Regulation Of The Electronic And Geometric Structure Of CO₂ Reduction Catalysts And The Performance Study

The growing consumption of conventional fossil fuels and the increased environmental pollution have motivate us to develop sustainable renewable energy.Electrochemical reaction,such as CO₂ reduction,which converts CO₂into value-added products and fuels,is promising candidate to store and utilize the renewable energy and also provides a stratagem to mitigate the green hours effect by reducing CO₂.A variety of products can be obtained from carbon dioxide.Among them,CO and C₂H₄ are the main raw materials for the preparation of hydrocarbons by Fischer-Tropsch synthesis and the production of polyethylene,respectively.Thus,we aim to catalyze the electrochemical catalytic CO₂ reduction to CO and C₂H₄.The electrocatalytic CO₂ reduction reaction is divided into two half reactions,the anode oxygen evolution reaction and the cathode CO₂ reduction reaction.Large overpotential of anode oxygen evolution and low selectivity of cathode CO₂ reduction products hinder the large-scale application of CO₂ reduction.It is urgently to develop efficient catalysts for oxygen evolution and CO₂ reduction.Ni,Co,and Fe-based 3d transition metal are regarded as one of the most promising candidates for oxygen evolution.However,the activity is still unsatisfied and needs to be improved.For the cathode CO₂ reduction reaction,a variety of products,such as CO,formic acid and value-added multi-carbon products can be obtained on Cu electrocatalyst.However,due to the similar thermodynamic potential for each product(including hydrogen),the selectivity to a single product is low.Therefore,in view of the problems existing in the two half reactions of electrocatalytic CO₂ reduction,this paper aims to reveal the relationship between the structure and performance of nanomaterials and regulate the electronic structure and geometric structure to realize highly efficient electrocatalytic carbon dioxide reduction with low overpotential for oxygen evolution and high CO or C₂H₄ selectivity for cathode CO₂ reduction.The details are shown below:1.Iron phosphate film supported on three-dimensional nickel foam(NF)is prepared by a simple alternating dipping method for anodic oxygen evolution.The introduction of phosphate groups modurate the electronic structure of Fe³⁺,which boost oxygen evolution activity.The three domentional NF not only promotes gas release,but also reduce"dead volume"for oxygen evolution.It only requires low overpotentials of 215 and 257 mV to drive current densities of10 and 100 mA cm^-2 in a 1 M KOH solution for Fe-Pi/NF.The Tafel slope is as low as 28 mV dec^-1.In the long-term test under the current density of 100 mA cm^-2,no significant increase in potential is observed(90 h),demonstrating the excellent stability of Fe-Pi/NF.2.A efficient strategy to prepare layered nanostructured Fe-O-Ni(OH)₂/NF with easily oxidized Ni²⁺species is proposed.In this strategy,two main steps are taken to prepare Fe-O-Ni(OH)₂/NF.Firstly,Ni(OH)₂ nanosheets(denoted as Ni(OH)₂/NF)are activated in KOH solution to form amorphous and hydrophilic NiO_xH_y(denoted as O-Ni(OH)₂/NF).Secondly,O-Ni(OH)₂/NF is employed as the substrate to prepare Fe-O-Ni(OH)₂/NF by electrodeposition method.The prepared Fe-O-Ni(OH)₂/NF only needs an overpotential of 185 mV to drive a current density of 10 mA cm^-2.Moreover,it exhibits high current densities of100 and 500 mA cm^-2 only with the overpotentials of 220 and 261 mV,respectively.During the 50-hour chronopotentiometric test,no significant deactivation was observed at current densities of 100 and 500 mA cm^-2.This is the first time to promote the oxidation of Ni²⁺species in NiFe-based catalysts without introducing any other elements.3.The covalent degree of metal oxygen(M-O)in CoFe-OH is regurated through anodizing in basic electrolyte.Combining XAS,Opparando Raman and DFT calculations,we found that PO-CoFe-OH with a moderate M-O covalent degree transforms the OER mechanism fromAEM to LOM,and also promotes deprotonation,both of which help to enhance the activity.PO-CoFe-OH has excellent OER performance under mild conditions.In a 0.1 M KHCO₃ aqueous solution(pH=8.3),the overpotential at current densities of 1 and 10 mA cm^-2are as low as 186 mV and 365 mV,respectively.It provides a new way to prepare high-efficiency OER catalysts for mild electrolysis.4.For the first time,NC-AuCu aerogel with abundant grain boundaries is applicated for CO₂ reduction reaction.We found that the grain boundaries in the aerogel can promote to increase the local CO₂ concentration,and its unsaturated coordination structure is also conducive to the activation of CO₂,promoting the formation of*COOH intermediates,and thus promoting the reduction of CO₂.At a less negative potential of-0.21 V,the Faraday efficiency of CO is as high as95%,and the particial current density of CO is up to 28.6 mA cm^-2.Additionally,the energy conversion efficiency is as high as 88%.When coupled with a Si solar cell to construct a PV-EC system,an extremely high solar-to-CO conversion efficiency of about 13.0%can be achieved.This work has deepened our understanding of grain boundaries and provided theoretical guidance for the design and preparation of new catalysts for CO₂ electrochemical reduction or solar-driven CO₂ reduction.5.Coupling of stepped Cu(110)and square Cu(100)in Cu(OH)₂-D/Cu foil are beneficial to promote the formation of C₂₊products.Combining theoretical calculations and in-situ Raman spectroscopy,we found that Cu(110)can promote CO adsorption,while Cu(100)facilitates C-C coupling.In the flow cell,the FE C₂H₄ and C₂₊products is up to 58%and 87%,respectively.Coupling with Si solar cells to realize solar-driven CO₂ reduction,the energy conversion efficiency of solar energy to C₂H₄ and C₂₊products is as high as 4.47%and 6.4%,respectively.This research provides a feasible strategy for the development of efficient catalysts for CO₂ reduction.