Biochar-Terracotta Conductive Composites: New Design for Bioelectrochemical Systems

Abstract

Research in the field of bioelectrochemical systems is addressing the need to improve components and reduce their costs in the perspective of their large-scale application. In this view, innovative solid separators of electrodes, made of biochar and terracotta, are investigated. Biochar-based composites are produced from giant cane (Arundo Donax L.). Two different types of composite are used in this experiment: composite A, produced by pyrolysis of crushed chipping of A.donax L. mixed clay; and composite B, produced by pyrolysis of already-pyrolyzed giant cane (biochar) mixed with clay. Electrical resistivity, electrical capacity, porosity, water retention, and water leaching of the two composites types (A and B) with 1, 5, 10, 15, 20, and 30 mass percentages of carbon (w/w) are characterized and compared. Less than 1 kΩ cm of electrical resistance is obtained for composite A with a carbon content greater than 10%, while physical and electrical performances of composite B do not significantly change. SEM micrographs and 3D microcomputed tomography of different composite materials are provided, demonstrating a different matrix structure of carbon in the terracotta matrix. The possibility of suitably decreasing electric resistance and increasing water retention/leaching of composite A opens the way for a new class of resistive materials that can be simultaneously used as electrolytic separators and as external electric circuits, allowing a compact microbial fuel cell design. A proof of concept of such an MFC design was provided for different tested composites. Although all the anolytes become anaerobic, only the MFCs equipped with the composite A30% were able to produce power, reaching the maximum power peak in correspondence to resistance of about 1 kΩ. The low, but significant, produced power (about 40 mW m−2, cathode area) confirm that the proposed solution is particularly suitable for nutrient recovery and environment pollution bioremediation, where energy harvesting is not requested.

Biochar based cathode enriched with hydroxyapatite and Cu nanoparticles boosting electromethanogenesis

“…As indicated by the results, the undoped biochar and the 20Cu produced 3 times higher current density than the CC (7.4 ± 0.2 vs 2.6 ± 0.1 mAcm -2 ), thus ideally increasing 3 times the H2 content (and consequently of CH4) available at the electrode, probably due to a bigger specific projected area (macropores). However, for the composites, the presence of insulating HAP (resistivity of HAP is in the order of 10 9 cm vs few cm of the biochar [32,82]) increased the electrode resistivity lowering the current density circulating in the cells at 3.9 ± 0.1 mAcm -2 (10HAP) and 1.2 ± 0.1 mAcm -2 (5Cu/5HAP and 20Cu/10HAP) The electrochemical analysis confirms that this outcome is related to both this effect and the actual electrochemical active surface area (ECSA) of the electrode, lowered by a homogeneous dispersion of HAP nanoparticles on the surface of the material. The presence of Cu which should increase this last parameter (particularly for the sample 20Cu/10HAP) has no beneficial effect.…”

“…The choice of a more cost-effective material drove recent research toward carbon of biological origin (biochar) [28][29][30], which assures high porosity, good conductivity, high biocompatibility, acceptable mechanical strength, and resilience. Biochar is generally characterized by a high specific surface (reaching 100 m 2 m -3 ) with a porosity and pore size distribution that makes its surface entirely available for extracellular electron transfer by microbes [31,32]. The performance of biochar can, therefore, in principle, approach that of an ideal electrode to produce CH4, as confirmed by recent studies [33,34].…”

Testing novel multicomposite materials for electromethanogenesis

“…The canes were positioned in a quartz tube inside a horizontal furnace (Carbolite) and pyrolyzed accordingly. The pyrolysis procedure of the material was carried out according to the following protocol: 2 hours at 25 °C, slow heating (10 °C/min) up to 900 °C, 1 h held at 900 °C and cooling down to 25 °C according to [24]. During all the pyrolysis treatment, nitrogen flowed constantly at 1 NL/h.…”

Interface properties of hydroxyapatite in ternary composites cathodes for electromethanogenesis

“…A highly conductive and electroactive biogenic charcoal (biochar), 44 known for its biocompatibility, mechanical resistance, and performance in microbial electrocatalysis, 45 was chosen as the support for copper nanoparticles (Cu NPs). Cu NPs serve as the active phase promoting the reduction of CO 2 to a variety of higher order products, such as CH 4 , C 2 , or C 3 .…”