Nanostructured NiO-GDC Anodes for Improving Solid Oxide Fuel Cell Performances

Solid Oxide Fuel Cells (SOFCs) are efficient electrochemical devices that directly transform chemical energy into electrical energy through electrochemical reactions, offering a clean means of energy conversion, and they have attracted increased attention due to their potential to lower operating temperatures, which is crucial for advancing the widespread application of SOFCs. Since the power output of a SOFC is closely related to the electrochemical performance of the electrodes, nanostructuration of the anode increases the surface-to-volume ratio of the three boundary conditions where the reactions take place. In this work, the preparation and characterization of nanostructured anodes based on nickel oxide and gadolinium-doped ceria nanowires (NiO-GDC NWs) are proposed. The NiO-GDC NWs were synthesized by Vapor-Liquid-Solid growth technique, and they have been systematically investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), and Raman spectroscopy. Functional characterization of the power output of the fuel cell performance together with Electrochemical Impedance Spectroscopy (EIS) analysis were carried out at different temperatures and for different fuel flows of hydrogen and air. The results obtained at 800 °C with an H2 and air flow of 100 sccm and 200 sccm respectively, showed an Open Circuit Voltage (OCV) of 1.06 V and a power density of 300 mW/cm2. The energy conversion efficiency of SOFCs can reach up to 60-80% in theory. This is because it is not limited by the Carnot cycle, as no combustion is involved in the SOFC process. SOFCs have other benefits such as low emissions, long-term stability, and relatively low cost. SOFCs are considered a sustainable energy source: when supplied with hydrogen and oxygen, they produce electricity through an electrochemical reaction between hydrogen and oxygen. Enhancing the anode performance by means of nanostructuration can lead to improved SOFC electrochemical performance. The electrochemical reaction in the anode takes place at the three-phase boundary (TPB), which refers to the area where the electrolyte, the electron-conducting metal phase, and the gas phase intersect. Lengthening the TPB will boost the electrochemical reaction and enhance the anode's performance. Currently, researchers are exploring the application of nanomaterials in SOFC technology as a potential solution to enhance its performance. It has been demonstrated that reducing the grain size of the electrode results in an increase in TPB length, particularly when the grain size of the electrode is below 2 μm. In NiO-GDC NWs anodes, through the reduction of NiO and GDC grain sizes to the nanoscale, the interfacial areas between NiO and GDC are significantly magnified. Consequently, this augmentation extends the length of the TPB, leading to enhancement in the electrical performance of the anode. After the systematic investigation (by SEM, XRD and Raman spectroscopy) on the growth parameters which lead to a good NiO-GDC NWs morphology and composition, the NiO-GDC NWs were grown on a commercial single-electrode button cell (with cathode only) to explore the cell and its electrochemical behavior. A comprehensive analysis of the results indicates that the NiO-GDC NWs exhibit promising potential as an anode for SOFCs. Ultimately, this study reports the synthesis and performance of NiO-GDC NWs based SOFCs, with a careful investigation on the morphology and composition of the NWs using SEM, XRD and Raman techniques. Finally, NiO-GDC NWs were grown directly to a commercial single-electrode button cell for the evaluation of the electrochemical performance. Overall, the preliminary results suggest that NiO-GDC NWs show considerable promise as an anode material for SOFCs.<br/><br/>Acknowledgements<br/>Funded by the “Ministero Affari Esteri e Cooperazione Internazionale” under the Italy-Singapore joint project PGR01187 “Thin-film solid oxide fuel cell with hierarchical mixed oxides nanostructured electrodes”.