Introduction Optimizing the nanostructure of the cathode is an effective approach to enhance the performance of solid oxide fuel cells at a triple-phase boundary (TPB). The most commonly used method is an impregnation method, which can produce nano-sized particles on the cathode framework structure. However, it is not able to achieve the related large-scale application due to its laborious preparation process and unstable performance. In this paper, nano-sized and submicron-sized composite powders of La0.6Sr0.4CoO3?δ?Ce0.8Gd0.2O2?δ (LSC?GDC) were synthesized by flame spray pyrolysis (FSP) and spray drying (SD) methods for the preparation of cathode, respectively. Methods A uniform submicron-sized LSC?GDC composite powder was prepared by SD with a solution of metal nitrates as a precursor solution. Also, a uniform nano-sized LSC?GDC composite powder was directly synthesized by FSP with a solution of metal acetates as a precursor solution. The submicron-sized and nano-sized powders were blended in different mass ratios (i.e., 100:0, 90:10, 80:20, 70:30, 60:40, 50:50, and 40:60) to produce cathode slurries. These slurries were then screen-printed onto the button cells of NiO?GDC|GDC|3YSZ|GDC|LSC?GDC|LSC structure with an effective electrode area of approximately 0.5 cm2. The voltammetric characteristics of the cells were tested by an electrochemical workstation. The electrochemical characterization was performed by electrochemical impedance spectroscopy (EIS) at open circuit voltage (OCV), and the impedance spectra were analyzed via distribution of relaxation time (DRT) analysis.Results and discussion Nano-sized particles synthesized by FSP and submicron-sized particles synthesized by SD can be distinguished via microscopic analysis. In addition, the fine particles are evenly distributed around the coarse particles, having a porous structure that meets an expected cathode microstructure. Under the experimental conditions, the overall ohmic impedance and polarization impedance both increase and then decrease as the proportion of nano-sized particles increases. The cathode performance is optimal when a mass ratio of SD powder: flame FSP powder is 70:30. Under SOFC mode at 850 ℃, the maximum power density of the button cell is 0.47 W/cm2, with an area specific resistance of 0.62 Ω·cm2. The corresponding ohmic impedance and polarization impedance values are 0.36 Ω·cm2 and 0.26 Ω·cm2, respectively. Combined with the results by DRT analysis, the doping of an appropriate amount of nano-sized powder significantly enhances the cathode O2 reduction reaction (ORR) process and cathode oxygen diffusion process.Conclusions Nano-sized and submicron-sized LSC?GDC composite materials were prepared by FSP and SD as one-pot methods, respectively. The feasibility of these two approaches for the large-scale preparation of SOFC cathode powders was investigated. The results showed that incorporating an appropriate amount of nano-sized powder into the submicron-sized powder for the preparation of the cathode could effectively enhance the cell performance.