Systhesis Of CuO-Cu₂O, SnO₂and SnO₂-CuO Nanocatalysts, And The Study On Their Catalized Properties Of CO₂Electroreduction

Carbon dioxide (CO2) reduction utilizing electrochemical method is of great importance andhas many advantages. The electroreduction reaction can be carried out at ambient temperature andpressure conditions and the reaction process is controllable. Moreover, the electrolyte used in theCO2electroreduction can be recycled, so there will not be secondary pollution. In addition, theelectronic energy used in CO2electroreduciton can be generated by new energy, such as solarenergy, wind energy, leading to the CO2reduction reaction clean and environmentally friendly.Therefore, CO2electroreduction can not only solve the greenhouse effect but also help to decreasethe dependence on fossil fuels of human beings. However, due to the slow kinetics and highoverpotential, the CO2electroreduction technique has its own flaws. Thus, developing novelcatalysts with high catalytic activity, good products selectivity and high stability is the key issuefor CO2elctroreduction.This work reports novel morphology controlled CuxO (CuO-Cu2O) nanospheres andsea-urchin like SnO2catalysts which were synthesized by hydrothermal reaction respectively, andcomposite SnO2-CuO nanocatalysts prepared by co-precipitation method. CV, LSV and i-t curveswere used to test electrochemical characterization of catalysts. SEM, TEM (including HR-TEM),XRD, BET and XPS techniques were used to characterize the morphology structures andcomponents of catalysts. Finally, the Faradaic efficiency of all catalysts, particular to formic acidproduction was test and calculated. The main points are summarized as follows:(1) Different hydrothermal conditions can result in different catalytic activity of CuxO in CO2electroredcution. When the hydrothermal condition is180oC for2h, the catalytic activity ofCuxO180-2is high that the onset potential can reach-0.55V and the current density at-1.25V canbe high as about-20.5mA cm-2. Increasing catalyst loading can promote catalytic activity ofCuxO180-2and the optimal catalyst loading is3mg cm-2. The active surface area of CuxO180-2/GDLelectrode is about4.7times higher than the GDL electrodes without any catalyst loaded on. Theformate Faradaic efficiency of CuxO180-2is high up to59.3%when the CuxO180-2catalyst was usedunder-0.7V and electrolysis for1hour. The stability of CuxO180-2is about20hours. (2) SEM, TEM, XRD and BET results indicate that CuxO180-2is made up of hierarchicalthree-dimensional nanospheres, which are consisted of secondary structure. Therefore CuxO180-2has a bigger BET surface area than that of CuxO180-15which is made up of one-dimensionalnanoparticles. XPS result suggests that after20h electrolysis at-1.1V in CO2-saturated KHCO3solution, there was Cu(0) appears induced by the reduction of CuxO180-2. Such induced Cu(0)could promote catalyst’s formate selectivity, so after20h electrolysis, the formate Faradaicefficiency reached high up to~62%. Moreover, according to HR-TEM, the {-111},{-202},{202},{-311},{113} planes of CuO might be the main active planes of CuxO180-2.(3) Different hydrothermal conditions can result in different morphology and catalyticactivity of sea-urchin like SnO2. SEM characterization indicates that the SnO2synthesized at180oC for5h has the most effective morphology. The sea-urchin spheres of SnO2-180-5are flabbier andthe width of urchin spines of SnO2-180-5is relatively larger (500nm). This structure can provideSnO2-180-5more active sites and larger active surface area so that the catalytic activity of SnO2-180-5is higher than SnO2prepared under other conditions. The onset potential of SnO2-180-5can reach to-1.0V and the current density at-1.0V can be high as about-8mA cm-2. Ion chromatography testshowed that when electrolysis at-1.0V for1h, the maximum Faraday efficiency of formic acidcan be high up to62.0%.(4) For composite SnO2-CuO nanocatalysts, increasing the ratio of SnO2could promote theactivity of composite SnO2-CuO. When the ratio of SnO2was50%, the SnO2(50%)-CuO(50%)shows the best catalytic performance. The onset potential of SnO2(50%)-CuO(50%) can reach to-0.75V and the current density at-1.25V can be high as about-24mA cm-2. SEM analysisindicates that SnO2(50%)-CuO(50%) was made up of nanoparticles with an average diameter ofabout50nm. Ion chromatography measurement demonstrates that when electrolysis at-1.0V for1h, the maximum Faraday efficiency of formic acid can be high up to74.1%. The stability ofSnO2(50%)-CuO(50%) is outstanding that even after30hours electrolysis, theSnO2(50%)-CuO(50%) catalyst can also keep a steady current density without any drop.