【作者】 李红；

【导师】 夏海兵；

【作者基本信息】 山东大学 ， 材料学， 2021， 博士

【摘要】 锌-空气电池(ZABs)因其原材料丰富、成本低廉、能量密度高等优点,被称为21世纪最具开发前景的绿色能源之一。然而,用于阴极处的氧还原反应(ORR)和析氧反应(OER)的贵金属纳米材料电催化剂,因成本高和耐久性低等缺点影响了 ZABs的商业应用。当前,研究者们普遍认为价格低廉、资源丰富的过渡金属负载杂原子掺杂碳纳米材料(M-N-C,M=Fe、Co、Ni、Cu等)是能够满足高效的氧电催化反应要求的候选双功能电催化剂。然而,目前报道的M-N-C催化剂的性能依然不能满足人们的使用需求。对于M-N-C催化剂,过渡金属物种的尺寸会影响其表面结合能。尺寸较大的纳米颗粒基(NP)催化剂的表面结合能很大,不利于反应产物的脱附,从而会影响活性位点的及时释放,导致电催化反应的周转效率下降。相反,尺寸很小的单原子(SA)催化剂表面对反应物的吸附能力又很弱,从而会增加活性位点吸附反应物过程中的势垒,导致电催化反应速率的下降。因此,为了最大程度地提高M-N-C催化剂的性能,应该使过渡金属物种具有适当的对反应物的吸附能力和对反应产物的脱附能力。最新研究发现,两个或两个以上过渡金属原子形成的过渡金属物种(尺寸小于5nm的多原子团簇)结合了 SA催化剂和NP催化剂的一系列优点(如,对反应物的吸附能力比其单原子强,而反应产物比纳米颗粒更容易脱附)。其次,多原子纳米团簇可以为ORR和OER等复杂的、动力学缓慢的多步电子转移反应途径提供足够的电子转移能力。最后,多原子纳米团簇中相邻原子和原子之间强烈的化学相互作用可以有效地稳定单个原子,防止其团聚,从而能保证活性位点的高稳定性。然而,目前只有极少的关于ORR活性和稳定性都很高的负载Fe纳米团簇的碳材料的报道。因此,制备尺寸在5nm以下的Fe纳米团簇负载杂原子掺杂多孔碳催化剂可以成为高活性、高耐久性的ORR电催化剂。此外,对于Fe-N-C催化剂,Fe元素具有较强的结合能。而Cu元素对反应物的吸附很弱。因此,Fe-Cu双金属合金纳米团簇催化剂应该能够使反应物的吸附和反应产物的脱附达到平衡,可以进一步提升Fe纳米团簇的ORR活性和稳定性。对于ZABs,要求需要同时具备很高的ORR和OER活性。在众多过渡金属中,Ni基催化剂的OER催化活性最高。然而,Ni-SACs对OER反应物的吸附能力过弱,会增加吸附过程中的势垒,降低OER反应速率。并且,Ni-SACs只有OER活性,而不具备ORR活性,无法满足ZABs所需要的双功能电催化剂。已报道Fe原子可以调节Ni原子的d带中心,使其对反应物的吸附和反应产物的脱附达到平衡。因此,基于Fe纳米团簇,制备出Fe-Ni合金纳米团簇负载的碳催化剂,应该能够同时具备优异的ORR和OER双功能催化活性和稳定性,这对于非贵金属催化剂在ZABs等的应用具有积极意义。基于以上问题,本文利用单宁酸(TA)和不同金属离子(Fe3+、Cu2+、Ni2+)之间的螯合作用以及金属离子与聚苯胺(PANI)链上的亚氨基官能团的络合作用,先制备了一系列新型过渡金属物种(Fe-单原子纳米团簇(Fe-SA-NC)、Fe-Cu合金纳米团簇(Fe-Cu ANC)和Fe-Ni合金纳米团簇(Fe-Ni ANC))修饰的三维N,S共掺杂多孔碳催化剂,然后测试了它们的ORR和OER催化活性和稳定性,最后测试以它们为空气阴极组装的锌-空气电池的性能。具体研究内容如下:首先,利用TA和Fe3+离子之间的强螯合作用以及Fe3+离子与PANI链上的亚氨基官能团的络合作用,成功制备了具有均匀分布的、密度高达5.6 wt%的Fe-SA-NCs的三维N,S共掺杂多孔碳催化剂(N,S共掺杂CPANI-TA-FeFe-SA-NC催化剂)。相对于Fe-SA催化剂来说,活性位点Fe-SA-NCs由多个N4-Fe-O2-Fe-N4部分组成。N,S共掺杂CPANI-TA-FeFe-SA-NC催化剂在碱性溶液中表现出极高的ORR 反应活性(E1/2=0.923 V,Eonset=1.09 V,在 0.9 V 处的 Jk=12 mA cm-2)、甲醇耐受性和长期稳定性。此外,以N,S共掺杂CPANI-TA-FeFe-SA-NC催化剂为空气阴极组装的锌-空气电池表现出了极高的性能,可以很好地代替现有的贵金属催化剂(如商业Pt/C催化剂)。其次,借助TA和Fe3+、C u2+离子之间的强螯合作用以及Fe3+、Cu2+离子与PANI链上的亚氨基官能团的络合作用,制备了具有均匀分布的、高密度Fe-Cu ANCs的N,S共掺杂多孔碳催化剂(Fe-Cu ANC@NSC)。其中,Fe-Cu ANCs由多个N4-Fe-Ox-Cu-N4部分组成。由于具有N4-Fe-Ox-Cu-N4配位结构以及Fe和Cu元素之间存在的协同作用,得到的Fe-Cu ANC@NSC催化剂表现出了更加优异的ORR催化活性,活性远高于商业Pt/C催化剂,半波电位为(0.951 V vs Pt/C为 0.89 V),起始电位为(1.1 V vs Pt/C 为 0.98 V),0.9 V 处的 Jk=38.4 mA cm-2(vs Pt/C为5.9 mA cm-2)。此外,Fe-Cu ANC@NSC催化剂还表现出了比Fe-SA-NC催化剂和商业Pt/C催化剂更好的稳定性。最后,基于TA和Fe3+、Ni2+离子之间的螯合作用差异以及Fe3+、Ni2+离子与PANI链上的亚氨基官能团相似的络合作用,制备了负载高密度Fe-Ni ANCs的N,S共掺杂多孔碳气凝胶(称为Fe-Ni ANC@NSCA催化剂)。当TA:Fe:Ni的摩尔比为1:2:5时得到的活性位点Fe-Ni ANCs具有N4-Fe-Ox-Ni-N4配位结构。由于尺寸的增大以及多个原子组成,Fe-Ni ANC@NSCA催化剂可以同时具有SA催化剂和NP催化剂的一系列优点。得到的Fe-Ni ANC@NSCA催化剂在10 mAcm-2的电流密度下表现出超低的OER过电位(ηj=10=260 mV vs.RHE),同时还具有很高的ORR半波电位(E1/2=0.891 V vs.RHE),优于商业的RuO2和Pt/C催化剂。此外,以Fe-Ni ANC@NSCA催化剂为空气阴极组装的锌-空气电池也表现出了卓越的性能和极高的稳定性。综上所述,本工作中成功制得了一系列尺寸均小于3 nm的过渡金属物种(Fe-SA-NC、Fe-Cu ANC和Fe-Ni ANC)修饰的N,S共掺杂多孔碳催化剂,并探究了其ORR和OER催化活性,将其作为空气阴极组装到了锌-空气电池中,表现出了出色的性能和持久的循环寿命。更多还原

【Abstract】 Zinc-air batteries(ZABs)are known as one of the most promising green energy sources in the 21st century due to their rich raw materials,low cost,high energy density,stable performance,etc.However,as an electrocatalysts for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)at the cathode,precious metal nanomaterials have hindered the practical applications of ZABs due to their high cost and low durability.Recently,the researchers proposed that the transition metal-loaded heteroatom doped carbon nanomaterials(M-N-C,M=Fe,Co,Ni,Cu,etc.)can meet the requirements of efficient oxygen electrocatalytic