Valuable 'green H(2) can be produced with a microbial electrolysis cell (MEC) To achieve a high volumetric production rate of high purity H(2) a continuous flow MEC with an anion exchange membrane a flow through bioanode and a flow through Ni foam cathode was constructed At an electrical energy input of 2 6 kWh m(-3) H(2) (applied cell voltage 1 00 V) this MEC was able to produce over 50 m(3) H(2) m(-3) MEC d(-1) (22 8 +/- 0 1 A m(-2)) The MEC had a low cathode overpotential compared to an MEC with Pt based cathode because of the high specific surface area of Ni foam (128 m(2) m(-2) projected area) The MEC performance however decreased during 32 days of operation due to an increase in anode and cathode overpotentials Scaling likely caused the increase in anode overpotential but it remained unclear what caused the increase in cathode overpotential (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved