Nano-Functionalization of SOFC Electrodes Via Inkjet Printing

Abstract

Introduction The future of the international accord on mitigating the impact of climate change is linked to the successful commercialisation and implementation of renewable energy technologies. The latter is strongly dependent on finding commercially viable methods for successful dimensional nano-functionalization of the ceramic materials utilized in the fabrication of various energy devices either in energy generation (fuel cells) or storage (batteries, supercapacitors). Inkjet printing digital methods combining scalability and low equipment cost with high-resolution patterning can be a feasible solution for some of the shortcommings of the conventional fabrication technologies. 3D functionalization - Composite solid oxide fuel cells LSCF/CGO cathodes were nano-engineered via “dual” inkjet printing infiltration. The nano-decorated microstructure was found to extend the active three-phase boundary and to promote adsorbtion – dissociation - surface exchange reactions. Composite La0.6Sr0.4Co0.2Fe0.8O3-δ/Ce0.9Gd0.1O1.9 cathodes were subjected to “dual” inkjet printing infiltration of nitrate salt solutions in a single step procedure. After calcination in air at 700 oC the cathodes were decorated with Ce0.9Gd0.1O1.9 and CoxOy nano particles. The effects of as created nano-decoration on the electrochemical activity and the performance stabilty in the intermediate temperature range (500-700 oC) were investigated. The infiltration was found to extend the active three-phase boundary and to promote adsorbtion-dissociation- surface exchange reactions. Electrochemical impedance tests conducted on symmetrical cells showed a reduction in the polarisation resistance of between 1.5 and 7.0 times depending on temperature (500-700 oC). The nano-decoration led to substantially enhanced stability (0.7 Ω•cm2 at 550oC after 100 hours of aging for CGO:CoxOy infiltration). As the composite LSCF/CGO cathodes had already percolating ionic and electronic networks, a low level loading of nanoparticles was sufficient to lead to an efficient short-range extension of the TPB and the density of ORR reaction sites. The sequence of infiltration was shown to influence the efficiency of the ORR promotion. CoxOy:CGO infiltration expanded the available surface area and promoted the catalytical activity towards ORR reaction. The superior effect of CGO:CoxOy infiltration was assigned to the introduction of additional promotion mechanisms (see Fig. 1) resulting in better electrochemical performance at lower temperatures (<650 oC). Both infiltrations suppressed the Sr surface segregation but only CGO:CoxOy infiltrated cathodes showed substantially improved stability after 100 hours of aging. Scaling up - Single step inkjet printing infiltration with doped ceria Ce0.9Ye0.1O1.95 (YDC) and cobalt oxide (CoxOy) precursor inks was performed in order scale-up the modification of the doped ceria interlayer in commercial (50x50x1 mm size) anode supported SOFCs. The penetration of the inks through the mono-phase La0.8Sr0.2Co0.5Fe0.5O3-δ porous cathode to the Gd0.1Ce0.9O2 interlayer was achieved by optimization of inks rheology jetting parameters. The low temperature calcination resulted in densification of the Gd-doped ceria porous interlayer as well as decoration of the cathode scaffold with nano-particles (~ 20-50 nm in size). The I-V testing in pure hydrogen showed maximum power density gain of 20% at 700oC and 97% at 800oC for the infiltrated cells (see Fig. 1). The effect was largely assigned to the improvement in the interfacial Ohmic resistance. The EIS study of the polarization losses of the reference and the infiltrated cells revealed reduction in the activation and concentration polarizations losses at 700oC due to the nano-decoration of the La0.8Sr0.2Co0.5Fe0.5O3-δ scaffold surface. Such effect was not clearly detectable at 800oC where the drop of Ohmic losses was dominant. This work demonstrated that single-step inkjet printing infiltration, a non-disruptive low-cost technique, could produce significant and scalable performance enhancements in commercial SOFCs. Figure 1