Preparation and Electrochemical Properties of Honeycomb-like Pt-Ni-P/Ti Electrode for Methanol Oxidation

A honeycomb-like metallic catalyst (Pt-Ni-P/Ti) supported on a Ti sheet was prepared by electrodeposition-displacement method. The Ni-P amorphous alloy was first electrodeposited on the Ti substrate, and then replaced by displacement of Ni in amorphous Ni-P with H2PtCl6. The morphology and methanol oxidation performance of the prepared catalyst were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), anodic linear sweep voltammetry (LSV), cyclic voltammetry (CV), and the anodic stripping of a pre-adsorbed CO monolayer. The SEM results show that the Pt-Ni-P nanoparticles obtained by displacement of Ni in amorphous Ni-P with H2PtCl6 had a honeycomb-like porous structure, while the Pt-Ni nanoparticles had a wheat-like structure. The formation of the honeycomb-like porous structure can be explained by the so-called "out-situ dissolution-deposition mechanism", in which the metallic Ni in Ni-P/Ti electrode preferentially dissolve to form pore structure and release electron. The released electrons can be captured by the PtCl62- ion adsorbed on the surface of Ni-P and reduced on the surface of Ni-P to form Pt shell, thereby forming a honeycomb-like pore structure. For the Pt-Ni/Ti electrode, the formation of wheat-like structure Pt-Ni nanoparticles can be explained by a so-called "in-situ dissolution-deposition mechanism", in which the Pt replacement reaction can only occur at the surface of Ni, and the replacement Pt monolayer can prevent the further chemical substitution of Pt on Ni, thereby forming a wheat-like structure. The electrochemical test results show that the methanol oxidation and CO oxidation onset potential on Pt-Ni-P/Ti electrode in alkaline solution is more negative than that on Pt-Ni/Ti electrode, indicating that P incorporation can significantly enhance the methanol oxidation activity and CO-tolerance. Moreover, the unique honeycomb-like porous structure is beneficial to the fast mass transportation during the catalytic reaction. The combination of compositionally and geometrically favorable factors provides a new avenue to design new electrocatalysts with excellent methanol oxidation activity and CO-tolerance.