Physical and electrochemical characterization of different ternary PtAuNi/MWCNT-N electrocatalysts for DMFC application

Abstract

Over the years, researchers have observed the importance of developing efficient and durable electrocatalysts for direct methanol fuel cell (DMFC) applications. This study develops ternary PtAuNi/MWCNT-N catalysts, by varying gold concentration as 0%, 50% and 100%. The physicochemical and electrochemical properties of the catalysts were studied using different techniques. The -OH (3200–3500 cm− 1), -C = O (1640 cm− 1), C-O (1000–1300 cm− 1), C = N (1700 cm− 1) and metal-oxygen peaks around 450–500 cm− 1 were observed using Fourier transform infrared spectroscopy (FTIR). Thermogravimetric analysis (TGA) was able to observe increasing residual masses of 8.50% (PtAuNi/MWCNT-N), 12.82% (PtAu50Ni/MWCNT-N) and 18.31% (PtAu100Ni/MWCNT-N), suggesting an improvement in thermal stability with increasing gold content. Exothermic peaks from 450 to 650 $$\:℃$$ were observed on the differential scanning calorimetry (DSC), aligning with the observations made in TGA. The sample with the most Au content (PtAu100Ni/MWCNT-N) exhibited an enhanced nanoparticle dispersion through Scanning Electron Microscope (SEM) micrographs. The progressive increase of Au content in the samples was confirmed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Au content increased from 0.023 wt% (PtAuNi/MWCNT-N) to 1.20 wt% (PtAu100Ni/MWCNT-N).), while Pt loading ranged from 3.80 wt% to 4.11 wt%. X-ray diffraction (XRD) displayed peaks around 26°, 39°, 46°, 68° and 80°, these peaks align with the face-centered cubic (fcc) alloy phases that are in line with platinum (Pt) and its alloys. Electrochemical measurements Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) were used to analyse the catalytic activity of the synthesized electrocatalysts. CV revealed PtAu100Ni/MWCNT-N had the lowest onset potential of 0.112 V vs. Ag/AgCl, highest peak current density of 0.374 A cm− 2 and a mass activity of 16.83 A mgPt− 1 compared to 13.42 A mgPt− 1 for PtAuNi/MWCNT-N. EIS calculations confirmed the lowest charge-transfer resistance of 7.02 Ω and the highest phase angle of 80° for PtAu100Ni/MWCNT-N, these results indicate faster electron transfer kinetics of the sample. This study, shows that progressive increase of Au content plays an important role in enhancing the structural properties, thermal stability and electrochemical performance of pt-based electrocatalysts.