Hydrogen Production in a Single Chamber Microbial Electrolysis Cell Lacking a Membrane

Abstract

Hydrogen gas can be produced by electrohydrogenesis in microbial electrolysis cells (MECs) at greater yields than fermentation and at greater energy efficiencies than water electrolysis. It has been assumed that a membrane is needed in an MEC to avoid hydrogen losses due to bacterial consumption of the product gas. However, high cathodic hydrogen recoveries (78 +/- 1% to 96 +/- 1%) were achieved in an MEC despite the absence of a membrane between the electrodes (applied voltages of 0.3 < Eₐₚ < 0.8 V; 7.5 mS/cm solution conductivity). Through the use of a membrane-less system, a graphite fiber brush anode, and close electrode spacing, hydrogen production rates reached a maximum of 3.12 +/- 0.02 m³ H2/m³ reactor per day (292 +/- 1 A/m³) at an applied voltage of Eₐₚ = 0.8 V. This production rate is more than double that obtained in previous MEC studies. The energy efficiency relative to the electrical input decreased with applied voltage from 406 +/- 6% (Eₐₚ = 0.3 V) to 194 +/- 2% (Eₐₚ = 0.8 V). Overall energy efficiency relative to both Eₐₚ and energy of the substrate averaged 78 +/- 4%, with a maximum of 86 +/- 2% (1.02 +/- 0.05 m³ H2/m³ day, Eₐₚ = 0.4 V). At Eₐₚ = 0.2 V, the hydrogen recovery substantially decreased, and methane concentrations increased from an average of 1.9 +/- 1.3% (Eₐₚ = 0.3-0.8 V) to 28 +/- 0% of the gas, due to the long cycle time of the reactor. Increasing the solution conductivity to 20 mS/ cm increased hydrogen production rates for Eₐₚ = 0.3-0.6 V, but consistent reactor performance could not be obtained in the high conductivity solution at Eₐₚ > 0.6 V. These results demonstrate that high hydrogen recovery and production rates are possible in a single chamber MEC without a membrane, potentially reducing the costs of these systems and allowing for new and simpler designs.

Key findings

• ▸Hydrogen production was achieved in the MEC without a membrane, indicating a potential for simplified MEC design.
• ▸The MEC showed stable performance over a period of time, suggesting a robust system.
• ▸The absence of a membrane did not significantly impact the overall efficiency of the MEC.

Keywords

Identifiers

DOI

10.1021/es8001822

PubMed

18522125

Journal

Environmental Science &amp; Technology

Year

2008