随着全球经济的快速发展，能源短缺问题和环境污染问题日益凸显，成为困扰整个人类社会可持续发展的顽疾；因此发展廉价、储量丰富、高效、稳定的清洁能源势在必行。而电解水产氢可在不产生附加污染的前提下大规模制取“理想绿色能源”—氢气，为解决上述难题提供了一个有效的方案。遗憾的是目前水分解产氢效率严重受限于析氧反应（OER）的缓慢动力学（涉及质子电子耦合的四电子转移过程），必须借助高效催化剂才能克服。对析氧反应而言，目前常用的高效催化剂仍然以Ru基和Ir基贵金属材料为主，但它们成本高昂、储量有限且稳定性较差，难以大规模商业化应用。而第一过渡系金属元素及化合物，特别是钴基材料因储量丰富、具有3d电子和空的d轨道，易与含氧官能团结合，使其成为极有潜力的非贵金属基OER催化剂。尽管如此，目前钴基材料仍然存在活性位点不足、本征导电性差等缺点。基于以上挑战，本论文旨在探索合成低维钴基纳米材料及其复合结构以提升材料的催化活性和导电性；具体来说通过调节钴基纳米片氧空位浓度来增加其活性和导电性，通过原位复合氧化石墨烯来显著提升钴基纳米片的导电性；具体研究成果如下：

        1.利用烷基胺辅助溶剂热法结合时间调控合成出不同厚度的Co₃O₄/Co₂(NO₃)(OH)₃杂化纳米片，其中反应时间为60min (标为Co₃O₄-Co₂(NO₃)(OH)₃-60 min)、80min（标为Co₃O₄-Co₂(NO₃)(OH)₃-80 min）、100min（标为Co₃O₄-Co₂(NO₃)(OH)₃-100 min）纳米片的平均厚度约为8.2 nm、10.3 nm、13.1 nm。电化学测试表明最薄Co₃O₄-Co₂(NO₃)(OH)₃-60 min纳米片在1 M KOH中表现出最优的电催化性能：在10 mA/cm² 电流密度下，其过电位仅为318 mV，Tafel斜率为85.3 mV/dec, 并显示出长时间的电解稳定性。综合透射电镜（TEM）、X射线光电子能谱（XPS）、莫特-肖特基曲线（Mott-schottky, MS）等表征结果，推测Co₃O₄-Co₂(NO₃)(OH)₃-60 min纳米片优异的OER催化性能可能归因于以下两个方面：①超薄二维纳米结构所带来显著大的比表面积和众多暴露的活性位点；②具有最高的氧空位含量，因而有利于含氧官能团的捕获和电子导电性的提升。本工作为设计开发高效且廉价的低维纳米材料钴基析氧催化剂提供了新的启示。

2. 以不同数量的氧化石墨烯纳米片为模板吸附钴前驱体，采用烷基胺辅助溶剂热法原位一步合成出氧化石墨烯负载的CoO-Co(OH)₂复合纳米片（即CoO-Co(OH)₂/0.8 mg GO、CoO-Co(OH)₂/1.4 mg GO、CoO-Co(OH)₂/2.0 mg GO）。电化学测试表明CoO-Co(OH)₂/1.4 mg GO样品在1 M KOH中表现出最优异的OER电催化性能：在电流密度为10 mA/cm²时，其过电位仅为283 mV，塔菲尔斜率低至57 mV·dec^-1，电化学活性面积高达90 mF/cm²，并且表现出良好电催化稳定性。综合表征结果推测CoO-Co(OH)₂/1.4 mg GO复合纳米片优异的OER电催化性能主要归因于以下三个方面：① 带正电性的超薄钴基纳米片与带负电的氧化石墨烯纳米片间比例恰当、结合紧密、复合高效；② 氧化石墨烯纳米片和钴基纳米片有效复合增强了材料整体的导电性；③复合有利于电子从氧化石墨烯纳米片转移至钴基纳米片，导致CoO-Co(OH)₂/1.4 mg GO样品3d电子中心上移，增强了对含氧物种的吸附进而提升了其OER催化活性。本项工作为如何提高二维纳米材料导电性和本征催化活性提供了有益的借鉴。

