【作者】 刘鹏；

【导师】 余林；

【作者基本信息】 广东工业大学 ， 化学工程与技术， 2021， 硕士

【摘要】 探索绿色能源汽车的电储能技术已成为可持续发展的必要需求。可充电式锌空电池（Rechargeable Zn-air batteries,ZABs）由于具有能量密度高、节能环保等优点,已成为传统锂离子电池的替代储能系统。然而,ZABs中氧还原和氧析出反应动力学缓慢,严重制约ZABs进一步发展。因此,需要开发经济高效的双功能电催化剂来实现ZABs的商业化。贵金属Pt-催化剂具有优异的氧还原（Oxygen Reduction Reaction,ORR）活性,而Ir-和Ru-催化剂是公认的（Oxygen Evolution Reaction,OER）基准催化剂,但它们不仅成本高、资源有限、寿命短,而且对OER和ORR的选择性较低,不利于ZABs大规模商业化应用。过渡金属基材料具有接近贵金属的活性,并且成本更低廉、耐腐蚀性能和稳定性更好,使其具有双功能电催化剂和应用于ZABs的潜力。围绕上述问题,本论文利用水热法-高温固相法制备了系列的改性碳负载钴基纳米催化剂,并研究了其电催化性能。主要内容和结论如下:（1）以葡萄糖为原料,通过NH₄Cl溶剂热法和高温煅烧得到N掺杂微孔碳球（N-C）,将吸附Co²⁺的N-C微孔碳球高温硒化,制备负载正交晶相CoSe₂纳米颗粒的N掺杂微孔碳球（o-CoSe₂@N-C）。研究表明,o-CoSe₂@N-C保持了N-C微孔碳球的高比表面积,电催化性能在负载后有明显提升,半波电位为0.81 V,略差于商用Pt/C,而极限电流与Pt/C一样,且更早达到稳态扩散控制。Tafel斜率为42 m V dec^-1、转移电子数为3.65左右,说明o-CoSe₂@N-C具有更快的ORR动力学反应过程,且反应接近四电子转移机制。催化剂的ORR性能提升主要受益于:N掺杂碳材料具有更多的吡啶N、石墨N以及o-CoSe₂与N-C之间的协同作用。（2）以浓硝酸（HNO₃）回流科琴碳（KC）得到的改性科琴碳（AK）为基底,四水合醋酸钴Co（AC）₂·4H₂O为钴源,采用水热合成法,合成出负载碳酸钴的酸改性碳纳米颗粒（CoCO₃/AK）,并将其作为前驱体,以硫粉为硫源,采用高温固相法进行煅烧,合成出负载硫化钴的酸改性碳颗粒（CoS₂/AK）。研究表明,所得的CoS₂/AK具有很好的结晶度,且保留较大比表面积,CoS₂纳米颗粒平均粒径为10 nm,并且高度分散在AK表面,确保具有活性位点更多。通过对比无硫粉高温固相煅烧得到的Co O/AK,结果证明,CoS₂/AK具有更优良的电催化ORR活性,其半波电流和极限电流密度分别为0.825 V和5.35 m A cm^-2,Tafel斜率为36 m V dec^-1,并且在使用计时电流法测试10 h后,材料仍然保持96%的初始活性。这主要归功于AK增强了复合材料的导电性,其表面的锚定效应使得CoS₂纳米颗粒避免高温团聚,而且CoS₂与AK之间的协同作用优化了材料电子结构,加快了电化学反应的电子传输,进而提升材料的电催化性能。（3）以CoCO₃/AK为前驱体、硒粉为硒源,通过高温固相法制备了酸性碳负载不同晶相硒化钴纳米颗粒。实验结果表明,两种晶型的硒化钴颗粒都具有优良结晶度,高温煅烧后未发生明显团聚,平均粒径均为10 nm。电化学测试结果表明,正交晶相o-CoSe₂/AK具有更优异的ORR和OER催化活性,在10 m A cm^-2处的OER过电位为390m V,优于Ir O₂;ORR半波电位为0.84 V,接近商用铂炭。这主要得益于CoSe₂内在的金属性质使其具有更丰富的电子云密度。与立方晶相c-CoSe₂/AK相比,正交晶相o-CoSe₂/AK具有更高比例的金属价态Co和更多的Co-Se共价键,这进一步提升了其双功能电催化活性。将该催化剂应用于锌空电池,结果显示,o-CoSe₂/AK比商用Pt/C和Ir O₂混合的催化剂具有更好的极化性能、更高的能量密度和循环稳定性。更多还原

