Relative electrochemical activity of bimetallic PtM catalysts electrodeposited on a composite of carbon black and carbon nanotubes for enhancement in formic acid oxidation reaction

Abstract

Recently, Pt-based catalysts on mixed carbon supporters have been introduced for enhancement of the formic acid oxidation (FAO) reaction. Herein, carbon black (CB) and carbon nanotubes (CNT) were combined as a hybrid CB-CNT carbon support. The Brunauer–Emmett–Teller (BET) surface area of CB-CNT support presented the increased pore size and volume, providing high surface areas for electroactive species diffusion. By cyclic voltammetry (CV), the noble metals (M) including platinum (Pt), palladium (Pd), gold (Au), and ruthenium (Ru) were utilized for catalytic electrodepositing on the CB-CNT support to obtain the catalysts. The M/CB-CNT and PtM/CB-CNT catalysts prepared under the controlled condition were characterized and compared their activities and stabilities. Among the prepared catalysts, the small particle sizes of PtM/CB-CNT, which occurred with high Pt(111) intensities from face-centered cubic (fcc) structure, were confirmed by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). Also, the X-ray photoelectron spectroscopy (XPS) indicated the highest peak ratio of metallic Pt from PtPd/CB-CNT that was related to its high catalytic active surfaces. In the monometallic systems, the Pt/CB-CNT and Pd/C-CNT catalysts actively promote the oxidation of formic acid molecules by their unique pathways. Among the prepared catalysts in both mono- and bimetallic systems, PtPd/CB-CNT showed the highest current intensity of 11.48 mA cm−2 at a potential of 0.70 V in FAO reaction for formic acid oxidation. Although Pt/CB-CNT provided the lowest potential at maximum current intensity (ECO = 0.51 V), PtPd/CB-CNT astonishingly presented the highest active surface area (ECSACO = 0.57 cm2) for CO oxidation. The PtPd/CB-CNT catalyst showed the co-existence between Pt and Pd nanoparticles, and the hybrid structure of CB-CNT provided the improved electrochemical results towards FAO reaction. Graphical abstract: [Figure not available: see fulltext.]