Developing highly active and stable air electrodes remains challenging for reversible solid oxide cells (R-SOCs). Herein, we report an A-site high-entropy engineered perovskite oxide, La_0.2Pr_0.2Nd_0.2Ba_0.2Sr_0.2Co_0.8Fe_0.2O_3−δ (HE-LSCF), and its electrocatalytic activity and stability property are systematically probed for tubular R-SOCs. The HE-LSCF air electrode exhibits excellent oxygen reduction reaction (ORR) activity with a low polarization resistance of 0.042 Ω·cm² at 700°C, which is much lower than that of La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF), indicating the excellent catalytic activity of HE-LSCF. Meanwhile, the tubular R-SOCs with HE-LSCF shows a high peak power density of 1.18 W·cm⁻² in the fuel cell mode and a promising electrolysis current density of −0.52 A·cm⁻² at 1.5 V in the electrolysis mode with H₂ (∼10% H₂O) atmosphere at 700°C. More importantly, the tubular R-SOCs with HE-LSCF shows favorable stability under 180 h reversible cycling test. Our results show the high-entropy design can significantly enhance the activity and robustness of LSCF electrode for tubular R-SOCs.

Multicomponent Gd_1−xSm_xBa_0.5Sr_0.5CoCuO_5+δ double perovskites are optimized for application in terms of chemical composition and morphology for the use as oxygen electrodes in solid oxide cells. Structural studies of other physicochemical properties are conducted on a series of materials obtained by the sol–gel method with different ratios of Gd and Sm cations. It is documented that changing the x value, and the resulting adjustment of the average ionic radius, have a significant impact on the crystal structure, stability, as well as on the total conductivity and thermomechanical properties of the materials, with the best results obtained for the Gd_0.75Sm_0.25Ba_0.5Sr_0.5CoCuO_5+δ composition. Oxygen electrodes are prepared using the selected compound, allowing to obtain low polarization resistance values, such as 0.086 Ω·cm₂ at 800°C. Systematic studies of electrocatalytic activity are conducted using La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ as the electrolyte for all electrodes, and Ce_0.8Gd_0.2O_2−δ electrolyte for the best performing Gd_0.75Sm_0.25Ba_0.5Sr_0.5CoCuO_5+δ electrodes. The electrochemical data are analyzed using the distribution of relaxation times method. Also, the influence of the preparation method of the electrode material is investigated using the electrospinning technique. Finally, the performance of the Gd_0.75Sm_0.25Ba_0.5Sr_0.5CoCuO_5+δ electrodes is tested in a Ni-YSZ (yttria-stabilized zirconia) anode-supported cell with a Ce_0.8Gd_0.2O_2−δ buffer layer, in the fuel cell and electrolyzer operating modes. With the electrospun electrode, a power density of 462 mW·cm⁻² is obtained at 700°C, with a current density of ca. 0.2 A·cm⁻² at 1.3 V for the electrolysis at the same temperature, indicating better performance compared to the sol–gel-based electrode.

The performance of the fuel electrode in a solid oxide electrolysis cell (SOEC) is crucial to facilitating fuel gas electrolysis and is the key determinant of overall electrolysis efficiency. Nevertheless, the commercialization of integrated CO₂-H₂O electrolysis in SOEC remains constrained by suboptimal catalytic efficiency and long-term stability limitations inherent to conventional fuel electrode architectures. A novel high-entropy Sr₂FeTi_0.2Cr_0.2Mn_0.2Mo_0.2Co_0.2O_6-δ (SFTCMMC) was proposed as a prospective electrode material of co-electrolysis in this work. The physicochemical properties and electrochemical performance in the co-electrolysis reaction were investigated. Full cell is capable of electrolyzing H₂O and CO₂ effectively with an applied voltage. The effects of temperature, H₂O and CO₂ concentrations, and applied voltage on the electrochemical performance of Sc_0.18Zr_0.82O_2-δ (SSZ)-electrolyte supported SOEC were investigated by varying the operating conditions. The SOEC obtains a favorable electrolysis current density of 1.47 A·cm^-2 under co-electrolysis condition at 850°C with 1.5 V. Furthermore, the cell maintains stable performance for 150 h at 1.3 V, and throughout this period, no carbon deposition is detected. The promising findings suggest that the high-entropy SFTCMMC perovskite is a viable fuel electrode candidate for efficient H₂O/CO₂ co-electrolysis.

