Performance Enhancement And Application Of Thermal Regeneration Ammonia-based Battery With Composite Electrodes

The survival and development of human beings are inseparable from the support of energy and environment,and the increasing depletion of fossil energy and increasing environmental pollution have become issues that humanity must pay attention to.In the current industrial production,the heat generated by the combustion of fossil fuels is only partially used effectively,and a large part of the waste heat is not used and is directly discharged into the atmosphere.This not only leads to reduced energy utilization,but also causes pollution to the ecological environment.Therefore,it is imperative to carry out comprehensive treatment of waste heat and improve energy utilization.In the recovery and utilization of waste heat resources,low-temperature waste heat has challenges such as low availability and high difficulty in recovery,and the existing technologies for low-temperature waste heat utilization also have problems such as low conversion rate,complex system and high-cost recovery.In recent years,the team of Professor Logan at the University of Pennsylvania in the United States had proposed a power generation system that uses the principle of electrochemistry to convert low-temperature waste heat into electrical energy,named the thermally regenerative ammonia battery（TRAB）.TRAB has the advantages of mild reaction conditions,low cost,good scalability,and environmental friendliness.It has good potential in the recovery and utilization of low-temperature waste heat,which has attracted wide attention from researchers.However,the current performance of TRAB is low and the practical application experience is insufficient to meet the needs of practical applications.One of the key factors affecting battery performance is structure and stability of electrode.Porous electrode structure not only affects the electrochemical reaction area but also affects the material transport in porous electrode.And the stability of electrode also affects the electron transport.The traditional copper plate or copper mesh electrode has a small electrode surface area and is easily corroded to broke,which causes the power generation process to be terminated.In addition,for the expanded application of thermally regenerated ammonia batteries,especially the application technology foundation related to environmental treatment is still lacking.This article is based on the strengthening of material transport,starting from the construction of the TRAB composite electrode and expanding the application of TRAB.On the one hand,the construction of composite electrode structures with different substrates and the modification of reduced graphene oxide were carried out to improve the power generation performance of TRAB.On the other hand,applying TRAB to the treatment and recycling of waste copper resources to improve practicality of TRAB has great research significance and practical value.The research content can be summarized as the following three points.Firstly,aiming at the problem of copper electrode which is easily corroded to fracture,copper-coated composite electrodes were constructed using different substrate materials,the effect of composite electrodes of different substrate materials on the electrical performance of TRAB was studied,and the composite electrodes with the best substrate material was obtained.Based on the best composite electrode,reduced graphene oxide was used to increase the electrode reaction area and adjust the electrode pores,which help to obtain a further improvement of TRAB performance.Secondly,using the principle of cathodic electrodeposition reaction,TRAB is applied to the treatment of industrial electroplating wastewater.The effect of different Cu²⁺concentrations in the catholyte on the power generation performance and Cu²⁺removal rate of TRAB was studied by configuring simulated electroplating wastewater with different Cu²⁺content.And the method of TRAB combined with electrocoagulation to treat electroplating wastewater was prospected.Finally,applying TRAB to copper resource recovery of waste printed circuit boards（PCB）by using TRAB anode reaction principle.After pretreatment,the waste PCB is used as the anode electrode of TRAB,and the simple copper is recovered by the three-step method of"dissolution-thermal regeneration-electrodeposition".The feasibility of the method was studied first,and the effects of external resistance and ammonia concentration on the dissolution rate of copper on the PCB,battery power generation capacity,thermal regeneration and copper recovery rate were studied.The main results are summarized as below:1)Carbon paper,carbon cloth,foamed nickel and stainless steel mesh are used as the base material of electrode for copper plating,the TRAB was constructed in a plate reactor,and the reasons for the different performance and power generation of the battery composed of different electrodes were studied and analyzed.The results show that the performance,power generation capacity,cathode and anode coulombic efficiency of foam nickel as the base material are higher than those of carbon paper,carbon cloth and stainless steel mesh as the base material.The method of"Cyclic voltammetry+Constant potential reduction"can finally attach reduced graphene oxide to the surface of nickel foam to form reduced graphene oxide foam nickel;TRAB composed of copper-coated reduced graphene oxide nickel foam electrode has a higher performance than TRAB composed of copper-coated nickel foam electrodes.2)Based on the cathodic reaction principle of TRAB,in the experiment,solutions with different amounts of copper were equipped to simulate Cu²⁺containing electroplating wastewater in Cubic reactors,studied the effects of different copper ion concentrations in catholyte on the power generation performance and Cu²⁺removal rate of thermally regenerated ammonia batteries.The research results show that with the increase of Cu²⁺concentration in the waste liquid,the maximum power density of the battery will increase,the battery’s voltage,discharge time,discharge capacity and energy density also show an increasing trend;Taking TRAB technology to remove Cu²⁺from the waste liquid has a high removal rate,and the removal rate increases with the increase of Cu²⁺concentration in the waste liquid.Subsequent research may consider to take TRAB combined with electrocoagulation to treat copper-containing electroplating wastewater in stages to achieve the copper ion discharge standard（2 mg/L）.3)Based on the anode reaction principle of TRAB,a double-sided PCB is used as the anode electrode of TRAB in a plate reactor to construct a PCB-TRAB.The effect of external resistance on the power generation and dissolution rate of PCB-TRAB was studied,and the feasibility of“dissolution+thermal regeneration+electrodeposition”three steps method to recover copper from PCB was proven.The research results show that the external resistor will affect the discharge speed of PCB-TRAB,and then affect the power generation cycle.The smaller the external resistor is,the shorter discharge time and larger discharge capacity it will be.The smaller external resistor is also helpful to reduce the effect of ammonia permeation caused by long-term discharge results in higher Coulomb efficiency.In the dissolution step,after fully discharging of PCB-TRAB-A with different ammonia concentration under same conditions,the discharge capacity was the largest at 1.5 M ammonia concentration.After fully discharging at different ammonia concentration,the copper dissolution rates of PCB anode are all close to 100%.In the process of thermal regeneration,heating can effectively separate the ammonia in the solution,but there is still some residue;Cu（NH₃）₄²⁺cannot be completely decomposed by heating,but can be completely decomposed after adding a small amount of dilute sulfuric acid;In the electrodeposition step,the presence of ammonia permeation will increase the copper recovery rate with the discharge time first and then decrease.The PCB-TRAB-B with 1 M ammoniaconcentration has a copper recovery rate of 49.59%at the highest,the decline rate of the recovery rate in the later stage of the experiment was greatly affected by the ammonia concentration.The copper recovery rate of the 2 M ammonia concentration in the middle stage of the discharge decreased the fastest,followed by 1.5 M,and 0.5 M was the smallest.