Electrospun Nanofiber Electrodes with in situ Exsolved Nanocatalysts for Symmetrical SOCs

Abstract

Solid oxide cells (SOCs) offer great promise for efficient energy generation and storage in a variety of applications. Symmetrical SOCs with identical anode and cathode materials configuration favoring an efficient reversible operation of the cells, allow both electricity production from traditional and renewable energy sources in fuel cell mode, and clean, efficient fuel production (in reverse/electrolysis mode). In addition, the symmetrical cell design is particularly advantageous, including: decreased number of cell components, simplification of fabrication process and alleviating the chemical stability issues related with materials, as well as the enhanced resistance to coking and sulphur poisoning, when cells are fuelled by alternative sources (non-H2) [1]. However, electrode material candidates with excellent redox stability and electrocatalytic activities in both oxidizing and reducing conditions for symmetrical SOCs are limited due to the strict criteria. The design of electrode materials with in situ exsolution of nanoparticles significantly benefits the performance of SOCs [2]. In the anode operation condition, metallic nanoparticles are in situ exsolved from the parent electrode materials decorating on the electrode surface, substantially improving the catalytic activity and electronic conductivity of anode, thus boosting the cell performance. The in situ exsolved nanoparticles can be socketed to the parent oxide, enhancing the stability and hydrocarbon coking tolerance, making the symmetrical SOCs fuelled by cheaper and readily available non-hydrogen alternatives. Moreover, the possible reversible exsolution/dissolution of nanoparticles can potentially resolve the particle agglomeration and coke formation during usage of non-hydrogen fuels [2, 3]. The electrospinning technique has been reported to obtain nanofiber-structured electrodes for SOCs, which efficiently contributes to the enhancement of the electrochemical performance of SOCs [4].In this work, the A-site deficient (Ln, Ba/Sr)2-α(Fe,M)2-x(Ni,Co)xO6-δ (Ln = selected lanthanides; M = Mn, Ti, Cr, Mo, W) perovskites were successfully obtained and evaluated as novel electrode materials for SOCs. It has been found that the A-site nonstoichiometry favours the in situ exsolution of metallic nanocatalysts (NixCo) from the parent materials in reducing condition. The selection of A-site cations (lanthanides) significantly affects the crystal structure (simple or double perovskite structure), while the B-site cations determine the stability of materials in air and reducing atmospheres. The reversibility of exsolved nanoparticles is systematically investigated under reducing and oxidizing conditions with different annealing temperatures. The possibility of in situ exsolution of nanooxides on the cathode (NixCoOy-like nanooxides) is also investigated. Nanofiber-structured electrodes with the ability of in situ exsolution of nanocatalysts are fabricated using the electrospinning technique, which significantly boost the electrochemical properties of constructed SOCs.