Carbon-Based Air-Breathing Cathodes for Microbial Fuel Cells

Irene Merino-Jimenez,Ioannis Ieropoulos,Santiago Rojas-Carbonell,Plamen Atanassov,John Greenman,Carlo Santoro

doi:10.3390/catal6090127

Abstract

A comparison between different carbon-based gas-diffusion air-breathing cathodes for microbial fuel cells (MFCs) is presented in this work. A micro-porous layer (MPL) based on carbon black (CB) and an activated carbon (AC) layer were used as catalysts and applied on different supporting materials, including carbon cloth (CC), carbon felt (CF), and stainless steel (SS) forming cathode electrodes for MFCs treating urine. Rotating ring disk electrode (RRDE) analyses were done on CB and AC to: (i) understand the kinetics of the carbonaceous catalysts; (ii) evaluate the hydrogen peroxide production; and (iii) estimate the electron transfer. CB and AC were then used to fabricate electrodes. Half-cell electrochemical analysis, as well as MFCs continuous power performance, have been monitored. Generally, the current generated was higher from the MFCs with AC electrodes compared to the MPL electrodes, showing an increase between 34% and 61% in power with the AC layer comparing to the MPL. When the MPL was used, the supporting material showed a slight effect in the power performance, being that the CF is more powerful than the CC and the SS. These differences also agree with the electrochemical analysis performed. However, the different supporting materials showed a bigger effect in the power density when the AC layer was used, being the SS the most efficient, with a power generation of 65.6 mW·m−2, followed by the CC (54 mW·m−2) and the CF (44 mW·m−2).

Highlights

Microbial fuel cells (MFCs) are an emerging technology, which offers a solution for two of the major challenges faced nowadays: energy production and wastewater management
Has a lower overpotential than carbon black (CB), which implies better catalytic ability of the activated carbon (AC) towards the oxygen reduction reaction (ORR), has a lower overpotential than CB, which implies better catalytic ability of the AC towards the ORR, as it has been studied in detail for other carbon containing materials [46]
The results show in all cases a significant difference in the conductivity of the material with the following order: stainless steel (SS) > carbon cloth (CC) > carbon felt (CF), underlining that the most conductive current collector was SS

Summary

Introduction

Microbial fuel cells (MFCs) are an emerging technology, which offers a solution for two of the major challenges faced nowadays: energy production and wastewater management. Recent field trials, where a stack of MFCs was directly connected to a urinal, demonstrated the capability of such device to light a room, showing the fast development of this technology [6]. MFCs generally consist of an anodic and a cathodic chamber separated by an ionic exchange membrane. The cation exchange membrane is generally used to avoid deterioration of the cathode electrode as a consequence of a biofilm formation and precipitation of calcium and sodium carbonate [13,14]. To minimize the internal resistance in air cathode MFCs, a membrane cathode assembly can be prepared by pressing the separator on the air cathode [15,16,17] or bringing both the membrane and the cathode into contact with hydrogel to improve membrane hydration [18,19]

Methods

Results

Conclusion