【作者】 王海花；

【导师】 陈代荣； 夏玉国；

【作者基本信息】 山东大学 ， 无机化学， 2024， 博士

【摘要】 近年来大气中的二氧化碳浓度急剧上升,目前二氧化碳浓度是自20世纪50年代开始连续测量以来所记录的最高值。二氧化碳浓度的持续升高导致了严重的环境问题,如极端气候事件、海平面上升、温度升高等。在自然界中,绿色植物靠光合作用从空气中捕获二氧化碳,将其转化为其他有价值的碳物种。然而,大自然的光合作用过程通常是缓慢的,它们本身并不足以抵消人类活动排放的大量二氧化碳。因此如何高效率的将二氧化碳转化为燃料和增值化学品对解决环境问题缓解能源短缺具有极其重要的科学和现实意义。为了从根本上解决二氧化碳浓度过大的问题,二氧化碳的化学转化是目前亟需研究的将二氧化碳转化为高附加值的化学品从而实现将二氧化碳变废为宝的最为便捷有效的方法。二氧化碳的化学转化方法主要包括二氧化碳加氢反应以及二氧化碳的电化学催化,然而二氧化碳加氢反应通常需要在高温高压的条件下发生并且该过程中需要消耗大量的氢气,更重要的是目前氢气的主要来源依旧是依靠大量的化石燃料。由于二氧化碳的电催化转化是利用风能、太阳能等可再生能源转化的电能在温和的条件下发生的一步反应,因此二氧化碳的电化学转化引起了人们的广泛关注。这种方法还具有以下几个优点,包括对生产速度的精细控制,模块化电解槽设计的广泛可扩展性,以及生产各种高附加值产品的潜力。更重要的是,电解系统可以很容易地由无碳能源提供动力,如风能、太阳能和核能,为商品化学品生产提供零二氧化碳排放(甚至负)途径。最近一项关于光伏(PV)的科学研究清楚地表明,随着时间的推移,光伏发电的价格会下降,预计在不久的将来,光伏发电的价格会低至每千瓦时0.03美元。类似的趋势也适用于风能,风电价格已经在每千瓦时0.02美元左右。低电价使得电化学驱动的二氧化碳利用技术在商品化学品生产中具有商业应用的潜在利润,利用二氧化碳作为碳原料替代传统的化石来源是减少二氧化碳排放的一个潜在解决办法。电化学还原二氧化碳不仅可以在温和的反应条件下将二氧化碳转化为多种有用的化学物质,而且可以在偏远地区利用可再生电力进行电化学还原,因此引起了人们的广泛关注。本论文主要研究内容如下:1.氧空位稳定的铜锡双单原子催化剂的设计及电催化二氧化碳还原性质的研究通过简单的水热反应制备了二氧化铈样品并进一步通过氩氢气氛煅烧调控二氧化铈中氧空位的浓度,从而利用氧空位进行锚定双单原子,促进单原子的稳定性。通过设计合理的原子结构对于提高电化学二氧化碳还原过程中产物的选择性至关重要。基于此,我们在CeO2-x上构建了一种由氧空位稳定的铜锡双原子电催化剂。利用氧空位锚定作用的同时进一步发挥铜锡金属协同作用促进催化剂的催化性能。该催化剂对甲酸盐的电化学选择性展现出优异的性能,甲酸盐法拉第效率超过90.0%,电流密度超过200mA cm-2,阴极电池效率超过50%,实现了工业应用的前提。实验表征和理论计算凸显了铜和锡单原子协同作用对催化反应降低活化能和促进中间*OCHO的形成具有重要的意义。同时,CeO2-x上的氧空位也在促进电化学性能和对甲酸盐的高选择性方面起着关键作用。这突出了电子金属-载体相互作用的重要性。这项工作为电催化二氧化碳还原催化剂的设计提供了新思路。2.Cu2SnS3中表面缺陷诱导极化调控对二氧化碳电化学还原性能的研究基于铜锡双金属的协同作用以及为了进一步提高催化剂的稳定性,我们选择了铜锡硫化物作为我们的电催化剂。由于Cu2SnS3具有易于调节的表面硫空位和较强的化学稳定性的优点,因此我们构建了具有协同p-嵌段Cu和d-嵌段Sn元素的电催化剂Cu2SnS3。通过简单的氩氢气氛煅烧调节其硫空位的浓度,进而调节催化剂表面亲疏水性以及表面极化作用。通过实验结果可得Cu2SnS3-x对还原产物HCOOH的性能令人满意,在-1.2V vs.RHE下,H型电解池和流动电解池的部分电流密度分别为192.5 mA cm-2和408.3 mA cm-2。此外,流动电解池的法拉第效率(FE)为91.7%,阴极电池转换效率为54.0%,这确保了其在工业应用中的可能性。此外,实验表征和理论计算都强调了表面极化调控在调节亲水性和稳定关键中间体方面的重要性。3.Cu2O/Ag串联催化剂的制备及其二氧化碳电化学还原性能的研究为了获得具有更高增值价值且易于储存和运输的液体乙醇燃料,我们通过简单的室温液相合成法制备了 Cu2O/Ag串联催化剂,并研究了该催化剂对于二氧化碳还原的电催化性能。该催化剂在二氧化碳还原电催化过程中表现出较为优异的催化性能。对乙醇选择性较为突出,呈现出38.6%的法拉第效率,H型电解池中电流密度大于350 mA cm-2,稳定性长达25小时,并且参与电催化反应前后催化剂的相关测试结果表明该催化剂具有较强的结构稳定性,这更加有利于工业化生产的需要,同时也为催化剂的设计提供了思路。更多还原

