Tuning Hydrogen versus Methane Production on Sustainable Biochar-Based Cathodes in Microbial Electrolysis Cells by Voltage Control

High Resolution Image Download MS PowerPoint Slide Due to the intermittency of solar and wind energy generation, efficient energy storage solutions are essential to ensure a global transition to renewable energy sources. Bioelectrochemical Power-to-Hydrogen systems are a promising storage pathway, yet their development is limited by high costs and low productivity compared to conventional hydrogen production. Novel, sustainable, and cost-effective materials, such as carbon-based electrodes, can help to overcome these challenges. This study evaluates five cathodes for hydrogen and methane production in microbial electrolysis cells (MECs) operated at 600 and 800 mV: stainless steel mesh (SSM), two custom-made biochars derived from olive mill waste (OMW-1, OMW-2), and two commercial carbon-based materials (Carbon Black and Black Pearls). OMW-1 achieved a H 2 yield of 257 ± 62 mL L –1 d –1 at 800 mV, showing the potential of noncommercial biochar. CB and SSM performed better, reaching 493 ± 57 and 496 ± 9 mL L –1 d –1 H 2, respectively. Cyclic voltammetry and next-generation sequencing revealed that hydrogen-oxidizing bacteria colonization negatively impacted H 2 yields. At 600 mV, increased CH 4 production was observed for OMW-2, BP, and CB. Energetically, OMW-2 (3.0 ± 0.2 kWh L –1 d –1 ) performed comparably to CB and BP (both 3.3 kWh L –1 d –1 ), outperforming SSM at both voltages. These findings support the viability of carbon-based cathodes as sustainable alternatives to metal-based ones with the potential to reduce electrode costs while maintaining or improving energy productivity.