Low-concentration coal mine methane (LC-CMM), which is predominantly composed of methane, serves as a clean and low-carbon energy resource with significant potential for utilization. Utilizing LC-CMM as fuel for solid oxide fuel cells (SOFCs) represents an efficient and promising strategy for its effective utilization. However, direct application in Ni-based anodes induces carbon deposition, which severely degrades cell performance. Herein, a medium-entropy oxide Sr₂FeNi_0.1Cr_0.3Mn_0.3Mo_0.3O_6−δ (SFNCMM) was developed as an anode internal reforming catalyst. Following reduction treatment, FeNi₃ nano-alloy particles precipitate on the surface of the material, thereby significantly enhancing its catalytic activity for LC-CMM reforming process. The catalyst achieved a methane conversion rate of 53.3%, demonstrating excellent catalytic performance. Electrochemical evaluations revealed that SFNCMM-Gd_0.1Ce_0.9O_2−δ (GDC) with a weight ratio of 7:3 exhibited superior electrochemical performance when employed as the anodic catalytic layer. With H₂ and LC-CMM as fuels, the single cell achieved maximum power densities of 1467.32 and 1116.97 mW·cm⁻² at 800°C, respectively, with corresponding polarization impedances of 0.17 and 1.35 Ω·cm². Furthermore, the single cell maintained stable operation for over 100 h under LC-CMM fueling without significant carbon deposition, confirming its robust resistance to carbon formation. These results underscore the potential of medium-entropy oxides as highly effective catalytic layers for mitigating carbon deposition in SOFCs.

In this study, compositionally complex cobaltites with the general formula BaLnCo₂O_6−δ with three to eight different lanthanides at the Ln-site were synthesized using the solid-state reaction method and studied. Analysis of entropy metrics and configurational entropy calculations indicated that these compounds are medium entropy oxides. All of these crystallize as tetragonal double perovskites from the space group P4/mmm. The unit cell parameters are controlled by the average ionic radius, not the configurational entropy. On the other hand, the oxygen non-stoichiometry is consistently higher than in the case of low entropy double perovskite cobaltites. The total electrical conductivity of all materials in studied conditions is well above 50 S/cm, peaking at 1487 S/cm for BaLa_1/3Nd_1/3Gd_1/3Co₂O_6−δ at 300°C. The electrical conductivity decreases with the number of substituents.

A series of solid solutions with high content of Tb₂O₃–(Tb_xTi_1−x)₄O_8−2x (x = 0.667–0.830) are synthesized in the Tb₂O₃–TiO₂ system via co-precipitation and/or mechanical activation. This is followed by high-temperature annealing for 4–22 h. The X-ray diffraction method showed that the fluorite structure was realized for (Tb_xTi_1−x)₄O_8−2x (x = 0.75–0.817). The solid solution Tb_3.12Ti_0.88O_6.44 (64mol% Tb₂O₃ (x = 0.78)) with a fluorite structure exhibited a maximum hole conductivity of ∼22 S/cm at 600°C. To separate the ionic component of the conductivity in the electronic conductor Tb_3.12Ti_0.88O_6.44, its high entropy analogue, (La_0.2Gd_0.2Tm_0.2Lu_0.2Y_0.2)_3.12Ti_0.88O_6.44, was synthesized in which all rare-earth elements (REE) cations exhibited valency of +3. Consequently, the contribution of ionic (proton) conductivity (∼7 × 10⁻⁶ S/cm at 600°C) was revealed with respect to the background of dominant hole conductivity. The proton conductivity of high-entropy oxide (HEO) (La_0.2Gd_0.2Tm_0.2Lu_0.2Y_0.2)_3.12Ti_0.88O_6.44 was confirmed by the detection of the isotope effect, where the mobility of the heavier O–D ions was lower than that of the O–H hydroxyls, resulting in lower conductivity in D₂O vapors when compared to H₂O.

The commercialization of solid oxide fuel cells depends on the cathode, which possesses both high catalytic activity and a thermal-expansion coefficient (TEC) that aligns with the electrolyte. Although the cobalt-based cathode La_0.6Sr_0.4CoO₃ (LSC) offers excellent catalytic performance, its TEC is significantly larger than that of the electrolyte. In this study, we mechanically mix Sm_0.2Ce_0.8O_2−δ (SDC) with LSC to create a composite cathode. By incorporating 50wt% SDC, the TEC decreases significantly from 18.29 × 10⁻⁶ to 13.90 × 10⁻⁶ K⁻¹. Under thermal-shock conditions ranging from room temperature to 800°C, the growth rate of polarization resistance is only 0.658% per cycle, i.e., merely 49% that of pure LSC. The button cell comprising the LSC-SDC composite cathode operates stably for over 900 h without Sr segregation, with a voltage growth rate of 1.11%/kh. A commercial flat-tube cell (active area: 70 cm²) comprising the LSC-SDC composite cathode delivers 54.8 W at 750°C. The distribution of relaxation-time shows that the non-electrode portion is the main rate-limiting step. This study demonstrates that the LSC-SDC mixture strategy effectively improves the compatibility with the electrolyte while maintaining a high output, thus rendering it a promising commercial cathode material.