【Abstract】 Exploring the electric energy storage technology of green energy vehicles has become a necessary requirement for sustainable development.Rechargeable Zn-air batteries（ZABs）are the alternative energy storage system for commercial lithium-ion batteries（LIBs）,resulting from their high energy density,energy saving and environmental protection.However,the sluggish reaction kinetics of oxygen reduction（ORR）and oxygen evolution（OER）on the air electrodes severely restricts the further development of ZABs.Therefore,it is necessary to develop cost-effective bifunctional electrocatalysts to realize the commercialization of ZABs.Pt-catalysts have excellent ORR activity,while Ir-and Ru-catalysts are recognized as the OER benchmark,but they are not only expensive,scarce,but also poor in stability and selectivity of OER and ORR,which are adverse in the commercialization of ZABs.Transition metal-based catalysts,with low cost,effective corrosion resistance and stability,possess catalytic performance comparable to precious metals,which make them bifunctional catalysts and potential applications of ZABs.Hence,focusing on the above-mentioned problems,a series of modified carbon-supported cobalt-based nanocatalysts were prepared by hydrothermal and high-temperature solid-phase method,and their electrocatalytic performance were studied in this thesis.The main contents and conclusions are as follows:（1）Using glucose as the raw material,N-doped microporous carbon spheres（N-C）were obtained by NH₄Cl solvothermal method and high temperature calcination.Then N-C spheres adsorbing Co²⁺were selenized at high temperature to prepare N-doped microporous carbon ball supported orthorhombic CoSe₂ nanoparticles（o-CoSe₂@N-C）.Results show that o-CoSe₂@N-C maintains the high specific surface of N-C microporous carbon spheres,providing more active sites for ORR.The electrochemical performance is significantly improved with a half-wave potential of 0.81 V,slightly worse than Commercial Pt/C.The limiting current density of o-CoSe₂@N-C possess is the same as Pt/C and reaches steady-state diffusion control earlier.Besides,the Tafel slope is 42 m V dec^-1 and the number of transferred electrons is around 3.65,indicating that o-CoSe₂@N-C has a faster ORR kinetic reaction process and the reaction is close to a four-electron mechanism.The improvement of ORR performance is mainly benefited from the fact that N-doped carbon materials have more pyridine-N and graphite-N,as well as the synergistic effect between o-CoSe₂ and N-C.（2）Using acidified Ketjenblack（AK）as the substrate modified by HNO₃,Co（AC）₂·4H₂O as the cobalt source,and urea as the precipitant,the modified carbon supported cobalt carbonate nanoparticles（Co CO₃/AK）was synthesized by hydrothermal method.Using Co CO₃/AK as a precursor,sulfur powder as a sulfur source,a high-temperature solid-phase method was used to synthesize modified carbon supported cobalt sulfide nanoparticles（CoS₂/AK）.Studies have shown that CoS₂/AK has fine crystallinity and retains a large specific surface area.Besides,CoS₂ nanoparticles,highly dispersed on the surface of AK,have an average particle size of 10 nm,which ensures more active sites.Compared with Co O/AK obtained by same calcination only without sulfur powder,the results prove that CoS₂ nano particles along with AK have stronger electronic interactions,contributing to better electrocatalytic ORR activity with the half-wave current of 0.825 V,limiting current density of 5.35 m A cm^-2,Tafel slope of 36 m V dec^-1.Furthermore,CoS₂/AK still maintains 96%of the initial activity after 10 h by chronoamperometry test.The decent ORR activity of CoS₂/AK mainly benefitted from the enhanced conductivity and anchoring effect of AK,avoiding the agglomeration of CoS₂ nanoparticles.Moreover,the synergy between CoS₂ and AK optimizes the electronic structure and accelerates the electron transport.（3）Using Co CO₃/AK as the precursor and selenium powder as the selenium source,carbon-supported different crystal phases cobalt selenide nanoparticles（CoSe₂/AK）were prepared by high-temperature solid-phase method.The results show that CoSe₂ nanoparticles have fine crystallinity and larger specific surface area,providing more active sites for OER and ORR.After calcination,neither o-CoSe₂nor c-CoSe₂ have obvious agglomeration.The nanoparticles with average particle size of 10 nm are highly dispersed on the surface of AK.Electrochemical results show that o-CoSe₂ has better ORR and OER catalytic performance.Its overpotential of OER at 10 m A cm^-2 is 390 m V,which is better than that of Ir O₂.The half-wave potential of ORR is 0.84 V close to commercial Pt/C.This is mainly due to the inherent metallic properties of CoSe₂,which makes it have a richer electron cloud density.Compared with c-CoSe₂,o-CoSe₂ have more Co0（Co metal）and Co-Se covalent bonds and stronger electronic interactions with the substrate AK,which further enhances its bifunctional electrocatalytic activity.The catalyst was assembled to a Zn-air battery,and the result showed that it has better polarization performance,higher energy density and decent cycle stability than a.cathode catalyst mixed with Pt/C and Ir O₂.更多还原