| Ammonia?NH3?is one of the most productive chemicals,which play important roles in the global economy.Currently,the ammonia production is about 200 million tons per year.Due to the high energy consumption and serious CO2 emission in the traditional Haber-Bosch ammonia synthesis process,it is of great significance to find an environmental-friendly low-energy ammonia fixation technology for the sustainable development of national economy.To promote the N2 reduction reaction?NRR?to NH3,various methods concerning biochemistry,electrochemistry,photocatalysis,and photoelectrochemistry.Among these,the photoelectrocatalytic approach benefiting from the effects between electrochemistry and photocatalysis has aroused wide and intense research interest.It is one of the feasible ways to develop new energy technology to transform natural cheap small molecule N2 into high value-added chemical NH3 by means of electrocatalysis and photocatalysis.But the excellent electrocatalyst usually uses precious metals as electrocatalyst material,and the high cost limits its industrial application.Although the photocatalysis method is cheap,clean and pollution-free,the single photocatalyst is difficult to achieve the expected catalytic efficiency,and it is also difficult to achieve industrialization at present.The purpose of this paper is to integrate the advantages of photocatalysis and electrocatalysis,and to achieve the efficient conversion of energy in the photocatalysis synthesis of ammonia by selecting cheaper catalyst materials.Herein,oxygen-deficient TiO2-x nanofibers were prepared via in-situ growth onto carbon cloth?CC?,and the effect of oxygen vacancies on ammonia fixation activity was investigate.BiO1-x Br/TiO2-x/CC and MoS2/TiO2-x/CC composite electrodes were also synthesized to achieve the enhanced ammonia production.Characterizations were performed by using XRD,SEM,TEM,XPS,Raman,UV-vis DRS,PL and electrochemical technology to clarify the relationship among the composition,structure and solid-liquid phase photoelectrocatalytic ammonia fixation activity of the as-prepared electrodes.The main content and results were presented as follows.?1?Oxygen-deficient TiO2-x nanofibers were prepared via in-situ growth onto carbon cloth,and the concentration of the oxygen vacancies were controlled by heat-treatment temperature.It was found that Ti3+-related energy levels are introduced below the conduction band of TiO2-x,resulting in the improved visible-light response and the remarkably enhanced separation efficiency of photoinduced electron-hole pairs.The doped Ti3+ species,favoring to the adsorption and activation of N2 molecules,consequently contributes to the increased photoelectrocatalytic activity towards ammonia fixation.When the heat-treatment temperature is fixed at 100 oC,the optimal NH3 production rate on the TiO2-x/CC electrode is determined to be 4.47?g·h-1·cm-2at a bias voltage of-0.9 V?vs.RHE?under visible light irradiation.?2?Oxygen-deficient BiO1-x Br nanoclusters were deposited onto the TiO2-x/CC electrode by a hydrothermal method.The resultant formation of two photon centers,account for the extended absorption light range.The heterojunction between BiO1-x Br and TiO2-x facilitates the charge separation,interfacial transfer,as well as the beneficial adsorption and activation of N2 molecules on the BiO1-x Br/TiO2-x/CC.When the surface Bi/Ti atomic ratio is tuned to 0.42,the optimal NH3 production rate on the electrode is found to be 8.42 ?g·h-1·cm-2 at a bias voltage of-0.8 V?vs.RHE?under visible light irradiation,which is 1.88 times as high as that on the TiO2-x/CC electrode.?3?MoS2 QDs were loaded onto the TiO2-x/CC electrode by a hydrothermal method.The MoS2 dopant dramatically enhances the charge separation efficiency on the TiO2-x/CC with an obvious increasement in current density.Acting as a cocatalyst,the MoS2 QDs supply additional active sites for the adsorption and reduction of N2 molecules,contributing to a significant improvement of NH3 evolution over the MoS2/TiO2-x/CC.When the surface Mo/Ti atomic ratio is tuned to 0.02,the optimal NH3 production rate on the electrode is found to be 19.98 ?g·h-1·cm-2 at a bias voltage of-0.7 V?vs.RHE?under visible light irradiation,which is 4.47 times as high as that on the TiO2-x/CC electrode. |
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