Wood‐Derived Sphere‐Like Biochar Granules as an Electrode Platform for Future Bed Electrodes

Microbial electrochemical technologies (MET), among others, facilitate sustainable CO 2 conversion into chemicals at ambient temperature and neutral pH. Reactors used in MET, called bioelectrochemical systems (BES), come in different types; bed electrodes are prominent; however, they lack reproducible, geometrically defined granular electrodes. Typical carbon granules are irregular, have wide size distributions, and poorly defined electrochemical properties, which limit their engineering applications. This study introduces sphere‐like granular biochar (GB) cathodes, produced by pyrolyzing beechwood spheres at 850°C (GB850). GB850 electrodes were modified and characterized on a single‐granule basis. The hydrogen evolution reaction (HER) at neutral pH models abiotic cathodic reactions, reflecting its important role as an intermediate in CO 2 ‐reducing BES. To improve electrocatalytic activity, GB850 was modified with nickel‐molybdenum (GB850‐NiMo), and the uniform electrodeposition was verified through structural and compositional analysis. GB850‐NiMo exhibited an HER overpotential of only 106 ± 9 mV at −1 mA/cm 2 , 85% lower than that of GB850. Its electrochemical double‐layer capacitance ( C dl ) increased fourfold after NiMo deposition, indicating a larger electrochemically active surface area. The apparent stability of GB850‐NiMo highlights its potential to optimize bed electrodes in CO 2 ‐reducing BES through controlled modifications. The highly defined geometry of sphere‐like GB offers a valuable tool for future engineering.