Achieving fast ionic conductivity in the electrolyte at low operating temperatures while maintaining the stable and high electrochemical performance of solid oxide fuel cells (SOFCs) is challenging. Herein, we propose a new type of electrolyte based on perovskite Sr_0.5Pr_0.5Fe_0.4Ti_0.6O_3-δ for low-temperature SOFCs. The ionic conducting behavior of the electrolyte is modulated using Mg doping, and three different Sr_0.5Pr_0.5Fe_0.4-xMg_xTi_0.6O_3-δ (x = 0, 0.1, and 0.2) samples are prepared. The synthesized Sr_0.5Pr_0.5Fe_0.2Mg_0.2Ti_0.6O_3-δ (SPFMg_0.2T) proved to be an optimal electrolyte material, exhibiting a high ionic conductivity of 0.133 S cm^-1 along with an attractive fuel cell performance of 0.83 W cm^-2 at 520 °C. We proved that a proper amount of Mg doping (20%) contributes to the creation of an adequate number of oxygen vacancies, which facilitates the fast transport of the oxide ions. Considering its rapid oxide ion transport, the prepared SPFMg_0.2T presented heterostructure characteristics in the form of an insulating core and superionic conduction via surface layers. In addition, the effect of Mg doping is intensively investigated to tune the band structure for the transport of charged species. Meanwhile, the concept of energy band alignment is employed to interpret the working principle of the proposed electrolyte. Moreover, the density functional theory is utilized to determine the perovskite structures of SrTiO_3-δ and Sr_0.5Pr_0.5Fe_0.4-xMg_xTi_0.6O_3-δ (x = 0, 0.1, and 0.2) and their electronic states. Further, the SPFMg_0.2T with 20% Mg doping exhibited low dissociation energy, which ensures the fast and high ionic conduction in the electrolyte. Inclusively, Sr_0.5Pr_0.5Fe_0.4Ti_0.6O_3-δ is a promising electrolyte for SOFCs, and its performance can be efficiently boosted via Mg doping to modulate the energy band structure.

Extending the ionic conductivity is the pre‐requisite of electrolytes in fuel cell technology for high‐electrochemical performance. In this regard, the introduction of semiconductor‐oxide materials and the approach of heterostructure formation by modulating energy bands to enhance ionic conduction acting as an electrolyte in fuel cell‐device. Semiconductor (n‐type; SnO₂) plays a key role by introducing into p‐type SrFe_0.2Ti_0.8O_3‐δ (SFT) semiconductor perovskite materials to construct p‐n heterojunction for high ionic conductivity. Therefore, two different composites of SFT and SnO₂ are constructed by gluing p‐ and n‐type SFT‐SnO₂, where the optimal composition of SFT‐SnO₂ (6:4) heterostructure electrolyte‐based fuel cell achieved excellent ionic conductivity 0.24 S cm⁻¹ with power‐output of 1004 mW cm⁻² and high OCV 1.12 V at a low operational temperature of 500 °C. The high power‐output and significant ionic conductivity with durable operation of 54 h are accredited to SFT‐SnO₂ heterojunction formation including interfacial conduction assisted by a built‐in electric field in fuel cell device. Moreover, the fuel conversion efficiency and considerable Faradaic efficiency reveal the compatibility of SFT‐SnO₂ heterostructure electrolyte and ruled‐out short‐circuiting issue. Further, the first principle calculation provides sufficient information on structure optimization and energy‐band structure modulation of SFT‐SnO₂. This strategy will provide new insight into semiconductor‐based fuel cell technology to design novel electrolytes.

