Biochar-based Electrodes and Catalysts for Microbial Fuel Cells: Engineering Strategies, Mechanisms, and Performance
Abstract
Microbial fuel cells (MFCs) require low-cost, durable electrodes to replace conventional carbon materials and precious-metal catalysts. Biochar, a carbon-rich product of biomass pyrolysis, has emerged as a sustainable alternative for both electroactive anodes and oxygen-reduction reaction (ORR) cathode catalysts. Its tunable pore structure, surface chemistry, and renewable feedstocks can reduce costs while improving electrochemical performance. Free-standing biochar anodes also avoid polymeric binders that increase resistance, block active sites, and reduce durability. As a cathode catalyst, biochar can be tailored to favor either the four-electron ORR pathway for higher power generation in conventional and photosynthetic MFCs or the two-electron pathway for in situ H2O2 production in bioelectro-Fenton (BEF) MFCs. This review critically summarizes recent progress in biochar engineering for MFCs by relating feedstock composition, pyrolysis conditions, and modification methods to physicochemical properties and electrochemical behavior. It compares powder-based and free-standing biochar anodes, examines biochar cathode catalysts for ORR control, and discusses techno-economic, environmental, and future perspectives for rational electrode design.
🔬 Key Findings
Biochar serves as a sustainable, low-cost alternative to conventional carbon electrodes and precious-metal catalysts in MFCs, with tunable pore structure, surface chemistry, and renewable feedstocks.
Feedstock composition and pyrolysis conditions directly govern biochar's surface area, porosity, surface chemistry, and conductivity, dictating its electrochemical performance in MFCs.
Free-standing biochar anodes outperform binder-assisted powder coatings by avoiding resistance increase, active site blockage, and reduced long-term durability associated with Nafion, PVA, PVDF, and PTFE binders.
Heteroatom (N, S) doping and metal nanoparticle (Fe, Co) incorporation effectively tune biochar's electronic structure, enhance capacitance, introduce additional electroactive sites, and prevent pore clogging.
ORR pathway selectivity depends on MFC type: conventional/photosynthetic MFCs require 4e⁻ ORR for maximum power output, while bioelectro-Fenton MFCs rely on 2e⁻ ORR for in situ H₂O₂ production in pollutant degradation.
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