Construction Of Carbon Based Noble Metal Electrode Materials Derived From Cucurbit[6]uril And Their Performance For Electrocatalytic Water Splitting

The development of new energy sources has been promoted owing to the ever-increasing energy crisis and environmental pollution.Hydrogen,as an environment-friendly and sustainable energy carrier,is of great importance to future energy supply.The electrochemical hydrogen evolution reaction has been developed as a kind of most popular technology for hydrogen production.It converts renewable electricity into storable hydrogen and offers a feasible device for relieving energy crises and environmental pollution.However,the electrochemical hydrogen evolution reaction has the problems of high overpotential of water electrolysis and low energy conversion efficiency,and thus the design and construction of catalysts with high activity and high stability are of great importance to the development of this technology.It is generally acknowledged that noble metals are regarded as the state-of-the-art electrocatalysts for hydrogen production by water splitting with excellent catalytic performances.However,their high price,low storage capacity and poor stability greatly impede the large-scale industrial application.The construction of carbon-based noble metal electrode materials has drawn tremendous research attention.The carbon as a stable and conductive substrate not only reduces the amount of noble metal but also tunes the electronic structure by interfacial interaction,improving the activity and stability of the material.The design of carbon-based noble metal electrode materials with outstanding performance has become a research focus in the past few years.Due to the unique molecular structural characteristics of supramolecular synthetic macrocycles cucurbituril,the carbon materials derived from cucurbituril show great potential in the preparation of efficient carbon-based catalysts.In this thesis,taking the design of efficient carbon-based noble metal materials as the foothold,using the carbon materials derived from synthetic macrocycle cucurbit[6]uril as the supports,we realized the optimization of the electronic structure of catalyst under the premise of fully exposed active sites to enhance the activity and stability of electrocatalyst by heteroatomic loading and constructing heterogeneous structures.The specific research contents include the following three points:1.Utilizing the advantages of supramolecular synthetic macrocycles cucurbit[6]uril with distinct porous structures,abundant N and O containing functional groups in the skeleton and ultra-high affinity for metal ions,a series of iridium nanoclusters doped electrocatalysts using cucurbit[6]uril as the carbon source precursor,are designed and prepared,namely CBC-Ir.Interestingly,owing to the numerous N-containing backbone and unique porous structure from cucurbit[6]uril self-assembly,the newly designed catalysts CBC-Ir possess abundant N-doped and mesoporous structures without the need of additional N sources and templates,which ensures the full exposure of the active site.The catalysts exhibit superior catalytic performance toward the hydrogen evolution reaction with high Faradaic efficiency（91.5%and 92.7%）,superior turnover frequency(2.1 H₂ s^-1 and 0.69 H₂ s^-1)at the 50 m V overpotential,and only 17 m V and 33 m V overpotentials in acidic and alkaline conditions reaching current density of 10 m A cm^-2,better than the commercial Pt/C（28 m V and 43 m V）.This work not only expands the application of supramolecular macrocycles in the water splitting field but also provides a new approach for preparing robust electrocatalysts.2.The sluggish kinetics of hydrogen evolution reaction（HER）in alkaline media caused by high water dissociation energy of noble metals materials largely hampered this electrocatalytic performance.To further improve the electrocatalytic activity of noble metals in the alkaline environment,we fabricate an effective porous carbon matrix derived from cucurbit[6]uril using a template-free method to support iridium-molybdenum（Ir Mo）nanoclusters.As a proof-of-concept,the resulting Ir Mo-doped N-rich carbon electrocatalyst（Ir Mo-CBC）was found to boost the alkaline HER significantly.Through a strategy of heteroatom doping,the introduction of the oxyphilic Mo species into Ir can enhance the ability of H₂O adsorption and water dissociation on the surface of Ir Mo-CBC,which play an important role in modifying the HER kinetics.The optimized material exhibits pronounced alkaline HER activity with an extremely low overpotential of 12 m V at the current density of 10 m A cm^-2,ultrasmall Tafel slope(28.06 m V dec^-1),superior Faradaic efficiency（98%）,and TOF of 11.6 H₂ s^-1 at overpotential of 50 m V,outperforming Ir-CBC,commercial Pt/C and most iridium-based electrocatalysts.3.Optimizing the electronic environment of active noble metal nanoclusters to boost the catalytic performance of materials is highly important but extremely challenging.To further improve the electrocatalytic capacity and reduce the cost of the catalysts,herein,ruthenium-doped N,S co-rich porous carbon electrocatalysts based on cucurbit[6]uril as the carbon source precursor was fabricated,namely Ru-CBS.The strategy of N,S co-doping not only promotes the reduction of the Ru nanocluster sizes but also tunes the electronic structure of Ru,boosting the catalytic activity of the Ru-based materials.Benefit from the N,S co-doping backbone,abundant porous structure,the ultrafine Ru nanoclusters as well as their synergistic effect,the optimized material shows pronounced alkaline HER activity with an extremely low overpotential of 16 m V at the current density of 10 m A cm^-2,ultrasmall Tafel slope(33.68 m V dec^-1),outperforming most Ru-based electrocatalysts and commercial Pt/C.Moreover,the conversed Ru-CBS into Ru-Ru O₂heterogeneous nanoparticles loaded catalyst（Ru-Ru O₂-CBS）by the high-temperature oxidation method,the optimized material shows prominent oxygen evolution reaction（OER）activity with the overpotential of 210 m V at the current density of 10 m A cm^-2.Taking advantage of the excellent HER/OER catalytic performance of Ru-CBS and Ru-Ru O₂-CBS,the two-electrode device was constructed for efficient overall water splitting with voltage of 1.48 V at the10 m A cm^-2 in the alkaline medium.