Electrolyte effects on hydrogen evolution and solution resistance in microbial electrolysis cells

Protonated weakacids commonly used in microbial electrolysis cell (MEC)solutions can affect the hydrogen evolution reaction (HER) through weak acid catalysis, and by lowering solution resistance between the anode and the cathode. Weak acid catalysis of the HER with protonated phosphate, acetate. and carbonate electrolyte species improved MEC performance by lowering the cathode's overpotential by Up to 0.30V at pH 5. compared to sodium chloride electrolytes. Deprotonation of weak acids into charged species at higher pHs improved MEC performance primarily by increasing the electrolyte's conductivity and therefore decreasing the Solution resistance between electrodes. The potential contributions front weak acid catalysis and solution resistance were compared to determine whether a reactor would operate more efficiently at lower pH because of the HER. or at higher pH because of solution resistance. Phosphate and acetate electrolytes allowed the MEC to operate more efficiently under more acidic conditions (pH 5). Carbonate electrolytes increased performance from pH5 to 9 due to a relatively large increases in conductivity. These results demonstrate that specific buffers call substantially contribute to MEC performance through both reduction in cathode overpotential and Solution resistance. (C) 2009 Elsevier B.V. All rights reserved.