Proton Conductors: Physics and Technological Advancements for PC-SOFC

Electroceramics are functional materials with a complex interplay between structural, chemical and electrophysical properties. Significant reliability over energy storage and conversion devices has outgrown over the years in search of sustainability. The advent of eco-friendly continuous energy extraction with liberty over fuel flexibility at intermediate temperatures (400–700 °C) reveals the monopoly of proton conductors (PCs) as an effective electrolyte for proton-conducting solid oxide fuel cells (PC-SOFC). They illustrate high operation efficiency (60–80%) and energy density over existing energy storage devices (capacitors, batteries and combustion engines) with a compromise over power density. The electrochemical activity of PCs is in principle different from distinct fuel cells which are categorized on the nature of electrolyte and diffusing charge carriers alongside operating temperature regimes. PC-SOFC thus bridges the research gap between high-temperature (SOFC) and low-temperature (PEMFC) applications. The intermediate operation devoid the use of catalysts for requisite electrochemical kinetics across the electrode–electrolyte interface with simultaneous compatibility of fuel cell’s components. Unlike key limitations in SOFC owing to high operating temperatures, PC-SOFC forbids major limitations. The anti-phase consistency between chemical and electrophysical parameters obstructs the commercialization of PCs for technological advancements. The fundaments of which lie with the physics of structural perturbations and inflexions in charge chemistry. Lower symmetry shifts (distorted structures) although assist unimpeded charge dynamics, yet lag in cooperative chemical compatibility. Attempts of material engineering via heterogeneous impurity substitutions in terms of acceptor dopants at the B-site of perovskite PCs have been executed to pacify the existing trade-off. Compositional-induced charge trapping effect constituted by increasing impurities presents novel material engineering limitations. Thus, preserving the host characteristics with additional improvement in thermal, chemical and electrical properties has recently become the principal motive of research with PCs. Since the charge kinetics is determined at the electrode–electrolyte interface, suitable sealant and blend of composite electrodes with thin epitaxially grown film electrolytes have cultivated a unique research perspective. The chapter encloses the backbone of energy materials for energy conversion devices (fuel cells) with a detailed emphasis on the physics of electrochemistry in perovskite-type PCs (BaCeO3 and BaZrO3). The miscellaneous motive also associates compiled outcomes and a summary of novel constraints (proton trapping effect) associated with material processing and architecture.