The Design,Preparation,and Application Of Porous Carbon Materials Derived From Plants

The advantages of porous carbon materials include easy microstructure control,surface modification with multiple elements,and excellent conductivity and thermal conductivity.Porous carbon materials have long been concerned in energy and environmental-related fields such as electrochemical energy conversion and storage,industrial catalysis,and purification.As a result,they are considered one of the key materials for new energy and environmental protection industries.Currently,porous carbon materials primarily rely on directionally synthesized precursors,which have relatively simple chemical structures,complex preparation processes,and a tendency to produce harmful by-products.These limitations restrict the expansion and application of porous carbon material systems.Therefore,developing environmentally friendly novel porous carbon materials and enhancing functional application potential are significant importance.Plants,the most abundant and sustainable biomass resources in nature,possess a wealth of organic compounds and multi-elemental components,making them ideal novel porous carbon sources.This article selects the by-products of high-yield crops,specifically corn stalks and corn stigmas,which exhibit naturally ordered morphologies and pore structures,as precursors to prepare a series of plant-based novel porous carbon materials.It reveals the evolution process and carbonization mechanism of plant-derived precursors into carbon materials,clarifies the structural inheritance characteristics of carbon materials from their precursors,and achieves the application of plant-based porous carbon materials in hydrogen evolution reaction electrode materials,iodine capture agents,oxygen reduction reaction electrocatalysts,and sodium-ion battery anode materials through precise modification and effective decoration.The main achievements are as follows:（1）Firstly,using corn stalks with natural vascular bundle structures as a carbon source,their pyrolysis evolution process and carbonization mechanism are elucidated.The polysaccharides in corn stalks undergo aromatization,depolymerization,decarboxylation,and other processes to achieve carbonization,while the inherent aromatic structure in lignin macromolecules promotes the formation of a carbon framework,contributing to the preservation of the natural structure.Corn stalks carbon exhibits a macroscopic three-dimensional porous structure,constructing a cellular carbon framework primarily composed of large pores（～10μm）and straight pores.It is hydrophilic and gas-repellent,with a water absorption rate exceeding 350%,an electrical conductivity of 40.65 S m^-1,and good mechanical strength,making it a highly potential self-supporting electrode carrier.（2）Based on the above research,the natural micro architecture of corn stalks precursors is utilized to promote effective modification with ruthenium ions.The capillary action and spatial steric hindrance brought by the natural structure during the pyrolysis process facilitate the high dispersion of ruthenium metal nanoparticles,significantly enhancing the utilization rate of ruthenium.The corn stalks carbon carrier inherits the naturally ordered three-dimensional parallel pore micro architecture characteristics of the plant precursor,which facilitates processes such as electrolyte infiltration,ion diffusion,and bubble desorption,significantly improving electrocatalytic activity.The binder-free self-supporting carbon-based electrode material prepared through a one-step pyrolysis process is used for hydrogen evolution reactions.In an alkaline electrolyte,it exhibits an overpotential of 7 m V at 10 m A cm^-2,which is only one-third of the overpotential of commercial Pt/C.（3）Leveraging the three-dimensional interconnected porous micro architecture of corn stalks,a series of nitrogen-doped corn stalks-based hierarchical porous carbon materials are prepared through a chemical activation method using urea as a nitrogen source.These materials exhibit a specific surface area of 1892.99 m² g^-1 and a nitrogen doping level of 2.32 at.%.They demonstrate a gaseous iodine capture capacity of 3.14 g g^-1 and an iodine removal rate exceeding 97%in seawater environments,while exhibiting good anti-interference properties.Mechanism studies reveal that electron-rich groups represented by pyrrolic nitrogen enhance the affinity for iodine molecules by donating lone electron pairs to form donor-acceptor complexes with iodine molecules.The high specific surface area of the porous carbon provides the necessary accommodation space for capturing iodine,while the abundant pore structure facilitates the diffusion of adsorbed species.（4）Using corn stigmas,which possess a naturally narrow and elongated tubular micro architecture,as the precursor,a lamellar hierarchical porous carbon material was prepared with a specific surface area of 1137.42 m² g^-1.As the anode material for sodium-ion batteries,the larger interlayer spacing(d₀₀₂of 4.2（?）)within its carbon structure facilitates the insertion and extraction of sodium ions,while the interconnected pore structure enhances electrolyte wettability and shortens the ion migration path.In a half-cell,the reversible sodium storage capacity reached 175.5 m Ah g^-1 at 0.1 A g^-1.In a full-cell,the reversible sodium storage capacity achieved 104.9 m Ah g^-1 at 0.05 A g^-1,maintaining a capacity retention rate of 94.2%after 200 cycles with a coulombic efficiency exceeding 99%,demonstrating excellent cycling stability.（5）Finally,using lamellar corn stigmas-based hierarchical porous carbon as the carrier and hemin and Na HS as sources of iron,nitrogen,and sulfur,a lamellar hierarchical porous carbon-based oxygen reduction electrocatalyst loaded with iron single atoms was prepared.Theoretical chemical calculations revealed that the non-metallic heteroatom sulfur breaks the original symmetric electronic structure of Fe-N₄,optimizes its adsorption energy for oxygen intermediates in the rate-determining step,and improves the intrinsic activity of the electrocatalyst.The iron single-atom-loaded corn stigmas-based porous carbon electrocatalyst exhibited a half-wave potential of 0.872 V vs.RHE in alkaline electrolyte,surpassing that of commercial Pt/C（0.859 V）,demonstrating excellent oxygen reduction electrocatalytic performance.When used in a cathode-assembled zinc-air battery,it achieved a peak power density of 117 m W cm^-2,outperforming a commercial Pt/C cathode(98 m W cm^-2).