Minimizing the thermal expansion coefficient (TEC) mismatch between the cathode and electrolyte in solid oxide fuel cells is crucial for achieving stable, durable operation and high performance. Recently, materials with negative thermal expansion (NTE) have attracted significant attention as effective additives for tailoring the thermomechanical properties of electrodes and enhancing cell durability. In this work, for the first time, single-phase NTE perovskite Sm_0.85Zn_0.15MnO_3−δ (SZM15) was successfully synthesized via the sol–gel method, eliminating the unwanted ZnO phase typically observed in materials obtained through the conventional solid-state reaction route. The sol–gel approach proved highly advantageous, offering low cost, robustness, excellent chemical homogeneity, precise compositional control, and high phase purity. After optimization of synthesis parameters, a negative TEC of approximately −6.5 × 10⁻⁶ K⁻¹ was achieved in the 400–850°C range. SZM15 was then incorporated as an additive (10wt%–50wt%) into a SmBa_0.5Sr_0.5CoCuO_5+δ (SBSCCO) cathode to tune the thermomechanical properties with a La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte, achieving a minimal TEC mismatch of only 1%. Notably, the SBSCCO + 10wt% SZM15 composite cathode exhibited the lowest polarization resistance of 0.019 Ω·cm² at 900°C, showing approximately 70% lower than that of the pristine cathode. Excellent long-term stability after 100 h of operation was achieved. In addition, a high peak power density of 680 mW·cm⁻² was achieved in a Ni-YSZ (yttria-stabilized zirconia)∣YSZ∣Ce_0.9Gd_0.1O_2−δ (GDC10)∣SBSCCO + 10wt% SZM15 anode-supported fuel cell at 850°C, highlighting the effectiveness of incorporating NTE materials as a promising strategy for regulating the thermomechanical properties and improving the long-term stability of intermediate temperature solid oxide fuel cells (IT-SOFCs).

Novel hydrogen storage materials have propelled progress in hydrogen storage technologies. Magnesium hydride (MgH₂) is a highly promising candidate. Nevertheless, several drawbacks, including the need for elevated thermal conditions, sluggish dehydrogenation kinetics, and high thermodynamic stability, limit its practical application. One effective method of addressing these challenges is catalyst doping, which effectively boosts the hydrogen storage capability of Mg-based materials. Herein, we review recent advancements in catalyst-doped MgH₂ composites, with particular focus on multicomponent and high-entropy catalysts. Structure-property relationships and catalytic mechanisms in these doping strategies are also summarized. Finally, based on existing challenges, we discuss future research directions for the development of Mg-based hydrogen storage systems.

Owing to the orbital hybridization between the transition metal and the B element and the electron-trapping effect of the B element, transition metal borides are considered very promising materials for energy catalysis. In this work, an amorphous scaly high-entropy boride (HEB) with electron traps was designed and fabricated via a facile reduction method to improve the hydrogen storage properties of magnesium hydride (MgH₂). For dehydrogenation, the onset temperature of MgH₂ + 10wt% HEB was dropped to 187.4°C; besides, the composite exhibited superior isothermal kinetics and the activation energy of the composite was reduced from (212.78 ± 3.93) to (65.04 ± 2.81) kJ/mol. In addition, MgH₂ + 10wt% HEB could absorb hydrogen at 21.5°C, and 5.02wt% H₂ was charged in 50 min at 75°C. For reversible hydrogen storage capacity tests, the composite maintained a retention rate of 97% with 6.47wt% hydrogen capacity after 30 cycles. Combining microstructure evidence with hydrogen storage performance, the catalytic mechanism was proposed. During ball milling, scaly high-entropy borides riveted a large number of heterogeneous active sites on the surface of MgH₂. Driven by the cocktail effect as well as the orbital hybridization of metal borides, numerous active sites steadily enhanced the hydrogen storage reactions in MgH₂.

