Nitrogen-doped carbon dot/activated carbon nanotube-supported copper nanoparticles as an efficient electrocatalyst for the oxygen reduction reaction

Abstract

Recent decades have witnessed remarkable progress in fuel cell technology for efficient energy conversion devices in stationary, automotive, and mobile systems. However, the choice of the electrode material in the fuel cell technologies is still limited to platinum and the other platinum group metals, necessitating further research for alternatives. Herein, activated carbon nanotubes (ACNTs) treated at a high temperature (500 °C) were used as a support to induce binding with N-doped carbon dots (NCDs). Cu(II) in the copper nanoparticles spontaneously reduced to Cu(0) using the NCDs as a reducing agent; thus, a Cu/NCD/ACNT hybrid catalyst was synthesized. The oxygen reduction reaction (ORR) activity of the Cu/NCD/ACNT catalyst (Eonset = 0.921 V) was higher than those of Cu/ACNT (Eonset = 0.821 V) and NCD/ACNT (Eonset = 0.869 V) catalysts. The Cu/NCD/ACNT catalyst also exhibited excellent tolerance to methanol, in relation to Pt/C, during a methanol fuel cell tolerance test. Moreover, the current decays after 10 h in the ORR durability test were 21% and 10% for the Pt/C and Cu/NCD/ACNT catalysts, respectively, demonstrating the greater durability of the non-metal catalyst. Thus, the Cu/NCD/ACNT catalyst, formed by the synergistic action of ACNT, N doping, and spontaneous reduction of Cu(II), is a promising alternative to commercial Pt/C catalysts.