Fabrication And Electrocatalytic Carbon Dioxide Reduction Perforamces Of Ag Nanowire Arrays

Converting carbon dioxide into energy-bearing products,can not only alleviate,if not eventually solve,the CO₂ problems associated with anthropogenic activities but also supplement the diminishing fossil fuel reserves.In nature,this process is being practiced perpetually as parts of the metabolism of green plants,providing feeds for animals and balancing the CO₂ concentration in atmosphere.To facilitate the carbon fixation process,the search for efficient biological and chemical pathways using renewable energy has been actively conducted for many years.Electrocatalytic reduction of CO₂ in aqueous electrolyte is one of the promising strategies that receives enormous attentions in recent years.However,this process in general requires a large overpotential and has to compete with hydrogen evolution reaction?HER?as a side reaction.Therefore,an efficient catalyst with low overpotential and high faradaic efficiency is crucial in order to implement this technology to practical applications.Researchers have explored plenty of metal materials in search of active catalysts.It is found that Au and Ag are promising candidates exhibiting major reduction selection towards CO.Although Au holds the benchmark electrochemical activity in CO₂conversion,it is not economically viable for practical implementation.As an alternative,Ag has attracted much attention due to its more affordable cost and good selectivity to CO and CO could be used as an important feedstock for further application such as Fischer–Tropsch synthesis if the overall CO₂ to CO conversion process could be efficiently improved.Here we present Ag nanowire arrays?NWA?obtained by a simple,cost-effective nanomoulding technique as an advanced catalyst for electrochemical reduction of CO₂.Although the nanomoulding method has been widely used for polymers and metallic glasses,it is believed not applicable to the metallic crystalline materials due to their size effect?the smaller the stronger?.Here we overcome this hurdle,successfully extend this technique on crystalline silver and obtain large scale Ag NWAs with many advantages,which endow them some superiorities on the catalytic application.Different from other nanowires fabrication techniques,nanomoulded Ag nanowires are single-crystal-like and rooted in the bottom Ag conducting film,suggesting a great electrical conductivity and facilitating the charge transfer process.The as-prepared Ag NWAs exhibited superior activity and selectivity towards CO production.For NWAs with 200 and 30 nm-in-diameter,the onset overpotential was only²00 mV which was 300 mV smaller than that of a polycrystalline Ag foil counterpart.At moderate potential of-0.6 V vs RHE,the j_coo of Ag nanowire array with 200 nm-in-diameter was more than 2500 times larger than that of Ag foil at a FE of 91%.Its specific j_co reached a high value of 18.78?A cm^-2?46-fold improvement?.Both a large electrochemically active surface area?more than 50 times enhancement?as well as the intrinsically enhanced activity(reflected by specific j_co)contributed to the superior performance.The different selectivity and efficiency between Ag nanowire arrays with diameter of 30 nm and 200 nm may arise from the mass transport limitation induced by different surface morphologies...