reaction,which is widely considered as a candidate of bifunctional electrocatalysts.However,the activity of the currently reported catalysts are still not satisfactory.Therefore,it is critical to improve the ORR and OER activity and durability of M-N-C catalysts such that they may be used as the bifunctional oxygen catalysts in ZABs.The surface binding energy of the M-N-C catalysts have a great relationship with the size of the transition metal species.The surface binding energy of large-sized nanoparticles(NP)based catalysts are very high and not conducive to the desorption of reaction products,which will affect the timely release of active sites,and further decrease the turnover efficiency during the catalytic process.In contrast,the single-atom catalysts(SACs)has a weak adsorption capacity for the reactants,which will increase the barrier during the adsorption process,and reduce the electrocatalytic reaction rate.Therefore,to maximally improve the electrocatalytic performance of the M-N-C catalysts,the adsorption rate of reactants and desorption rate of products should be well balanced in the surface of the catalysts.The latest research has found that the transition metal species formed by two or more atoms(multi-atom nanoclusters ≤5nm)have stronger adsorption energy for reactants than SACs,and the reaction products are easier to desorb than NP catalysts,combining the merits of SA catalysts and traditional NP catalysts.Furthermore,multi-atom nanoclusters catalysts can provide sufficient electron transfer capability for the multi-electron process during OER or ORR process,which is a kinetically sluggish process involving more energy consumption due to its multistep electron transfer reaction pathway.In addition,the strong chemical interactions between neighboring atom-atom in the mlti-atom nanoclusters catalysts can efficiently stabilize the individual species and prevent agglomeration,further improve the stability of active sites.Therefore,the design and preparation of heteroatom doped carbon catalysts with homogeneously distributed Fe multi-atoms nanoclusters as electrocatalysts,will be an effective strategy to further promote their ORR activity and durability.Moreover,the Fe-N-C catalysts have a strong binding energy while the Cu-N-C catalysts have weak adsorption of reactants.Therefore,it is necessary to prepare Fe-Cu bimetallic nanoclusters catalysts which can achieve a balance between the adsorption of reactants and the desorption of reaction products to further improve the ORR activity and stability of the catalysts.In addition,it is critical importance to explore bifunctional catalysts with efficient OER/ORR activity for the development of Zinc-air battery.However,the adsorption ability of Ni SACs for OER reactants is too weak,which will increase the barrier during the adsorption process and reduce the OER reaction rate.Furthermore,it is difficult for Ni SACs to become a bifunctional catalysts with efficient OER/ORR activity.It has been reported that Fe atoms can upgrade the d-band center of Ni atoms,and can balance the adsorption of reactants and the desorption of products.Therefore,it is necessary to prepare Fe-Ni alloy nanoclusters catalysts with excellent ORR and OER bifunctional catalytic activity and stability,which is of positive significance to better expand the application of non-precious metal catalysts in zinc-air batteries.Based