Investigation of Pd2B- and NiB-Doped Pd-Ni/C Electrocatalysts with High Activity for Methanol Oxidation

The Pd-Ni/C catalyst was synthesized under medium strongly acidic media regulated by ammonia solution, using NaBH4 as a reducing agent and polyvinylpyrrolidone (PVP) as a protector. The TEM, HRTEM, and XRD results exhibited that the Pd-Ni/C catalyst was successfully synthesized and doped with Pd2B and NiB. The XPS analysis showed that Pd and Ni mainly existed with an oxidized state in the Pd-Ni/C catalysts, and Pd and Ni also had a strong electronic interaction. Moreover, B and Ni were respectively inserted into the atomic spacing of Pd-Pd, which significantly changed the surface electronic state and atomic spacing of Pd, helping to improve the activity of the Pd-Ni/C catalyst. The electrochemical performance analyzed through cyclic voltammetry, chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) displayed that the Pd-Ni/C catalyst had good activity and CO tolerance for methanol electro-oxidation. Furthermore, the Pd-Ni/C catalyst synthesized at which the ratio between the actual and stoichiometric amounts of NaBH4 was 25 (Pd-Ni/C-25) showed the optimal ECSA and anodic current density for methanol electro-oxidation, respectively reaching 1602.2 cm(2) mg(-1) Pd and 1406.5 mA mg(-1) Pd. Moreover, the linear relationship between the methanol oxidation on the Pd-Ni/C-25 catalyst and the square root of the scan rate indicated that the electrokinetics of this electrochemical reaction was a diffusion-controlled process, further implying its excellent electrocatalytic performance. The results of the CA curves showed that the Pd-Ni/C-25 catalyst also had excellent durability because of its good antitoxicity. The EIS results presented that the Pd-Ni/C-25 catalyst had the best charge transfer efficiency among these Pd-Ni/C catalysts. The good activity, CO tolerance, durability, and charge transfer efficiency of the Pd-Ni/C-25 catalyst demonstrated its wide potential application in direct methanol fuel cells.