| Hydrogen energy is one of the attractive measures for solving the energy supply scarcity and the greenhouse gas reduction.And in the process of combustion,it produces only water without any other contaminants.As one kind of secondary energy,H2 should be produced from renewable resources to realize sustainable development.Photocatalytic water splitting is one of the ideal methods,since hydrogen can be produced from water by using solar energy.To obtain the higher hydrogen generation efficiency,methanol or ethanol with high concentrations were generally used as sacrificial agents,and the applications of other organics were relatively rare,much less the organic wastewater with high chroma.The noble metal Pt is usually used as cocatalyst or hydrogen evolution electrode,which is not conducive to popularization and promotion.Due to the high stability,Ti O2is the most commonly used photocatalyst.But it just absorbs the ultraviolet,which make up a minority of the solar spectrum.Based on our former research,in this dissertation,focusing on the bottleneck problem of photocatalytic production of hydrogen,some mainly works were carried out.In allusion to the low utilization ratio of irradiation energy resulting from the absorption of solution in the photocatalytic system,we constructed a rotating-disk photo fule cell and used ethanol with 10-4 mol?L-1?1.0 mol?L-1 to verify the practicability and optimize the operating parameters.A proton exchange membrane divided the reactor into two compartments,two different electrolytes of different p H values were used in the two compartments.The anode compartment was open to atmosphere and the cathode compartment was exposed to N2 protection.By the photoelectrochemical performance testing,the p H difference between anolyte and catholyte were used to establish a chemical bias.And a low concentration of ethanol as the sacrificial agent could provide 0.4 V bias for the system and rapidly consume the photogenerated holes to promote the separation of hole-electron pairs,thus improving the photoelectric conversion efficiency and power output.With the increase of Et OH concentration from 10-4 mol?L-1 to 1 mol?L-1,the photocurrent density and the generation rate of H2 all increased exponentially,this result was consistent with that Ti O2/UV photocatalytic reaction rate constants of various organic compounds have exponent relation to the initial substrate concentration.From an economic point of view,the operation parameters of the rotating-disk photo fuel cell were optimized at electrode rotating speed 90rpm,anolyte p H above 14 and system temperature 25°C.During the prolong experimental period,the generation of H2increased linearly in the first 6 h,and with prolongation of time,the generation rate of H2 slowed down and then tended to stop,this was due to that chemical bias could not be self-sustaining and continuously decreased with the prolong reaction time.When the bias was too low to drive electrons to transfer through external circuit,the generation of H2 ended.By comparison,the cogeneration of H2and electric flow obtained by rotating-disk photo fuel cell was more than 7 times as that of conventional reactor.Especially,when using alcohol effluents with high chroma,the rotating-disk photo fuel cell could effectively reduce the irradiation energy losses and maintain the high efficient and stable performance of cogeneration of hydrogen and electricity.To convert dye wastewater into useful forms of energy,Rhodamine B(RB)and reactive brilliant red X-3B(X-3B),as representative of cationic dye and anionic dye,respectively,were used as the model dye wastewater to assess the reactivity of the rotating-disk photo fuel cell.The addition of dyes did not much affect the bias but significantly increased the photocurrent density,indicating that the dye molecule was oxidized by holes to generate various ions and release photogenerated electrons.When exposed to UV illumination,the maximum decolourization efficiency of RB and X-3B obtained in the rotating-disk photo fuel cell(evaluated by color)were all 99%or more,and they are much higher than that of the conventional reactor(71.9%for RB and 77.7%for X-3B).Moreover,the generation of H2 and electricity in rotating-disk photo fuel cell were 10 times higher than that of the conventional reactor.X-3B was easier to decolorize than RB,and the generation of H2 and electricity obtained were all 1.4 times as that of the RB.This is due to that the chromophoric group of X-3B was one azo group(-N=N-),which possess a much lower bond energy than that of(-C=N-)RB.The azo group of X-3B was easier to be broken to generate colorless substance,thus just investigating the color removal efficiency or the absolute removed quantity of dyes was incomplete.Through the comparison analysis of COD before