Designed Synthesis Of Alanine-based Cobalt/Nickel/Copper Complexes Derived Materials For Electrocatalytic Oxygen Reaction

With the rapid development of modern society,more and more attention has been paid to the global energy crisis.Therefore,the development of clean and efficient energy storage and conversion devices has become an important subject of scientific research.Electrochemical oxidation and reduction reactions are the basis of many energy storage and conversion equipments.In order to further develop the practical application of these energy storage devices,decrease the oxygen evolution reaction(OER)energy barrier and improve the reaction efficiency,many researchers are committed to the development of low cost and high performance OER electrocatalysts.The activity of electrocatalysts is influenced by the intrinsic properties of materials,crystal structure,bond energy between metal and oxygen-involed intermediate,oxygen vacancy,and the ability of electron conduction and charge transfer during the reaction.How to balance these factors and find a balance between electrocatalytic activity and stability is a common challenge faced by researchers.Transition metal complexes are materials composed of transition metal ions/clusters and ligands,which have a variety of crystal structures,unique porosity and adjustable functions.However,due to the properties of transition metals,the ion and electron transfer of most of the transition metal complexes in the electrode reaction process is blocked,leading to their activity cannot be fully and effectively utilized.Derivative materials of transition metal complexes can ameliorate this problem.Through the further derivation of the transition metal complexes,it can obtain the new materials,adjust the composition and control the morphology,so that the materials have good structural stability,mechanical strength,ion and electron transport ability.In addition,the synergistic effect produced by the combination of other materials can make up for the deficiency of the single transition metal complex to maximize the electrocatalytic activity.In this work,from the perspective of the hierarchical structure design,electronic structure regulation and specific electrocatalytic interface construction,cobalt/nickel/copper-alanine complexes are synthesized through a room temperature chemical precipitation method,and then they derived a variety of novel OER electrocatalysts.By controlling the synthesis conditions,the composition,morphology,electronic structure and other factors affecting the activity of OER were regulated.Combined with theoretical calculation and a variety of characterization techniques,the structure-activity relationship between materials and properties is summarized.The specific work is mainly carried out from the following five sections:1.N-doped cobalt oxide nanostructures derived from cobalt-alanine complexes for high-performance oxygen evolution reactionsTaking advantage of the self-assembling function of amino acids,cobalt-alanine complexes were synthesized by straightforward process of chemical precipitation.Through a controllable calcination of the cobalt-alanine complexes,N-doped Co3O4 nanostructures(N-Co3O4)and N-doped CoO composites with amorphous carbon(N-CoO/C)were obtained.These N-doped cobalt oxide materials with novel porous nanostructures and minimal oxygen vacancies show a highly active and stable oxygen evolution reaction.Moreover,the influence of calcination temperature,electrolyte concentration and electrode substrate on the reaction are compared and analyzed.And the results of experiments and DFT calculations account for that N-doping promotes the catalytic activity through improving electronic conductivity,increasing OH-adsorption strength and accelerating reaction kinetics.Using a simple synthetic strategy,N-Co3O4 reserves the structural advantages of micro/nanostructured complexes,showing exciting potential as a catalyst for an oxygen evolution reaction with good stability.2.Microbelt superstructure of nickel oxide nanoparticles:initial surface amorphosity-driven electrochemical surface-reconstruction for superior electrocatalysisCurrently,tailoring of intrinsic electronic structure and extrinsic hierarchical morphology is widely recognized as a promising strategy to enhance the OER performance of non-precious-metal electrocatalysts.Moreover,within electrochemical operation,the interface of metallic electrocatalysts surface against alkaline electrolyte is highly oxidized and reconstructed,forming an amorphous layer which is favorable active for OER but hard to controllably prepare by conventional methods.Accordingly,a facile synthesis is presented to prepare heterogeneous nickel oxide superstructure assembled of crystalline NiO nanoparticles coating with amorphous Ni3+ oxide layer(?5nm).With electrochemical activation,the outer amorphous Ni3+ phase introduce in situ surface-reconstruction of the nickel oxide superstructure which continually transform