Photocatalytic Fuel Cells With The CuS/Cu₂O/Cu Photocathodes

Environmental pollution and energy crisis have become two serious problems in the sustainable development.Among various environmental pollutions,water pollution has received more and more attention all over the world.On the other hand,the wasterwater contains a considerable amount of the chemical energy.Therefore,it is important to seek a clean and efficient wastewater treatment technology,which can simultanesouly recover the chemical energy contained in the wastewater.Photocatalytic fuel cell is such a wastewater treatement technology,which can degrade the pollutants and simultaneously convert the chemical energy contained in the wastewater into electricity by photoelectrochemical reaction using the solar energy.Hence,photocatalytic fuel cells can address the issues of the water pollution and clean energy production,which have great potential for industrial applications.However,the cathode in conventional photocatalytic fuel cells usually adopts the noble metal as the catalyst,which results in high capital cost and cannot further utilize the solar energy.In recent,numerous efforts have been devoted to the development of the cost-effective semiconductors as the cathode materials,in particularly Cu₂O.Although the Cu₂O has been widely investigated,there exist several problems to be resolved.For example,the Cu₂O based photocathode encounters the problems of easy recombination of the photo-excited electron/hole pairs,poor stability and low specific surface area and so on.Aiming at these issues,a photocathde based on CuS/Cu₂O/Cu was developed for the photocatalytic fuel cell.Based on this photocathode,a dural photo-responsive photocatalytic fuel cell was constructed,which can reduce the capital cost and increase the solar utilization.Main outcomes of this thesis are summarized as follows.（1）CuS/Cu₂O/Cu cubic nanoparticle photocathode based photocatalytic fuel cellIn this chapter,Cu₂O/Cu cubic nanoparticle was synthesized by the hydrothermal method,which was then modified by CuS using the successive ionic layer adsorption and reaction method.As a result,the CuS/Cu₂O/Cu cubic nanoparticle photocathode was achieved.The prepared photocathode was characterized by the EIS,LSV and time-current testing,and compared with the Cu₂O/Cu photocathode.The experimental results showed that the electrochemical impedance of the CuS/Cu₂O/Cu cubic nanoparticle photocathode was smaller than the Cu₂O/Cu cubic nanoparticle photocathode,and the oxygen reduction reaction was enhanced.The CuS/Cu₂O/Cu cubic nanoparticle photocathode was able to stably operate for a long time.It was found that the performance of the cell with the CuS/Cu₂O/Cu photocathode was improved significantly as compared to the cell with the Cu₂O/Cu photocathode.The effects of the light intensity,Na₂SO₄concentration and liquid flow rate on the cell performance was experimentally studied.It was found that the PFC performance increased with the increase of the light intensity and concentration of Na₂SO₄,but decreased slightly with the increase of the flow rate.It should be pointed out that the CuS/Cu₂O/Cu cubic nanoparticle photocathode still faced the problem of slow electron transfer rate.In this case,the photo-exicted electron-hole pairs were recombined easily,decreasing the oxygen reduction reaction rate.（2）CuS/Cu₂O/Cu nanowire photocathode based photocatalytic fuel cellThe CuS/Cu₂O/Cu nanowire photocathode was prepared by the wet oxidation-reduction method.This one-dimensional structure not only increased the specific surface area and provided more catalytically active sites,but also promoted the electron diffusion rate to inhibit the recombination of the electron-hole pairs.The newly-developed photocathode was characterized by the SEM,EDS,UV-vis and time-current testing.It was found that the cluster-type CuS was deposited uniformly on the Cu₂O/Cu nanowire,which showed good photo-response to visible light,and could run stably for a long time.The effects of the light intensity,Na₂SO₄ concentration and flow rate on the performance were studied.The results showed that with the increase of the light intensity and Na₂SO₄concentration,the performance was improved.But with the increase of the flow rate,the PFC performance decreased.（3）Three-dimensional CuS/Cu₂O/Cu hydrophobic photocathode based photocatalytic fuel cellIn this thesis,three-dimensional CuS/Cu₂O/Cu hydrophobic photocathode was prepared based on copper foam,which not only increased the specific surface area of the electrode but also provided more catalytically active sites.This three-dimensional hydrophobic photocathode was characterized by the SEM,EDS,LSV,and wettability testing.The experimental results showed that the three-dimensional CuS/Cu₂O/Cu hydrophobic photocathode had a contact angle of 147°,exhibiting good hydrophobicity.The LSV testing results indicated that the three-dimensional CuS/Cu₂O/Cu hydrophobic photocathode had a strong oxygen reduction ability.Finally,the photo-response characteristics,and the effect of the light intensity and Na₂SO₄ concertration on the PFC performance were experimentally studied.It was found that the PFC with the three-dimensional CuS/Cu₂O/Cu hydrophobic photocathode had good photo-response behavior.As the light intensity and Na₂SO₄ concentration increased,the PFC performance was also improved.