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 cm2 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.