crystalline phase to disordered amorphous Ni3+phase,further facilitating electrocatalysis.The nickel oxide superstructure with crystalline-amorphous dual phases and surface-reconstruction optimization exhibited both high electrocatalytic activity and superior durability with remaining original superstructure after 50000 s I-t test in three-electrode system.3.Cu-alanine complex-derived CuO electrocatalysts with hierarchical nanostructures for efficient oxygen evolutionNowadays,Cu-based materials have attracted extensive attention as electrocatalysts,while the inherent reason of the filling of high anti-bonding state of Cu d band(3d10 4s1)makes it difficult to hybridize with O 2p band of oxygen intermediates during the adsorption process of oxygen evolution reaction(OER).To increase the efficiency of Cu-based electrocatalysts,efforts have been made to optimize the electronic structures and to create surface defects and hierarchical nanostructures with more exposed accessible active sites.Herein,we report a facile method for preparing CuO electrocatalysts with hierarchical nanostructures using the Cu-alanine complex as a precursor through room-temperature chemical precipitation and subsequent calcination in air.Investigations of products obtained at different calcination temperatures reveal the relationship between OER activities and the material characteristics such as specific surface areas,crystal growth orientations,and element components.The product obtained at 500? exhibits the smallest overpotential of 290 mV in 1.0 M KOH for electrocatalyzing OER.Combining with various characterizations of CuO electrocatalysts after OER activities,the possible catalytic mechanism and the influence factors of their OER performance are also discussed.4.Bimetallic-alanine complexes optimally construct electrocatalysts:Cu/Ni nanoalloy@N-doped carbon.The nanoalloy particles show excellent electrocatalytic activity due to their altered electronic structures and tailored d-band centers through incorporating other metal atoms into the lattice of the host metal.Nevertheless,the designed sythesis of nanoalloy electrocatalysts confronts challenges of hard-operating procedures,biased phase separation,imprecise control of distribution and content of elements as well as the micro-nano structures.Herein,a propagable strategy is reported to synthesize atomically dispersed nanoalloy electrocatalysts controllably regulating above-mentioned features.Through pyrolyzing a series of Cu/Ni bimetallc complexes with varying Cu/Ni ratios,multilevel structures of CuNi alloy nanoparticles encapsulated in functionalized carbon(noted as CuNi nanoalloy@N/C)were obtained.Combing the results of DFT calculation,the d-band center and work functions of homogeneous CuNi nanoalloy particles are optimally regulated.Moreover,the carbon with N-doping and edge-plane defects renders a large surface area for electrolyte diffusibility,smooths pathway for electron and mass transfer,and relatively stabilizes skeletal structure.Based on the interplay between CuNi nanoalloy particles and functionalized carbon,the CuNi nanoalloy@N/C boosting an active OER with a superior overpotential of 180 mV as well as excellent structural stability.5.Optimized design of Cu-alanine derived Cu nanorods@N-doped carbon in situ growing HKUST-1 composites for electrocatalysis.Metal-organic frameworks(MOFs)as a new type of porous materials have been widely studied,different from other porous materials,the MOFs have well-organized crystal properties make it easy to regulate gap characteristics,so as to achieve the expected performance.Reasonable design of MOFs combined with other functional materials not only realize more functional composite material as a whole,but also produce new physical and chemical properties which does not exist in single component.However,compositing multicomponent materials usually need to undergo a hard-handle synthesis procedure.In this chapter,cupric homophthalate(HKUST-1)octahedron in-situ grow on the basis of maintaining the original micron-scale layered structure in an alkaline water-ethanol system at room temperature stirring method,meanwhile an active layer(?5 nm)of copper hydroxide was formed on the surface of the original copper nanorods.The octahedral HKUST-1 with a diameter of?1.5?m greatly improves the porosity of the original composite,and HKUST-1 obtained from alkalescence can remain stable during the OER process,which serve as support between the micro-layers to improve the exposure of active sites and facilitate material transport and electron transfer.At the same time,the alkaline water-alcohol system oxidizes the surface of copper nanorods to form an active layer of Cu(OH)2,and the high-valence metal is more favorable for the adsorption of intermediates during OER.Therefore,when used as OER electrocatalysis,the composite of HKUST-1 and heterogeneous copper oxide nanorods attached to nitrogen-doped carbon shows good OER activity and structural stability.