The hydrogen storage mechanism of a single-phase nanocrystalline mechanically alloyed Al–Cr–Cu–Fe–Ni high-entropy alloy (HEA) was investigated in this study. The alloys were synthesized from the elemental powders using high-energy attritor ball mill with hexane as the process control agent. The material obtained after 40 h of milling was nanocrystalline and exhibited body-centered cubic (BCC) phase with a lattice parameter of 0.289 nm. The nanocrystalline Al–Cr–Cu–Fe–Ni HEA demonstrated remarkable hydrogen storage capacity at 300°C and 50 atm hydrogen pressure, absorbing 2.1wt% of hydrogen within 3 min and desorbing approximately 1.6wt% of hydrogen in 6 min. These rapid absorption and desorption processes highlighted the efficiency of the alloy for hydrogen uptake and release. Additionally, the alloy exhibited good cyclic stability, with a loss of only 0.2wt% of its hydrogen capacity across 25 cycles. The exceptional cycle stability and rapid kinetics of hydrogen storage and release make the nanocrystalline Al–Cr–Cu–Fe–Ni HEA a viable choice for hydrogen storage applications.

The study investigated the influence of Ce alloying and cold rolling on the activation behavior of V₇₀Ti₁₀Cr₂₀-based alloys. The activation conditions of single cold rolled (V₇₀Ti₁₀Cr₂₀-0.3) and single Ce replaced (V₇₀Ti₁₀Cr₂₀Ce₁) samples were reduced from the original two heat treatments to one heat treatment, and the incubation time was about 105 min. Unexpectedly, the two modification methods produce excellent synergistic effects that the co-modified sample (V₇₀Ti₁₀Cr₂₀Ce₁-0.5) was activated at room temperature (25°C) without incubation period, and reached saturation capacity (4wt%) within 12 min. Further studies show that CeO₂ formed through Ce doping, serves as an active site for hydrogen absorption, facilitating the passage of hydrogen atoms through the dense oxide layer on the surface of vanadium-based alloys. Upon the foundation of Ce doping, cold rolling leads to the aggregation of dislocations around CeO₂ sites, thereby further establishing a hydrogen diffusion pathway from the surface into the bulk phase, thus significantly improving the activation performance of the alloy. This work establishes a robust basis for the practical engineering use of vanadium-based hydrogen storage alloys.

TiFe alloys are AB-based hydrogen storage materials with unique characteristics and a wide range of applications. However, the presence of impurity gases (such as O₂, CO, CO₂, and CH₄) has a considerable impact on the hydrogen storage capacity and kinetics of TiFe alloys, drastically limiting their practical application in hydrogen storage. Consequently, in this study, we investigated the hydrogen absorption kinetics and cycling performance of the TiFe_0.9 alloy in the presence of common impurity gases (including CH₄, CO, CO₂, and O₂) and determined the corresponding poisoning mechanisms. Specifically, we found that CH₄ did not react with the alloy but acted through physical coverage. In contrast, CO and CO₂ occupy the active sites for H₂, significantly impeding the dissociation and absorption of H₂. In addition, O₂ reacts directly with the alloy to form a passivating layer that prevents hydrogen absorption. These findings were further corroborated by in situ Fourier transform infrared spectrometry (FTIR) and density functional theory (DFT). The relationship between the adsorption energies of the impurity gases and hydrogen obtained through DFT calculations complements the experimental results. Understanding these poisoning behaviors is crucial for designing Ti-based high-entropy hydrogen storage alloy alloys with enhanced resistance to poisoning.

The development of efficient and robust oxygen non-precious catalysts for the oxygen evolution reaction (OER) remains a critical scientific hurdle in realizing cost-effective renewable energy conversion systems. Herein, we present a rapid laser irradiation synthesis strategy for the successful fabrication of sub-10 nm FeCoNiMnCr high-entropy alloy nanoparticles (HEA-NPs) on multi-wall carbon nanotube (MWCNT) paper, serving as highly efficient OER electrocatalysts. The synthesis of high-entropy alloy nanoparticles with precise control was accomplished through systematic optimization of laser processing parameters. Structural characterization via X-ray diffraction, high-resolution transmission electron microscopy, and high-angle annular dark-field scanning transmission electron microscopy collectively verified the formation of a phase-pure face-centered cubic crystal structure with homogeneous elemental mixing at the atomic scale. Furthermore, COMSOL Multiphysics simulations confirm that this rapid and discontinuous laser irradiation approach enables the precursor material to undergo ultrafast heating and quenching processes, effectively suppressing Ostwald ripening phenomena, which is conducive to the formation of ultrafine (sub-10 nm) high-entropy alloy nanoparticles. The synthesized HEA-NPs catalyst demonstrates exceptional oxygen evolution activity in alkaline electrolyte (1 M KOH), achieving a current density of 10 mA·cm⁻² at a low overpotential of 255 mV while maintaining remarkable stability with negligible activity decay during prolonged operation (>100 h), representing state-of-the-art performance among non-precious metal catalysts. This study provides perspectives on the rapid preparation and performance regulation of HEA-NPs catalysts.

