泡沫铜负载石墨烯基催化剂协同TiO2纳米管光电催化还原CO2研究

CO2 conversion is beneficial in advancing the practice of energy saving and emission reduction as well as low-carbon economy. Electrocatalytic reduction of CO2 using renewable energy to realize high conversion of electricity into chemicals is a research hot spot, especially its combination with solar photocatalytisis to improve CO2 reduction efficiency and reduce energy consumption. However, nowadays the energy barrier of CO2 reduction is still high; the efficiency and product selectivity of CO2 photoelectrocatalytic (PEC) reduction is still low. It is quite necessary to find new catalytic materials and reaction systems with high efficiency. In this project, graphene-based catalysts loaded on 3D copper foam and TiO2 nanotube prepared by anodization are combined as electrocathode and photoanode, to form a novel PEC system for revealing the molecular mechanisms of CO2 reduction. The 3D copper foam catalysts are used to increase the cathode specific surface area and current density to improve CO2 reduction. It is also beneficial to lower the energy barriers and improve products selectivity by doping graphene-based catalysts with Pt, Cu, and their complexes. Modified TiO2 nanotubes are used as anode catalysts for water decomposition to provide more H+ for CO2 reduction. Anode photovoltage is used to compensate CO2 reduction potential on cathode to reduce energy consumption, while the photo-induced electrons are also driven towards the cathode for CO2 reduction. Energy and mass transfer are optimized and thermodynamic reaction mechanisms are regulated to realize efficient reduction of CO2 with low energy consumption.

利用可再生能源发电催化还原CO2实现电能向化学能的转换储存，结合太阳能光催化提高CO2还原效率并且降低碳转化能耗，是推动节能减排和低碳经济的研究热点。但是目前光电催化还原CO2的能耗高、效率低并且产物选择性差，迫切需要革新光电催化剂材料以及构建高效还原CO2反应体系。本项目提出将石墨烯基催化剂负载于泡沫铜制成三维立体催化剂作为电阴极，与阳极氧化法制备的TiO2纳米管光阳极相结合，构建新型光电催化反应体系揭示CO2分子还原的能量质量传递和热动力学新机制。提高三维泡沫铜催化剂电阴极的比表面积和电流密度强化还原CO2，将石墨烯负载铂和铜等助催化剂降低CO2还原能垒，提高CO2还原产物的定向选择性和转化效率。利用改性TiO2纳米管光阳极分解水生成质子为电阴极还原CO2提供更多氢源，阳极光电压补偿降低电阴极还原CO2的过电位以减少能耗。优化调控CO2光电还原的能质传递和热动力学机制，实现CO2在低能耗下的高效还原。

光电催化还原CO2能够在减排利用温室气体CO2的同时生产可再生合成燃料，是国内外节能减排和新能源领域的前沿热点研究方向。本项目构建了石墨烯基电阴极与载铂TiO2纳米管光阳极结合的光电催化还原CO2体系。制备了载铂石墨烯气凝胶阴极催化剂用于催化还原反应，实验得到电极还原碳原子转化率提升到5040 nmol/(h⸱cm2)，显著高于粘结剂载铂石墨烯电极上的碳原子转化率[3660 nmol/(h⸱cm2)]。构建了过渡金属-氮的不饱和活性位点促进CO2还原为一氧化碳和甲烷等气体产物，实验表明：Ni-N2C2催化剂在-0.7V电压下还原CO的法拉第效率高达98.4%。CuN3（I）配位结构对于甲烷生成具有高选择性，与该催化剂还原CO2的总碳原子转化率达到4113.4 nmol·h-1·cm-2，甲烷选择性达到95.6%。将过渡金属纳米颗粒与碳基底构建复合界面催化剂，抑制析氢反应增强了醇类产物选择性。在铂修饰的碳化铜金属有机骨架表面，实验优化调节催化剂中的铂和钯含量，使CO2还原反应对醇类产物的选择性达到93.2%。将硫化铜纳米粒子锚定在铜卟啉有机骨架纳米片上作为阴极催化剂，CO2光电还原过程中的总碳原子转化率达到5174nmol⸱h-1⸱cm-2，对乙醇单一产物的选择性到达74.4%。利用上海光源同步辐射探明了CuxZny-N-C催化剂中铜原子和锌原子与氮原子的配位数，实证揭示了催化剂中含有一个铜原子与两或三个氮原子相连的空位-铜-氮配位结构，其中Cu1Zn1-N-C催化剂中Cu-N配位数最低为2.7（±1.2）。根据X射线吸收近边结构谱图（XANES）表征结果，构建了空位-铜-氮和空位-锌-氮等多种配位结构模型。据此进行量子化学计算表明：在CuN3（I）配位结构模型上，CO2还原反应生成甲烷的关键中间产物*CHO的自由能（-1.395 eV）远低于CO的自由能（-0.568eV），揭示了CuN3（I）配位结构对于甲烷生成具有高选择性，与实验结果相吻合。本项目已发表和录用国际期刊SCI论文22篇和中文期刊EI论文2篇，包含最高影响因子IF=26.4和3篇IF=10.652。申请发明专利5项（其中已授权3项）。培养博硕士生10名（其中4名已毕业），国际会议做特邀报告2次和分会主席3次。