【Abstract】 Atmospheric carbon dioxide concentrations have risen sharply in recent years,and current carbon dioxide levels are the highest since continuous measurements began in the 1950s.Serious environmental problems such as extreme weather events,rising sea levels,rising temperatures,etc.have been caused by the continuing increase in carbon dioxide concentrations.In nature,green plants capture carbon dioxide directly from the air and convert it into other valuable carbon species through the sunlight-driven process of photosynthesis.However,nature’s photosynthesis processes are usually slow,and by themselves they are not sufficient to offset the large amounts of carbon dioxide emitted by human activities.How to efficiently convert carbon dioxide into fuels and high value-added chemicals is of great scientific and practical importance in solving environmental problems and energy shortages.In order to solve the problem of excessive carbon dioxide concentration,the chemical conversion of carbon dioxide is the most convenient and effective way to convert carbon dioxide into high value-added chemicals and thus turn carbon dioxide into treasure.The main chemical conversions of carbon dioxide include carbon dioxide hydration and carbon dioxide electrocatalysis,but the hydration reaction typically takes place under high temperature and pressure conditions,consuming a lot of hydrogen,and more importantly,the primary source of hydrogen currently depends on a lot of fossil fuels.The electrocatalytic transformation of CO2 has attracted a lot of focus because it is a one-step reaction that takes place under mild conditions using electricity generated from renewable energy sources such as wind and solar power.This process also offers a number of advantages,including the fine control of the production rate,the high scalability of the modular design of the electrolyser,and the potential to produce a wide range of high value-added products.Most important of all,the electrolytic system is readily powered by zero-carbon energy sources like wind,solar and nuclear.A recent scientific study on photovoltaics(PV)clearly shows that the price of PV electricity is falling over time and is expected to be as low as $0.03 per kWh in the near future.A similar trend applies to wind power,which is already priced at around $0.02 per kWh.Low electricity prices make electrochemical CO2 utilisation technology commercially viable for commodity chemical production,and using CO2 as a carbon feedstock to replace traditional fossil sources is a potential solution for reducing CO2 emissions.Electrochemical reduction of carbon dioxide is attracting considerable attention due to its ability to convert carbon dioxide into a range of useful chemicals under mild reaction conditions and its ability to operate in remote locations using renewable power.The main research of this thesis is as follows:1.Design of oxygen vacancy-stabilised Copper-Tin bis-monoatomic catalysts and study of electrocatalytic carbon dioxide reduction propertiesOxygen vacancy-rich cerium dioxide samples were prepared by a simple hydrothermal reaction and the concentration of oxygen vacancies in cerium dioxide was further regulated by calcination in an argon-hydrogen atmosphere,so as to utilize the oxygen vacancies for the anchoring of the dual single atoms and to promote the stability of the single atoms.A welldesigned atomic structure is essential to improve the product selectivity during electrochemical CO2 reduction.Based on this,we constructed a copper-tin diatomic electrocatalyst stabilized by oxygen vacancies on CeO2-x.The oxygen vacancy anchoring effect was utilized while further exploiting the Copper-Tin metal synergy to promote the catalytic performance of the catalyst.The catalyst exhibits excellent electrochemical selectivity for formate,with formate Faraday efficiency exceeding 90.0%,current density exceeding 200 mA cm-2,and cathode cell efficiency exceeding 50%,which is a prerequisite for industrial applications.Experimental characterization and theoretical calculations highlight the importance of copper and tin single-atom synergism in catalyzing the reaction to reduce the activation energy and promote the formation of intermediate*OCHO.Also,oxygen vacancies on CeO2-x play a key role in promoting electrochemical performance and high selectivity towards formate.This highlights the importance of electronic metal-carrier interactions.2.Surface defect-induced polarisation modulation in Cu2SnS3 on the electrochemical reduction properties of carbon dioxideBased on the synergistic effect of copper-tin bimetallic and in order to further improve the stability of the catalyst,we chose copper-tin sulphide as our electrocatalyst.Due to its easily adjustable surface sulfur vacancies and strong chemical stability,we constructed an electrocatalyst Cu2SnS3 with synergistic p-block Cu and d-block Sn elements,and adjusted its sulfur vacancy concentration by simple calcination in an argon-hydrogen atmosphere to regulate the surface hydrophilicity and the surface polarization of the catalyst.The satisfactory performance of Cu2SnS3-x for HCOOH can be obtained from the experimental results,with partial current densities of 192.5 mA cm-2 and 408.3 mA cm-2 for the H-type electrolytic cell and the flow electrolytic cell,respectively,at-1.2 V vs.RHE.In addition,the flow electrolytic cell exhibits a Faraday efficiency(FE)of 91.7%,and the cathodic cell conversion efficiency is 54.0%.This ensures its possibility for industrial applications.Furthermore,both experimental characterization and theoretical calculations highlight the importance of surface polarization modulation in regulating hydrophilicity and stabilising key intermediates.3.Preparation of Cu2O/Ag catalysts and their performance in the electrochemical reduction of CO2In order to obtain liquid ethanol fuel with higher value-added and easy to store and transport,we prepared a Cu2O/Ag tandem catalyst by a simple room-temperature liquid-phase synthesis method and investigated the performance of this catalyst for electrocatalytic carbon dioxide reduction.The catalyst showed excellent catalytic performance in the electrocatalytic process of CO2 reduction.The selectivity to ethanol was outstanding,showing a Faraday efficiency of 38.6%,the current density of the H-type electrolytic cell was greater than 350 mA cm-2,and the stability was up to 25 h.The results of the tests before and after the participation in the electrocatalytic reaction showed that the catalyst had a strong structural stability,which was more conducive to the needs of the industrial production,and also provided ideas for the design of the catalysts.更多还原