甲醇燃料電池Pt基合金催化劑電催化甲醇氧化的理論和實(shí)驗(yàn)研究
發(fā)布時(shí)間：2019-06-30 23:15
【摘要】：直接甲醇燃料電池(DMFC)是直接以甲醇為燃料,將甲醇氧化時(shí)產(chǎn)生的化學(xué)能轉(zhuǎn)變成電能的能源裝置。因具有能量轉(zhuǎn)化效率高,環(huán)境友好,易于儲(chǔ)存和運(yùn)輸?shù)葍?yōu)點(diǎn)而被認(rèn)為是一種理想的清潔能源。貴金屬鉑(Pt)具有較高的催化活性,是目前應(yīng)用最廣泛的DMFC催化劑。但是由于Pt資源稀少、價(jià)格昂貴,制約了其商業(yè)化發(fā)展。此外,電催化甲醇氧化機(jī)理復(fù)雜,催化劑表面的活性位點(diǎn)容易被氧化過(guò)程中生成的CO等中間物種占據(jù),導(dǎo)致催化劑中毒,催化活性降低,從而阻礙了甲醇的進(jìn)一步催化氧化。因此,尋找并設(shè)計(jì)高Pt利用率、高催化活性、穩(wěn)定性和抗CO中毒性強(qiáng)的催化劑勢(shì)在必行。在本文中,我們利用密度泛函理論(DFT)研究了甲醇在PtAu和PtPd催化劑表面的催化反應(yīng)機(jī)理,探索了二者抗CO中毒能力以及電催化甲醇氧化活性差異的本質(zhì)原因,并通過(guò)實(shí)驗(yàn)方法驗(yàn)證理論計(jì)算結(jié)果。最后,通過(guò)軟模板法制備了具有不同原子比例的PtCo合金納米線(xiàn)催化劑并應(yīng)用于甲醇催化氧化。我們的研究旨在為設(shè)計(jì)和優(yōu)化性能更加的燃料電池催化劑提供一定的理論和實(shí)驗(yàn)指導(dǎo),為推動(dòng)燃料電池的商業(yè)化發(fā)展貢獻(xiàn)一點(diǎn)綿薄之力。本論文將從以下五個(gè)部分進(jìn)行研究:第一部分,主要介紹了直接甲醇燃料電池的工作原理、發(fā)展現(xiàn)狀以及電極的反應(yīng)機(jī)理,同時(shí)對(duì)催化劑的制備方法進(jìn)行了簡(jiǎn)單介紹。另外,我們還闡述了本論文研究工作的意義。第二部分,詳細(xì)介紹了本文研究所用到的理論計(jì)算方法:密度泛函理論(DFT)和過(guò)渡態(tài)理論(TST)。另外還對(duì)實(shí)驗(yàn)過(guò)程中催化劑所采用的物理表征和電化學(xué)表征手段進(jìn)行了簡(jiǎn)單的描述。第三部分,基于周期性密度泛函理論(DFT)系統(tǒng)的研究了甲醇在PtAu(111)表面的催化反應(yīng)機(jī)理。在所涉及的最穩(wěn)定的中間體的吸附研究中,我們考慮的反應(yīng)途徑有兩種:CO途徑和non-CO途徑。根據(jù)最穩(wěn)定中間體及反應(yīng)所需的過(guò)渡態(tài),最終確定最有可能的兩種途徑為:CH3OH→CH2OH→CHOH→CHO→CO(CO途徑)和CHO→HCOOH→COOH→CO2(non-CO途徑)。對(duì)CO和non-CO途徑進(jìn)行比較,我們發(fā)現(xiàn)甲醇在PtAu(111)表面的反應(yīng)主要是通過(guò)non-CO途徑發(fā)生。且計(jì)算結(jié)果表明:在生成CO2之前,甲醇更傾向于生成CO,在CO途徑中CHO分解生成CO的能壘僅為0.21 eV,而消除CO需要克服0.74 eV的能壘。因此,我們預(yù)測(cè)non-CO途徑的發(fā)生并不能完全抑制CO的產(chǎn)生,在PtAu(111)表面仍然有部分CO的沉積,從而造成催化劑的中毒,使其催化活性及穩(wěn)定性降低。第四部分,采用密度泛函理論(DFT)的方法對(duì)甲醇在PtPd(111)表面的分解反應(yīng)進(jìn)行了研究,并與甲醇在PtAu(111)表面的分解反應(yīng)進(jìn)行比較,探索了二者抗CO中毒能力以及催化甲醇氧化活性差異的本質(zhì)原因,然后通過(guò)電化學(xué)沉積的方法合成PtAu和PtPd合金催化劑,并將其負(fù)載在單壁碳納米管上,研究其對(duì)甲醇的電催化性能,以此來(lái)驗(yàn)證理論計(jì)算結(jié)果。計(jì)算結(jié)果表明,甲醇在PtPd(111)表面分解的主要途徑為CH3OH→CH2OH→CHOH→CHO→CO(CO途徑)。對(duì)甲醇在PtAu(111)和PtPd(111)表面催化反應(yīng)機(jī)理進(jìn)行比較研究,我們發(fā)現(xiàn)甲醇在PtPd(111)表面分解的反應(yīng)速率決定步驟的能壘比其在PtAu(111)表面的低0.26 eV,表明PtPd催化劑的活性高于PtAu催化劑的活性。甲醇在PtAu(111)表面的分解主要通過(guò)non-CO途徑發(fā)生,而CHO分解生成CO的能壘僅為0.21 eV,表明non-CO途徑的發(fā)生并不能完全抑制CO的產(chǎn)生,仍然有部分CO的沉積。而甲醇在PtPd(111)表面的分解主要通過(guò)CO途徑發(fā)生,且生成CO需要克服的能壘為0.26 eV,表明反應(yīng)過(guò)程中會(huì)有很多的CO沉積。因此,PtAu催化劑的抗CO中毒能力優(yōu)于PtPd催化劑。實(shí)驗(yàn)結(jié)果表明,PtPd催化劑的催化活性和穩(wěn)定性?xún)?yōu)于PtAu催化劑。第五部分,通過(guò)軟模板法合成了PtCo、PtCo2、PtCo3和Pt3Co合金納米線(xiàn)催化劑,并將其負(fù)載在碳黑上,研究其對(duì)甲醇的電催化活性及穩(wěn)定性。循環(huán)伏安測(cè)試表明PtCo2/C在甲醇催化氧化實(shí)驗(yàn)中表現(xiàn)出最高的電催化活性�；诹黧w動(dòng)力學(xué)的方法,通過(guò)線(xiàn)性?huà)呙璺睬�(xiàn)分析并計(jì)算了PtCo、PtCo2、PtCo3和Pt3Co催化劑在甲醇氧化反應(yīng)中速率決速步的電子轉(zhuǎn)移系數(shù)(α)和電極表面溶液的擴(kuò)散系數(shù)(D0)。計(jì)算結(jié)果表明,PtCo2合金納米線(xiàn)催化劑的α和D0最大。因此從動(dòng)力學(xué)的角度分析,PtCo2合金納米線(xiàn)催化劑催化活性的提高與α和D0有關(guān)。
