The use of natural hierarchical porous carbon from Artemia cyst shells alleviates power decay in activated carbon air-cathode

Activated carbon (AC) air-cathode is demonstrated to be promising for the energy recovery from wastewaters. However, it suffers from the performance decay after long-term operation in microbial fuel cells (MFCs). Here we add a natural hierarchical porous nitrogen-rich carbon material, carbonized Artemia cyst shells (LC), to alleviate the power decay. When the air-cathode is made of a mixture of AC and LC with a mass ratio of 1:2 (named 1AC2LC), the current densities are 28% (the beginning) and 65% (after 1 year's operation) higher than AC cathodes, and the long-term power densities increase from 0.871 +/- 0.002 (AC) to 1.296 +/- 0.005 Wm(-2) (1AC2LC) after one year's operation. The Coulombic efficiency increases by 20% than the control. This can be primarily attributed to these inerratic hierarchical pores enhancing oxygen transfer in the catalyst layer since the oxygen mass transfer coefficient is increased by 3.4 times, where the meso-and macro-pores are enlarged, showing the importance of oxygen transfer on the longevity and energy production. Our results show a novel way, addition of inexpensive carbonized Artemia cyst shells, to optimize cathodic porous structure and enhance the longevity of MFCs. (C) 2019 Elsevier Ltd. All rights reserved.