Hydrogen production in single-chamber microbial electrolysis cell under high applied voltages

Area of Science:

• Bioelectrochemical systems
• Renewable energy
• Microbial electrolysis

Background:

• Microbial electrolysis cells (MECs) offer a promising route for sustainable energy production.
• Operating MECs at voltages exceeding typical water electrolysis can enhance performance but risks unwanted side reactions.
• Understanding the impact of applied voltage and solution pH on MEC stability and efficiency is crucial for practical applications.

Purpose of the Study:

• To investigate the performance of single-chamber MECs at applied voltages higher than that for water electrolysis.
• To determine optimal conditions for high hydrogen production and current density while minimizing water electrolysis.
• To assess the feasibility of reducing MEC size and cost through high-voltage operation.

Main Methods:

• Single-chamber MECs were operated with acetate as substrate at concentrations of 1.0-2.0 g/L.
• Applied voltages ranged from 0.8 V to 2.2 V over 2600 hours (54 cycles).
• Experiments included varying acetate concentrations, applied voltages, and solution pH (7.0 vs. 11.2).

Main Results:

• MECs operated stably for over 20 cycles at 2.0 V and 2.2 V without significant water electrolysis.
• Maximum current density reached 27.8 ± 1.4 A/m² at 2.0 V, approximately three times that at 0.8 V.
• At 1.6 V and pH 11.2, current density reached 42.0 ± 10.0 A/m², with 97.2% hydrogen content in biogas, indicating inhibited methanogenesis.

Conclusions:

• Operating MECs at higher applied voltages (up to 2.2 V) is feasible and stable, avoiding significant water electrolysis.
• High voltage (1.6 V) combined with alkaline conditions (pH 11.2) maximizes hydrogen production and current density.
• This approach allows for significant reduction in MEC size and investment costs, paving the way for practical applications.