Design,Synthesis,and Electrocatalytic Performance Of Nickel-Chromium-Based Electrocatalysts For Hydrogen Production

Based on the increasingly serious energy crisis and environmental pollution problems,the development of clean and efficient renewable energy is an important direction for future energy development.Hydrogen（H₂）is a green and non-polluting energy carrier with high energy density,which is expected to become an important part of the future energy architecture.Currently,hydrogen production by water electrolysis driven by renewable energy is one of the cleanest and greenest ways.However,the efficiency of hydrogen production and large-scale application of this technology are still limited by the inherent defects of the applied catalysts.On the other hand,replacing fresh water with abundant reserves of seawater as electrolyte can relieve the pressure on fresh water resources and reduce the cost of water electrolysis,which is one of the effective measures to promote the large-scale application of water electrolysis.Meanwhile,replacing the conventional OER with the hydrazine oxidation reaction（Hz OR）,which has a lower thermodynamic potential,can break the high voltage barrier of conventional overall water splitting（OWS）and realize energy-saving electrolytic hydrogen production.Currently,the precious metals platinum（Pt）and ruthenium dioxide（Ru O₂）are the most efficient HER and Hz OR electrocatalysts,respectively,but the high cost and rare reserves severely limit their large-scale industrial applications.Therefore,it is of great significance to develop low-cost,high-performance and long-life transition metal-based HER and Hz OR electrocatalysts.In this thesis,the transition metals chromium（Cr）,nickel（Ni）and their compounds are used as the main targets.The research focuses on the design and preparation of high-performance electrocatalysts applied to alkaline HER and Hz OR processes,and the intrinsic correlation of electrocatalyst composition-structure-catalytic performance.The main research progress is as follows:（1）Density functional theory（DFT）calculations reveal that the Cr N/Ni heterojunction electrocatalyst can effectively promote H₂O dissociation through hydrogen bonding induction effect,and the N site optimized by heterogeneous coupling interaction has good hydrogen adsorption desorption,thus significantly enhancing the basic HER kinetics.Followed by the preparation of nitrogen-doped carbon（NC）-covered Cr N/Ni nanosheet electrocatalysts（NC@Cr N/Ni）by secondary hydrothermal and nitriding treatments.The catalyst exhibits excellent HER activity in alkaline freshwater/seawater,requiring only 24 and 28m V to drive a current density of 10 m A cm^-2,respectively,and show good durability in alkaline seawater due to their high intrinsic activity,adequate exposure of active sites and good corrosion resistance of the constituent phases.This work exemplifies the key role of the dual effect of hydrogen bonding induction and heterogeneous coupling in enhancing the intrinsic activity of alkaline HER electrocatalysts,which has implications for the design of efficient and robust heterostructured electrocatalysts.（2）DFT calculations indicate that the doping of oxygenophilic Cr can effective in reducing the energy barrier of H₂O dissociation of Ni.Subsequently,Ni-based metal organic metal framework（Ni-BDC）were used as precursors,and carbon coated Cr doped Ni nanosheets electrocatalysts（Cr-Ni@C）were prepared by combining hydrothermal and reduction heat treatment methods.The obtained catalyst exhibits Pt like HER activity and good stability in alkaline freshwater/seawater.In addition,the Cr-Ni@C catalyst exhibits excellent Hz OR activity,requiring only 30 and 139 m V overpotentials to drive current densities of 100 and 500 m A cm^-2,respectively.The operating potential of the overall hydrazine splitting（OHz S）system constructed in alkaline seawater electrolyte with its two poles is 0.20 V at 100 m A cm^-2,which is 0.87 V lower than the conventional overall water splitting（OWS）（2.07 V）under the same conditions.