Hybrid Electrochemical Deposition Route for the Facile Nanofabrication of a Cr-Poisoning-Tolerant La(Ni,Fe)O_3−δ Cathode for Solid Oxide Fuel Cells

Abstract

Cr poisoning of cathode materials is one of the main degradation issues hampering the operation of solid oxide fuel cells (SOFCs). To overcome this shortcoming, LaNi 0.6 Fe 0.4 O 3−δ (LNF) has been developed as an alternative cathode material owing to its superior chemical stability in Cr environments. In this study, we develop a hybrid electrochemical deposition technique to fabricate a nanostructured LNF− gadolinium-doped ceria (GDC) (n-LNF−GDC) cathode with enhanced active reaction sites for the oxygen reduction reaction. For this purpose, Fe and Ni cations are co-deposited onto an electrically conductive carbon nanotube-modified GDC backbone by electroplating, whereas La cations are successively deposited through a chemically assisted electrodeposition method. The proposed method involves a low-temperature (900 °C) calcination step of electrodeposited cations, which avoids the need of fabricating a GDC diffusion barrier layer which is otherwise needed to avoid the formation of insulating phases (e.g., La 2 Zr 2 O 7 ) when fabricating by conventional high-temperature (≥1000 °C) sintering. Scanning electron microscopy images reveal a unique nanofibrous structure of n-LNF−GDC, which is believed to play an instrumental role in enhancing the electrochemical characteristics by increasing the active triple-phase boundaries. An anode-supported SOFC with the n-LNF−GDC cathode showed the superior performance of 0.984 W cm −2 at an intermediate temperature of 750 °C as compared to the power densities of 0.495 and 0.874 W cm −2 produced by LNF−GDC and state-of-the-art La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ (LSCF)−GDC composite cathodes fabricated by conventional sintering. A short-term accelerated Cr-poisoning durability test indicated good electrochemical stability of n-LNF−GDC, whereas LSCF exhibited severe degradation. The electrochemically engineered nanostructured n-LNF−GDC can serve as an effective cathode for SOFCs to achieve high performance and long-term durability.

Surface decorations to abrupt change performance, robustness, and stability of electrodes for solid oxide cells

“…CAED provides good control over the morphology and loading of the precursor without the need for a repeated deposition process. It was demonstrated on high‐performance perovskite cathodes with stable performance 40 . This method allows the fabrication of perovskite cathodes, such as LaCoO 3 , 41 LaNiO 3 , 42 La(NiFe)O 3 , 40 and many others with a unique nanofibrous structure, at reduced temperatures (∼900°C) to the preestablished surfaces, while avoiding the formation of pyrochlore phases, typically observed during conventional high‐temperature sintering processes.…”

“…It was demonstrated on high‐performance perovskite cathodes with stable performance 40 . This method allows the fabrication of perovskite cathodes, such as LaCoO 3 , 41 LaNiO 3 , 42 La(NiFe)O 3 , 40 and many others with a unique nanofibrous structure, at reduced temperatures (∼900°C) to the preestablished surfaces, while avoiding the formation of pyrochlore phases, typically observed during conventional high‐temperature sintering processes. This method is able to improve the electrochemical properties by providing a large number of active reaction sites and by facilitating mass transport through the porous nanofibrous structure 38 …”

Opportunities, Challenges and Prospects for Electrodeposition of Thin-Film Functional Layers in Solid Oxide Fuel Cell Technology

“…Chemically assisted electrodeposition (CAED) is a relatively new technique for fabricating nanostructured SOFC cathodes in a single loading step which has the advantage of the simultaneous deposition of multiple cations while using dilute aqueous solutions of salts. It was developed by Rehman et al [ 52 , 53 , 54 ]. The proposed method involves CAED of mixed-metal hydroxide onto a carbon nanotube (CNT) template, followed by a low-temperature heat-treatment process (see the scheme in Figure 2 ).…”

“…The sintering temperature can be significantly reduced using electrodeposition methods, including modified CAED. In [ 54 ], an integrated approach to the formation of an anode-supported SOFC with a thin-film ScCeSZ electrolyte (~5 µm) and a nanostructured LNF–gadolinium-doped ceria (GDC; n-LNF–GDC) cathode using various ceramic technologies (cold pressing, dip-coating, screen printing), as well as impregnation from solutions, CCVD, electroplating and CAED. The anode substrate was formed by isostatic pressing of a NiO–YSZ mixture (55:45) with 12 wt% pore former (graphite), followed by preliminary sintering at 1200 °C and applying a functional layer of NiO–ScCeSZ and a ScCeSZ electrolyte layer by dip-coating.…”

“… Cross-sectional SEM images illustrating the microstructural evolution during the fabrication of the n-LNF−GDC cathode: ( a ) CNT-modified GDC backbone, ( b ) magnified image of the CNTs, ( c ) Ni−Fe-coated GDC backbone, ( d ) magnified image of Ni−Fe coating, ( e ) nanofibrous n-LNF−GDC cathode annealed at 900 °C, and ( f ) magnified image of the n-LNF−GDC cathode [ 54 ]. …”