| Since the second industrial revolution,with the gradual increase of human modernization,the consumption of fresh water resources has increased unprecedentedly,which has led to an insufficient supply of fresh water resources.Therefore,it is rational that we move our target to seawater.Desalination may be the most direct and effective solution to the freshwater crisis.However,the existing seawater desalination technology is faced with the problems of high maintenance cost,secondary contradictions,high energy consumption,huge carbon emissions,low water utilization rate and secondary pollution,so it cannot be applied in practice on a large scale.Thus,developing a low-cost,sustainable desalination strategy is urgently required.As a new seawater desalination technology,CDI(Capacitive deionization)has aroused more and more people's concern for low cost,high efficiency,and environmental friendliness.When the voltage is applied,ions will move towards desalination electrodes.However,carbon-based CDI suffers from various problems such as insufficient desalination capacity(due to the limited double-layer capacitance),relatively low charge utilization efficiency,and anode corrosion,which greatly hinder the further development of carbon-based CDI.To solve the above-mentioned issues,it is better to decipher the desalination mechanism of EDI(Electrochemical deionization)and identify the key reasons for these issues.It has the characteristics of no secondary pollution,high energy efficiency,high desalination capacity,and high desalination utilization ratio.However,it also faces some problems,for example,although EDI significantly improves the desalination capacity,the desalination rate still in the same range or even lower.As a result,the high desalination capacity cannot be matched with the desalination rate and it cannot meet the needs of practical applications.At the same time,most concerned focuses on the development of Faradic electrode materials for Na ion capture.This thesis focuses on the insufficient desalination capacity and poor cycling stability issues of EDI,by constructing one-dimensional pseudocapacitive electrodes.At the same time,we further explored the influence of the cell architecture on its desalination performance(i.e.,Rocking-chair Capacitive Deionization,RCDI and Dual-ion intercalation Electrochemical Deionization,EDI),in order to provide a solution to the above EDI bottleneck problem from the aspects of materials and devices.The details are as follows:1)The development of high-efficiency electrochemical desalination technology with minimal energy consumption and high stability is an urgent requirement to solve the global water crisis.Herein,Mo S2nanoflakes-coated carbon nanofibers(CNFs@Mo S2)are obtained by electrospinning and subsequent hydrothermal reaction.The CNFs@Mo S2shows excellent dual-mode capacitive performance,and the CNFs@Mo S2-based RCDI exhibits excellent desalination performances(desalination capacity:53.03 mg g-1;desalination rate:0.157 mg g-1s-1)with good long-term stability(11.2%reduction in 30 cycles).The superior performance should be due to the dual-mode capacitive behavior of the CNFs@Mo S2and the rational cell architecture(the ion intercalation/deintercalation capacity of“rocking-chair”capacitive deionization is more balanced than that of the asymmetrical cells like Hybrid Capacitive Deionization).This study is interesting because it exemplifies the key importance of dual-mode capacitive electrode materials and rational battery structures,which can provide a reference for the further development of efficient electrochemical desalination systems.2)Slow desalination kinetics and poor durability of the electrodes are two key limitations of EDI that are considered to be the next generation of CDI.Herein,we report the design of a high-efficiency chloride removal electrode material for accelerating the desalination kinetics and concurrently improving the durability of EDI,which is based on coating Ni Mn-Cl layered double hydroxides(LDHs)on the surface of electrospinning carbon nanofibers(CNFs@LDHs).The salient features of the as-developed CNFs@LDHs are that applying layer-structured LDHs with abundant redox-active sites to accelerate the pseudo-capacitive ion storage via fast ionintercalation/deintercalation,and leveraging the rigid CNF backbone to strengthen its durability by preventing the potential aggregation of LDHs.As expected,the CNFs@LDH based EDI system displays an ultrafast desalination rate of 0.51 mg g-1s-1and outstanding long-term stability(only 10.66%desalination capacity reduction after 35 cycles),which is achieved without sacrificing its excellent desalination capacity(72.04 mg g-1).This work could be inspirational for the future design of ultrafast and durable EDI approaching industrial desalination applications.3)Through the above two aspects of research,we have obtained the Faradic materials with outstanding performance of one-dimensional Na ion and Cl ion storage in desalination performance and cycling ability respectively,to further combine the advantages of the two.It lays the foundation for constructing DEDI system,and provides a rare platform for us to further study the effects of different EDI device structures on its desalination performance.As a result,we design CNFs@Mo S2|CNFs@LDH based DEDI desalination system.And the CNFs@Mo S2|CNFs@LDH based DEDI system showed excellent desalination performance(In the current density of 50 m A g-1,Na Cl remove quantity was 8.102 mg)and good cycle stability(Na Cl remove quantity decreased 28.42%under 30 cycle).And the CNFs@Mo S2||CNFs@LDH based electrode can effectively improve the desalination capacity and cycle stability of DEDI system.By comparing RCDI and DEDI desalination systems,it is found that DEDI system has an obvious advantage in desalination capacity,while RCDI system is better in desalination rate and cycle stability.This study provides a new scheme for material selection of DEDI system and a new idea for the development of EDI system. |
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