Technological Challenges and Advancement in Proton Conductors: A Review

Proton conductors (PCs) are multifunctional perovskite materials with structural, electrical, and chemical compatibilities that serve as principal components in proton conducting solid oxide fuel cells (PC-SOFC). The synergetic advantages of PC-SOFC dominate lucrative applications of conventional SOFC. However, adequate advantages accompany certain key limitations in PCs. The inverse interplay between proton conductivity and chemical stability are two broader challenges which demonstrate a clear trade-off. As a consequence, different reactive constituents within the host BaCeO3 and BaZrO3 PCs enforce the gradient in chemical stability under diverse atmospheres, while altered charge chemistry and structural perturbations escalate the activation barrier and impose reduced proton conductivity. Such occurrences are more pronounced in acceptor-doped PCs. Although material engineering via acceptor defect substitutions assists protonation and charge dynamics, on the other hand, it provokes novel challenges (proton trapping effect) at a higher dopant volume fraction beyond the threshold. The principal entropy among chemical and electrophysical parameters is proportionally associated with dopant-incorporated subcategorical material limitations. In this study, a compilation of factors responsible for structural and electrophysical diversities as a consequence of compositional-induced symmetry variations is highlighted with a plausible conclusion and future research perspectives for smart and advanced energy applications.