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大规模储能技术需要多功能的能量转换与存储系统，包括金属-空气电池、金属-二氧化碳电池以及电解水系统。为了应对当前世界面临的能源危机，我们迫切需要开发多功能电催化剂。近年来，人们致力于为二氧化碳还原反应（CO2RR）、氧还原反应（ORR）、析氧反应（OER）和析氢反应（HER）设计高效且经济的电催化剂。但是，开发一种能够同时高效催化上述所有过程的单一催化剂仍然是一个巨大的挑战。本论文针地这一问题，开展了系统研究，以获得高催化活性的多功能电催化材料，具体研究成果如下： 首先设计、合成了高效的兼具ORR和OER双功能电催化剂。该催化剂是在惰性条件下热解经双氰胺改性的ZIF-67而获得。热解后，Co单原子均匀地分散在具有清晰形态、高孔隙率和独特结构的碳纳米管表面上。所得电催化剂对ORR和OER均表现出显著的催化性能，在碱性介质条件下的ORR过程中，催化剂的起始电位为0.99 V（相对于可逆氢电极RHE），比Pt/C的起始电位高。而且其半波电位为0.86 V（相对于RHE），还具有较小的塔菲尔斜率，呈现出较高的四电子还原选择性。此外，催化剂在OER过程中，当起始电位为1.53 V（相对于RHE）时，达到10mA/cm2时过电位为300 mV。 进一步，我们设计了一条高效多功能催化剂的简单合成策略，该催化剂能够在相应条件下催化上述所有过程，并且具有优异的活性和稳定性。该催化剂以N掺杂碳纳米管为基底，将双金属合金和单原子结合在一起。因此，该工作首次报道了具有多活性位点协同效应的四功能电催化剂在多种能量转换与存储系统中的应用。所得电催化剂对ORR、OER、HER和CO2RR均表现出优异的性能。在OER过程中，该催化剂的正起始电位（0.98 V）和半波电位（0.86 V）均高于Pt/C的。同时还具有250 mV的极低过电位（η10），以及为0.62 V的ORR/OER电位差。在碱性介质中，该催化剂还表现出优异的HER性能（η10 = 49 mV），并且在全水解过程中获得了目前为止较小的电池偏压（为1.57 V）。此外，在0.5 M的KHCO3介质中，该催化剂还获得了法拉第效率为99%的优异CO2RR性能。 进一步，合成了一种新型三功能Br掺杂和缺陷富集的多孔碳骨架（BrHT@CoNC），该复合结构对ORR、OER和HER均具有良好的电催化活性。通过热解由表面活性剂二甲基十八烷基溴化铵（DODAB）改性的ZIF-67，巧妙地将大量缺陷和Br掺杂结合到了多孔炭中。当BrHT@CoNC复合材料作为可充电锌-空电池和全水解的催化剂/电极时显示出巨大的潜力。新型电催化剂的研究结果将为研究此类材料以及设计更多优异的电催化剂开辟新的道路，这对未来的可再生能源技术具有革命性的意义。这些工作也为探索在一个独立电极上高效集成三个或多个功能的高性价比的电催化剂提供了方向。;Scalable energy storage technologies require multi-functional energy conversion and storage systems, including metal–air batteries, metal–CO2 batteries and water splitting. The development of multi-functional electrocatalysts is urgently needed to combat the current energy crisis faced by the world. Recently much effort has been devoted to design efficient and cost-effective electrocatalysts for CO2 reduction reaction (CO2RR), oxygen reduction reaction (ORR), oxygen evolution reactions (OER), and hydrogen evolution reactions (HER), but the development of single catalyst which can catalyze all the processes simultaneously and efficiently is still a great challenge and no reports are being published to the date. In the present work, report a simple strategy for designing highly efficient catalyst for both oxygen reduction (ORR) and oxygen evolution reactions (OER). The catalyst is derived from dicyandiamide modified ZIF-67 by subsequent pyrolysis under inert conditions. Co single atoms are well dispersed over the surface of entire carbon nanotubes network formed upon pyrolysis with well-defined morphology, high porosity and unique structural features. The prepared electrocatalyst has shown up remarkable performance for both ORR and OER. The bifunctional property of the material is best amongst the previously reported catalysts. The catalyst shows highly positive onset potential value of ~0.99 V vs. reversible hydrogen electrode (RHE) higher than that of Pt/C for ORR and half wave potential value of 0.86 V vs. RHE, also more positive than Pt/C in alkaline medium with small Tafel slope as well and high selectivity for four electron reduction process. A lower overpotential for OER of 300 mV is observed for onset potential of 1.53 V vs. RHE. Smaller value of overvoltage (rE) 0.78 V pronounces the excellency of material for bifunctional catalysis. In second project, we report a simple strategy for designing highly efficient catalyst capable of catalyzing all these process with excellent activity and stability under technological conditions. The catalyst integrates bimetallic alloy and single atoms, with N-doped CNTs acting as substrate. As a result, the first ever tetra-functional electrocatalyst utilizing synergetic effect of multiple active sites is reported for utilization in multi-model energy conversion and storage system. The prepared electrocatalyst has shown up remarkable performance for ORR, OER, HER and CO2RR. The catalyst exhibits more positive onset (0.98 V) and half wave potential (0.86 V) than Pt/C for ORR, extremely low overpotential (η10) of 250 mV for OER and thus the lowest ORR/OER potential gap of 0.62 V. In alkaline medium, the catalyst also shows excellent HER performance with η10 of 49 mV, resulting in the smallest cell bias of 1.57 V for overall water splitting to date. An excellent CO2RR with FE of 99% is achieved in 0.5 M KHCO3 medium. In another work, a novel trifunctional Br doped and defect-enriched porous carbon framework (BrHT@CoNC) is designed, which shows excellent electrocatalytic activity for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER). Combination of extensive defects and Br-doping into porous carbon is simply achieved by pyrolysis of the surfactant, dimethyldioctadecylammonium bromide (DODAB) modified ZIF-67. The BrHT@CoNC composite shows great potential as an economical catalyst/electrode for both rechargeable Zn–air batteries and overall water splitting. The successful doping of Br atoms into the carbon framework introduces more defects and thus electronic redistributions, which lead to excellent activity for electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER). For ORR, the prepared catalyst exhibits more positive onset and half wave potential (by 40 mV and 80 mV respectively) than commercial Pt/C. Overpotential (h10) of only 254 mV and 77 mV is required for OER and HER respectively in alkaline medium. The rechargeable Zn-air battery was assembled by using the catalyst as air cathode, which showed an output power density of 165 mW cm-2.The promising results shown by novel electrocatalysts will open up new paves for the scientific community to explore and investigate such materials and design more stellar electrocatalyst which could be revolutionary for future renewable energy technology. This work also provides avenue toward the exploration of cost effective heteroatom doped catalysts for efficient integration of three or more functions in one freestanding electrode.
|SOBIA DILPAZIR . 金属有机框架衍生多功能电催化材料的设计及性能研究[D]. 中国科学院大学,2020.|
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