Boosted performance of NiOx/Pt nanocatalyst for the electro-oxidation of formic acid: A substrate's functionalization with multi-walled carbon nanotubes

Abstract

A novel NiOx/Pt on “mutli-wall” carbon nanotubes nanocatalyst is recommended for efficient electro-oxidation of formic acid (EOFA), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). At the NiOx/Pt/CNTs/GC catalyst, EOFA tuned the typical dual (direct/indirect) pathway mechanism (left image) to the single direct pathway mechanism (right image); overcoming efficiently the CO poisoning. • A propitious CNTs-amended NiOx/Pt nanoanode was fabricated. • It showed a promising catalytic activity toward the formic acid electro-oxidation. • The reaction proceeded exclusively via the desirable dehydrogenation pathway. • A complete suppression of the undesirable poisoning dehydration route was obtained. • Electronic and geometric enhancements were elucidated and quantified. A NiOx/Pt nanostructured catalyst was developed on a glassy carbon substrate that was functionalized with “mutli-walled” carbon nanotubes (CNTs) for the electro-oxidation of formic acid (EOFA); the essential oxidation reaction in the direct formic acid fuel cells (DFAFCs). The sequential deposition technique was adapted for the electrodeposition of platinum (n-Pt) and nickel oxide (n-NiOx) nanoparticles onto a CNTs-functionalized glassy carbon (GC) substrate. The presence of CNTs in the catalyst restricted the deposition of n-Pt and n-NiOx mostly onto their walls. Interestingly, this NiOx/Pt/CNTs/GC catalyst displayed a significant enhancement in the catalytic activity toward EOFA. This occurred by driving the reaction mechanism exclusively via the desirable direct dehydrogenation pathway with a large (−116 mV) shift (relative to that of the Pt/GC catalyst) in the onset potential with a complete suppression for the undesirable poisoning dehydration route. It also offered a much (up to 5-fold) better tolerance against the CO poisoning that normally deteriorates the performance of the DFAFCs. The electrochemical impedance spectroscopy and the Tafel representations agreed on the effective role of n-NiOx in improving the electronic properties of Pt at the surface. On parallel, an oxidative stripping voltammetry of CO from the NiOx/Pt/CNTs/GC catalyst confirmed the potential geometrical influence of CNTs in the divergence of n-Pt that mitigated the CO poisoning.