Influence of silver addition on the morphological and thermal characteristics of Nickel Oxide-Samarium Doped Ceria Carbonate (NiO-SDCC) composite anode

In the past decade, research efforts have focused on developing high-performance composite anodes by mixing nickel oxide (NiO) as anode material with ceria-based electrolytes, such as nickel oxide samarium-doped ceria (NiOSDC) and nickel oxide gadolinium-doped ceria. However, the cell performance of composite anodes is limited at the intermediate temperature region of 600°C800 °C [13]. At reduced temperature <600 °C, cell stability is affected due to the partial stability of cerium (Ce to Ce). To overcome this issue, high-performance composite electrolytes, such as samarium-doped ceria carbonates (SDCCs), were developed and gained much popularity. Thus, the research and development of lowtemperature solid oxide fuel cells (LT-SOFCs; 400°C600 °C) greatly accelerated. SDCC is developed by the addition of binary carbonate (Li/Na)2CO3 into SDC, yielding good electrochemical performance and preventing the partial stability of cerium faced by pristine ceria-based electrolytes. A combination of NiOSDCC may provide promising performance, and considerable systematic research on this topic is in progress. Moreover, the potential of NiOSDCC composite anode has been explored with promising cell performance at low temperature (400°C600 °C) [4,5]. Polarisation resistance is one of the main challenges for reducing operating temperature. To reduce polarisation resistance, incorporating highly catalytic noble metal, such as platinum (Pt) and palladium (Pd), into electrodes is one possible strategy to improve the triple phase boundary (TPB) length [6,7]. These noble metals are usually expensive for cell commercialization. Alternatively, silver (Ag) is an inexpensive candidate with high electrocatalytic activity, high oxygen reduction rate, low electrical and contact resistance, good mechanical properties and stable in both oxidising and reduction atmospheres [8,9]. The addition of Ag into cathode components has been studied extensively for intermediate-temperature solid oxide fuel cells, resulting in promising cell performance by a significant reduction in cathode polarisation resistance as compared to Ag-free cathodes [10,11]. Aside from attaining good electronic conductivity and low polarisation resistance, an anode component requires good microstructure, adequate chemical compatibility and thermomechanical stability that are equally important for effective cell performance. To date, the effects of Ag addition into LT-SOFC cathodes has been found to influence the thermal expansion and cell microstructure, thereby affecting the cell performance [1213]. A wide range the amount of Ag has been reported to enhance the properties of cathode. For example Ag loading ranging Abstract: Addition of silver (Ag) as an electro-catalyst has been widely investigated to enhance the cathode performance for intermediate-to-low temperature solid oxide fuel cells. Ag is seldom incorporated into composite anode materials, especially for low temperature application. Therefore, this study aimed to investigate the effects of a small amount of Ag on the microstructure and thermal behaviour of nickel oxidesamarium-doped ceria carbonate (NiOSDCC) composite pellets. A high-speed ball milling technique was employed to prepare the NiOSDCC composite anode powder. Subsequently, a small amount of Ag (1, 3, and 5 wt.%) was added into NiOSDCC composite powder via ball milling. The pellets were manually pressed and sintered at 600 °C. Characterisation of the composite anodes included X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), energy-dispersive spectroscopy, scanning electron microscopy, dilatometry and porosity measurement. NiOSDCC maintained good chemical compatibility regardless of Ag loading. FTIR analysis also verified the presence of carbonates, suggesting that Ag did not influence the carbonate bonding in all NiOSDCC. The porosity of all composite anodes was maintained within the satisfactory level for good anode performance (20%40%). The thermal expansion of the composite samples matched well with the SDCC electrolyte. This finding indicated that the addition of small Ag loading into NiOSDCC was within the acceptable range, demonstrating promising potential as low-temperature solid oxide fuel cell composite anode.