| Greenhouse and energy crisis are two major problems plaguing human development. Currently, due to the large number of CO2 released from burning fossil fuels, making the atmospheric concentrations of greenhouse gases strong endothermic CO2 continues to rise, increasing the greenhouse effect, caused by melting glaciers, rising sea levels and other environmental problems. Thus reducing CO2 emissions, rational and efficient use of this potential CO2 carbon resources, build new green renewable energy systems become a hot topic. CO2 in the processing means, the photoelectro-catalytic reduction technology with water as a source of hydrogen, solar-powered, is clean, the advantages of environmentally friendly technologies, and became one of the hottest areas of CO2 reduction. The core of photoelectro-catalytic reduction of CO2 is to prepare the photoelectric catalytic electrode with excellent performance, on the one hand, the use of photocatalytic activity of the electrode, generating photoelectrons in the light conditions, can reduce the external energy inputs, reduce energy consumption; on the other hand, the use of electro-catalytic activity of the electrode, thereby increasing the reduction product selectivity and controllability.SiC conduction band because of its potential is almost the most negative, with excellent physical properties, its nanomaterials also showed significant quantum size effect, that the conduction band and valence band into a discrete energy levels, the band gap widens lead change potentiometer more negative, while the price charged bit becomes correct. Therefore, when there is sufficient energy optical radiation, SiC generated by the excited electron- hole pairs with strong oxidizing and reducing power. However, due to its nature of boron-doped diamond with a similar, though with a very wide potential window, but their electrocatalytic poor performance. And usually the SiC powder particles nanomaterials are obtained by the more demanding methods, or between some of the non-conductive substrate in situ growth of the SiC substrate obtained by binding loose material. And only after doping Cu can be a good remedy deficiencies poor conductivity SiC can also improve the catalytic reduction of carbon dioxide light activity, thereby improving the selective reduction of carbon dioxide to methanol product.We first used a two-step metal-assisted chemical etching method to prepare Si NWs. According to SEM characterization of the preparation can be found in the length of Si NWs regular and orderly, consistent orientation, the line about 3 μm, diameter of about 10 nm. And its band gap of 1.25 eV, described wavelength of 992 nm or less light can inspire. Meanwhile Si NWs electro-catalytic reduction of CO2 net current density is greater than zero, indicating that it has considerable electro-catalytic reduction performance. After the introduction of light, its net current density was significantly higher than that of individual electrical, indicating catalytic reduction with excellent optoelectronic properties of CO2. Optical catalytic reduction of CO2 is the main product of methanol, 6 h after the reaction proceeds, the largest methanol production reached 213 μmol·L-1·cm-2.Preparation of carbon-thermal reduction SiC NWs structure entirely inherited from the base Si NWs, and the line about 1 μm, diameter of about 10 nm, and the substrate are linked closely to solve the binding between the matrix and the SiC loose shortcomings. The band gap of SiC NWs preparation obtained was 2.28 eV, its XRD pattern consistent with JCPDS card 29-1129, a 3C-SiC. Electro-catalytic reduction will be applied to their CO2 found over potential-0.68 V, indicating that the electrode has a certain electro-catalytic reduction performance. After the introduction of light, overpotential by-0.68 V down-0.6 V, reducing 80 mV, show their excellent photoelectrocatalytic CO2 performance. Photoelectrocatalysis main product CO2 reduction as methanol, when the reaction is continued for 6 h, the yield on the SiC NWs methanol was 440.52 μmol·L-1·cm-2, is greater than the individual photocatalysis and electro-catalytic reduction of simple addition and 367.01 μmol·L-1·cm-2, reflecting the excellent photoelectric synergistic effect, when its maximum Faraday current efficiency for 64.55 %.Select pulse deposition of Cu atoms in the SiC NWs, to compensate the lack of poor conductivity SiC and CO2 reduction products to improve the selectivity of methanol. Characterization by SEM shows that the material deposited on the surface of the SiC NWs Cu atom takes on a smooth spherical, the maximum diameter of about 900 nm. SiC NWs/Cu composite electrode prepared compared with SiC NWs, the band gap reduced 0.52 eV, oxidation while preparing SiC NWs/Cu reduction current maximum, minimum impedance value, the electron transport ability, excellent optoelectronic properties. When the reaction after 6 h photoelectrocatalysis methanol yield CO2 reduction can be achieved 551 μmol·L-1·cm-2, is 1.25 times the catalytic reduction of SiC NWs CO2 methanol production is Si NWs catalytic reduction of 2.59 times that of CO2 methanol production, reflecting the excellent photoelectrocatalytic performance.In this paper, based on Si substrates prepared three novel catalytic electrode has a good electrical and optical properties, and apply it to the catalytic reduction of CO2, and achieved good results, not only for the rational use of CO2 and CO2 emission reduction potential of this carbon resources is important, but also on the photoelectric synergistic catalytic reduction of CO2 provides new ideas and learn. |
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