Controllable Synthesis And Application Of Novel Carbon-based Functional Nanomaterials For Energy Conversion And Storage

Because of increasing energy crisis and environmental pollution in the new century,it is imperative to develop clean and renewable energy technology for sustainable development of human society.New energy devices such as fuel cells and metal-air batteries can directly convert the chemical energy of fuels into electrical energy,which exhibit the characteristics of high energy density,less environmental pollution,low cost and convenient use.However,the cost-effectiveness,catalytic activity and durability of electrode catalysts still cannot meet the needs of large-scale commercialization.Hence,the development of catalytic materials for the needs of practical applications is a great challenge.Among the reported catalytic materials,carbon-based nanomaterials have a wide application potential in energy conversion and storage technologies due to their earth-abundant,high conductivity,large specific surface area,diverse morphologies,and easy modification.It is of great significance to design and develop the low-cost and high-performance multifunctional carbon-based electrocatalysts for the promoting the large-scale application of clean new energy technology.Great efforts have been made to improve the multifunctional electrocatalytic activity of carbon-based electrode materials,but there is still a gap between the catalytic performance of the carbon-based and noble metal catalysts,which cannot meet the large-scale commercialization.To overcome this obstacle,the carbon frameworks with the hierarchical connected pore structures were constructed using graphene and carbon nanotubes as building blocks.The type and distribution of active species on the surface of carbon materials can be modulated by corroding,splicing,doping,coupling design and control of microhole structure,etc.to construct highly active centers,increase the active species and density of active sites and improve the performance of non-noble metal carbon-based electrocatalysts.The main research results are as follows:1?A novel boric acid-hydrothermal and pyrolysis treatment strategy is proposed to fabricate the unadulterated carbontube-graphene complexes?D/G-CTs-n,n:heat treatment temperature?with multifarious intrinsic defects by using graphene nanosheets and carbon nanotubes as building block and boric acid?H₃BO₃?as splicing agent.The close contact or juncture between open nanotubes and few-layer graphene in D/G-CTs-1000 constructs the hierarchical networks with plentiful channels,the larger surface area and outstanding conductivity.The as-prepared D/G-CTs-1000 exhibits efficient catalytic activity and long-term stability as trifunctional electrocatalyst for ORR,OER and HER.Impressively,the D/G-CTs-1000 have the catalytic ORR performance superior to commercial Pt/C,OER activity comparable to the benchmark IrO₂ catalysts and the catalytic HER efficacy higher than those catalysts reported in the literature.The primary zinc-air battery assembled with D/G-CTs-1000 as the electrode catalysts delivers higher power density and cycling stability outperforming the advanced Pt/C-based counterparts.The performance of overall water splitting system using D/G-CTs-1000 as electrode materials also exhibits a low cell voltage and a high durability,which is superior to most non-metal carbon-based materials.This work provides a universal and efficient synthetic strategy to produce the unadulterated carbons with high activity and long-time durability as trifunctional electrocatalysts and promote the widespread applications of metal-free electrocatalysts in sustainable energy conversion technology.2?Based on the boric acid-etched graphene and carbon nanotube,the high density pyridinic-N doped graphene-nanotube complexes with hierarchical networks?denoted NGT_B-n,n:heat treatment temperature?are fabricated by a facile and efficient hydrothermal-pyrolysis two-step control strategy using urea as nitrogen source.These controls and manipulations can significantly enhance the connection between the few-layer graphene and carbon nanotubes in the hierarchically porous carbon framework and create abundant defects that affect the electronic structure of carbon matrix and contribute to the oriented synthesis of the desired pyridinic-N species.The derived NGT_B-900 displays the excellent performance for catalyzing oxygen reduction reaction?ORR?and energy storage.In alkaline solution,the prepared NGT_B-900 as electrocatalyst for ORR exhibits efficient catalytic activity(E_1/2=0.89 V)and long-term stability,superior to the top-notch Pt/C(E_1/2=0.85 V)and other analogous catalysts reported in the literature.Moreover,it also delivers a high specific capacitance of 458 F g^-1 at the current density of 1 A g^-1 and good capacitance retention of 94.6%after 3,000 cycles.The liquid zinc-air battery?ZABs?using NGT_B-900 as cathode catalyst affords a higher open-circuit voltage?1.54 V?,power density(149 mW cm^-2)and specific capacity(873 mAh g_Zn^-1),as well as excellent cycling