Throughtheuseofamembrane-lesssystem, a graphite fiber brush anode, and close electrode spacing, hydrogen production rates reached a maximum of 3.12 ( 0.02 m3 H2/m3 reactor per day (292 ( 1 A/m3) at an applied voltage of Eap ) 0.8 V. This production rate is more than double that obtained in previous MEC studies.