Ni/NiO heterojunction anchored on N-doped carbon for the enhanced methanol oxidation

Abstract

The reasonable construction of an economical catalyst with excellent performance for methanol oxidation reaction (MOR) is one of the key problems to be solved to enhance the efficiency of direct methanol fuel cells (DMFC). Herein, Ni/NiO heterojunction loaded on N-doped carbon substrates (Ni/NiO@NC-T) have been constructed by pyrolyzing metal-organic polymer hydrogel formed by the reaction of Ni2+ and sodium alginate (SA), in which the strong interaction between Ni2+ and SA ensures the nickel content of the as-synthesized samples. The optimum Ni/NiO@NC-300 sample has an excellent activity for MOR with the current density (j) of 225 mA∙cm−2 at 1.6 V under an alkaline medium, which is higher than those of some MOR catalysts previously reported. In addition, the stability and anti-CO poisoning ability of Ni/NiO@NC-300 catalysts are superior to that of Pt/C, which indicates that Ni/NiO@NC-300 has potential application prospect as an MOR catalyst. By density functional theory (DFT) calculation, the superior performance of Ni/NiO@NC-300 is mainly ascribed to the Ni/NiO heterojunction, which can effectively reduce the energy barrier of the rate-determining step (CO* → COOH*) in the MOR process. The work opens a new route for the synthesis of transition metal-based materials as MOR catalysts.