Design Of Novel Metal-based Nanoporous Electrocatalysts On Morphology Control And Study On CO₂ Electrochemical Reduction

As a leading cause of global warming,carbon dioxide(CO2)has been accumulated in the atmosphere by industrial combustion of fossil fuels.Electrochemical reduction of CO2(ERC)into useful products with renewable energy can be an attractive strategy to mitigate greenhouse effect by reducing carbon emission.Considerable attempts are need to improve the performance of metal-based electrocatalysts in the ERC due to their poor activity,selectivity and high overpotential.The previous results showed the catalytic activity and selectivity of the catalysts considerably depend on the surface morphology.In this thesis,based on morphology control,we designed and fabricated a series of metal nanoporous electrocatalysts with novel construction by some innovative simple methods and demonstrated their high performance for CO2 reduction in electrochemisty systems.Firstly,a facile and scalable technique-hydrogen bubble dynamic template was employed to create efficient electrocatalysts for the ERC.We developed a novel porous Cu electrode which was electrodeposited in a H2SO4/CUSO4 aqueous electrolyte containing Cl-.The presence of Cl-ions induced a dramatic change on the morphology of the Cu foams with anisotropic growth.We have observed the enhanced faradaic efficiencies for formate and CO.This result exhibits our porous Cu foam electrodeposited with Cl-has excellent catalytic activity as compared to the regular Cu foam.In addition to Cu,we reported another needle-like porous Indium electrode electrodeposited using the hydrogen bubble dynamic template.This novel electrode displayed improved electrocatalytic activity,enhanced conversion efficiencies and a lower onset potential.The faraday efficiency of HCOOH is as high as 86%.We also explored the catalytic mechanism of nanoporous copper and Indium catalysts.This noteworthy excellent catalytic activity of the porous nanostructure In and Cu catalysts,is the result of a large electrochemical surface area and needle-like dendrite structures in the presence of Cl-salts.The concept field-induced reagent concentration(FIRC)is introduced to account for the excellent performance of our nanoporous electrocatalysts.Utilization of the novel nanostructured electrocatalysts and understanding of the role of FIRC in the electrolyte can contribute to the design of more improvements of the ERC.Secondly,we developed a novel SnO2 porous catalyst with wire-in-tube(WIT)structure by facile and cost-effective electro-spinning synthesis process.The reduced SnO2 showed superior selectivity for C1 products(HCOOH and CO).Using the WIT SnO2 as the ERC catalyst,very high Faraday efficiency of Ci products(FE=93%)can be achieved at a wide potential,thus substantially suppressing hydrogen evolution reaction,Faraday efficiency can be less than 10%under wide potentials(-0.89—1.29 V).The electrocatalyst also exhibited excellent long-term stability.Large surface area,WIT nanostructure,high density of grain-boundaries as well as the FIRC effect are likely attributed to its excellent catalytic performance.The developed facile and cost-effective synthesis process,high current density and selectivity to Ci products,and robust chemical stability make the novel WIT SnO2 nanofiber a promising catalyst for ERC.In the end we developed novel cooper nanoporous catalysts by couping hydrogen bubble dynamic template with electroplating of alloy process.Compared to the regular nanoporous copper,the CO selectivity of the copper-tin nanoporous electrode was improved greatly(FE>50%),which is attributed to the unique structure of CuSn alloy.The result will present a strategy to provide low-cost metal porous nanostructure catalysts for ERC.