and after treatment,the dye could be completely mineralized in this rotating-disk photo fuel cell,and the removal tendency of COD was consistent with the trend of the cogeneration of H2 and electricity.The above mentioned results showed that the rotating-disk photo fuel cell was constructed with three-simultaneity functions:cogeneration of H2and electricity concomitantly with the degradation of dye wastewater.To develop a low cost,earth abundant and high performance catalyst as the alternative of Pt,polypyrrole(PPy)functionalized nickel(Ni)electrode is facilely prepared through the potentiostatic electrodeposition of PPy on Ni substrate.The obtained PPy film looks like wrinkled skin,which doubtlessly increased the specific surface area and decreased the hydrogen evolution overpotential.The H2 amount detected was 97.5%of the theoretical calculating value,indicating that PPy-functionalized Ni foam cathode could effectively catalyze the electrons transfered through external circuit to combine with proton to generate H2.The electrodeposition voltage and duration were optimized at+0.8 V(vs.SCE)for 20 min.The H2 producing performance of the PPy-modified Ni substrates decreased in the following order:foam-type>net-type>plate-type.Ni foam,possessed three-dimensional(3D)cross-linked grid structure,was conducive to the deposition of PPy and the evolution of H2.Thirteen runs were carried out to investigate the reproducibility of the PPy-functionalized Ni foam cathode,the H2 accumulation rate fluctuates between 2.88 and 2.38?mol?min-1.The variation trend of the simultaneous current flow was the same as that of the H2 evolution rate and it fluctuated between9.32 and 7.72 m A,indicating a potential stable catalytic property and excellent durability.Compared with Pt-group electrodes,the generation performance obtained by PPy-functionalized Ni foam was 77%of that of pure Pt foil,1.4 times as that of commercial Pt-plated plate and almost consistent with the result obtained by the Pt black-Ni foam.PPy film,possesses an anion intercalation,is assumed to collect and to channel the protons to the polymer/Ni interface.Under the catalyzing of Ni,H+combined with e-to produce H2.Compared with poly(3,4-ethylenedioxythiophene)(PEDOT)or polyaniline(PANI)modified Ni electrodes,the combination of PPy and Ni formed a synergistic effect and thus shown the best performance.In the photoelectrochemical and electrolytic production of H2,the PPy-functionalized Ni foam cathode showed a satisfactory performance.The results mentioned above indicate that the PPy-modified Ni foam electrode exhibits an excellent hydrogen-evolution catalytic activity comparable to Pt-group electrodes and has a great application potential in a wide range of fields.To achieve the utilization of visible-light in photo production of H2 as soon as possible and based on the reports about the visible-light absorption and ultraviolet excitation of PANI,PANI was polymerized on Ti palte through galvanostatic electrodeposition to construct the PANI-modified Ti photoanode.The polymerization of PANI film was a two-stage film formation,resulting in granular surface morphology with the incorporation of PANI precipitates into the continuous layer.The granular structure was in favor of the multiple reflections of light on the surface of the electrode.The formed PANI was conducting emeraldine salt and had the strong absorption in the visible area,the band gap energy was calculated at 2.3 e V.The PANI-Ti electrode could be exited by UV-light(254 nm)and visible light(430 nm?720 nm).Irradiated by UV(254 nm)and visible light(>400 nm),the rotataing-disk PFC with PANI photoanode could achieve the three-simultaneity functions for the cogeneration of H2 and electricity with dye degradation.Under the UV irradiation,the maximum color removal efficiency and the total generation amount of H2 was 99.2%and 300?mol,respectively.When using visible light,the obtained results were 17.2%and 158?mol.When repeated using the PANI-modified Ti anode,the color of anode turned from deep green to puce and the generation amount of H2 decreased with the number of use from 300?mol to 79.3?mol.After each use,the emeraldine salt structure of PANI could be regenerated by doping with H2SO4 aqueous solution.And the generation amounts of regeneration experiments fluctuated between 298?mol?325?mol.Therefore,PANI-modified Ti anode showed a good regenerability and exhibited a reasonable repeatability on the hydrogen-evolution performance within the margin of error.When it was applied to photoelectrochemical production of H2,PANI-modified Ti anode could maintain the emeraldine salt structure,and realize the linear increase of the H2 generation amount and the high decolorization efficiency of dye. |
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