Ultra-low nickel-doped copper aerogels as highly efficient and stable electrocatalysts for the formic acid oxidation reaction

Abstract

Noble-metal-free electrocatalysts are inexpensive and exhibit low onset potential, adequate stability, and excellent conductivity, making them highly attractive for advancing direct formic acid fuel cells. In this study, we modulated the surface electronic structure of copper aerogel by incorporating an ultra-low amount of nickel, resulting in the formation of a Cu₉₈Ni₂ aerogel catalyst. The compositional, morphological, structural, and electrochemical properties of the as-prepared electrocatalyst were extensively studied using XPS, TEM, SEM/EDX, SEM, XRD, ICP-OES, and CV techniques. The Cu₉₈Ni₂ aerogel exhibits mass activity values that are 13.3, 2.8, and 4.5 times higher than those of undoped Cu, Cu₉₅Ni₅, and Cu₉₂Ni₈ aerogels, respectively, along with onset potentials that are negatively shifted by 45, 25, and 12 mV. Notably, the Cu₉₈Ni₂ aerogel maintains about 82% of its initial steady-state current density after 10 hours of formic acid oxidation, indicating a significant improvement in catalyst performance. Furthermore, Cu₉₈Ni₂ attains the smallest Tafel slope (81.5 mV dec⁻¹) and apparent activation energy (23.8 kJ mol⁻¹), suggesting faster and easier charge transfer kinetics for formic acid oxidation compared to undoped Cu and Cu aerogels with higher Ni loading. The outstanding performance of the electrocatalyst in formic acid oxidation is mainly attributed to superior conductivity, effective mass and electron transfer, minimal CO poisoning, and the synergistic effects of its constituents. This study promotes the production of highly stable and efficient electrocatalysts made from non-precious metals.