Recently, semiconductor-ionic materials (SIMs) have emerged as new functional materials, which possessed high ionic conductivity with successful applications as the electrolyte in advanced low-temperature solid oxide fuel cells (LT-SOFCs). In order to reveal the ion-conducting mechanism in SIM, a typical SIM pellet consisted of semiconductor La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and ionic conductor Sm and Ca Co-doped ceria Ce0.8Sm0.05Ca0.15O2-δ (SCDC) are suffered from sintering at different temperatures. It has been found that the performance of LSCF-SCDC electrolyte fuel cell decreases with the sintering temperature, the cell assembled from LSCF-SCDC pellet sintered at 600 °C exhibits a peak power density (Pmax) of 543 mW/cm2 at 550 °C and also excellent performance of 312 mW/cm2 even at LT (500 °C). On the contrary, devices based on 1000 °C pellet presented a poor Pmax of 106 mW/cm2. The performance difference may result from the diverse ionic conductivity of SIM pellet through different temperatures sintering. The high-temperature sintering could severely destroy the interface between SCDC and LSCF, which provide fast transport pathways for oxygen ions conduction. Such phenomenon provides direct and strong evidence for the interfacial conduction in LSCF-SCDC SIMs.

Operating within the 300–500 °C range, low‐temperature solid oxide fuel cells (LT‐SOFCs) enable efficient and sustainable energy conversion, addressing the limitations of conventional high‐temperature SOFCs. However, achieving >0.1 S cm ⁻¹ ionic conductivity in electrolytes remains challenging. Here, a novel approach utilizing CuO self‐nucleation and electron‐ion (E‐I) coupling in x CuO/(1‐ x ) CeO ₂ (CCO) semiconductor ionic membranes ( x = 0–0.4) is presented. At the optimal 0.2CuO/0.8CeO ₂ composition, ionic conductivity exceeds 0.15 S cm ⁻¹ , driven by E‐I coupling at the CuO/CeO ₂ heterojunction. This coupling creates a built‐in electric field (BIEF) via interfacial charge transfer, facilitating ion transport by lowering the activation energy for ion migration. The dual‐conduction pathway enabled by E‐I coupling not only facilitates electronic transfer and ionic transport but also optimizes charge transfer kinetics, achieving exceptional power densities of 750–900 mW cm ⁻² at 500–550 °C and 78 mW cm ⁻² at 300 °C. Density functional theory (DFT) calculations further validate the role of Cu ²⁺ and Ce ⁴⁺ valence states in generating interfacial charge transfer and enhancing ionic mobility. This innovative approach positions CuO/CeO ₂ as a state‐of‐the‐art electrolyte, building the critical conductivity‐performance gap in LT‐SOFCs. This study pioneers LT‐SOFC innovation by leveraging E‐I coupling and electrode–electrolyte synergy, unlocking superior ion transport and practical applicability.

The introduction of heterostructures is a new approach in gas sensing due to their easy and quick transport of charges. Herein, facile hydrothermal and solid-state techniques are employed to synthesize an α -Fe ₂ O ₃ /Nb ₂ O ₅ heterostructure. The morphology, microstructure, crystallinity and surface composition of the synthesized heterostructures are investigated by scanning electron microscope, transmission electron microscope, x-ray diffraction, x-ray photoelectron spectroscopy and Brunauer–Emmett–Teller analyses. The successful fabrication of the heterostructures was achieved via the mutual incorporation of α -Fe ₂ O ₃ nanorods with Nb ₂ O ₅ interconnected nanoparticles (INPs). A sensor based on the α -Fe ₂ O ₃ (0.09)/Nb ₂ O ₅ heterostructure with a high surface area exhibited enhanced gas-sensing features, maintaining high selectivity and sensitivity, and a considerable recovery percentage towards ethanol gas. The sensing response of the α -Fe ₂ O ₃ (0.09)/Nb ₂ O ₅ heterostructure at lower operating temperature (160 °C) is around nine times higher than a pure Nb ₂ O ₅ (INP) sensor at 180 °C with the flow of 100 ppm ethanol gas. The sensors also show excellent selectivity, good long-term stability and a rapid response/recovery time (8s/2s, respectively) to ethanol. The superior electronic conductivity and upgraded sensitivity performance of gas sensors based on the α -Fe ₂ O ₃ (0.09)/Nb ₂ O ₅ heterostructure are attributed due to its unique structural features, high specific surface area and the synergic effect of the n–n heterojunction. The promising results demonstrate the potential application of the α -Fe ₂ O ₃ (0.09)/Nb ₂ O ₅ heterostructure as a good sensing material for the fabrication of ethanol sensors.