The effects of the core material (M = Co, Ni) and catalyst support (N = MWCNTs and rGO) on the performance of M@Pd/N core-shell electrocatalysts for formate oxidation and direct formate-hydrogen peroxide fuel cells

In this work, M@Pd/N (M = cobalt, nickel; N = multi-walled carbon nanotube, reduced graphene oxide) anodic electrocatalysts are synthesized and studied for formate oxidation, and used directly in formate-hydrogen peroxide fuel cells (DFHPFCs) for the first time. The effect of core materials (M = cobalt, nickel) on the activity of M@Pd/MWCNTs for formate oxidation has been studied. For this purpose, a Co@Pd/MWCNT electrocatalyst is synthesized using a two-step reduction method. Comparing the electrochemical surface area (ECSA), the formate oxidation current density (Ip) and onset potential of formate oxidation (Eons) values of Co@Pd/MWCNTs and Ni@Pd/MWCNTs showed that the presence of Ni in the core instead of Co improved the catalytic performance of the M@Pd/MWCNT catalyst due to the synergistic effects between Ni and Pd. The ECSA and Ip values of the Ni@Pd/MWCNTs are 1.01 and 1.78 times higher than those of Co@Pd/MWCNTs. After optimizing the core material, in the next step, the effect of the catalyst support on the performance of Ni@Pd nanoparticles is evaluated. Comparing the ECSA, Ip and Eons values of Ni@Pd/MWCNTs and Ni@Pd/rGO showed that Ni@Pd/rGO performs better for formate oxidation because of the high surface area and conductivity of rGO compared to MWCNTs. The ECSA and Ip values of Ni@Pd/rGO are 1.09 and 1.57 times higher than those on Ni@Pd/MWCNTs. Finally, the effect of these electrocatalysts in DFHPFC is evaluated and the results are in good agreement with the three electrode results. The maximum power density of the Co@Pd/MWCNTs, Ni@Pd/MWCNTs and Ni@Pd/rGO is 49.90, 62.29 and 107.29 mW cm-2, respectively. The obtained results show that the presence of Ni at the core instead of Co and using rGO as catalyst support instead of MWCNTs increased the catalytic performance of the synthesized electrocatalyst towards formate oxidation.