A series of nano-Mg(OH)(2)/graphene (Gr) composites was synthesized via simple hydrothermal method using MgSO4 center dot 7H(2)O and graphene oxide (GO) as precursors, hydrazine hydrate as additive. Linear sweep voltammetry tests showed that the 2# composite synthesized from 50 wt.% MgSO4 center dot 7H(2)O and 50 wt.% GO with a surface density of 1.5 mg cm(-2) exhibited the best catalytic activity for hydrogen evolution reaction. The 2# composite was utilized as the cathodic catalyst in a microbial electrolysis cell (MEC) to facilitate hydrogen production. In the MEC tests, the nano-Mg(OH)(2)/Gr cathode was comparable with the Pt/C cathode in terms of current densities and energy efficiency. The hydrogen recovery, cathodic hydrogen recovery and hydrogen production rate obtained with nano-Mg(OH)(2)/Gr MEC were 71 +/- 12%, 83 +/- 9% and 0.63 +/- 0.11 m(3) H-2 m(-3) d(-1), slightly higher than those obtained with the Pt/C cathode MEC. The nano-Mg(OH)(2)/Gr cathode exhibited good stability, and it was inexpensive (less than 1.7% of the cost of the Pt/C cathode). These results demonstrated that the nano-Mg(OH)(2)/Gr composite was an effective HER catalyst because of its good catalytic capacity, durability, and low price. (c) 2016 Elsevier Ltd. All rights reserved.