Synthesis Of Copper Based Nanocomposites For Electrochemical Reduction Of CO₂

Currently,the world is dealing with two issues that intertwine extremely closely:the climatic changes that are a direct result of the increasing amounts of carbon dioxide（CO₂）in the atmosphere,and the rising demand for energy all over the world.The CO₂ concentration is increasing fast with rapid industrial growth.CO₂ is the core component of greenhouse gases and is the leading cause of the greenhouse effect.Numerous approaches have been developed for CO₂ mitigation.Electrochemical reduction of CO₂ is an encouraging alternate route for converting waste CO₂ into useful chemicals,which simultaneously facilitates the reduction in CO₂ emission to achieve carbon neutrality.The electrocatalytic system for the reduction of CO₂ involves the reaction between CO₂ and protons from water splitting in the presence of electricity generated from renewable energy sources.The selection of appropriate material as an electrocatalysts is an important step toward the facile synthesis of an electrocatalyst for the targeted product.However,the electrochemical reduction of CO₂ is confronted with significant obstacles,such as a low faradaic efficiency（FE）,a high overpotential,and poor stability.As a result,there is still need to develop new catalysts in order to solve the aforementioned problems with efficiency and selectivity.In contrast to noble metals such as platinum and gold,copper based materials are found to be a preferable choice of catalytic materials for the CO₂electroreduction to C₂₊products such as ethylene,ethanol,propanol,etc.due to its tendency to promote C-C coupling reaction,low cost,and high catalytic activity.In 1^st part of this research work,series of silver-decorated cuprous oxides（Ag/Cu₂O）with various crystal morphologies were selectively synthesized using the simple chemical reduction method at room temperature without use of any surfactant as a capping agent.The chemical reduction method is most commonly used to alter Cu₂O crystal with exposed facets because it can tailor nucleation and crystal growth rates along with several orientations.Copper salt as a starting material is reduced by ascorbic acid in the presence of sodium hydroxide（Na OH）as a precipitating agent.Alteration in the morphology of cuprous oxide can be achieved by simply tuning the concentration of Na OH.Silver decorated cuprous oxide nanocomposite with nanosheets,truncated octahedral,sphere,cube,and dodecahedral morphologies were obtained.The synthesized catalysts were characterized by X-ray Diffraction technique（XRD）,Scanning Electron Microscopy（SEM）,and Transmission Electron Microscopy（TEM）for the evaluation of crystal structure,morphology,and elemental valence of the synthesized catalysts.Electrochemical reduction of CO₂ on synthesized catalysts were performed in an H-Type cell.The Ag/Cu₂O-1.5 having cubic morphology showed the best performance for the electrochemical conversion of CO₂ with more than 44%faradaic efficiency for C₂₊products at-1.1 V（versus reversible hydrogen electrode,vs.RHE）.The edges of copper cubes was regarded as active site for adsorption of reaction intermediate（COOH*）and also inhibits HER reaction.The Cu⁰ was formed during electrochemical reduction of CO₂ through reduction of Cu⁺into Cu⁰.The interface between Cu⁺and Cu⁰ may be possible active site for the C-C coupling reaction.Highest faradaic efficiency for formic acid of 20.5%was obtained on Ag/Cu₂O-0.1 containing sheet like morphology.The competing hydrogen evolution reaction was observed on Ag/Cu₂O-0.1 and Ag/Cu₂O-0.5 with sheet and spherical morphology,respectively.In 2^nd part of this work,Cd O/Cu₂O and Zn O/Cu nanocomposites were successfully synthesized using chemical reduction method.The cubic and triangular shaped morphologies were obtained for Cd O/Cu₂O and Zn O/Cu nanocomposites,respectively.The Cd O/Cu₂O with cubic morphology promotes the formation of H₂ through HER reaction.The larges active surface area of Cd O/Cu₂O possibly occupied by adsorbed hydrogen and less active sites available for carbon based reaction intermediates.The Zn O/Cu nanocomposite was found to be very selective for liquid-phase products such as formic acid and ethanol.The highest faradaic efficiency around 48%for liquid-phase product was achieved on Zn O/Cu at-1.1 V vs.RHE.This work will pave the way for the facile and sustainable synthesis of electrocatalysts that are not only efficient but also have the potential to be cost-effective in the large-scale manufacturing of fuels from CO₂.