title: The electron donating capacity of biochar is dramatically underestimated.
abstract: Biochars have gathered considerable interest for agronomic and engineering applications. In addition to their high sorption ability, biochars have been shown to accept or donate considerable amounts of electrons to/from their environment via abiotic or microbial processes. Here, we measured the electron accepting (EAC) and electron donating (EDC) capacities of wood-based biochars pyrolyzed at three different highest treatment temperatures (HTTs: 400, 500, 600 °C) via hydrodynamic electrochemical techniques using a rotating disc electrode. EACs and EDCs varied with HTT in accordance with a previous report with a maximal EAC at 500 °C (0.4 mmol(e(-)).gchar(-1)) and a large decrease of EDC with HTT. However, while we monitored similar EAC values than in the preceding study, we show that the EDCs have been underestimated by at least 1 order of magnitude, up to 7 mmol(e(-)).gchar(-1) for a HTT of 400 °C. We attribute this existing underestimation to unnoticed slow kinetics of electron transfer from biochars to the dissolved redox mediators used in the monitoring. The EDC of other soil organic constituents such as humic substances may also have been underestimated. These results imply that the redox properties of biochars may have a much bigger impact on soil biogeochemical processes than previously conjectured.
authors.affiliation: Center for Microbial Ecology and Technology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Antonin
authors.initials: A
authors.lastname: Prévoteau
authors.affiliation: Department of Biosystems Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Frederik
authors.initials: F
authors.lastname: Ronsse
authors.affiliation: Department of Biosystems Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.|Laboratory of Applied Physical Chemistry, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Inés
authors.initials: I
authors.lastname: Cid
authors.affiliation: Laboratory of Applied Physical Chemistry, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Pascal
authors.initials: P
authors.lastname: Boeckx
authors.affiliation: Center for Microbial Ecology and Technology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Korneel
authors.initials: K
authors.lastname: Rabaey
mesh_terms: D000327:Adsorption; D002606:Charcoal / Q000737:chemistry*; D055664:Electrochemical Techniques; D004566:Electrodes; D004579:Electron Transport; D004583:Electrons; D006358:Hot Temperature; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D016062:Porosity; D012987:Soil; D013696:Temperature; D014934:Wood
chemical_list: D006812:Humic Substances; D012987:Soil; C540010:biochar; D002606:Charcoal