The electron donating capacity of biochar is dramatically underestimated

Area of Science:

• Environmental Science
• Soil Science
• Electrochemistry

Background:

• Biochars are of significant interest for agronomic and engineering uses.
• Biochars can exchange electrons with their environment through abiotic or microbial actions.
• Understanding biochar's redox properties is crucial for soil biogeochemical processes.

Purpose of the Study:

• To accurately measure the electron accepting capacity (EAC) and electron donating capacity (EDC) of wood-based biochars.
• To investigate the influence of pyrolysis temperature on biochar's redox properties.
• To re-evaluate the underestimation of biochar EDC.

Main Methods:

• Hydrodynamic electrochemical techniques using a rotating disc electrode.
• Analysis of wood-based biochars pyrolyzed at highest treatment temperatures (HTTs) of 400, 500, and 600°C.
• Comparison of measured EAC and EDC with previous studies.

Main Results:

• Electron accepting capacities (EAC) showed a maximum at 500°C (0.4 mmol(e⁻)/gchar⁻¹).
• Electron donating capacities (EDC) were underestimated by at least one order of magnitude in previous studies.
• EDC reached up to 7 mmol(e⁻)/gchar⁻¹ for biochar pyrolyzed at 400°C, significantly higher than previously reported.

Conclusions:

• Slow electron transfer kinetics to redox mediators likely caused underestimation of biochar EDC.
• The EDC of soil organic constituents like humic substances may also be underestimated.
• Biochar's redox properties could have a more substantial impact on soil biogeochemical processes than currently recognized.