[Abstract]:Direct methanol fuel cell (DMFC) is an energy device that converts chemical energy generated when methanol is oxidized into electric energy directly with methanol as fuel. Has the advantages of high energy conversion efficiency, environment friendliness, easy storage and transportation, and the like, and is considered to be an ideal clean energy source. The noble metal platinum (pt) has higher catalytic activity and is the most widely used dmfc catalyst at present. However, because of the scarcity of the Pt resources, the price is expensive and the commercial development is restricted. In addition, that oxidation mechanism of the electrocatalytic methanol is complex, the active site of the catalyst surface is easily occupied by the intermediate species such as CO generated in the oxidation process, the catalyst is poisoned, the catalytic activity is reduced, and further catalytic oxidation of the methanol is hindered. Therefore, it is imperative to find and design a catalyst with high Pt utilization ratio, high catalytic activity, stability and high toxicity in CO. In this paper, we use the density functional theory (DFT) to study the catalytic reaction mechanism of methanol on the surface of PtAu and PtPd catalyst, and explore the intrinsic reason of the difference between the anti-CO poisoning ability and the oxidation activity of the electrocatalytic methanol, and verify the theoretical calculation results by the experimental method. And finally, a PtCo alloy nanowire catalyst with different atomic proportions is prepared through a soft template method and is applied to catalytic oxidation of methanol. Our research is designed to provide some theoretical and experimental guidance for the design and optimization of the fuel cell catalyst with improved performance, which can contribute to the commercialization development of the fuel cell. In the first part, the working principle of direct methanol fuel cell, the development status and the reaction mechanism of the electrode are introduced, and the preparation method of the catalyst is briefly introduced. In addition, we also set forth the significance of the research work in this paper. In the second part, the theoretical calculation method used in this study is described in detail: the density functional theory (DFT) and the transition state theory (TST). In addition, the physical characterization and electrochemical characterization of the catalyst in the course of the experiment are briefly described. In the third part, the mechanism of the catalytic reaction of methanol on the surface of PtAu (111) is studied based on the cyclic density functional theory (DFT) system. In the adsorption study of the most stable intermediates involved, there are two types of reaction pathways that we consider: the CO pathway and the non-CO pathway. The most likely two routes are: CH3OH, CH2OH, CHOH, CHO-CO (CO) and non-CO (non-CO approach), according to the transition state required by the most stable intermediate and the reaction. The CO and non-CO approaches were compared, and we found that the reaction of methanol on the surface of PtAu (111) was mainly through the non-CO approach. The results show that, before CO2 is generated, the methanol is more prone to the formation of CO, the energy barrier of the generation of CO in the CO pathway is only 0.21 