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Recent studies have shown that the networking and interaction between N, S, and CQDs activate reactions by creating additional active sites that bind more oxygen molecules. In this study, we used nitrogen-doped graphene quantum dots as a support for Ni–Au nanoparticles and investigated the influence of different Ni–Au ratios on the N-doped graphene quantum dots as an electrocatalyst for ethanol and formate oxidation. Indeed, three electrocatalysts containing gold and nickel nanoparticles are synthesized in 1 : 1, 1 : 3, and 3 : 1 (Ni1Au1, Ni1Au3, and Ni3Au1) ratios on the nitrogen-doped graphene quantum dots as a catalyst support by the reduction process. The synthesized electrocatalysts are characterized by XRD, FESEM, and EDX methods. The electrocatalytic activity of the Ni1Au1-NGQD, Ni1Au3-NGQD, and Ni3Au1-NGQD (nickel–gold–nitrogen-doped graphene quantum dot) electrocatalysts towards ethanol and formate oxidation are evaluated in half-cell and single-fuel cell configurations. The half-cell results confirm the superiority of the Ni1Au1-NGQD electrocatalyst towards oxidation of both fuels compared to the two other electrocatalysts, and the corresponding chronoamperometry shows its high stability. Therefore, the Ni1Au1-NGQD is used as an anodic electrocatalyst in a single fuel cell configuration using ethanol and formate as fuels and hydrogen peroxide as an oxidant. The maximum power density of 8.20 and 14.23 mW cm−2 is obtained at 60 °C with 2 M ethanol and 4 M formate as the fuel in a direct ethanol–hydrogen peroxide fuel cell (DEHPFC) and direct formate–hydrogen peroxide fuel cell (DFHPFC), respectively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]