stability over the noble-metal counterparts?Pt/C;Pt/C+IrO₂?.This work provides an effective strategy for taking advantage of the abundant and low-cost resources to construct the highly efficient multifunction carbon-based materials with hierarchical networks for the promotion of large-scale development of the renewable energy conversion and storage technologies.3?S,N co-doped graphene/nanotube complexes?S,N-GCs-n,n:heat treatment temperature?are fabricated by multi-component self-assembly using defect-enriched graphene and nanotube as building blocks,urea as N source,and dibenzyl disulfide as S source.This synthesis route is conducive to enhancing the close connection between graphene and carbon nanotubes and inducing the anchoring of highly active pyridinic-N and thiophene-S species to the defects.Based on the high surface area and porosity as well as high-density S/N active sites,the prepared S,N-PCs-900 catalyst shows excellent ORR activity in alkaline medium.The ORR half-wave potential on S,N-PCs-900 catalyst could reach 0.90 V,which is 50 mV higher than that on commercial Pt/C and better than those on other non-metallic materials reported in the literature.In addition,S,N-GCs-900 electrode also shows high specific capacitance and capacity retention in the alkaline electrolyte.It delivers a high specific capacitance of 276 F g^-1at the current density of 1 A g^-1 and good capacitance retention of 95%after 5,000cycles.S,N-GCs-900 as an air cathode in a liquid rechargeable zinc-air battery,which has a high open circuit potential?1.52 V?,power density(164 mW cm^-2)and excellent cyclic stability without significant change after 24 h operation,superior to the advanced Pt-based battery in the practical application of metal-air batteries.The work provides an effective synthetic strategy for the preparation of low-cost and high-performance non-metal carbon-based multifunctional electrode materials.The prepared S,N-GCs-900 electrocatalyst exhibits widespread practical prospects.4?Two-dimensional?2D?graphene nanosheets and one-dimensional?1D?carbon nanotubes are constructed into wool ball-like carbon embedded NiCo bimetal alloy nanocomposites?NiCo@N-C-X,X:heat treatment temperature?with 3D open aisles by the hydrothermal and pyrolysis treatment.The built graphene/nanotube networks show highly 3D open aisles and peculiar microstructures,which not only facilitate mass and electron transport but also increase the active site density.In alkaline solution,the half-wave potential(E_1/2)of ORR on NiCo@N-C-900 could reach 0.88 V and the overpotential?E??of OER at a current density of 10 mA cm^-2 is 0.28 V,superior to those on the benchmark Pt/C(E_1/2=0.84 V)and IrO₂?E?=0.32 V?catalysts as well as the best Ni-Co electrocatalysts reported in the literature(E_1/2=0.87 V,E?=0.31 V).In acidic solution,the catalytic ORR activity on NiCo@N–C-900 is comparative to that on Pt/C and significantly higher than those on all reported Ni-Co electrocatalysts.The primary zinc-air batteries using NiCo@N-C-900 as the air electrode exhibite higher open-circuit potentials?OCPs?,peak power density and rechargeability than that using the Pt/C-based counterpart,exhibiting a higher practical value.5?A graphene/nanotube-constructed tremella-like carbon framework with 3D open aisles embedded with coupled Co_5.47N and Co₃Fe₇ nanoparticles(Co_5.47N@Co₃Fe₇/N-C-X,X:heat treatment temperature)is created via a hydrothermal-pyrolysis strategy.The mutual entanglement and connection of the few-layer graphene and nanotubes creates a carbon network with a hierarchically porous structure and multifarious active centers such as Fe-Co,Co?Fe?-N_x moieties and nitrogen-doped carbon?N-C?co-existing on the surface of the prepared Co_5.47N@Co₃Fe₇/N-Cs,exhibiting excellent trifunctional electrocatalytic performance for the ORR,OER and HER.The derived Co_5.47N@Co₃Fe₇/N-C-900 catalyst exhibits the highest ORR catalytic activity among the reported ORR electrocatalysts in basic medium and outstanding OER and HER performance.A primary zinc-air battery assembled with Co_5.47N@Co₃Fe₇/N-C-900gains an advantage over that with Pt/C-based counterparts.Besides,the performance of an overall water splitting device using Co_5.47N@Co₃Fe₇/N-C-900 as the electrode material is comparable to that using the Pt/C-IrO₂ mixtures.To the best of our knowledge,this is a top-notch trifunctional electrocatalyst for the ORR,HER and OER in comparison to those reported so far,demonstrating a large-scale commercial potential.In summary,the preparation method of highly efficient multifunctional non-noble metal catalysts and the effects of the composition,structure,morphology,and component interactions of catalysts on the catalytic and storage properties and their intrinsic correlations have been systematically studied in this work,which provides theoretical and experimental basis for the design and synthesis of low-cost,durable and high-efficiency carbon-based electrocatalysts.It is conductive to accelerate the large-scale commercialization process of non-noble metal carbon-based electrocatalysts.