From compost to clean energy: influence of cathode potential evolution on hydrogen production in bioelectrochemical reactors.

Microbial bioelectrochemical technologies rely on the development of biofilms on electrode surfaces; therefore, a high surface area in packed anodes is advantageous for their performance. In addition, bioelectrochemical reactors (BERs) for hydrogen production require low-cost installation materials to enable large-scale implementation. In this study, a one-liter BER was constructed using 0.38 L of carbon felt as a packed bioanode, 0.65 L of compost leachate as the electrolyte, and a stainless-steel mesh cathode. The reactor was operated under an anode potential of 0.05 V vs. Ag/AgCl (KCl, 3.5 M) in batch cycles of 24 h each. After medium replacement, the maximum accumulated gas volume reached 2.37 L, corresponding to a production rate of 7.38 m⁻3 gas m⁻3 packed reactor d⁻1. The cathode potential varied over time, leading to fluctuations in energy efficiency, which exceeded 100%. Average energy, cathode and coulombic efficiencies over eight operational cycles were 124 ± 64%, 118 ± 56%, and 120 ± 61%, respectively. The gas yield obtained from compost leachate in the BER was within the upper range of productivity reported for microbial electrolysis cells. This work demonstrates a sustainable alternative for BER installation and operation and proposes a monitoring strategy to track energy efficiency during hydrogen production.