Microwave dielectric ceramics have emerged as highly promising materials for high-frequency applications due to their exceptional dielectric properties. Nevertheless, achieving an optimal balance among the interdependent parameters of relative permittivity (ε_r), quality factor (Q×f), and temperature coefficient of resonant frequency (τ_f) to satisfy the technical requirements of microwave components continues to pose a substantial challenge. In this work, an interpretable machine learning framework was proposed to elucidate the structure–property relationships, thereby guiding the compositional design of the candidate microwave ceramic Ca₃SnSi₂O₉. Based on the machine learning insights, we developed a Ca₃Sn_1−xGe_xSi₂O₉ (0.025 ≤ x ≤ 0.20) ceramic system where controlled Ge⁴⁺ substitution for Sn⁴⁺ was strategically designed to synergistically optimize both Q×f and τ_f values while maintaining low ε_r. This improvement was achieved through the enhanced relative covalency (r_c) of Sn–O and Si–O bonds, along with intensified octahedral distortion (δ) and polyhedral chain angles (σ) in the single-phase Ca₃Sn_1−xGe_xSi₂O₉ ceramics. Remarkably, the Ca₃Sn_1−xGe_xSi₂O₉ (x = 0.05) ceramics demonstrated outstanding performance, exhibiting an ultrahigh Q×f value of 120,413 GHz coupled with a favorably small negative τ_f value of −25.8 ppm/°C. These results clearly demonstrate that the collaborative optimization strategy can significantly enhance the microwave dielectric properties of Ca₃SnSi₂O₉-based ceramics. Furthermore, a single-mode topological metasurface filter operating in the X-band was designed and fabricated using the ultralow dielectric loss Ca₃Sn_1−xGe_xSi₂O₉ (x = 0.05) ceramics. Leveraging the bulk-edge correspondence, we established a relationship between structural morphology with transitional deformations and operating frequency. Experimental results demonstrated that the topological metasurface filter can operate at any frequency within the range of 9.6–10.3 GHz. This advancement extends the potential applications of Ca₃SnSi₂O₉-based ceramics to metasurface filters for high-frequency communication systems.

The electrolysis of natural seawater powered by abundant offshore renewable energy is widely considered as a sustainable hydrogen production technique. However, the competitive chlorine evolution reaction severely damages the catalyst durability in the anodic seawater oxidation. Here, we demonstrate that the in situ chromate cover restructured from a preformed Cr-based metal organic framework (MIL-101(Cr)) stabilizes anodic seawater oxidation while maintaining high activity on an optimized NiFe-layered double hydroxide (NiFe-LDH) array catalyst. Impressively, such a cover enables an over 20-fold reduction in overpotential attenuation rate (0.11 mV·h⁻¹) in comparison to the unmodified NiFe-LDH counterpart (2.38 mV·h⁻¹) against a stable 185 h operation. A combination of experiment studies and theoretical calculations has unveiled that the in situ generated chromate cover weaken unfavorable Cl⁻ adsorption more notably over reactive OH⁻, therefore mitigating the Cl-related corrosion on the NiFe-LDH. The present study advances a stability breakthrough in the feasible implementation of direct seawater electrolysis for sustainable green hydrogen production.

Excellent microwave dielectric properties and ultra-low thermal expansion are essential for dielectric ceramics in high-frequency substrate applications. However, the inherent constraints among these three key microwave dielectric properties make it challenging to achieve ultra-low relative permittivity (ε_r), high quality factor (Q×f), and near-zero temperature coefficient of the resonance frequency (τ_f) values simultaneously in existing materials. In particular, the coefficient of thermal expansion (CTE) of microwave dielectric ceramics often reaches approximately 10 ppm/°C, indicating limited tunability. In this work, based on novel osumilite-type BaMg₂Al₆Si₉O₃₀ ceramics with high crystal structural symmetry and excellent stability, we designed a strategy involving the substitution of Si⁴⁺ with larger Ge⁴⁺ ions. Replacing Si⁴⁺ with larger Ge⁴⁺ ions directly elongated the Si/Al(1)–O bond length while reducing the Si/Al(1)–O(1)–Si/Al(1) angle (σ₂). This structural modification suppressed the longitudinal vibration of 2-coordinate O(1) along the a-axis, effectively inhibiting negative thermal expansion and yielding a reduced CTE within the operational temperature range. Simultaneously, the elongation of the Si/Al(1)–O bond cooperatively increased the Si/Al(1)–O(2)–Si/Al(1) angle (σ₁) and enhanced the relative covalency of the Si/Al(1)–O bond, synergistically improving the Q×f values. Importantly, Ge⁴⁺ substitution preserved ultra-low ε_r and near-zero τ_f values by maintaining the polarization characteristics and crystal structural stability of BaMg₂Al₆Si₉O₃₀-based ceramics. The optimized BaMg₂Al₆Si_7.75Ge_1.25O₃₀ ceramics achieved excellent microwave dielectric properties: ε_r = 5.84, Q×f = 32,351 GHz, τ_f = −7.27 ppm/°C, and an ultra-low CTE of +1.07 ppm/°C. The successful co-regulation of the Q×f and CTE values was attributed to the polyhedral coupling strategy, which leveraged the structural features of the osumilite-type ceramics to synergistically optimize the tilting and distortion of critical polyhedra.

Zn-air batteries (ZABs) as a class of promising energy storage setups are generally powered by efficient and robust catalysts at the oxygen-involving cathode. Although the existing non-noble catalysts have outperformed noble Pt benchmark in the alkaline liquid-state ZABs, to the best of our knowledge few have excelled Pt in quasi-solid-state (QSS) ZABs. Herein, we found that an integrated Mn-Co cathode derived from the bimetallic Mn/Co metal organic frameworks generates a 1.4-fold greater power density in the QSS ZABs than a Pt cathode while its power density in liquid-state ZABs is only 0.8-fold of the latter. Moreover, such Mn-Co catalyst delivers high-rate oxygen reduction reaction (ORR) capability with half-wave potential of 0.84 V. The in-depth characterizations and analyses have demonstrated that the Co and Mn species show the specific affinity towards H₂O and O₂, respectively, synergizing the ORR process in the water-deficient environment of QSS ZABs. This work has enlightened the rational design of non-noble metal catalysts to improve the power density of QSS ZABs.