Synthesis Of CoO/CoSe₂ And Single-atom Au/Ni-Fe LDH Heterogeneous Catalysts For Water Electrolysis

Efficient electrocatalytic overall water splitting,including hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?,is a promising technology for clean and sustainable energy,but efficient catalysts are needed to improve the efficiency of electrolyzed water.Up to now,Pt and RuO₂ materials are considered as active catalysts for HER and OER,but their high cost and scarcity severely prohibit the wide applications.At the same time,there are still many problems in the synthesis,stability and multifunction of non-noble metal catalysts.In order to solve this problem,we present a facile in situ conversion strategy to prepare an economical,efficient and stable bifunctional non-noble metal catalyst,and a pulse electro deposition method to prepare a single atom catalyst with extremely low load and high utilization rate,as well as systematically studying their morphology,structure and corresponding electrocatalytic activity.The main works in this dissertation contain following contents:1.We present a facile in situ partial surface-oxidation strategy to integrate CoO domains with CoSe₂ nanobelts on Ti mesh?denoted as CoO/CoSe₂?as a novel,highly active and stable self-supported electrocatalyst for both HER and OER under neutral conditions.The novelty of strategy is that the produced hybrids successfully anchor many small CoO domains,rather than CoO oxidation layer,on CoSe₂ nanobelts.Such a smart strategy can not only avoid the additional increase of nanobelt thickness,but also make the hybrid materials combined tightly.As for HER and OER,CoO/CoSe₂shows a small onset overpotential and large exchange current density.Moreover,we used CoO/CoSe₂ electrocatalyst as both anode and cathode in a two-electrode system to make a neutral electrolyzer for water splitting.It's believed that the flexible nanobelt and further assembling into three-dimensional?3D?self-supported porous architecture,and thus large active surface area,effcient electron,and mass transport,as well as the chemical synergistic effect between metallic CoSe₂ and surface oxidized CoO domains thereon lead to the excellent performance.2.We report a pulse electrodeposition method to synthesize a single-atom catalyst which consists of only isolated single Au atoms anchored to the surfaces of Ni-Fe layered double hydroxides.And we employ single-atom Au supported Ni-Fe LDH?^sAu/Ni-Fe LDH?catalyst as a model to evaluate the OER activity and understand the activity origin at the atomic level.Theoretical results demonstrate that each of single-atom Au,Ni-Fe oxyhydroxide transformed from LDH,and LDH itself with interlayer CO₃^2-anions has contributed to the local chemical environment of the surface site and thereby the corresponding OER activity improvement.Further experimental measurements also suggest the catalyst exhibits an outstanding electrochemical OER performance.When the current density of 10 mA cm^-2 is required,^sAu/Ni-Fe LDH needs the overpotential of only 232 mV.We further determinated the electrochemical stability of ^sAu/Ni-Fe LDH,the current density can maintain around 100 mA cm^-2 for 20 h.