on the current issues mentioned above,a series of new transition metal species(Fe-single-atom-nanoclusters(Fe-SA-NC),Fe-Cu alloy nanoclusters(Fe-Cu ANC)and Fe-Ni alloy nanoclusters(Fe-Ni ANCs))modified three-dimensional N,S co-doped porous carbon catalysts can be prepared due to the chelation ability between tannic acid(TA)and metal ions(Fe3+,Cu2+,Ni2+)as well as interaction between metal ions and the imino group of polyaniline(PANI)chain for the first time.Then,their OER and ORR performances were investigated in alkaline media,respectively.Finally,the performance of a homemade rechargeable Zn-air battery assembled with these catalysts were also investigated.The detailed research content is as follows:Firstly,three-dimensional N,S co-doped carbon with high density(5.6 wt%) Fe-SA-NCs of homogeneous dispersion(N,S co-doped CPANI-TA-Fe Fe-SA-NC catalysts)is successfully prepared due to the controlled chelation between TA and Fe3+ions and the interaction between Fe3+ions and PANI chains.Compared with Fe-SA,the active site Fe-SA-NCs consists of several N4-Fe-O2-Fe-N4 moiety.The resulting N,S co-doped CPANI-TA-Fe Fe-SA-NC catalysts exhibit a excellent ORR performance(E1/2=0.923 V,Eonset=1.09 V,jk=12 mA cm-2 at 0.9 V),better methanol tolerance and better long-term durability in alkaline media.Additionally,the performance of the zinc-air battery prepared with N,S co-doped CPANI-TA-Fe Fe-SA-NC catalysts as the air electrode exhibited a high performance,which are better than those of the state-of-the-art commercial Pt/C catalysts.Secondly,three-dimensional N,S co-doped carbon with high density Fe-Cu ANCs of homogeneous dispersion(Fe-Cu ANC@NSC)is successfully prepared due to the controlled chelation between TA and Fe3+,Cu2+ions and the interaction between Fe3+,Cu2+ions and PANI chains.Among them,the active site Fe-Cu ANCs consists of several N4-Fe-Ox-Cu-N4 moiety.The resulting Fe-Cu NC@NSC catalysts perform better ORR catalytic activity,the half-wave potential is(0.951 V vs Pt/C is 0.89 V),the onset potential is(1.1 V vs Pt/C is 0.98 V),and the kinetic current density at 0.9 V is 38.4 mA cm-2.In addition,the stability of Fe-Cu NC@NSC catalyst is higher than that of Fe-SA-NC catalysts and commercial Pt/C catalysts.Finally,three-dimensional N,S co-doped carbon aerogel with high density Fe-Ni ANCs(Fe-Ni ANC@NSCA catalysts)are successfully prepared due to the difference chelation between TA and Fe3+,Ni2+ions and the nearly same interaction between Fe3+,Ni2+ions and PANI chains.When the molar ratio of TA:Fe:Ni was 1:2:5,the active site Fe-Ni ANCs consisting of N4-Fe-Ox-Ni-N4 moiety.The resulting Fe-Ni ANC@NSCA catalysts show excellent performance in ORR(E1/2=0.891 V)and OER(260 mV@10 mA cm-2)in alkaline media as bifunctional catalysts,which are better than the state-of-the-art the commercial Pt/C catalysts and RuO2 catalysts.Moreover,a Zn-air battery assembled with the Fe-Ni ANC@NSCA catalysts also shows a remarkable performance and exceptionally high stability.In summary,in this thesis,a series of new transition metal species(Fe-SA-NC,Fe-Cu ANC and Fe-Ni ANC)modified three-dimensional N,S co-doped porous carbon catalysts can be prepared,and the OER and ORR performances were also investigated.Finally,a homemade rechargeable Zn-air battery assembled with these catalysts as an air cathode shows a remarkable performance and exceptionally high stability.更多还原