Synthesis And Electrocatalytic Performance Of Cobalt-based Multidimensional Composite Nanomaterials

With the progress of the times,more and more people have realized that it is important to develop sustainable energy.Hydrogen is considered as an environmentally friendly energy source because it emits no greenhouse gases when burned.What’s more,hydrogen has the characteristics of light weight,storability and high calorific value,which are the reasons why it can be an ideal energy carrier.Accelerating the development of hydrogen energy will help to realize the larger-scale use of clean,safe and economical renewable energy in the future.Among various methods of hydrogen production,water electrolysis with the advantages of proven technology,high product purity and low energy consumption is an ideal way to produce hydrogen.To date,some noble metal-based electrocatalysts have been used as commercial catalysts.However,these catalysts generally have the problems of high price,low abundance and poor stability.How to reduce the cost of overall water splitting to achieve good efficiency and durability for long-term large-scale production of H₂ is still a big problem.Thereby,the development of efficient,inexpensive and stable transition metal electrocatalysts has become the focus of recent research.Here,we developed a series of cobalt-based multidimensional composite electrohydrolysis catalysts.The performance of electrocatalysts had been further improved from the aspects of the optimization of morphology,the construction of heterointerface structure,the regulation of electronic structure and the in-situ reconstruction of active sites.The electrical conductivity,the reaction kinetics,and the number of active sites of the materials were successfully optimized,which enabled these electrocatalysts to work stably and efficiently.The electrocatalysts designed in this paper are as follows:1.Superhydrophilic/superaerophobic 2D/3D hierarchical Co（OH）₂-Ce O₂/Co as efficient catalyst for overall water splittingA 2D/3D hierarchical electrocatalyst consisting of Co（OH）₂-Ce O₂ nanosheets decorated Co dendrites on nickel foam（Co（OH）₂-Ce O₂/Co@NF）is proposed.Based on the strong electronic interaction of Co（OH）₂-Ce O₂ heterojunction,the electron transferred from Co sites to Ce sites,which facilitated the adsorption of intermediates and the dissociation of water molecules.Besides,the open 2D/3D structure formed by the introduction of Co substrate further reduces the accumulation of heterogeneous nanosheets and promotes the radial diffusion of the electrolyte,significantly improving active sites utilization and shortening the electron transfer pathways.In addition,the superhydrophilic/superaerophobic interface achieved by constructing hierarchical micro-nanostructure is beneficial to electrolyte infiltration and bubble desorption,thus ensuring a favorable mass transfer.Therefore,Co（OH）₂-Ce O₂/Co@NF exhibits an outstanding water splitting performance with a low cell voltage of 1.62 V at 10 m A cm^-2in alkaline electrolyte.2.Electronic regulation and core-shell hybrids engineering of palm leaves-like Ni Fe/Co（PO₃）₂ bifunctional electrocatalyst for efficient overall water splittingThe core-shell hybrids consisted of Co（PO₃）₂ nanorod cores and Ni Fe alloy shells in situ grown on nickel foam（Ni Fe/Co（PO₃）₂@NF）are synthesized.Owing to the hierarchical palm leaves-like structures and the strong adhesion between Ni Fe alloys,Co（PO₃）₂ and substrates,the catalyst has a large surface area and rapid charge transfer which facilitates active sites exposure and conductivity enhancement.The interfacial effect in the Ni Fe/Co（PO₃）₂ core-shell structure modulates the electronic structure of the active sites around the boundary,thereby boosting the intrinsic activity.Benefiting from the stable structure,the durability of the catalyst is not impaired by the inevitable surface reconfiguration during HER/OER.The Ni Fe/Co（PO₃）₂@NF electrode presents a low cell voltage of 1.63 V at 10 m A cm^-2 and manifest durability for up to 36 h at different current densities.This work verifies that the synergy between electronic regulation and core-shell hybrids engineering offers an effective avenue to design cost-efficient and robust electrocatalysts for overall water splitting.3.Hierarchical Co₃O₄/Ni₂P@CC hybrids as efficient electrocatalysts for hydrogen evolution reactionBased on the Co-mediated phase change engineering,Co₃O₄/Ni₂P@CC hybrids are prepared on the carbon cloth（CC）as an efficient electrocatalyst for hydrogen evolution.In this strategy,3D CC coated with 0D metallic Ni nanoparticles is used to simulate nickel foam to investigate the phosphating products of metallic Ni and the actual source of catalytic activity.Due to the induction of Co,the phosphating products of metallic Ni are transformed from the original mixture consists of Ni₂P,Ni₅P₄ and Ni（PO₃）₂ to pure Ni₂P.With the phase transition,the electrochemical performance of the material is dramatically enhanced,too.Lattice defects and oxygen vacancies in Co₃O₄ can also increase the lattice disorder,thereby tuning the electronic structure of sites,increasing the number of active sites,and enhancing the intrinsic activity of the catalyst.The synergy of doping effect,interfacial engineering,and defect engineering together enhances the electrocatalytic water splitting efficiency.In 1.0 M KOH,Co₃O₄/Ni₂P@CC only presents an overpotential of 109 m V at 10 m A cm^-2 for HER and exhibits remarkable mechanical robustness.This study not only discloses a novel idea for heteroatom-mediated regulation of phosphating products,but also provides a promising approach for the development of inexpensive and stable electrocatalysts.