eV, and the elimination of CO need to overcome the energy barrier of 0.74 eV. Therefore, we have predicted that the non-CO approach can not completely inhibit the production of CO, and the surface of PtAu (111) still has a partial CO deposition, thus causing the poisoning of the catalyst, and the catalytic activity and the stability of the catalyst are reduced. In the fourth part, the decomposition reaction of methanol on the surface of PtPd (111) was studied by the method of density functional theory (DFT) and compared with the decomposition reaction of methanol on the surface of PtAu (111). And then the PtAu and PtPd alloy catalysts are synthesized by the method of electrochemical deposition, and the PtAu and PtPd alloy catalysts are loaded on the single-wall carbon nano-tubes, and the electrocatalytic performance of the PtAu and PtPd alloy is researched, so that the theoretical calculation results are verified. The results show that the main way of the decomposition of methanol on the surface of PtPd (111) is CH3OH-CH2OH-CHOH-CHO-CO (CO approach). The mechanism of the catalytic reaction of methanol on the surface of PtAu (111) and PtPd (111) was studied. It was found that the energy base of the reaction rate determination step on the surface of PtPd (111) was lower than that of the PtAu (111) surface, indicating that the activity of the PtPd catalyst was higher than that of the PtAu catalyst. The decomposition of methanol on the surface of PtAu (111) is mainly through the non-CO approach, and the energy barrier of the CHO decomposition to generate CO is only 0.21 eV, indicating that the non-CO approach can not completely inhibit the generation of CO, and there is still some CO deposition. The decomposition of methanol on the surface of PtPd (111) is mainly through the CO approach, and the energy barrier to which CO needs to be overcome is 0.26 eV, indicating that there will be a lot of CO deposition in the reaction. Therefore, the anti-CO poisoning capability of the PtAu catalyst is superior to that of the PtPd catalyst. The results show that the catalytic activity and stability of PtPd catalyst are better than that of PtAu catalyst. In the fifth part, PtCo, PtCo2, PtCo3 and Pt3Co alloy nanowire catalysts were synthesized by soft template method, and supported on carbon black, and the electrocatalytic activity and stability of PtCo, PtCo2, PtCo3 and Pt3Co were studied. The cyclic voltammetry test showed that PtCo2/ C exhibited the highest electrocatalytic activity in the catalytic oxidation of methanol. The electron transfer coefficient and the diffusion coefficient of PtCo, PtCo2, PtCo3 and Pt3Co (PtCo, PtCo2, PtCo3, and Pt3Co catalysts in the methanol oxidation reaction and the diffusion coefficient (D0) of the electrode surface solution were calculated and calculated on the basis of the fluid dynamics. The results show that the catalyst of PtCo2 alloy is the largest and the D0 is the largest. The improvement of the catalytic activity of the PtCo2 alloy nano-wire catalyst is related to the content of D0 and D0.
