| Nowadays,the energy utilization efficiency in industrial production is not high,which leads to a large amount of energy waste.These energy losses are mainly discharged in the form of heat energy,which could also cause environmental pollution and other problems.Therefore,comprehensive utilization and recycling of waste heat energy is an important way to solve the problems of fossil energy shortage and environmental pollution.Nowadays,the medium and high-temperature waste heat utilization technology in China is relatively mature,while the low-temperature waste heat resources,especially low-temperature waste heat with temperature lower than 130degrees centigrade,have low recovery efficiency due to the challenges of difficult recovery,high initial investment and low available energy.Thermally regenerative ammonia battery(TRAB),as a novel low-temperature waste heat power generation technology,has attracted wide attention from researchers due to its mild reaction conditions,good scalability,and low investment cost.However,TRAB is currently unable to meet actual application requirements,mainly due to its low power density.There are many factors that affect the performance of TRAB,among which the specific surface area of the electrode and material transfer are the key factors.In order to improve the performance of TRAB,it is particularly necessary to use a three-dimensional electrode with a high electrode specific surface area,but this will lead to a larger internal mass transfer resistance in TRAB.In addition,the problem of battery self-discharge caused by the transmembrane transport of ammonia has not yet been solved.Aiming at the two existing problems of the TRAB with 3-D copper electrode,different flow reactor structures were constructed to strengthen the internal mass transfer of the copper foam electrode.To further improve the mass transfer of the reactor,the TRAB with three-dimensional fluidized electrode was also constructed.At the same time,the self-discharge mechanism of TRAB was explored,and ammonia crossover was suppressed by the modification of anion exchange membrane(AEM)and reactor structure design.The research contents of this paper mainly include:(1)Aiming at the problem of the large internal mass transfer resistance of the 3-D copper foam electrode,different flow reactors were designed to guide different flow methods such as flow-over,flow-through and penetrating flow to strengthen the mass transfer.On this basis,the battery performance was enhanced by optimizing the pore density of electrode and the flow rate of electrolyte;(2)To futhur enhance the mass transfer of the reactor,the TRAB with 3-D fluidized electrode was constructed and the stability of its power generation was studied.On this basis,the effects of particle size,stirring rate and current collector arrangement were also studied;(3)The self-discharge mechanism of TRAB was explored,and an effective ammonia crossover barrier was constructed by electrochemical deposition of graphene oxide on the surface of the exchange membrane.The intermediate buffer TRAB with double-layer AEM and the membraneless sequential cathode-anode flow battery structure were performed to regulate the transport of ammonia.The main results are as follows:1)The flow battery structure design was adopted to study the electricity generation characteristics of the TRAB with copper foam electrode.The results show that the utilization of flow conditions can enhance the mass transfer,and the penetration electrode flow method greatly improved the performance of TRAB,and the maximum power density reached 22.9 W/m~2.The pore size of the electrode material could affect the mass transfer of anode.When the pore density was lower than 100 PPI,the TRAB performance increased with the increase of the pore density.But much higher pore density led to a high resistance for mass transfer,which led to battery performance decrease,and the best pore density was 100 PPI.The flow rate of the electrolyte could also affect the mass transfer,and the battery performance will increase with the increase of the flow rate in a certain range,but the improvement was less and less obvious.2)The TRAB with three-dimensional fluidized electrode was constructed to enhance the mass transfer of the reactor.The results show that compared with the TRAB with copper foam electrode under the same condition,the performance of the TRAB with fluidized-bed reactor was significantly improved by 36.5%,which was mainly due to the enhanced internal mass transfer of the reactor.At the same time,the TRAB with fluidized-bed reactor had excellent reversibility and thermoelectric conversion efficiency in 15 batch cycles.The particle diameter could affect the fluidization of copper particles and subsequently affect the performance of the battery.The optimal copper particle diameter of the TRAB with fluidized-bed reactor was 187.5μm in this research.In addition,increasing the stirring rate within a certain range can further enhance the mass transfer and improve the performance of the TRAB with fluidized-bed reactor.3)The self-discharge mechanism of TRAB was investigated and the ammonia transport was regulated by the modification of anion exchange membrane.The results show that the self-discharge of TRAB was mainly caused by the transmembrane transport of ammonia and hydroxide,of which ammonia permeation occupied the main part.The ammonia that penetrated into the cathode will react with the cathode electrode and generated a mixed potential,resulting in a decrease in battery performance.The electrochemical deposition method can effectively modify the graphene oxide on the surface of AEM.The AEM modified with graphene oxide delivered a lower ammonia permeability,and the resistivity of the membrane did not change significantly.During the discharging process of the TRAB with the modified AEM,the ammonia crossover could be effectively suppressed.4)From the perspective of battery structure design,the ammonia crossover was further effectively regulated.The intermediate buffer structure with double-layer AEM can effectively inhibit the ammonia crossover,but it could increase the internal resistance of the battery and affect its power output.Considering the effects on battery performance and ammonia crossover,a comprehensive performance evaluation criterion(PEC)was proposed.The results show that the flow structure using ammonium sulfate buffer had the highest PEC.In order to realize the practical application of TRAB in the future,a sequential cathode-anode membraneless TRAB with flow-through electrode was constructed,which effectively inhibited the ammonia crossover while reducing battery cost and enhancing the mass transfer. |
PDF Full Text Request