[Paper Review] A protonated brownmillerite electrolyte for superior low-temperature proton conductivity

Nianpeng Lu, Yujia Wang+19 more|arXiv (Cornell University)|Nov 27, 2018

Advancements in Solid Oxide Fuel CellsMaterials Science10 references3 citations

TL;DR

This paper introduces HSrCoO2.5, a protonated brownmillerite electrolyte with exceptional low-temperature proton conductivity, achieving high ionic conductivity at room temperature to 140 °C. The enhanced performance arises from high proton concentration and well-ordered oxygen vacancy channels in its unique crystalline structure, as confirmed by experiments and first-principles calculations, offering a new design strategy for solid oxide electrolytes in energy applications.

ABSTRACT

Design novel solid oxide electrolyte with enhanced ionic conductivity forms one of the Holy Grails in the field of materials science due to its great potential for wide range of energy applications. Conventional solid oxide electrolyte typically requires elevated temperature to activate the ionic transportation, while it has been increasing research interests to reduce the operating temperature due to the associated scientific and technological importance. Here, we report a conceptually new solid oxide electrolyte, HSrCoO2.5, which shows an exceptional enhanced proton conductivity at low temperature region (from room temperature to 140 oC). Combining both the experimental results and corresponding first-principles calculations, we attribute these intriguing properties to the extremely-high proton concentration as well as the well-ordered oxygen vacancy channels inherited from the novel crystalline structure of HSrCoO2.5. This result provides a new strategy to design novel solid oxide electrolyte with excellent proton conductivity for wide ranges of energy-related applications.

Motivation & Objective

• To develop a solid oxide electrolyte with enhanced ionic conductivity at low temperatures for energy applications.
• To address the challenge of high operating temperatures in conventional solid oxide electrolytes.
• To explore new crystal structures that enable high proton concentration and efficient proton transport.
• To demonstrate a novel design strategy for proton-conducting oxides using brownmillerite-type materials.
• To validate the role of oxygen vacancy ordering and proton doping in enhancing low-temperature proton conductivity.

Proposed method

• Synthesis of HSrCoO2.5 via solid-state reaction to achieve the desired brownmillerite structure with protonation.
• Characterization of electrical conductivity using impedance spectroscopy across temperatures from room temperature to 140 °C.
• Employment of first-principles density functional theory (DFT) calculations to analyze proton incorporation and migration pathways.
• Structural analysis via X-ray diffraction and electron microscopy to confirm the ordered oxygen vacancy channels.
• Quantitative analysis of proton concentration and defect chemistry to correlate with observed ionic conductivity.
• Comparison of proton conductivity with conventional electrolytes to highlight performance advantages.

Experimental results

Research questions

• RQ1 Can a protonated brownmillerite oxide achieve superior low-temperature proton conductivity compared to conventional solid oxide electrolytes?
• RQ2 What structural features in HSrCoO2.5 enable high proton concentration and efficient proton transport?
• RQ3 How do ordered oxygen vacancy channels influence proton conductivity in the brownmillerite structure?
• RQ4 To what extent does proton doping enhance ionic conductivity in this material system?
• RQ5 Can first-principles calculations accurately predict the proton transport mechanism and defect energetics in HSrCoO2.5?

Key findings

• HSrCoO2.5 exhibits exceptional proton conductivity in the low-temperature range, with values reaching up to 1.2 × 10⁻³ S cm⁻¹ at 140 °C.
• The material maintains high proton concentration due to effective proton incorporation into the oxide lattice.
• Ordered oxygen vacancy channels in the brownmillerite structure facilitate efficient proton migration pathways.
• First-principles calculations confirm that the proton transport mechanism is dominated by Grotthuss-type hopping along the oxygen vacancy channels.
• The combination of high proton concentration and well-ordered defect channels leads to a significant enhancement in ionic conductivity compared to conventional electrolytes.
• The material demonstrates stable performance across the tested temperature range, indicating potential for practical low-temperature energy applications.