Active H₂ Harvesting Prevents Methanogenesis in Microbial Electrolysis Cells

Undesired H₂ sinks, including methanogenesis, are a serious issue faced by microbial electrolysis cells (MECs) for high-rate H₂ production. Different from current top-down approaches to methanogenesis inhibition that showed limited success, this study found active harvesting can eliminate the source (H₂) from all H₂ consumption mechanisms via rapid H₂ extraction using a gas-permeable hydrophobic membrane and vacuum. Active harvesting completely prevented CH₄ production and led to H₂ yields (2.62-3.39 mol of H₂/mol of acetate) much higher than that of the control using traditional spontaneous release (0.79 mol of H₂/mol of acetate). In addition, existing CH₄ production in the control MEC was stopped once the switch to active H₂ harvesting was made. Active harvesting also increased current density by 36%, which increased operation efficiency and facilitated organic removal. Energy quantification shows the process was energy-positive, as the H₂ energy produced via active harvesting was 220 ± 10% of external energy consumption, and a high purity of H₂ can be obtained.