The development of highly active, durable, and low-cost electrocatalysts is crucial for electrocatalytic hydrogen production. Ultrathin two-dimensional (2D) nanomaterials have extremely large specific surface areas, making them highly desirable electrocatalyst morphologies. Medium-entropy alloys (MEAs) exhibit compositional tunability and entropy-driven structural stability, making them ideal electrocatalyst candidates. In this study, MoCoNi MEA with ultrathin 2D morphology was successfully developed using a facile ionic layer epitaxial method. The ultrathin 2D MoCoNi MEA showed an excellent oxygen evolution reaction (OER) electrocatalytic performance, with a low overpotential of 167 mV at a current density of 10 mA/cm² and small Tafel slope of 33.2 mV/dec. At the overpotential of 167 mV, the ultrathin 2D MoCoNi MEA exhibited ultrahigh mass activity of 3359.6 A/g, which is three orders of magnitude higher than that of the commercial noble metal oxide RuO₂ (1.15 A/g). This excellent electrocatalytic performance was attributed to the synergy of multiple active metal-induced medium entropies, as well as the ultrathin thickness, which considerably shortened the charge-transfer distance and thus significantly promoted charge transfer. Owing to the natural entropy-stabilizing effect, the ultrathin 2D MoCoNi MEA maintained 90% of the initial current after a continuous OER electrocatalytic test for 134 h, showing impressive electrocatalytic stability. This study opens new avenues for the development of high-performance and low-cost electrocatalyst materials by creating MEAs with ultrathin 2D morphology.

High-entropy alloys (HEAs) have emerged as promising catalysts for the hydrogen evolution reaction (HER) due to their compositional diversity and synergistic effects. In this study, machine learning-accelerated density functional theory (DFT) calculations were employed to assess the catalytic performance of PtPd-based HEAs with the formula PtPdXYZ (X, Y, Z = Fe, Co, Ni, Cu, Ru, Rh, Ag, Au; X ≠ Y ≠ Z). Among 56 screened HEA(111) surfaces, PtPdRuCoNi(111) was identified as the most promising, with adsorption energies (E_ads) between −0.50 and −0.60 eV and high d-band center of −1.85 eV, indicating enhanced activity. This surface showed the hydrogen adsorption free energy (ΔG_H*) of −0.03 eV for hydrogen adsorption, outperforming Pt(111) by achieving a better balance between adsorption and desorption. Machine learning models, particularly extreme gradient boosting regression (XGBR), significantly reduced computational costs while maintaining high accuracy (root-mean-square error, RMSE = 0.128 eV). These results demonstrate the potential of HEAs for efficient and sustainable hydrogen production.

High-entropy materials (HEMs), an innovative class of materials with complex stoichiometry, have recently garnered considerable attention in energy storage applications. While their multi-element compositions (five or more principal elements in nearly equiatomic proportions) confer unique advantages such as high configurational entropy, lattice distortion, and synergistic cocktail effects, the fundamental understanding of structure–property relationships in battery systems remains fragmented across existing studies. This review addresses critical research gaps by proposing a multidimensional design paradigm that systematically integrates synergistic mechanisms spanning cathodes, anodes, electrolytes, and electrocatalysts. We provide an in-depth analysis of HEMs’ thermodynamic/kinetic stabilization principles and structure-regulated electrochemical properties, integrating and establishing quantitative correlations between entropy-driven phase stability and charge transport dynamics. By summarizing the performance benchmarking results of lithium/sodium/potassium-ion battery components, we reveal how entropy-mediated structural tailoring enhances cycle stability and ionic conductivity. Notably, we pioneer the systematic association of high-entropy effects to electrochemical interfaces, demonstrating their unique potential in stabilizing solid-electrolyte interphases and suppressing transition metal dissolution. Emerging opportunities in machine learning-driven composition screening and sustainable manufacturing are discussed alongside critical challenges, including performance variability metrics and cost-benefit analysis for industrial implementation. This work provides both fundamental insights and practical guidelines for advancing HEMs toward next-generation battery technologies.

