Study On The Performance Of Nanaostructrued Electrodes In Electrochemical CO₂ Reduction

The technology of using renewable electric energy to drive the electrochemical CO2 reduction into high value-added products in aqueous solution system is considered as the most promising solution to alleviate future energy crisis and realize carbon neutral cycle.Although some progress has been made in the current research,due to the inertia of CO2 molecules,low solubility in aqueous solution system and low reaction potential barrier of electrolytic water,strong hydrogen evolution side reactions usually occur in the process of electrochemical CO2 reduction reaction.In addition,the adsorption strength of CO2 reduction intermediate CO and CHO or COH on the catalyst surface and the scale relationship between the intermediates make the regulation of electrochemical CO2 reduction selectivity become another big challenge.In this paper,the performance of nanostructured electrode in electrochemical CO2 reduction was studied by targeting the inhibition of hydrogen evolution and selective regulOation.Faradaic efficiency,overpotential and product selectivity of electrochemical CO2 reduction can be adjusted by means of surface wettability and the regulation of surface components or valence states.The research contents and conclusions of the whole work are mainly divided into the following aspects:1.Porous nitrogen-doped carbon nanosheets with adjustable nitrogen species content and types were prepared by one-step heat treatment,and the performance of electrochemical CO2 reduction in aqueous solution was studied.The results show that the CO Faradaic efficiency reached 90%at-1.1 V(vs.Ag/AgCl)over NC-1000.Moreover,the mixing gas that the ratio of H2 and CO is 3/1 can produce at-1.3 V(vs.Ag/AgCl),which can directly use in the process of fischer-tropsch synthesis.These excellent properties can be attributed to the NC-1000 carbon nanomaterial has a higher pyridine nitrogen content,as well as surface hydrophobicity.In addition,due to the removal of nitrogen in the heat treating process,more active sites with full exposure of pore structure were formed on the material surface,avoiding that the coverage of reactive sites by interlayer stacking of two-dimensional materials.2.The nanoporous Sn/SnOx core-shell structures were fabricated by electrochemical deposition at high potential.The surface was coated with an oxide layer with a large number of oxygen vacancy defects and a thickness of about 2 nm through mild thermal oxidation treatment.The ratio of water molecules and CO2 molecules on the catalyst surface can be adjusted by the low surface energy substance PTFE modified on the internal and external surfaces of porous Sn/SnOx.It is found that both current density and faradaic efficiency of formic acid over Sn/SnOx@PTFE(B)-0.05 can be greatly improved and reached 23 mA/cm2 and 80%,respectively.3.Amorphous SnOx powders with array nano-pore structure were prepared by electrooxidation method.By heat treatment at different temperatures under the air condition,the oxygen precipitation in SnOx phase would compete with the oxidation of SnOx,so as to regulate the oxygen vacancy concentration.The results showed that under 300℃ calcination form samples have the greatest oxygen vacancy concentration.And in the process of electrochemical CO2 reduction,the SnOx-300 exhibited excellent performance,that the formic acid faradaic efficiency can reach more than 90%,and almost no CO produced,and confirmed that the oxygen vacancy in the surface of the catalyst for the CO2 adsorption mainly adopt the way of oxygen adsorption,which is beneficial for the improvement in the formation of formic acid.4.Bismuth-based catalysts with different morphologies,such as nanospheres,nanowires and nanosheets,were prepared by solvent-thermal method.Through characterization,it was found that the bismuth nanospheres were agglomerated with small bismuth nanoparticles and were polycrystalline,while the main exposed crystal surfaces of the nanowires and nanosheets were(110)and(012),respectively.The relationship between the calculation of the texture coefficient of the three bismuth structures on different crystal planes and the electrochemical CO2 reduction performance indicates that the sites with the highest electrochemical CO2 reduction catalytic activity are mainly distributed on(012)crystal plane and a small amount on(110)crystal plane,which determines that the flake structure has the best electrochemical CO2 reduction performance.5.Cu nanowires were prepared by the liquid reduction method.On this basis,Cu/Cu2O intertface structure nanowires were prepared by the in situ electrochemical surface reconstruction in KCl solution.In the process of electrochemical CO2 reduction,the C2H4 and total C2+faradaic efficiency can reach 53%and 65%over Cu/Cu2O interface nanowires electrode,respectively.The results confirmed the previous density functional theory calculation(DFT report that the the Cu0 and Cu+ interface model can promote the coupling of C-C bond.The carbon atom binding with Cu+ site is positively charged and the carbon atom binding with Cu0 site is negatively charged,the two carbon atom can be coupled by the electrostatic interaction.