Preparation Of Copper-Based Nanocomposites By Higee Method And Their Electrocatalytic CO₂ Reduction Properties

As human society advances industrially and technologically,the demand for and use of fossil fuels is increasing day by day,and as a result,environmental problems and energy crises need to be solved.Electrochemical CO₂ reduction（ECRR）has gained much attention because of its mild conditions,low cost and effective conversion of greenhouse gas CO₂ into high value-added products.Cu,as an element that can catalyze the production of multi-carbon compounds,is a very important component of ECRR catalysts,but due to the low selectivity and poor electrochemical stability of Cu-based materials for ECRR products,there is a need to However,due to the low selectivity and poor electrochemical stability of Cu-based materials for ECRR products,their selectivity and stability for the target products need to be enhanced by methods such as structural modifications.In this paper,Ni/Cu-NC and Ag@Cu₂O nanocomposite ECRR catalysts were prepared by supergravity technique to construct Cu-based nanocomposites with special morphology based on the specific catalytic selectivity characteristics of different elements and from a reasonable structural design to obtain better catalytic selectivity and stability.The main research contents and conclusions of this paper are as follows.Ni/Cu-NC composite catalysts in the form of flakes were synthesized by heat treatment using urea as the carbon and nitrogen sources,nickel and copper chloride as the nickel and copper sources,and rapid preparation of precursors by a self-assembly process of graphitic phase carbon nitride（g-C₃N₄）and metal ions using a supergravity technique.The effects of the preparation process conditions on the morphology and structure of Ni/Cu-NC and the performance of ECRR for CO were investigated,and a better preparation process was determined:Ni and Cu loading of 8 wt%and 3 wt%,respectively,supergravity speed of 1100 rpm,reaction time of 0.5 h,and heat treatment temperature of 800℃.It was found that in addition to the presence of Ni singlet particles,there existed Ni/Cu in the form of coordination with N elements,and the addition of Cu would affect the bonding of Ni and N,lowering the reaction energy barrier and improving the catalytic performance;the specific surface area of Ni/Cu-NC exceeded 600 m²/g,which could greatly promote the diffusion of gas and catalytic performance;the Ni/Cu-NC catalyst prepared by the supergravity method was effective for The Faraday efficiency of ECRR to generate CO products is slightly higher than that of the Ni/Cu-NC material prepared by the conventional stirring method,while the reaction time is reduced by nearly 50 times,and and can maintain more than 90%selectivity over a potential range of-0.75 V～-1.25 V（vs RHE）.Ag nanoparticles（Ag NPs）of 5-10 nm were rapidly synthesized from silver nitrate using the supergravity technique,and silver-copper composite nanoflower（Ag@Cu₂O NF）catalysts were prepared by in situ growth of copper oxides on top of Ag NPs.The ECRR CO production performance of Ag NPs with different particle sizes was investigated,and the catalytic activity of ECRR C₂H₄ production from Ag@Cu₂O NF was improved by modulating the silver-copper elemental ratio and the structure of copper species（mainly pore channels and morphology）.The smaller the particle size of Ag NPs,the higher the catalytic activity of ECRR for CO production;the appropriate amount of Ag NPs in Ag@Cu₂O NF not only can well inhibit the hydrogen precipitation side reaction,but also its catalytic CO intermediates can provide abundant raw materials for further reduction on copper species to generate C₂H₄,while the flower-like porous structure of Ag@Cu₂O is conducive to mass transfer,which further improves the electrocatalytic performance.further improves the electrocatalytic performance.At an Ag/Cu mass ratio of 5.25,the catalyst exhibited good C₂H₄ selectivity in a 0.1 M KHCO3 solution at-1.05 V（vs RHE）in an H-type cell,with an improved Faraday efficiency of C₂H₄ from25%to 43%compared to pure Cu₂O particles,and can maintain catalytic stability within 7 h.