Adjustment Of The Electronic Structure And Morphology Of Electrocatalytic CO₂ Reduction Catalysts And The Performance Study

In recent years,environmental problems caused by the massive emission of greenhouse gases such as carbon dioxide（CO₂）have become increasingly serious.However,CO₂ is also one of the most readily available sources of carbon in nature.Transformation and utilization through appropriate methods can not only alleviate or eliminate the ecological crisis caused by climate change,but also create certain economic value.Driven by renewable energy,reducing CO₂ to fuels or chemicals with higher industrial added value through electrocatalysis is one of the current research hotspots.Carbon monoxide（CO）is one of the important raw materials for Fischer-Tropsch synthesis,and it also plays an extremely key role in the metallurgical industry.Therefore,the electrocatalytic reduction of CO₂ to CO has great application potential.However,the cathode and anode half-reactions that make up the electrocatalytic CO₂ reduction reaction（CO₂RR）are respectively limited by lower product selectivity and higher reaction overpotential,making it difficult for industrial applications.The development of efficient catalysts for anode oxygen evolution reaction（OER）and cathode CO₂RR is the key to solving the above problems.Nickel-iron-based materials are currently widely recognized as a type of oxygen evolution catalyst.Under strong alkaline conditions,nickel-iron bimetallic layered hydroxide（Ni Fe-OH）is one of the most efficient catalysts,but its activity in the neutrality medium is very limited,mainly because it is difficult to be oxidized under mild conditions to produce active species containing high-valence nickel(Ni^+3/+4Fe O_xH_y),so further optimization is required.For the cathode half-reaction,silver-based or zinc-based materials are used as catalysts,and CO₂ can usually be selectively reduced to CO.Zinc-based catalysts are one of the most likely candidates for large-scale applications due to their relatively low cost.However,due to the existence of fierce competition reaction（hydrogen evolution reaction）at the cathode,its selectivity is still difficult to meet the ideal requirements.In this thesis,through the strategies of pre-oxidation and morphology control,the electronic structure of the catalyst and the exposure of active sites are adjusted to increase the catalytic activity of OER and CO₂RR,respectively,so as to promote the high efficiency of the electrocatalytic CO₂ reduction reaction.The specific research content is as follows:1.The Ni Fe-OH supported on foam nickel（Ni Fe-OH/NF）by hydrothermal method is post-treated by pre-oxidation in a high-concentration alkaline solution to obtain an amorphous surface on the NF.The extremely low crystallinity of a-Ni Fe-OH and the enhanced Ni-O covalent bond effectively promote the oxidation of Ni²⁺under near-neutral conditions.The amorphous structure is conducive to the increase of the electrochemical active area of the catalyst,and exposure of more active sites make it obtain good OER activity.In 0.1 M KHCO₃electrolyte（p H=8.3）,a-Ni Fe-OH loaded on NF（a-Ni Fe-OH/NF）only needs 350 m V overpotential to drive a current density of 10 m A cm^-2.The corresponding Tafel slope is as low as 89 m V dec^-1.This work has certain guiding significance for the development of OER catalysts under near-neutral conditions.2.Using a simple hydrothermal synthesis method,by adjusting the ratio of raw materials,different thickness of zinc hydroxyfluoride（Zn OHF）nanorods were synthesized and used to catalyze CO₂RR.It was found that when the molar ratio of ammonium fluoride to urea in the raw material was 1:4,the Zn OHF nanorods obtained were a single pure phase with a diameter of about 200 nm and the synthesis mechanism was explained.The larger specific surface area of nanorods is conducive to the exposure of more active sites,and the halogen atoms contained in the material itself can inhibit the progress of the hydrogen evolution reaction（HER）so that it has a higher CO selectivity.In the Flow-cell,when the cathode potential is-1.28 V（vs.RHE）,the Faraday efficiency of CO is close to 80%,and the current density of CO is as high as 57.53m A cm^-2.This work used materials such as Zn OHF for the first time in electrocatalytic CO₂RR,enriching the types of zinc-based catalysts with specific CO selectivity.