Sodium-ion batteries (SIBs) have recently gained wildly interest due to the abundance of sodium, lower production costs, and better low-temperature performance compared to lithium-ion batteries (LIBs). Among various cathode materials of SIBs, O3-type NaNi_0.4Fe_0.2Mn_0.4O₂ (NFM424) demonstrates high capacity and ease of synthesis, yet suffers from structural degradation and sluggish Na⁺ kinetics caused by large ionic radius and strong electrostatic interactions. To overcome these issues, a configuration strategy combined with TiO₂ and Co₃O₄ by a simple solid-state reaction method was introduced to improve structural and electrochemical stability. XRD, SEM, TEM, and various electrochemical characterizations as well as TGA/DSC tests were conducted. The resulting NaNi_0.4Fe_0.2Mn_0.3Co_0.05Ti_0.05O₂ (NFMCT) cathode mitigated Jahn-Teller distortions and Na⁺/vacancy ordering while enhancing phase integrity and diffusion pathways. The obtained NFMCT maintained 93.7 mAh·g⁻¹ after 550 cycles at 1 C, with superior rate capabilities at 2 C and 5 C. These findings deepen the understanding of configuration strategy by using multi-element oxide and highlight a practical strategy for designing high-performance SIB cathodes.

Despite their attractive features of high energy density, low cost, and safety, polysulfide/iodide flow batteries (SIFBs) are hampered by the sluggish kinetics of the iodide redox couple, which restricts overall performance. Multicomponent sulfides are demonstrated as promising catalysts for accelerating I⁻/I₃⁻ redox reactions. Concurrently, the enhanced configurational entropy arising from multinary compositions drives synergistic effects among constituent elements, establishing a viable pathway to optimize catalytic performance. Building on these foundations, this work introduces a targeted orbital hybridization-optimized electron density strategy to enhance the catalytic activity. Implementing this concept, we developed an in-situ solvothermal synthesis process for an entropy-enhanced AgCuZnSnS₄ loaded graphite felt (ACZTS/GF) electrode. The engineered electrode demonstrates exceptional electrocatalytic performance with improved bulk conductivity and interfacial charge transfer kinetics within a SIFB. The cell achieves a high energy efficiency of 88.5% at 20 mA·cm⁻² with 10% state-of-charge. Furthermore, the battery delivers a maximum power density of 119.8 mW·cm⁻² and exhibits excellent long-term cycling stability. These significant results stem from orbital hybridization-driven electronic state optimization and entropy effect-induced synergistic catalysis.

A high-entropy matrix with highly polarizable elements sharing a rare-earth element at the same crystallographic site was designed using the chemical formula Ba_1/5Pb_1/5Sr_1/5RE_1/5K_1/5TiO₃ (BPSREKTO), where rare-earth (RE) = La, Nb, Sm, Gd, Dy, Ho, Y, and Lu. Single-phase stability was observed only in the BPSREKTO with RE = La, Nd, and Sm high-entropy compounds. The crystal structure, optical properties, and ferroelectric nature of the single-phase ceramic compounds were investigated. Elemental and structural analyses revealed that all the cations were homogeneously distributed in a global centrosymmetric cubic structure (S.G.

). Optical absorption showed that the RE = Nd compound is more photoactive in the 200–1000 nm wavelength range, unlike the RE = La, Sm high-entropy compounds. The introduction of RE elements in high-entropy ceramic (HEC) systems affects the indirect bandgap of BPSREKTO with RE = La, Nd, and Sm. It was also found that cationic disorder increases the Urbach energy, leading to a decrease in the indirect energy bandgap in the HEC compound compared to the homologue BaTiO₃/SrTiO₃ single-phase. The dielectric spectra show a broad peak in the dielectric constant and dielectric loss, which are shifted in temperatures with increasing frequencies due to a relaxor ferroelectric transition typical of the diffuse phase transitions. This relaxor behavior was unexpected, because the global crystal structure was centrosymmetric, implying an increase in the number of polar nanoregions (PNRs). These PNRs coexisting with non-polar regions (NPRs) were observed using piezo-force microscopy. Furthermore, the slim polarization loop confirmed the relaxor behavior of BPSREKTO with RE = La, Nd, and Sm. These ferroelectric features make these RE-modified HEC materials good candidates for high-energy storage applications.