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

## TL;DR

This paper explores how different cathode materials in microbial electrolysis cells affect hydrogen and methane production, aiming to find sustainable and cost-effective alternatives.

## Contribution

The study introduces biochar-based cathodes as a sustainable alternative to metal-based ones in microbial electrolysis cells.

## Key findings

- OMW-1 biochar achieved a hydrogen yield of 257 ± 62 mL L–1 d–1 at 800 mV.
- Carbon Black and stainless steel mesh outperformed biochar in hydrogen production.
- OMW-2 and commercial carbon materials showed comparable energy efficiency at 600 mV.

## Abstract

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 H2 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 H2, respectively.
Cyclic voltammetry and next-generation sequencing revealed that hydrogen-oxidizing
bacteria colonization negatively impacted H2 yields. At
600 mV, increased CH4 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.