Controllable Synthesis And Catalytic Properties Of Novel Copper Nanostructures

In order to solve the energy crisis,many countries are vigorously developing the green energy.As green and clean methods of electrochemistry,fuel cell and electrochemical nitrogen reduction reaction?NRR?have attracted wide attention.Because the oxidation reduction reaction?ORR?of fuel cell cathode is inefficient,commercial platinum carbon is often used as catalyst to improve the reaction efficiency.Due to the high price and low stability of platinum,the fuel cell cannot be widely used in industry.Besides,ammonia,as a product with large demand for global production,can be obtained by electroreduction of nitrogen,which will greatly reduce the energy burden.However,there is still a problem of low activity and selectivity of NRR catalysts.Recently,more and more attention has been paid to the replacement of noble metal catalysts with cheaper transition metals.As a high-content and relatively inexpensive transition metal,copper has abundant d electrons and a variety of stable valence states.It can not only undergo single-electron oxidation,but also carry out multi-electron transfer processes,making it comparable to platinum-based metals in catalytic activity.We synthesized copper nanorod arrays self-assembled from nanoparticles by high temperature thermal solvent method.By adding template CTAB,we synthesized copper nanoflowers,which were self-assembled from sub-2 nm nanowires.Copper nanoflowers expose?100?and?111?crystal planes at the same time,while copper nanorod arrays only have?111?crystal planes.Two kinds of copper nanostructures were used as catalysts in ORR of fuel cell.It was found that both of them exhibited higher ORR activity,stability and toxicity resistance than commercial platinum carbon catalysts.Moreover,the ORR activity of copper nanoflowers is higher than that of copper nanorod array structure.By calculating the adsorption and desorption energies of copper?111?and copper?100?planes by density functional calculations?DFT?,the oxygen dissociation and hydrogen peroxide activation on both crystal planes of copper are very easy.However,the difference between Cu?100?and Cu?111?planes is the adsorption and dissociation energy of O₂.The adsorption and activation of oxygen molecules on Cu?100?planes is easier than that on Cu?111?planes,which was the reason for the different activity of the two catalysts.We also synthesized copper-tin nanoplates alloy with diameters between 25 and 30nm by high temperature thermal solvent method.The thickness of the plates is about 13nm.And the nanoparticles showed the excellent NRR properties.The yield of ammonia reached 28.9?g?mg^-1h^-1 at the potential of-0.6 V vs.RHE,and the Faraday efficiency reached 19%at this potential,meantime,the catalyst maintained good performance under long-term test,which proved NRR is a promising research direction.