Efficient H2 production in a novel separator electrode assembly (SEA) microbial electrolysis cell

MECs convert organics from wastewater to H2 as a fuel, which has a higher value than CH4 produced by anaerobic digestion. So far, the deterioration of H2 recovery during long-term operation is considered the most concerning obstacle for MEC development and is mainly caused by H2 consumption by exoelectrogens, methanogens, and homoacetogens, especially in a single-chamber MEC. Thus, reducing H2 consumption is of great scientific significance to improve effective H2 recovery in MECs. Previous studies have adopted diverse measures to reduce H2 consumption in MEC, but still not efficient and sustainable for long-term operation. Inspired by the design of a diaper, a novel configuration of separator-electrode assembly (SEA) was developed, where the cathode was sandwiched between a hydrophilic polyvinylidenedifluoride (PVDF) membrane and a hydrophobic polytetrafluoroethylene (PTFE) membrane. The porous PVDF membrane is highly water-permeable to separate anode and cathode, guarantee proton transfer, and form a "water barrier" to effectively block H2 crossover. The PTFE membrane is gas breathable to accelerate H2 diffuse out of the membrane to a gas collecting chamber and prevent water leakage. By the virtue of the SEA cathode design, SEA-MECs demonstrated a high current density of 482.5–515 A/m3 and a high H2 production rate of 4.53–5.02 m3/m3/d for over 30 days with up to 90 % cathodic hydrogen recovery rate, under 0.8 V of applied voltage without any chemical bacterial inhibitors. This study proves that a novel MEC configuration design is greatly important, and by no means, will shed light on effective H2 harvesting from wastewater.