Mass-Producible 2D-MoS2-Impregnated Screen-Printed Electrodes That Demonstrate Efficient Electrocatalysis toward the Oxygen Reduction Reaction

Samuel J Rowley-Neale,Graham C Smith,Craig E Banks

doi:10.1021/acsami.7b05104

Abstract

Two-dimensional molybdenum disulfide (2D-MoS2) screen-printed electrodes (2D-MoS2-SPEs) have been designed, fabricated, and evaluated toward the electrochemical oxygen reduction reaction (ORR) within acidic aqueous media. A screen-printable ink has been developed that allows for the tailoring of the 2D-MoS2 content/mass used in the fabrication of the 2D-MoS2-SPEs, which critically affects the observed ORR performance. In comparison to the graphite SPEs (G-SPEs), the 2D-MoS2-SPEs are shown to exhibit an electrocatalytic behavior toward the ORR which is found, critically, to be reliant upon the percentage mass incorporation of 2D-MoS2 in the 2D-MoS2-SPEs; a greater percentage mass of 2D-MoS2 incorporated into the 2D-MoS2-SPEs results in a significantly less electronegative ORR onset potential and a greater signal output (current density). Using optimally fabricated 2D-MoS2-SPEs, an ORR onset and a peak current of approximately +0.16 V [vs saturated calomel electrode (SCE)] and -1.62 mA cm-2, respectively, are observed, which exceeds the -0.53 V (vs SCE) and -635 μA cm-2 performance of unmodified G-SPEs, indicating an electrocatalytic response toward the ORR utilizing the 2D-MoS2-SPEs. An investigation of the underlying electrochemical reaction mechanism of the ORR within acidic aqueous solutions reveals that the reaction proceeds via a direct four-electron process for all of the 2D-MoS2-SPE variants studied herein, where oxygen is electrochemically favorably reduced to water. The fabricated 2D-MoS2-SPEs are found to exhibit no degradation in the observed achievable current over the course of 1000 repeat scans. The production of such inks and the resultant mass-producible 2D-MoS2-SPEs mitigates the need to modify post hoc an electrode via the drop-casting technique that has been previously shown to result in a loss of achievable current over the course of 1000 repeat scans. The 2D-MoS2-SPEs designed, fabricated, and tested herein could have commercial viability as electrocatalytic fuel cell electrodes because of being economical as a result of their scales of economy and inherent tailorability. The technique utilized herein to produce the 2D-MoS2-SPEs could be adapted for the incorporation of different 2D nanomaterials, resulting in SPEs with the inherent advantages identified above.

Highlights

The creation of a global energy system, where economic growth is decoupled from increased greenhouse gas emissions and other air pollutants, has been the aim of researchers since the implications of anthropogenic climate change and poor air quality issues were realized
We have reported upon the production, characterization, and implementation of 2D-MoS2 electrocatalytic inks that are utilized to produce SPEs/surfaces (2D-MoS2-SPE)
Through tailoring the lateral width of the MoS2 flakes utilized in the 2D-MoS2-SPE production from an average size ranging from approximately 400 nm to 2 and 6 μm, it was possible to optimize the 2D-MoS2-SPE electrocatalytic activity toward the oxygen reduction reactions (ORR)

Summary

INTRODUCTION

The creation of a global energy system, where economic growth is decoupled from increased greenhouse gas emissions and other air pollutants, has been the aim of researchers since the implications of anthropogenic climate change and poor air quality issues were realized. Hrdee2ssOuirlt2abi+nle2tahHse+tOh+eR2rReea−oc→tcicoun2rrHpinr2ogOdb.uyActnaistiwnweoffa-teeelcret,ci1vt0reoOen2lep+cattr2hoHwca+aty+a,l1y26s−et−1w8→,2il1l leading to the production of H2O2 that can cause the degradation of the proton exchange membrane and a fouling effect upon the anode and the cathode This will result in the PEMFC having a severe decline in its achievable voltage.[10] Literature suggests that there are direct[11] and indirect[12] H2O2 poisoning mechanisms. To overcome the critical issues identified above, we report the design, fabrication, and evaluation of inks that incorporate 2D-MoS2 that are able to be screen-printed producing 2DMoS2 screen-printed electrodes (2D-MoS2-SPEs). These inks and 2D-MoS2-SPEs are shown to be electrocatalytic toward the ORR. Future studies could seek to incorporate any of the plethora of the 2D nanomaterials into inks to produce SPEs designed to meet a niche in electrochemical applications

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

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