Effect of Ni-Doping in LaCo_1-x Ni _x O₃ on Electrocatalytic Oxygen Reduction Reaction

Methanol crossover severely limits the performance of direct methanol fuel cells (DMFCs) by introducing methanol to the cathode compartment, where it competes with the oxygen reduction reaction (ORR) and poisons platinum-based ORR electrocatalysts, making it essential to develop methanol-tolerant ORR electrocatalysts. Here, Ni doping is explored as a means of improving the electrocatalytic activity and methanol tolerance of LaCo_1-x Ni _x O₃ (x = 0, 0.1, 0.15, and 0.2) perovskite oxide electrocatalysts synthesized using a simple sol-gel method. X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray (EDAX) analysis confirm the formation of LaCoO₃ and successful Ni doping at the Co site. Field-emission scanning electron microscopy (FE-SEM) analysis reveals that the particle size of the synthesized nanoparticles slightly increases upon Ni doping. Although a corresponding decrease in Brunauer-Emmett-Teller (BET) surface area with increasing Ni doping is also found, LaCo_0.8Ni_0.2O₃ possesses the highest pore volume and pore radius among all the synthesized perovskite oxides. This optimized composition exhibits superior ORR catalytic activity (0.724 and 0.678 V vs reversible hydrogen electrode (RHE) at current densities of -0.1 and -0.3 mA cm^-2, respectively) comparable to Pt/C (0.758 and 0.709 V vs RHE) derived from the linear sweep voltammetry (LSV) study performed at 1600 rpm. In the presence of methanol, all the synthesized perovskite oxides experienced a small negative potential shift (0 to 14 mV) during ORR, suggesting these materials can be used as methanol-tolerant ORR electrocatalysts in DMFCs.