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

Abstract

The Pd−Ni/C catalyst was synthesized under medium strongly acidic media regulated by ammonia solution, using NaBH 4 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 Pd 2 B 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 NaBH 4 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.

Phosphorus-Doping Enables the Superior Durability of a Palladium Electrocatalyst towards Alkaline Oxygen Reduction Reactions

“…Nevertheless, the sluggish kinetics of oxygen reduction reactions (ORRs) substantially hampers the energy efficiency of the battery and necessitates substantial amounts of scarce and costly Pt, thereby impeding their widespread implementation in fuel cells [ 10 , 11 , 12 , 13 ]. As an alternative to Pt-based catalysts, Pd-based catalysts have garnered increasing interest owing to their electronic structure similarity to platinum and comparatively greater mineral reserves [ 14 , 15 , 16 , 17 , 18 ]. As a result of its substandard durability and diminished intrinsic activity, it is critical to enhance the performance of Pd to fulfill the operational requirements of AFCs [ 19 , 20 , 21 ].…”

“…PGM catalysts doped with nonmetals may be durable due to the strong nonmetal–metal connection [ 35 , 36 , 37 ]. PGM-based catalysts are now doped with boron, nitrogen, sulfur, carbon, and hydrogen [ 14 , 30 , 38 ]. More importantly, the leaching of nonmetal elements produces anions, which will not catalyze the Fenton reaction and damage the membrane and ionomer [ 39 ].…”