Factors Constituting Proton Trapping in BaCeO₃ and BaZrO₃ Perovskite Proton Conductors in Fuel Cell Technology: A Review

Abstract

Urbanization with increasing demand for energy at a rapid pace has prompted researchers to explore effective and efficient energy storage technology. Fuel cells, being well-known among other existing devices, are categorized based on the nature of the electrolyte employed. In several areas, proton conduction solid oxide fuel cells have surpassed conventional solid oxide fuel cells. Nonetheless, there still prevail drawbacks accompanied with the proton-conducting electrolyte materials. However, the disadvantages associated with proton-conducting electrolytic materials persists. Besides chemical stability, one of the significant concerns is the fluctuation in proton conductivity among acceptor-doped compositions. Recent introspection interprets the proton trapping effect in the vicinity of the substituent attenuating proton mobility, the fundamentals of which point toward a proton-dopant complex interaction and altering basicity of the dopant neighboring oxygen atoms, escalating the activation energy. This implies a pronounced affinity of proton-trapped sites in the close coordination of the acceptor dopant while implying trap-free sites elsewhere. In the following review article, we direct our attention to the assimilation of factors responsible for the genesis of proton trapping sites with an additional motive to explore the optimal composition while achieving maximum productivity.

Technological Challenges and Advancement in Proton Conductors: A Review

“…Binding energy between dopants and OH with varying ionic radius. Figure reproduced with permission from ref . Copyright 2022, American Chemical Society.…”

“…Nevertheless, promising proton conductivity is predominantly achieved between x = 0.1–0.2 doping concentrations with most acceptor substituents. , Additionally, the consequence of enhanced doping concentration influences negative impacts. A majority of protonation within the material is retained close to the acceptor dopant and demands high activation energy for long-range delocalization through the bulk material. − Recent computational studies using static density functional theory (DFT) reveal maximum symmetry distortions to occur in the dopant neighborhood that constitute proton trapping phenomenon. ,− On the contrary, a distorted structure displays effective proton conductivity with low activation energy. Hereby, a clear interpretation is still demanded to avail sufficient understanding about the influence of acceptor dopants over structural instability and proton conductivity …”

“…Multiple review and research articles concerning SOFC and PC-SOFC published in recent years present a short overview about the historical background of PC-SOFC alongside few narrow functional challenges (poor sinterability, chemical instability, and proton conductivity) of cerates and zirconates which limits the scope of practical solutions to improvise the addressed electrolytes with aging. , Additionally, a recent review article by Vignesh et al solely concentrates upon the factors responsible for the proton trapping effect within acceptor-doped cerates and zirconates, while a fundamental research gap persists concerning the genesis of such variable proton chemistry and factors influencing defect-induced structural phase transition. Nonstochiometric deviations due to facile reductions in strongly correlated f-electronic cerate systems and the dopant–host hybridization differences within cerates and zirconates predominantly alter the fuel cell performance at intermediate temperatures.…”

Advances and challenges in symmetrical solid oxide electrolysis cells: materials development and resource utilization

“…5c shows a possible proton conduction pathway (represented by a green dot). 51 Currently, the doping of H-SOEC is mainly focused on ordinary perovskite materials doped with Dy, K, and Ba metal elements, or on improving the proton conductivity of BaZrO 3 , a material with high proton conductivity. [52][53][54][55] RP perovskites such as La 2 NiO 4+d and Pr 2 NiO 4+d , which exhibit excellent performance in O-SOEC, have conductivity and electrocatalytic performance that can continue to improve in H-SOEC.…”

Enhanced ORR Activity of A-Site-Deficient SrCo0.8Nb0.1Ti0.1O3−δ as a Bifunctional Air Electrode for Low-Temperature Solid Oxide Fuel Cells

“…Perovskite oxides with an ABO 3 structure have been developed as air electrode materials. − Alternative perovskite oxides with mixed ion and electron conduction (MIEC) have been employed for O-SOFCs and H-SOFCs. The MIEC allows the ORR active site to diffuse over the entire surface of the cathode to enhance ORR activity. − SrCoO 3−δ -based materials have received much attention owing to their superior oxygen ionic and electronic conductivity. Nevertheless, the chemical stability and thermal matching of these materials are not very satisfactory. − …”