【學(xué)位授予單位】：西南大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：O643.3
本文編號(hào)：2508330
[Abstract]:Direct methanol fuel cell (DMFC) is an energy device that converts chemical energy generated when methanol is oxidized into electric energy directly with methanol as fuel. Has the advantages of high energy conversion efficiency, environment friendliness, easy storage and transportation, and the like, and is considered to be an ideal clean energy source. The noble metal platinum (pt) has higher catalytic activity and is the most widely used dmfc catalyst at present. However, because of the scarcity of the Pt resources, the price is expensive and the commercial development is restricted. In addition, that oxidation mechanism of the electrocatalytic methanol is complex, the active site of the catalyst surface is easily occupied by the intermediate species such as CO generated in the oxidation process, the catalyst is poisoned, the catalytic activity is reduced, and further catalytic oxidation of the methanol is hindered. Therefore, it is imperative to find and design a catalyst with high Pt utilization ratio, high catalytic activity, stability and high toxicity in CO. In this paper, we use the density functional theory (DFT) to study the catalytic reaction mechanism of methanol on the surface of PtAu and PtPd catalyst, and explore the intrinsic reason of the difference between the anti-CO poisoning ability and the oxidation activity of the electrocatalytic methanol, and verify the theoretical calculation results by the experimental method. And finally, a PtCo alloy nanowire catalyst with different atomic proportions is prepared through a soft template method and is applied to catalytic oxidation of methanol. Our research is designed to provide some theoretical and experimental guidance for the design and optimization of the fuel cell catalyst with improved performance, which can contribute to the commercialization development of the fuel cell. In the first part, the working principle of direct methanol fuel cell, the development status and the reaction mechanism of the electrode are introduced, and the preparation method of the catalyst is briefly introduced. In addition, we also set forth the significance of the research work in this paper. In the second part, the theoretical calculation method used in this study is described in detail: the density functional theory (DFT) and the transition state theory (TST). In addition, the physical characterization and electrochemical characterization of the catalyst in the course of the experiment are briefly described. In the third part, the mechanism of the catalytic reaction of methanol on the surface of PtAu (111) is studied based on the cyclic density functional theory (DFT) system. In the adsorption study of the most stable intermediates involved, there are two types of reaction pathways that we consider: the CO pathway and the non-CO pathway. The most likely two routes are: CH3OH, CH2OH, CHOH, CHO-CO (CO) and non-CO (non-CO approach), according to the transition state required by the most stable intermediate and the reaction. The CO and non-CO approaches were compared, and we found that the reaction of methanol on the surface of PtAu (111) was mainly through the non-CO approach. The results show that, before CO2 is generated, the methanol is more prone to the formation of CO, the energy barrier of the generation of CO in the CO pathway is only 0.21 eV, and the elimination of CO need to overcome the energy barrier of 0.74 eV. Therefore, we have predicted that the non-CO approach can not completely inhibit the production of CO, and the surface of PtAu (111) still has a partial CO deposition, thus causing the poisoning of the catalyst, and the catalytic activity and the stability of the catalyst are reduced. In the fourth part, the decomposition reaction of methanol on the surface of PtPd (111) was studied by the method of density functional theory (DFT) and compared with the decomposition reaction of methanol on the surface of PtAu (111). And then the PtAu and PtPd alloy catalysts are synthesized by the method of electrochemical deposition, and the PtAu and PtPd alloy catalysts are loaded on the single-wall carbon nano-tubes, and the electrocatalytic performance of the PtAu and PtPd alloy is researched, so that the theoretical calculation results are verified. The results show that the main way of the decomposition of methanol on the surface of PtPd (111) is CH3OH-CH2OH-CHOH-CHO-CO (CO approach). The mechanism of the catalytic reaction of methanol on the surface of PtAu (111) and PtPd (111) was studied. It was found that the energy base of the reaction rate determination step on the surface of PtPd (111) was lower than that of the PtAu (111) surface, indicating that the activity of the PtPd catalyst was higher than that of the PtAu catalyst. The decomposition of methanol on the surface of PtAu (111) is mainly through the non-CO approach, and the energy barrier of the CHO decomposition to generate CO is only 0.21 eV, indicating that the non-CO approach can not completely inhibit the generation of CO, and there is still some CO deposition. The decomposition of methanol on the surface of PtPd (111) is mainly through the CO approach, and the energy barrier to which CO needs to be overcome is 0.26 eV, indicating that there will be a lot of CO deposition in the reaction. Therefore, the anti-CO poisoning capability of the PtAu catalyst is superior to that of the PtPd catalyst. The results show that the catalytic activity and stability of PtPd catalyst are better than that of PtAu catalyst. In the fifth part, PtCo, PtCo2, PtCo3 and Pt3Co alloy nanowire catalysts were synthesized by soft template method, and supported on carbon black, and the electrocatalytic activity and stability of PtCo, PtCo2, PtCo3 and Pt3Co were studied. The cyclic voltammetry test showed that PtCo2/ C exhibited the highest electrocatalytic activity in the catalytic oxidation of methanol. The electron transfer coefficient and the diffusion coefficient of PtCo, PtCo2, PtCo3 and Pt3Co (PtCo, PtCo2, PtCo3, and Pt3Co catalysts in the methanol oxidation reaction and the diffusion coefficient (D0) of the electrode surface solution were calculated and calculated on the basis of the fluid dynamics. The results show that the catalyst of PtCo2 alloy is the largest and the D0 is the largest. The improvement of the catalytic activity of the PtCo2 alloy nano-wire catalyst is related to the content of D0 and D0.
【學(xué)位授予單位】：西南大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：O643.3
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