Preparation And Study On The Electrocatalytic Performance Of 3D Nickel-based And Copper-based Catalysts

Greenhouse effect and energy crisis threaten the survival and development of human beings.Based on the sustainable development strategies,hydrogen production by water electrocatalytic and resource conversion of CO₂ is of great significance under the adopted of the renewable power system.It is an advantageous approach for the development of electrocatalysis technology by study on efficient electrodes.In addition to the affect of active components,the morphology and structure were considered as important factors for the activity of the electrodes,especially the 3D porous structures with abundant active sites.In this paper,a simple direct writing 3D printing technology was used to realize the prototyping of bimetallic electrodes as 3D network structure rapidly.Spherical metal powders were used as the raw materials,and polyvinyl alcohol was used as dispersant and binder.By this way,it avoided the uniformly formed of multiple metals due to the differences in metal physical properties.The 3D structure electrodes were modified by thermal oxidation,electrodeposition,and hydrothermal methods.The modified electrodes showed the excellent performance in hydrogen production by water electrolysis and the electroreduction of CO₂（CO₂RR）.Based on the material properties prepared by direct writing 3D printing technology,there are four main research aspects of this paper as following:1.Study on the thermal oxidation modified 3D printed Ni Cu porous electrodes and the activity of hydrogen evolution.The surface properties and structural reconstruction of 3D printed Ni Cu electrodes were carried out by two-step thermal oxidation and electrochemical pre-reduction method.The ratio of Ni and Cu and the temperature and time of the thermal oxidation were investigated on the hydrogen evolution activity of the 3D electrodes.The catalytic activity and stability of the electrodes were characterized by electrochemical tests.The results showed that the 3D Ni Cu55 electrode exhibited higher HER activity after the thermal oxidation treatment at 500°C for 2 hours.The overpotentials at 10 m A cm^-2 and 100 m A cm^-2 were 70 m V and 210 m V in 1 M KOH,respectively.And the Tafel slope was 67 m V dec^-1.It showed good stability in the continuous electrolysis experiments up to 100hours.The characterization analysis results showed that abundant Cu nanowires were grown on the surface of the modified electrode,and a micro-nano structure was formed with coexistence of micro-grid structure and nano-wire structure,which can effectively increase the active surface area and promote the transfer of electrons and the decomposition of water molecules.In addition,the formation of Cu/Cu₂O and Ni/Ni O interfaces promoted the adsorption and conversion of hydrogen intermediates,and the synergistic effect of Ni Cu realized the regulation of the adsorption strength of hydrogen intermediates.2.Study on the modified of the thermal oxidation treatment 3D Ni Cu electrodes by Co deposition and the hydrogen evolution performance.The thermal oxidation modified 3D Ni Cu electrode was further treatment by Co deposition by electrochemical deposition and hydrothermal method.The optimal experimental conditions and the catalytic activities of the modified electrodes by Co deposition were studied.Electrochemical test results showed that the deposition of Co enhanced the electron transfer,which exhibited high hydrogen evolution activity under alkaline condition.And the hydrothermally modified Co@3D Ni Cu exhibited an overpotential of 172 m V at 100 m A cm^-2and a Tafel slope of 54.6 m V dec^-1,and showed good stability during 100hours’continuous electrolysis.The results of physical characterization analysis showed that nanosheet-like Co O and nanowire-like Ni Co₂O₄ were formed on the surface of the electrode after the treatment of Co deposition,which effectively improved the active surface area of the electrode.The synergistic effect of active sites and 3D Ni Cu substrate is the main reason for the improvement of the HER activity of the electrode.The formation of spinel structure and the oxide layer improved the corrosion resistance of the electrode and effectively improve the stability of the electrode.3.Study on yhe hydrothermal modification of 3D Ni Fe electrode and the oxygen evolution activity.The 3D Ni Fe electrode was modified in urea and NH₄F urea solution.The effects of the ratio of Ni and Fe,the concentration of urea and NH₄F,and the temperature and time of hydrothermal modification were studied on the catalytic activity of the electrode.The results showed that the 3D Ni Fe electrode modified in the NH₄F urea solution had higher oxygen evolution activity,with an overpotential of 220 m V at a current density of 100m A cm^-2,a Tafel slope of 49.1 m V dec^-1.It also showed a good stability in 100hours’continuous electrolysis,and the overpotential at 1 A cm^-2 only increased by 65 m V.After modification by NH₄F urea solution,a stamen-like structure of Ni Fe₂O₄ nanoneedles wrapped by Fe OOH nanosheets were grown on the surface of the 3D Ni Fe electrode,which further improved the catalytic activity and kinetics of the electrode.The inverse spinel structure of Ni Fe₂O₄ provided a good stability for the electrode.4.Preparation of 3D Cu Zn electrode and the electrocatalytic reduction of CO₂.The three-dimensional structure of Cu Zn was formed by first calcination and then degreasing process.The effects of Cu Zn ratio and temperature and time of the calcination treatment were studied on the catalytic activity of the electrode.The experimental results showed that the prepared 3D Cu Zn electrode can effectively convert the CO₂ and water into CO/H₂ syngas,the faraday efficiency of generating CO can be up to 52.4%,and the total faraday efficiency of syngas can reach more than 80%.It can be achieved the synthesis of syngas in the range of H₂:CO=0.46-3.2,and the current density can reach 36 m A cm^-2 under-1.7 V（vs.SCE）.A large number of Zn O nanowires were grown on the surface of the prepared 3D Cu Zn electrode,and there were oxygen cavities present in the electrode.The activity of the electroreduction of CO₂can be originated from the synergistic effect of Zn O and Cu.In this study,3D Ni Cu,3D Ni Fe and 3D Cu Zn electrodes were prepared by direct writing 3D printing technology.The construction of 3D micro-nano structured were respectively realized by thermal oxidation,electrodeposition and hydrothermal modified methods,which showed good performance in HER,OER and CO₂RR.This study provided a reference for the application and development of chemical modified 3D printed metal electrodes in electrocatalysis.