In Situ Phase‐Transformation Forming a Bicontinuous (Ni, Co, Ti, and Al)‐Oxide/Li₂CO₃ Interpenetrating Network Electrolyte for Solid Oxide Fuel Cells

Abstract Designing heterogeneous electrolytes with superior interface charge transfer is promising for low‐temperature solid oxide fuel cells (LT‐SOFCs). However, a rational construction with optimal interfaces to maximize ionic conduction remains a challenge. Here an in situ phase‐transformation strategy is demonstrated to prepare a highly conductive heterogeneous electrolyte. A pristine LiNiO₂‐TiO₂ nanocomposite precursor undergoes chemical reactions and phase‐transformation upon heating and feeding H₂, destroying the original phases, and forming new species, including an amorphous Li₂CO₃ scaffold within a (Ni, Co, Al, and Ti)‐oxide (NCAT) matrix. It creates an intertwining and continuous network inside the electrolyte with plentiful interfaces. The in situ formed NCAT/Li₂CO₃ heterogeneous electrolyte displays superior ionic conductivity and impressive fuel cell performance. This work emphasizes the potential of rational heterogeneous structure design and interface engineering for LT‐SOFC electrolyte through an in situ phase‐transform approach. The generated interfaces enhance ion transport, presenting an opportunity for further optimizing electrolyte candidates, and lowering the operating temperatures of SOFCs.