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

Area of Science:

• Electrochemistry
• Renewable Energy Storage
• Biotechnology

Background:

• Renewable energy sources like solar and wind require efficient storage due to intermittency.
• Bioelectrochemical Power-to-Hydrogen systems offer a promising energy storage pathway.
• High costs and low productivity limit current bioelectrochemical systems, necessitating novel materials.

Purpose of the Study:

• To evaluate five different cathode materials for hydrogen and methane production in microbial electrolysis cells (MECs).
• To assess the performance of custom-made biochars derived from olive mill waste (OMW) and commercial carbon materials.
• To investigate the impact of operating voltage (600 and 800 mV) and microbial colonization on system efficiency.

Main Methods:

• Microbial electrolysis cells (MECs) were operated at 600 and 800 mV using five cathode types: stainless steel mesh (SSM), two biochars (OMW-1, OMW-2), and two commercial carbons (Carbon Black - CB, Black Pearls - BP).
• Hydrogen and methane yields were measured.
• Cyclic voltammetry and next-generation sequencing were used to analyze electrode performance and microbial community composition.

Main Results:

• OMW-1 biochar achieved a notable H2 yield of 257 mL L−1 d−1 at 800 mV.
• Commercial Carbon Black (CB) and stainless steel mesh (SSM) exhibited the highest H2 yields (493 and 496 mL L−1 d−1, respectively) at 800 mV.
• Hydrogen-oxidizing bacteria colonization negatively affected H2 yields. OMW-2, BP, and CB showed increased methane production at 600 mV. OMW-2 demonstrated energy efficiency comparable to CB and BP, outperforming SSM.

Conclusions:

• Carbon-based cathodes are viable, sustainable alternatives to traditional metal electrodes for MECs.
• Custom biochars, particularly OMW-1, show potential for cost-effective hydrogen production.
• Optimizing electrode materials and managing microbial communities are crucial for enhancing energy productivity in bioelectrochemical systems.