Nanocomposites Prepared from Carbon Nanotubes and the Transition Metal Dichalcogenides WS2 and MoS2 via Surfactant-Assisted Dispersions as Electrocatalysts for Oxygen Reactions.

Pedro Ferreira,Bárbara Abreu,Eduardo F Marques,Cristina Freire,Diana M Fernandes

doi:10.3390/ma14040896

Abstract

Fuel cells are emerging devices as clean and renewable energy sources, provided their efficiency is increased. In this work, we prepared nanocomposites based on multiwalled carbon nanotubes (MWNTs) and transition metal dichalcogenides (TMDs), namely WS2 and MoS2, and evaluated their performance as electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), relevant to fuel cells. The one- and two-dimensional (1D and 2D) building blocks were initially exfoliated and non-covalently functionalized by surfactants of opposite charge in aqueous media (tetradecyltrimethylammonium bromide, TTAB, for the nanotubes and sodium cholate, SC, for the dichalcogenides), and thereafter, the three-dimensional (3D) MoS2@MWNT and WS2@MWNT composites were assembled via surfactant-mediated electrostatic interactions. The nanocomposites were characterized by scanning electron microscopy (SEM) and structural differences were found. WS2@MWNT and MoS2@MWNT show moderate ORR performance with potential onsets of 0.71 and 0.73 V vs. RHE respectively, and diffusion-limiting current densities of −1.87 and −2.74 mA·cm−2, respectively. Both materials present, however, better tolerance to methanol crossover when compared to Pt/C and good stability. Regarding OER performance, MoS2@MWNT exhibits promising results, with η10 and jmax of 0.55 V and 17.96 mA·cm−2, respectively. The fabrication method presented here is cost-effective, robust and versatile, opening the doors for the optimization of electrocatalysts’ performance.

Highlights

Long-lasting and clean energies are vital to the development of future energetic sustainability
The images suggest that the 1D and 2D blocks interact, forming tightly bound and mixed composites, as could be expected from the fact that the blocks are coated by surfactants of opposite charge, and strong electrostatic interactions in solution are at play
Nanocomposites of multiwalled carbon nanotubes and transition metal dichalcogenides (TMDs) were successfully assembled via a colloidal method based on surfactant-assisted dispersions and electrostatic interactions between oppositely charged surfaces

Summary

Introduction

Long-lasting and clean energies are vital to the development of future energetic sustainability. The search for electrocatalyst-mediated energy conversion processes has delivered some technologies that, when coupled with renewable energies, are able to convert molecules present in the atmosphere (water, nitrogen or carbon dioxide) in addedvalue products (hydrogen, hydrocarbons and ammonia). Such processes can be found in many energy storage and conversion devices like metal-air batteries and fuel cells [1,2,3]. In reversible fuel cells, electrocatalysts should be bifunctional for ORR and OER and high performing. The state-of-the-art OER electrocatalysts (RuO2 and IrO2 )

Methods

Results

Conclusion