Metal Organic Framework Derived MnO2-Carbon Nanotubes for Efficient Oxygen Reduction Reaction and Arsenic Removal from Contaminated Water.

Vadahanambi Sridhar,Hyun Park,Kwang Hyo Jung,Inwon Lee

doi:10.3390/nano10091895

Abstract

Even though manganese oxides are attractive materials for batteries, super-capacitors and electro-catalysts for oxygen reduction reactions, in most practical applications MnO2 needs to be hybridized with conductive carbon nano-structures to overcome its inherent poor electrical conductivity. In this manuscript we report microwave-assisted synthesis of MnO2 embedded carbon nanotubes (MnO2@CNT) from Mn-H3BTC (benzene-1,3,5-carboxylic acid) metal organic frameworks (MOF) precursors. Using graphene oxide as microwave susceptible surface, MnO2 nano-particles embedded in three dimensional reduced graphene oxide (rGO) -CNT frameworks (MnO2@CNT-rGO) were synthesized which when applied as electro-catalysts in oxygen reduction reaction (ORR) demonstrated comparable half-wave potential to commercial Pt/C, better stability, and excellent immunity to methanol crossover effect in alkaline media. When carbon fiber (CF) was used as substrate, three-dimensional MnO2@CNT-CF were obtained whose utility as effective adsorbents for arsenic removal from contaminated waters is demonstrated.

Highlights

One of the major obstacles in the commercial development of fuel cells is the sluggish oxygen reduction reaction (ORR) at the cathode
Using graphene oxide as microwave susceptible surface, MnO2 nano-particles embedded in carbon nanotubes-reduced graphene oxide three dimensional, mesoporous frameworks (MnO2@CNT-rGO) were obtained which were applied as electro-catalysts for ORR reaction
A total of 12 mL of the above well dispersed suspension was dropped onto a 5 mm diameter glassy carbon rotating disk electrode (RDE) or rotating ring-disk electrode (RRDE, 4.93 mm inner diameter and 5.38 mm outer diameter) for two times and air dried naturally, fixed with a total loading mass of about 0.6 mg/cm2. 0.1 M KOH aqueous solution was used as the electrolyte whereas counter electrode was saturated calomel electrode (SCE) and Pt wire served as the reference electrode

Summary

Introduction

One of the major obstacles in the commercial development of fuel cells is the sluggish oxygen reduction reaction (ORR) at the cathode. There have been intensive efforts by researchers to develop low-cost and durable non-PGM electro-catalysts These efforts resulted in promising ORR catalysts which can be broadly classified into three categories: non-PGM metal catalysts [2], metal-free catalysts especially hetero-atom doped carbons [3] and hybrids of non-PGM catalysts with carbon nano-structures [4]. Pre-synthesized MnO2 nano-particles are mixed with functionalized carbon substrates whereas in in situ techniques, MnO2 nano-particles are synthesized either by sol-gel [40], hydrothermal [41], electrochemical reduction [42] of manganese salts in solutions in which nano-carbons like graphene or CNTs are dispersed. Using graphene oxide as microwave susceptible surface, MnO2 nano-particles embedded in carbon nanotubes-reduced graphene oxide three dimensional, mesoporous frameworks (MnO2@CNT-rGO) were obtained which were applied as electro-catalysts for ORR reaction. More ever by using carbon fibers as the microwave absorbers, MnO2 nano-particles embedded in carbon nanotubes anchored on carbon fibers (MnO2@CNT-CF) were obtained and its utility in removal of arsenic from contaminated water is reported

Materials and Methods

Electrochemical Measurements

Findings

Arsenic Removal Tests