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<p>Interfacial ionic conduction plays a pivotal role in governing the electrochemical performance of semiconductor-ionic heterostructures for low-temperature solid oxide fuel cells (LT-SOFCs). This study explores a series of heterostructure electrolytes composed of transition-metal doped semiconductor Na<sub>0.7</sub>Co<sub>0.9</sub>M<sub>0.1</sub>O<sub>2−δ</sub> (M = Mn, Fe, Ni, Cu), integrated with ionic conducting Sm<sub>0.2</sub>Ce<sub>0.8</sub>O<sub>2−δ</sub> (SDC). Doping Na<sub>0.7</sub>CoO<sub>2−δ</sub> with the transition metal cation effectively modulates the Fermi-level alignment at the semiconductor-ionic interfaces, inducing localized built-in electric fields that promote interfacial proton transport. Further, the formation of heterostructure enhances the concentration of oxygen vacancies, facilitating both hydration and proton migration processes. The porous nature of LiNi<sub>0.8</sub>Co<sub>0.15</sub>Al<sub>0.05</sub>O<sub>2−δ</sub> (NCAL) electrodes enable capillary diffusion, resulting in Li<sup>+</sup> ion penetration into the electrolyte and leading to the formation of a Li<sup>+</sup>-enriched interfacial region, which serves as a high-speed channel for ion transport. The coexistence of charge species such as Li<sup>+</sup>, LiOH, and Li<sub>2</sub>CO<sub>3</sub> at the interface significantly enhances ionic conductivity by facilitating charge carrier migration predominantly along interfacial pathways rather than through the bulk material. Electrochemical impedance spectroscopy (EIS) demonstrated that the Na<sub>0.7</sub>Co<sub>0.9</sub>Cu<sub>0.1</sub>O<sub>2−δ</sub>-Sm<sub>0.2</sub>Ce<sub>0.8</sub>O<sub>2−δ</sub> heterostructure exhibited superior performance, with an ionic conductivity of 0.287&#xa0;S/cm at 550&#xa0;°C. Notably, proton conductivity increased progressively over time under humidified conditions, indicating enhanced proton transport. The redox behaviour of the transition metal dopants further supports charge compensation during proton incorporation, with Co<sup>3+</sup> demonstrating a higher tendency for oxidation to Co<sup>4+</sup> compared to the Cu<sup>2+</sup>/Cu<sup>3+</sup> redox couple. These findings highlight the efficacy of Na<sub>0.7</sub>Co<sub>0.9</sub>Cu<sub>0.1</sub>O<sub>2−δ</sub>-Sm<sub>0.2</sub>Ce<sub>0.8</sub>O<sub>2−δ</sub> heterostructure as a promising electrolyte material for LT-SOFC, even under low concentration hydrogen.</p> Graphical Abstract <p></p>

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Interfacial ionic transport enhancement via transition-metal doping in Na0.7CoO2−δ-Sm0.2Ce0.8O2−δ heterostructure electrolytes for low-temperature solid oxide fuel cells

  • 期刊论文

  • 发表日期：

    2026年7月9日

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  • S Kalaimathi,
  • K Gunasekaran,
  • Naoki Wakiya,
  • K Suresh Babu

摘要

Interfacial ionic conduction plays a pivotal role in governing the electrochemical performance of semiconductor-ionic heterostructures for low-temperature solid oxide fuel cells (LT-SOFCs). This study explores a series of heterostructure electrolytes composed of transition-metal doped semiconductor Na0.7Co0.9M0.1O2−δ (M = Mn, Fe, Ni, Cu), integrated with ionic conducting Sm0.2Ce0.8O2−δ (SDC). Doping Na0.7CoO2−δ with the transition metal cation effectively modulates the Fermi-level alignment at the semiconductor-ionic interfaces, inducing localized built-in electric fields that promote interfacial proton transport. Further, the formation of heterostructure enhances the concentration of oxygen vacancies, facilitating both hydration and proton migration processes. The porous nature of LiNi0.8Co0.15Al0.05O2−δ (NCAL) electrodes enable capillary diffusion, resulting in Li+ ion penetration into the electrolyte and leading to the formation of a Li+-enriched interfacial region, which serves as a high-speed channel for ion transport. The coexistence of charge species such as Li+, LiOH, and Li2CO3 at the interface significantly enhances ionic conductivity by facilitating charge carrier migration predominantly along interfacial pathways rather than through the bulk material. Electrochemical impedance spectroscopy (EIS) demonstrated that the Na0.7Co0.9Cu0.1O2−δ-Sm0.2Ce0.8O2−δ heterostructure exhibited superior performance, with an ionic conductivity of 0.287 S/cm at 550 °C. Notably, proton conductivity increased progressively over time under humidified conditions, indicating enhanced proton transport. The redox behaviour of the transition metal dopants further supports charge compensation during proton incorporation, with Co3+ demonstrating a higher tendency for oxidation to Co4+ compared to the Cu2+/Cu3+ redox couple. These findings highlight the efficacy of Na0.7Co0.9Cu0.1O2−δ-Sm0.2Ce0.8O2−δ heterostructure as a promising electrolyte material for LT-SOFC, even under low concentration hydrogen.

Graphical Abstract