Although biomass-derived carbon and metal-organic-framework-based materials have been widely studied, their integration as self-supported cathodes for sediment microbial fuel cells remains limited. This study investigated carbonized wood cathodes functionalized with cobalt- and nickel-based metal-organic frameworks to improve charge storage and pulse power performance in sediment microbial fuel cells. The P. orientalis wood was first carbonized, functionalized with cobalt- and nickel metal-organic frameworks formed using benzene-1,3,5-tricarboxylic acid as the organic ligand, and then subjected to a second pyrolysis step to obtain self-supported composite cathodes. Structural and surface characteristics were examined using Fourier transform infrared spectroscopy, Field-emission scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, Raman spectroscopy, and X-ray diffraction. Electrochemical performance was evaluated using electrochemical impedance spectroscopy and galvanostatic discharge tests. The nickel-functionalized and cobalt-functionalized cathodes showed surface areas of 346.4 and 327 m2 g−1, respectively. Compared with the unmodified carbonized wood cathode, the MOF-functionalized cathodes exhibited lower impedance, smaller initial voltage drops, lower equivalent series resistance, faster voltage recovery, and higher apparent capacitance. The highest apparent capacitance reached 151.7 mF at −1.5 mA and a 5 s pulse duration for the nickel-functionalized cathode. In addition, the modified cathodes delivered a maximum pulse power density of about 3 W m−2. These results showed that cobalt- and nickel metal-organic framework functionalization improved the electrochemical response of carbonized wood cathodes and provided a sustainable route to developing high-performance cathodes for sediment microbial fuel cells.

Hierarchically porous carbon aerogels offer significant potential for next-generation energy storage, yet controlling their structure and electrolyte infiltration remains a key challenge. Here, we develop fully biobased carbon aerogels (CAs) derived from a lignin-cellulose nanocrystal blend via ice-templating and carbonization. The resulting anisotropic hierarchical porous structures are infused with poly(vinyl alcohol)-potassium hydroxide gel polymer electrolyte to form semi-solid composite electrodes. Time-resolved synchrotron X-ray microtomography enables direct visualization of structural evolution during carbonization and three-dimensional electrolyte infiltration. Image-based pore-scale modeling performed directly on reconstructed synchrotron X-ray tomographic volumes reveals how the real hierarchical pore network governs gel electrolyte distribution, accessible porosity, and ion transport pathways. The results show that aligned and interconnected pore networks enable deep, uniform electrolyte penetration, reduce transport tortuosity, and increase electrochemically active volume. The structure-transport-performance relationship is validated by electrochemical testing of symmetric supercapacitors, demonstrating stable capacitance and reduced internal resistance. This work establishes a concept for renewable porous carbon electrodes and introduces a scalable CA-gel electrolyte system for high-performance solid-state energy storage.

This study investigates the use of X-ray microtomography (XMT) to reveal the structure of complex porous biological tissues and the fluid flow through them during wetting. It also evaluates fluid dynamical simulations based on XMT data to reproduce and analyse these flows, with a final aim of revealing fluid transport and void formation in such tissues. To fulfil the objectives, the wetting flow of a polymer liquid through an initially dry conditioned Norway spruce wood sample is visualised using XMT at the MAX IV synchrotron. The liquid flow front progression captured after 24 s and 48 s reveals uneven filling of longitudinal tracheids and flow between them via the tiny pits which connect tracheids. Most tracheids fill between 24 and 48 s, possibly due to removal of air inclusions. Large density gradients near cell walls suggest that the fluid followed and deposited along wall structures. Computational fluid dynamics simulations (CFD) of saturated flow through the tomography-based geometry indicate velocity profiles that resemble pipe flow in longitudinal tracheids and flow rate differences among them. The latter indicates that the geometry itself may cause the experimentally observed uneven flow. Streamlines show intra-tracheid flow development and clear flow direction change at the pits. Additionally, wetting simulations, using a constant contact angle, capture initial uneven filling between the tracheids on shorter time scales than could be capture by the experiments. These simulations furthermore show air entrapment during filling, consistent with experimental observations. Combining XMT with CFD enables detailed studies of flow in biological porous media. Faster X-ray scanning, incorporating dynamic contact angles and accounting for diffusion in simulations could further refine insights into fluid progression during capillary-driven flow into complex structures of porous biological tissues.

The supercapacitive hierarchical porous carbon electrodes are obtained from wood species as feedstock, and their performance is investigated as a green alternative to conventional cathodes for use in sediment microbial fuel cells (SMFCs). In this context, wood-based electrodes are directly obtained by pyrolysis of spruce (Picea abies), cypress (Cupressus sempervirens), sycamore (Platanus orientalis) and poplar (Populus deltoides) wood blocks at 900 °C following a top-down synthesis route. The results show that wood-based cathodes perform much better than conventional carbon felt. The maximum power density of 1500 mWm−2 is achieved by cathodes derived from sycamore compared to 145 mWm−2 for carbon felt as cathodes. The high capacitance of wood-derived electrodes obtained from all wood species is demonstrated in electrochemical tests. The comparison of cathode performance shows that carbonized cypress and sycamore have a greater chance of being used as bio-inspired cathodes in the SMFC applications.