       With the rapid development of the global economy, energy shortage and environmental pollution have become increasingly serious issues that impedes sustainable development of the entire human society. It is thus imperative to develop cheap, abundant, efficient, renewable clean energy sources to replace traditional fossile fuel The electrolysis of water to generate hydrogen can produce "ideal green energy" (i.e., hydrogen) on a large scale without casuing additional pollution, which provides an effective solution to the above-mentioned problems. Unfortunately, the current hydrogen production efficiency of water splitting is severely limited by the slow kinetics of the oxygen evolution reaction (OER), a four-electron transfer process involving proton-electron coupling, which need to be overcome with the help of high-efficiency catalysts. For the oxygen evolution reactions, the currently commonly used high-efficiency catalysts are still mainly limited to Ru-based and Ir-based noble metal materials, but they are expensive, rare, and unstable, making them difficult to be applied on a large scale. The first-row transition metal elements and compounds, especially cobalt-based materials, are easy to combine with oxygen-containing functional groups due to their abundant 3d electrons and empty d orbitals, showing a promise to become potential highly efficienent OER catalysts. Nevertheless, the current cobalt-based materials still have suffered from insufficient active sites and poor intrinsic conductivity. In view of above challenges, this paper aims to explore the synthesis of low-dimensional cobalt-based nanomaterials and their composites with high catalytic activity and conductivity. Specifically, various measurments, including increasing oxygen vacancy content or hybridization with graphene oxide sheets (GOs), were adopted to either increase their intrinsic activity or conductivity.The main research results of this thesis are listed as follows:

   1.Co₃O₄/Co₂(NO₃)(OH)₃ hybrid nanosheets were synthesized using an alkylamine-assisted solvothermal method, and their average thicknesses could be adjusted from 8.2 nm, 10.3 nm, to 13.1 nm with prolongation of reaction time from 60 min (labeled as Co₃O₄-Co₂(NO₃)(OH)₃-60 min), 80 min (labeled as Co₃O₄-Co₂(NO₃)(OH)₃-80 min) to 100min (labeled as Co₃O₄-Co₂(NO₃)(OH)₃-100 min). Electrochemical tests show that the thinnest Co₃O₄-Co₂(NO₃)(OH)₃-60 min nanosheets possess the best electrocatalytic performance in 1 M KOH: with an overpotential at a current density of 10 mA/cm² (?₁₀) of only 318 mV, a Tafel slope of 85.3 mV/dec, and good long-term electrolytic stability. Based on the characterization results of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Mott-schottky curve (Mott-schottky, MS), we speculated that the excellent OER catalytic performance of Co₃O₄-Co₂(NO₃)(OH)₃-60 min sample may be attributed to the following two aspects: ① its ultrathin two-dimensional nanostructure can bring a significantly large specific surface area and numerous exposed active sites; ② It has the highest oxygen vacancy content, which is beneficial to the capture of functional groups and the improvement of electronic conductivity. This work provides new inspiration for the design and development of efficient and inexpensive low-dimensional nano-based oxygen evolution catalysts.

        2.With using different amounts of graphene oxide nanosheets as templates to adsorb cobalt precursor, an alkylamine-assisted solvothermal method was developed to synthesize a series of graphene oxide-supported CoO-Co(OH)₂ composite nanosheets (i.e., CoO- Co(OH)₂/0.8 mg GO, CoO-Co(OH)₂/1.4 mg GO, CoO-Co(OH)₂/2.0 mg GO). Electrochemical tests show that the CoO-Co(OH)₂/1.4 mg GO sample exhibits the best OER electrocatalytic performance in 1 M KOH: with a ?₁₀ of only 283 mV , a Tafel slope as low as 57 mV·dec^-1, an electrochemically active area as high as 90 mF/cm², and showing good electrocatalytic stability. According to comprehensive characterization results, we attributed the excellent OER electrocatalytic performance of CoO-Co(OH)₂/1.4 mg GO composite nanosheets to the following three aspects: ①the static electricity interaction between cobalt-based nanosheets and GOs allowing them to properly bind together; ② upon bining, GOs can effectively enhance the overall conductivity of the hybrid nanomaterials; ③ the binding facilitates the transfer of electrons from the GOs to the cobalt-based nanosheets, thus causing the 3d electron center of the CoO-Co(OH)₂/1.4 mg GO sample to move upward and enhancing the adsorption to oxygen-containing species accordingly. This work offers a useful reference for how to improve the conductivity and intrinsic catalytic activity of two-dimensional nanomaterials.