Microbial electrolysis cell (MEC): A step ahead towards hydrogen-evolving cathode operated at high current density

Abstract

A microbial electrolysis cell (MEC) 6 L in volume was designed with the objective of maximizing the current density at the cathode. The highly saline electrolyte (NaCl 45 g·L−1) led to a low ohmic resistance, of 0.10 Ω, and made it possible to maintain current density of around 50 A·m−2 for weeks, with peak values up to 90 A·m−2 for hours. This was the highest current density reached in a MEC prototype so far. The gas outlet contained at least 66% H2, which gave a hydrogen flow rate up to 650 Ld−1 m−2 of cathode surface area. The energy and thermal yields were discussed. A numerical mass balance model was designed, which explained the value of the anode Faradaic yield above 100% and pointed out new issues related to high current density operation. In particular, it was shown that, at high current density, carbonate deposit can impact the gas composition.