Preparation Of Water Hyacinth-derived Porous Carbon Catalysts And Their Applications

The growing global energy crisis and serious environmental concerns have driven extensive research into rechargeable zinc-air batteries（ZABs）,which are considered a viable energy source of the future due to their high theoretical energy density,lack of pollution and safety.Among them,the Oxygen Reduction Reaction（ORR）is severely limited in overall efficiency by its high overpotential,low exchange current density and slow kinetic process.Pt-based catalysts are generally considered to have significant electrocatalytic activity for ORR,but their high price,scarce resources,unsatisfactory durability and poor toxicity resistance have fundamentally hindered the commercialization of these energy devices.Therefore,it is crucial to find alternative Pt-based catalysts that are rich in earth’s natural resources,low in cost,and have high catalytic activity.Porous carbon materials have been extensively studied for their excellent electrical conductivity,tunable morphology,high surface area,abundant precursors,and chemical and structural stability.Although carbon nanotubes,graphene and other carbon materials have good catalytic activity,their large-scale commercialization is limited by their high cost and synthetic processes.Therefore,advanced carbon-based catalysts based on biomass resources have received a lot of attention and are considered as ideal substrates for electrocatalysts due to their renewable,environmentally friendly and low-cost advantages.Thus,in this paper,biomass-derived porous carbon materials were prepared by a facile method for application in ZABs.The two main studies are as follows:（1）A two-step pyrolysis method for producing N-doped porous carbon catalysts from water hyacinth is provided.The produced catalysts have enhanced ORR activity,a superior half-wave potential(ΔE_1/2=0.843 V)as comparison to commercial Pt/C(ΔE_1/2=0.83 V),and noteworthy cycling stability after 2000 cycles.Additionally,this catalyst is utilized to create a rechargeable Zn-air battery（ZAB）,which performs better than the Pt/C-Ru O2 battery already on the market thanks to its high specific capacity（775 m Ah/g）and battery charge/discharge cycle stability（212 h）.This finding paves the way for the creation of biomass-derived heteroatom-doped carbon catalysts that are cost-effective,high-performing,and ecologically benign.（2）ORR electrocatalysts were prepared by a one-step pyrolytic reduction strategy in which non-precious metal elements were doped with N elements in a carbon carrier.The catalysts were prepared using water hyacinth（SHL）,which has an internal lamellar structure and is enriched for metal and N elements,as a template,and the ORR electrocatalysts containing uniform Fe-N_Xactive sites in a porous carbon network resembling the shape of worm-eaten rotten wood.After impurity removal by acid leaching,the catalyst SHL-Fe-HMNC exhibited excellent ORR catalytic activity with a half-wave potential up to 0.881 V,which was better than the commercial Pt/C（0.838 V）.When used as a cathode material for liquid ZABs,it has a power density of 108 m W/cm²,higher than commercial Pt/C-Ru O₂（92 m W/cm²）;and over 45 hours of cycling stability at a current density of 10 m A/cm².This is attributed to the unique and stable rotten wood-like structure of water hyacinth and the uniformly dispersed active sites on porous carbon,offering promising application potential for portable electronic zinc-air battery-related devices.In this paper,porous carbon material electrocatalysts are prepared using water hyacinth as a precursor by incorporating different forms of doping and Zn Cl₂activators to promote ORR catalytic performance.Both catalysts prepared exhibit excellent ORR performance and are used to prepare liquid-and solid-state ZABs with satisfactory cycling stability,which paves the way for the development of water hyacinth as a carbon substrate material and provides a new idea for the study of ZABs.