Enhancing energy efficiency and H2 production in lab-scale dual chamber microbial electrolysis cells: A focus on catholyte composition and voltage losses

Microbial electrolysis cells (MECs) have emerged as a promising technology for sustainable hydrogen production from wastewater treatment. An MEC consists of a microbial anode and a hydrogen evolution cathode, where microorganisms in the anode oxidize organic compounds, allowing the cathodic hydrogen production at lower potentials compared to abiotic electrolysis. The present study focuses on optimizing the catholyte composition and configuration in a MEC reactor to maximize hydrogen production rates while minimizing energy consumption. Indeed, buffer solutions of HCO3-, HPO42-, and H2PO4- at different concentrations and operation mode were tested as catholytes analysing hydrogen production rates and energy consumptions of the process. The results demonstrate the stability of the anodic electroactive biofilm over a 220-day period, achieving consistent COD removal and hydrogen production. The findings reveal that the catholyte composition and operating mode significantly affect the cathodic performances of the MEC. Indeed, catholytes with higher buffer concentrations allow for a limited catholyte alkalinisation improving hydrogen production rates while a low buffer solution promotes an increase in process energy consumption. Bicarbonate buffer solution utilized under batch operation mode showed the better performances for hydrogen production at the cathodic side of MECs showing a higher cathodic coulombic efficiency coupled with stable pH levels and cathodic potentials. Overall, this research demonstrates the potential of MECs for sustainable hydrogen production and highlights the importance of optimizing catholyte composition and operating mode to increase energy efficiency of process.