Coupling the oxyphilic metals and NbN to modulate the electronic structure of Pd and enhance the efficiency for alkaline MOR

Abstract

It is essential to design and produce stable, high-activity, and low-cost anode catalysts for direct methanol fuel cells (DMFCs). To improve the efficiency of the methanol oxidation reaction (MOR) in alkaline media, a series of PdM-NbN/C (M = Co, Ni, Cu) bi-component catalysts were synthesized by introducing various oxyphilic metals. Electrochemical evaluations show that the presence of Ni and Co significantly enhances catalytic activity, charge transfer kinetics, CO tolerance, and long-term stability compared to Pd-NbN/C. Among these, PdNi-NbN/C exhibits the highest mass activity of 4806.67 A·g_Pd⁻¹, the lowest onset potential and charge transfer resistance, as determined from electrochemical testing. The rate-determining step (RDS) is identified as the CO_ads oxidation reaction. Characterization analysis confirms that the second oxyphilic metals primarily optimize the Pd electronic structure and modulate the interaction between Pd and NbN, making a favorable shift in the d-band centers. Additionally, Ni and Co elements tend to form hydroxides in higher proportions, which aids in the removal of CO_ads and accelerates the RDS. The electronic interactions between Pd, Ni, and NbN species are key to the enhanced catalytic performance for MOR. Pd nanoparticles in the electron-deficient condition may aid in the activation of methanol and its intermediates, as indicated by the linear relationship between the mass activities and d-band centers. This work offers important information for the logical design of efficient anode catalysts for DMFCs.