Enhanced hydrogen generation using a saline catholyte in a two chamber microbial electrolysis cell

Abstract

High rates of hydrogen gas production were achieved in a two chamber microbial electrolysis cell (MEC) without a catholyte phosphate buffer by using a saline catholyte solution and a cathode constructed around a stainless steel mesh current collector. Using the non-buffered salt solution (68 mM NaCl) produced the highest current density of 131 ± 12 A/m 3, hydrogen yield of 3.2 ± 0.3 mol H 2/mol acetate, and gas production rate of 1.6 ± 0.2 m 3 H 2/m 3·d, compared to MECs with catholytes externally sparged with CO 2 or containing a phosphate buffer. The salinity of the catholyte achieved a high solution conductivity, and therefore the electrode spacing did not appreciably affect performance. The coulombic efficiency with the cathode placed near the membrane separating the chambers was 83 ± 4%, similar to that obtained with the cathode placed more distant from the membrane (84 ± 4%). Using a carbon cloth cathode instead of the stainless steel mesh cathode did not significantly affect performance, with all reactor configurations producing similar performance in terms of total gas volume, COD removal, r cat and overall energy recovery. These results show MEC performance can be improved by using a saline catholyte without pH control.