Electrochemical Reduction Of CO₂ On Compound Derived Nanosized Metal Catalysts

The efficient electrochemical reduction of CO₂?CO₂ER?to value-added carbon-based fuels and building blocks for the chemical industry has the promise to enable the storage of intermittent renewable energies such as solar and wind while simultaneously achieving a net reduction of greenhouse gases emissions.The active,selective and stable electrocatalysts play a key in CO₂ER.The usage of metal foil as substrates greatly reduce the materials utilization efficiency.Therefore,to develop a facile,scalable and cost-effective preparation method to obtain nanosized catalysts plays a key role in realizing the large-scale CO₂ER.Compound-derived nanosized metal catalysts can achieve significantly improved CO₂ electroreduction activity and selectivity.In addition to the properties of catalysts,electrolyte also plays an important role in improving the performance of the catalysts.Herein,we have prepared several compound-derived catalysts with high performance.Furthermore,the effect of KHCO₃concentration on catalyst performance was studied.The main contents and achievements are as follows:?1?Zn₄CO₃?OH?₆·H₂O and ZnO?prepared by annealing Zn₄CO₃?OH?₆·H₂O?derived 2D nanosheet catalysts shown the enhanced activity and faradaic efficiency?FE?towards CO as compared with Zn foil at high overpotentials.At–1.0 V vs.reversible hydrogen electrode?RHE;all potentials reported here are given on the RHE scale unless noted otherwise?,Zn₄CO₃?OH?₆·H₂O derived catalysts demonstrated a good selectivity of 82.02%toward CO with a partial current density of CO of 6.47 mA cm^–2.By contrast,the partial current density and FE of CO of Zn foil were 3.40 mA cm^-2 and 64.30%,respectively.It indicated that Zn compound-derived catalyst was a kind of highly efficient catalyst of CO₂ER with high activity and selectivity.Furthermore,by comparing the performance of nanosized catalyst and Zn foil over low overpotentials,it was found that the FE of nanosized catalyst for CO at low overpotential still needed to be improved.?2?The active,selective and stable nanoporous Ag catalyst was synthesized by electrochemical reduction of AgCl.The effect of KHCO₃ concentration on the catalytic performance was systematically investigated on the as-prepared catalyst.It was found that increasing the KHCO₃ concentration could further promote the selectivity towards CO over low overpotentials.At-0.6 V,FE of CO dramatically changed from 48.33 to82.76%when the KHCO₃ concentrations were increased from 0.1 to 0.7 M.In addition,the KHCO₃ concentration demonstrated the remarkable influence on the catalytic activity.The total partial current density dramatically changed from 13.63 to 41.61 mA cm^–2 when the KHCO₃ concentrations were increased from 0.1 to 0.7 M.Furthermore,the selectivity of Ag catalyst to CH₄ was further explored,and the high concentration of KHCO₃ was helpful to improve the selectivity to CH₄.?3?Although precious metals such as Au,Ag and Pd have been proved to be efficient catalysts for CO₂ER,the development of catalysts based on non-noble metals is the key to the popularization and application of this technology.Indium?In?modified Cu catalyst was prepared by electrochemical reduction the mixture of Cu₂O and In?OH?₃.It is found that the composition of Cu-In binary metal catalyst has a crucial effect on the selectivity.The selectivity of the catalyst can be controlled by changing the proportion of Cu/In element in the Cu-In binary metal catalyst.In 0.1 M KHCO₃,a high Faraday efficiency of 90.37%for CO was obtained.The performance of the Cu-In binary metal catalyst can match or even exceed that of the noble metal catalyst.Based on the Cu-In binary metal catalyst with the highest selectivity for CO,the effect of KHCO₃ concentration on its activity and selectivity was also studied.?4?Cu₂O@SnO_x nanoparticles with core-shell structure were obtained by modifying as-synthesized Cu₂O nanoparticles in SnCl₄ ethanol solution at room temperature.Under the condition of electrochemical reduction of CO₂,the nano-binary metal catalysts with different spatial configurations of Cu/Sn elements were obtained by electrochemical reduction of Cu₂O@SnO_x nanoparticles.The FE for CO of the catalyst was up to 90.47%in 0.1 M KHCO₃ solution.In addition,the catalyst showed good stability in 24 h continuous test.Based on the Cu-Sn nano binary metal catalyst,we studied the influence of KHCO₃ concentration on its activity and selectivity.Increasing the concentration of KHCO₃ can significantly improve the activity of the catalyst,which is related to the role of K⁺and HCO₃^-in the process of CO₂ER,as well as the high buffering capacity of high concentration KHCO₃ solution.In addition,the high buffering capacity of high concentration KHCO₃ solution will also reduce the concentration gradient of reactant near the electrode caused by the electrochemical process.The concentration overpotential of the electrode process was reduced so that the CO₂ER can be carried out at a lower overpotential.In 0.7 M KHCO₃,the catalyst achieved a high FE of 98.07%for CO at an overpotential of 590 mV.KHCO₃ solution with high concentration fully explored the performance of the catalyst for CO₂ER.In 0.7 M KHCO₃,the FE for H₂ of the catalyst was less than 10%at all test potentials,indicating that the conversion ability of the catalyst for CO₂ remained at a high level throughout the tested potential range.It demonstrated that to prepare nanoparticles with special structure is an effective way to obtain high-performance binary metal catalysts.