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 (I_p) and onset potential of formate oxidation (E_ons) 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 I_p 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, I_p and E_ons 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 I_p 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.