A methane-producing microbial electrolysis cell (MEC) is a promising energy-recovery technology, yet its, performance is generally inhibited by the insufficient cathode/anode ratio. In this study, a novel stacked stainless-steel-mesh cathode was designed to investigate the effect of the cathode/anode ratio on methane production in semi-continuous MECs.. Overall, energy recovery was significantly enhanced by increasing the cathode/anode ratio. The methane production rate in R3 (cathode/anode ratio of 4 cm(2)/cm(3)) reached 0.14 m(3) m(-3) day(-1) with an applied voltage- of 0.9T,-Which increased by 56-180% compared to the methane production rates in R2 (2.5 cm(2)/cm(3)) and R1 (1 cm(2)/cm(3)). The overall energy efficiency an R3 was 66-94% higher than the overall energy efficiencies in R2 and RI. The cathode area was sufficient for obtaining and maintaining a maximum current when the cathode/anode ratio was higher than 2.5 cm(2)/cm(3). According to electron balance analysis, when the cathode/anode ratio was less than 2.5 cm(2)/cm(3), the methane production enhancement was mainly attributed to the promotion of bioelectrochemical performance, while the sole biomass contribution was enhanced and led to further improvement in overall-1-methaneliroduction when the ratio was above 2.5 cm(2)/cm(3). In general, increasing the cathode/anode ratio of the staked-style cathode would be an effective strafeg-y to improve the methane production in the membraneless MECs.