BACKGROUNDMicrobial electrosynthesis (MES) is a biocathode-driven process, producing high-value chemicals, from CO2. However, the low efficiency of the biocathode hinders the MES process efficiency significantly. RESULTSA novel 3D graphene-nickel foam (G-NF) cathode has been fabricated, by hydrothermal approach for the improvement of microbially-catalyzed reduction at the MES cathode. An increase of 1.8 times in the volumetric acetate production rate was obtained, compared with the untreated nickel foam. In MES with G-NF, a volumetric acetate production rate of 3.11 mmol L-1 day(-1) has been achieved; 70% of the electrons consumed were recovered and the final acetate concentration reached 5.46 g L-1 within 28 days. CONCLUSIONThe hierarchical porous G-NF cathode improved bacterial colonization and the efficiency of mass, nutrients and protons transfer due to its 3D composition; the graphene coating considerably increased the effective surface area for microbial adhesion, as well as the electron transfer rate of biofilm in the MES. This study attempted to improve the efficiency of the biocathode, and provides a promising large electrode for large-scale MES devices. (c) 2017 Society of Chemical Industry