Research Of The Preparation And Electrocatalytic Performance Of Metal-organic Framework-derived Electrocatalyst

To cope with the global energy demand and emerging environment problems of modern society,it is urgent to pursuit innovative sustainable clean energy with low-cost,therfore,the development of energy conversion and storage technologies have been promoted.Generally,the performance of energy conversion and storage devices depends on the properties of the electrocatalyst materials so that researchers have focus on the exploration of the key materials in these devices.Among the energy conversion and storage devices,fuel cells,metal-air batteries and electrochemical water splitting devices are the most promising candidates,but the energy conversion efficiency have been severely limited by the activity of the electrocatalyst.Moreover,the large-scale application of these devices is prohibited by the high-cost and poor stability of noble-metal electrocatalyst,thus the development of cost-efficient and durable electrocatalyst with excellent performance is highly desired.Specially,the oxygen evolution reaction and oxygen reduction reaction with very sluggish kinetics and ultrahigh overpotential become the bottleneck of these energy conversion and storage technologies.In summary of above reasons,we focus on the preparation and electrcatalytic performance of the metal-organic frameworks-derived electrocatalyst in a bid to obtain electrocatalyst with superior electrocatalytic activity and excellent durability.The details are exhibited as below:In the first work,we use the metal-organic frameworks ZIF-8 and metal salt asprecursor,loading the ultrafine FeCo nanoparticles?NPs?on the N-doped porous carbon matrix?NC?to prepare the FeCo-NC electrocatalyst for oxygen reduction reaction?ORR?and Zn-air batteries.ORR is a key process in renewable energy conversion and storage technologies,including fuel cells and metal-air batteries.Pt is a highly efficient ORR electrocatalyst,but its large-scale application is severely prohibited by the high cost.In the pursuit of cost-effective electrocatalysts,it is urgent to develop non-noble metal ORR catalysts.Herein,we report a facile strategy for synthesizing an ORR electrocatalyst based on ultrafine bimetal FeCo nanoparticles anchoring on N-doped porous carbon matrix?FeCo-NC?.By optimizing the ratio of Fe and Co,the FeCo-NC-1 catalyst exhibits excellent performance for ORR with the half-wave potential of 0.84 V and limiting current density of-5.3 mA cm^-2,which is comparable to the commercial Pt/C catalyst.When applied to Zn-air batteries,FeCo-NC-1 catalyst possesses a high open-circuit potential?1.50 V?and large specific capacity(726.2 mA h g^-1)with a good long-term stability and methanol-tolerant capability,which are even superior to the commercial Pt/C catalyst.The first-principle calculations indicate the bimetallic FeCo-NC has stronger O₂ adsorption than the single metal nitrogen-doped carbon catalysts?Fe-NC and Co-NC?,which is the primary reason for the better ORR performance.We believe this work can be helpful for the development of inexpensive and high-efficient ORR electrocatalysts.The second work focus on the in situ oxidation process of the metal-organicframeworks during oxygen evolution reaction.Among the energy conversion and storage devices,electrochemical water splitting devices,which can be applied for large-scale production of high purity hydrogen,are regarded as the key technology for the application of hydrogen energy.Nevertheless,the energy conversion efficiency of electrochemical water splitting devices are limited by the oxygen evolution reaction in the anode.In a bid to pursuits high efficiency electrocatalysts with low cost to replace the noble-metal based electrocatalysts,the exploration of non-noble metal based electrocatalysts have attracted a lot of attentions of researchers.Currently,the MOFs have became one of the hot topic in electrocatalysts.Moreover,tremendous amounts of works have been made on the MOFs derived materials,especially ZIFs.We find that the ZIF will be oxidized during the oxygen evolution reaction,which has not been noticed.Thus,we select the ZIF-L,one of the two dimension MOFs,as the object to explore the in situ oxidation process during oxygen evolution reaction.We believe that this work may provide a reference for the transformation process during the oxidation process.In addition,it will provide a deeper sight into the in situ oxidation process.