| With the global temperature continue to rise, lingering drought, melting glaciers, frequent natural disasters and a series of disasters are appeared all over the world. CO2, the principal greenhouse gas, has caused great indelible influence not only to environment but also human. The traditional transformation method has two problems: one is the source of hydrogen, the other is energy consumption. Considering the above problems and efficient catalytic, we eventually choose photoelectrocatalytic reduction of CO2. On the one hand, photocatalytic reaction use sunlight to induce photogenerated electrons, reduce electronic input and energy consumption, on the other hand the reaction use external electric field to improve the current efficiency and product selectivity, high efficient photoelectrocatalytic reduction of CO2 was achieved according the synergistic function between photocatalytic and electrocatalytic.CO2 is characterized as linear type, very stable and must pass through activation to participate in a variety of reactions. So, it is very imporment to look for appropriate photoelectrocatalyst. ZrO2 has excellent mechanical property and thermal stability, high strength, big fracture toughness, low electrical conductivity, high dielectric constant and excellent corrosion resistance, particularly the excellent resistance to chemistry and biochemistry. In additional to the performance itself, researchers also find out that Zr O2 belongs to p-type semiconductor materials. The surface hydroxyl group has two categories of properties: acid properties and alkaline properties and brings high selectivity, activity and interact with active ingredients when reduction of CO2. In the various structure of ZrO2, Zr O2 nanotubes are found have bigger specific surface area, more regular arrangement, more excellent stability and electron transfer ability. It is very suitable to participate in the reduction reaction as a carrier and finally we choose ZrO2 NTs as the study target.Although there are some advantages in mechanical property and electrocatalytic reduction, there are also some disadvantages in conductivity and photocatalytic performance because of that Zr O2 mainly absorbs ultraviolet light and is not sensitive enough to the visible light, it cannot use visible sunlight efficiently and is very suitable to participate in the reduction reaction as a carrier. In order to facilitate its advantages and learn from each other in mutual emulation, we design three kinds of modified methods and successful prepare Cu/ZrO2 NTs, NiO/ZrO2 NTs and ZrS2/ZrO2 NTs to photoelectrocatalytic reduction of CO2.Aimed at improving its poor conductivity and catalytic efficiency, we selected Cu as modified metal. Cu had good electrical conductivity and wide absorption spectra. After loading, the optical activity and efficiency of light energy utilization could been improved. Experimental results showed that the loaded-catalyst had an increased electrical conductivity and the EIS value was only one seven of original catalyst. Cu/ZrO2 NTs also had better absorption ability of visible light region, higher conversion efficiency which arrived about 75% and better products selectivity, the yield of methanol arrived 9.86 mmol/L.The inner diameter of ZrO2 NTs was only 30 nm, general method could only load on the surface and the effective catalytic area was very low. Atomic layer deposition, which could layer material in the form of a membrane on basal surface, was similar to general chemical deposition. The differents were that the layers were associated to each other and it had large force to deposite which could improve efficient load. Those provided a boost for the surface contact between the reactants. Through literature review and comparative study, we prepared NiO/ZrO2 NTs by atomic layer deposition. Experimental results showed that we exhibited strengths of atomic layer deposition while kept its excellent mechanical property, specific surface area and thermal stability. NiO/ZrO2 NTs had better absorption ability and sensitivity of visible light region, the material reductive performance was greatly enhanced.Because of the band gap value of Zr O2 was wide and it had better absorption ability of ultraviolet light, ZrO2 NTs had low visible light utilization. All of above factors limited us to use sunlight to photocatalytic reduction of CO2. When combined with Zr S2 with narrow band gap(1.82 eV) and high absorption coefficient, the performance of catalyst was optimized. Experimental results showed that ZrS2/ZrO2 NTs had narrow band gap which fell to 2.21 eV from 3.39 eV and an improved utilization of sunlight, it is easy to be excited by light. The value of EIS was reduced, ZrS2/Zr O2 NTs had a stronger ability of electrocatalytic reduction of CO2 and more stable current conversion efficiency. It still had higher conversion efficiency under low potential which provided a basis for further exploration of low potential reduction. |
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