The increasingly growing demand for energy and the indiscriminate use of fossil fuels have exacerbated a series of issues such as energy crises, environmental pollution, and climate change. Therefore, it is imerative to urgently investigate not only efficient but also clean energy sources as replacements with fossil fuels. As one of the most promising green energy sources, hydrogen possesses advantages such as high energy density, lack of pollution, and renewability. Electrolysis of water can generate high-purity hydrogen, representing the sole pathway for large-scale hydrogen generation. The process of electrolyzing water is comprised of two distinct reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). OER is constrained by its sluggish reaction kinetics, necessitating efficient catalysts to expedite its reaction process. Noble metal catalysts like RuO₂ and IrO₂ exhibit outstanding OER catalytic activity, yet factors such as limited natural resource reserves, high cost, and poor stability hinder their widespread application. Consequently, the development of novel non-noble metal OER catalysts has become a pivotal topic for hydrogen production through water electrolysis. Over the past few decades, transition metal-based catalysts have been discovered to possess excellent electrocatalytic activity, such as transition metal sulfides, selenides, and oxides. This thesis, starting from the characteristics of materials, synthesizes several efficient transition metal-based OER catalysts. By means of doping, heterostructure construction, vacancy regulation, and other strategies to regulate the active sites, the oxygen evolution performance and stability of the catalysts are enhanced. The specific contents are as follows:

In chapter 1, the research progress in electrocatalytic water splitting and related reactions is introduced. An extensive overview of nanomaterials catalysts based on transition metals is presented, emphasizing their numerous advantages, diverse preparation methodologies, innovative modification strategies, comprehensive characterization methods, and their extensive applications in catalysis-related fields.

In chapter 2, Ni-doped W₁₈O₄₉ nanorod arrays prepared on carbon cloth (CC/WO-Ni-x) by hydrothermal followed by different time low-temperature plasma treatment are described. Compared to standalone CC/WO and CC/Ni, the prepared CC/WO-Ni-4 catalyst exhibits the best OER catalytic activity. In 1M KOH alkaline medium, CC/WO-Ni-4 showcasing an overpotential of 265, 306 and 331 mV to deliver the current density of 10, 50 and 100 mA cm^-2, respectively with long-time stability. The excellent electrocatalytic performance of this catalyst may be attribute to several factors: (1) The presence of oxygen vacancies in the W₁₈O₄₉ nanorods provides active sites for the oxygen evolution reaction, promoting catalytic activity; (2) The doping of Ni induces surface amorphization, which reduces the electron transfer impedance of the catalyst; (3) The strong electronic interaction between nickel (Ni) and tungsten (W) facilitates electron transfer from Ni to W, resulting in the formation of more high-valence Ni³⁺ and low-valence W⁴⁺ species in the CC/WO-Ni-4 catalyst. During the reaction process, the presence of more high-valence Ni³⁺ species helps enhance the adsorption of various reaction intermediates, lowering the energy barrier heights, optimizing the reaction pathways, and accelerating reaction kinetics. (4) nanorod arrays structure facilitates sufficient contact with the electrolyte, speeding up the progress of the reaction. Additionally, the catalytic performance of this catalyst for urea oxidation reaction was explored. In a solution containing 0.5M urea in 1M KOH, the CC/WO-Ni-4 catalyst necessitates a mere working voltage of 1.32V_RHE to attain a current density of 10 mA cm^-2, which is less 172 mV than OER. This indicates that the addition of urea can significantly reduce the energy consumption required for hydrogen production via water electrolysis, which is beneficial for achieving energy-saving hydrogen production.

In chapter 3, present a novel strategy to optimize the concentration of V_CN in the NiFe PBA nanocubes by H₂ or O₂ plasma processing. Despite the inherently strong affinity between metals and CN ligands, the energy of V_CN formation can be overcome by ionizing H₂ to produce unconventional V_CN. By adjusting the H₂ plasma processing time, the concentration of V_CN can be modulated. Moreover, V_CN significantly activates the activity of Fe sites, inducing preferential adsorption of OH^- on Fe sites, followed by adsorption on Ni sites, thereby optimizing the reaction pathway and extensively promoting OER performance. When the concentration of V_CN is around 6.5% and the OER performance of NiFe PBA is the best. In addition, V_CN suppresses the leaching of Fe ions into the electrolyte during OER, consequently causing excellent durability. The precise role of Fe in the NiFe PBA catalyst during OER is investigated by in situ Raman scattering, which reveals that the Fe sites in NiFe PBA preferentially adsorb OH^– species compared to the Ni sites in NiFe PBA to expedite the OER kinetics.

In Chapter 4, we introduce a simplified, one-step hydrothermal method for the preparation of Fe-doped CoCH (formula: Co(CO₃)_0.5(OH)·0.11H₂O) nanoneedles grown directly on carbon cloth (CC). By fine-tuning the atomic molar ratio of Co/Fe, we successfully synthesized a range of Co_1-xFe_xCH/CC (x = 0, 0.2, 0.4, 0.6, and 1) catalysts. Notably, after enduring 100 cycles of cyclic voltammetry (CV), surface reconstruction was observed on the nanoneedles with ultrathin CoFe(OOH)_x nanosheets growth on the nanoneedles, among which the Co_0.6Fe_0.4CH-100 catalyst exhibited the most superior OER catalytic performance. Remarkably low overpotential of 259 mV is sustained in a 1M KOH electrolyte, even under a current density of 10 mA cm^-2, showcasing exceptional long-term stability. The excellent catalytic activity of Co_0.6Fe_0.4CH/CC-100 can be attributed to the following factors: (1) Following electrochemical activation and reconstruction, nanosheets emerge on the nanoneedle framework, boasting a substantial specific surface area. This vast area facilitates comprehensive contact with the electrolyte, thereby enhancing reaction kinetics and accelerating chemical processes. (2) Moderate Fe doping preserves catalytic active sites and enhances the surface oxidation capability of Co_1-xFe_xCH nanowires, thereby enhancing OER activity.

In Chapter 5, the thesis concludes with a summary of the preparation of transition metal-based nanomaterials and their application in the electrocatalytic OER, along with a comparative analysis with other materials. Additionally, future work based on the findings of this thesis is proposed.