. Ni migration within SOECs is a multifaceted phenomenon influenced by several factors, including the electrolysis current density, electric field strength and distribution caused by Ni distribution, concentration gradients of hydrogen and steam, and temperature gradients [40]. This complex process lacks a definitive mechanistic explanation owing to the interplay of various factors. The absence of pronounced Ni migration despite 1800 operational hours in this study suggests that the conditions within the cell might not have reached the thresholds required for significant Ni migration, or that the migration rate was too slow to be detected. This finding is critical because it indicates that the stability of the Ni-YSZ can be maintained under certain operational conditions, potentially leading to longer cell lifetimes.
EDS analysis revealed the presence of minute nickel-containing particles, as evidenced by the EDS mapping results shown in Fig. 8. Mogensen et al. [41, 42] attributed the migration dynamics of nickel (Ni) to the generation of Ni(OH)x volatile species diffusing by the vapor pressure gradient. Specifically, under conditions of elevated water vapor pressure (
EDS point scanning of both the small-particle aggregation region and the block-like area, as shown in Fig. 9, provides significant insights into the distribution and migration of Ni within the SOEC structure. The EDS point-scanning results revealed a stark contrast in the Ni content between these regions, with a 6.67% Ni content in the blocky region and a significantly higher 73.56% Ni content in the particle agglomeration area. This analysis provides further support for previous observations and analyses, highlighting the complexity of Ni migration within SOECs and underscoring the need for further research to understand and mitigate Ni migration. By optimizing the operational parameters, conducting in-depth microstructural analyses, and exploring material innovations, the stability and performance of SOECs can be enhanced.
Microstructural analysis of the oxygen electrode post-electrolysis was performed using SEM and EDS. The investigation uncovered changes and potential degradation mechanisms within the SOEC, which could significantly affect its performance and durability. The SEM images shown in Fig. 10 reveal the presence of microcracks at the interface between the oxygen electrode and electrolyte. These cracks undermine the mechanical stability of SOEC and lead to further degradation under operational stresses, accelerating cell degradation [38]. In addition, the SEM images show the formation of a dense layer at the interface, likely resulting from Sr segregation. The dense layer identified through EDS mapping is likely composed of strontium-containing phases, such as SrZrO3. SrZrO3 is an electrical insulator with poor ionic conductivity, measured at 1.87×10-6 S cm-1 at 800 °C [43]. The formation of the SrZrO3 phase at the electrode/electrolyte interface can obstruct ion migration [44]. Additionally, the diffusion of Sr to the YSZ surfaces results in Sr depletion in the LSC oxygen electrode, promoting the formation of Sr-free LaCoO3, which has significantly reduced electrocatalytic activity for the oxygen reduction reaction (ORR) [45]. The emergence of these Sr-containing high-resistance phases, along with potential electrolyte cracking, is expected to increase the overall resistance of the electrolysis cell [46, 47]. Increased resistance leads to higher energy losses and decreased efficiency, posing significant challenges for long-term operations.
In the SOEC analysis, EDS mapping indicated that Sr segregation towards the cell surface was not significant. To gain a deeper understanding of the surface chemistry and potential segregation phenomena, XPS was employed to examine the chemical composition and environment, particularly the oxidation state of Sr, in both reference and aged SOECs. The results, depicted in Fig. 11, show the photoelectron spectra of Sr 3d for the two samples, along with the corresponding Sr elemental percentages.
Figure 11a illustrates the fitting results of the Sr 3d peak for the reference cell, whereas Fig. 11b shows the fitting outcomes for the aged sample. The Sr 3d energy level exhibited a dual state. The low binding energy (BE) state of
This outcome implies that, despite the absence of significant differences in intensity in the EDS mapping, there is an increased tendency for Sr segregation towards the surface of the electrolysis cell after 1818 h of operation.
Sr segregation in LSC electrodes is a well-documented phenomenon, influenced by factors such as material stoichiometry [51], strain [52], temperature [51], oxygen partial pressure [53], LSC microstructure [54], and electrochemical polarization [55]. In this study, the relatively mild electrolysis conditions suggest that Sr segregation to the LSC electrode surface is likely driven by the reaction of Sr with atmospheric CO2 or H2O, forming stable compounds such as SrCO3 and Sr(OH)2. These compounds are more stable at the surface, thereby promoting the migration of Sr from the bulk material to the surface [47].
Conclusion
To achieve direct coupling between an MSR and SOEC, the robust stability of the SOEC below the outlet temperature of the nuclear reactor is required. Stability tests were conducted on fuel electrode support cells featuring a Ni-YSZ|YSZ|GDC|LSC architecture at 650 °C, employing a current density of -0.5 A cm-2. Throughout the testing period from 90 h to 1818 h, an average voltage degradation rate of 2.63% kh-1 was observed. This degradation process unfolded in distinct stages, encompassing an initial rapid decay phase from 90 to 1120 hours, characterized by a degradation rate of 3.58% kh-1. Subsequently, a stable decay process ensued from 1120 to 1818 hours, maintaining a decay rate of 2.14% kh-1. These results indicate the viability of SOECs for direct coupling with MSRs at intermediate temperatures, exhibiting a minor voltage degradation rate at 650 °C and demonstrating commendable long-term stability.
Following an electrolysis duration of 1818 h, minute nickel particles were observed within the Ni-YSZ fuel electrode, possibly associated with the diffusion and subsequent re-deposition of Ni(OH)x. Concurrently, a compact strontium-containing layer formed at the interface between the oxygen electrode and electrolyte, leading to interface microcracking. Although pronounced Sr segregation to the surface was not evident in the EDS analyses, the XPS data calculations revealed a tendency for Sr surface segregation.
To further improve the stability of the cell and enhance the efficiency and economic return of the hybrid energy system, efforts should be focused on mitigating Ni migration in the fuel electrode and preventing Sr segregation in the oxygen electrode. Strategies to address these issues may include optimizing material compositions, refining microstructural designs, and controlling operational parameters to reduce the impact of degradation mechanisms.
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. J. Phys. Chem. Lett. 3, 40–44 2012). https://doi.org/10.1021/jz201523yJian-Qiang Wang is an editorial board member for Nuclear Science and Techniques and was not involved in the editorial review, or the decision to publish this article. All authors declare that there are no competing interests.