InxGa1-xN纳米线电极的构筑及其光催化分解水制氢研究

InxGa1-xN alloys are very promising for solar water splitting because the bandgap can be tuned from the ultraviolet (UV) to the near-infrared region by increasing the indium content, thus covering the entire solar spectrum. Moreover, nanowires (NWs) are known to accommodate lattice mismatch by lateral elastic relaxation which suppresses the formation of defects. The objective of the current research is to develop high quality InxGa1-xN NWs with tunable band gap and to setup photo-electrode systems with highest photoelectrochemical (PEC) conversion efficiencies. InxGa1-xN NWs will be prepared using Vapor-Liquid-Solid based chemical vapor deposition (VLS-CVD). To obtain high crystalline quality InxGa1-xN NWs, optimum growth conditions of VLS-CVD will be determined by changing substrates, V/III gas ratio, temperatures, source precursors, catalytic metal seeds, etc. The microstructure of the InxGa1-xN NWs will be examined by SEM/EDS, FTIR, Raman, XRD, TEM, PL, and UV-vis for compositions, growth directions, morphologies, crystalline defects, band gap, etc. The PEC properties of the InxGa1-xN NWs electrodes will be tested by J-V, i-t, CV, EIS under illuminations for water splitting. The relationship will be correlated between the growth methods, structures, and the PEC properties. The fundamental scientific and technological issues will be addressed, including (1) Understanding VLS-CVD growth mechanism for ternary InxGa1-xN NWs and identifying the control step of the InxGa1-xN NWs growth on different substrates; (2) Design and application of suitable substrates for n- and p-type InxGa1-xN NWs respectively, so that photon-excited electron-hole pair can be effectively separated; (3) Determination of the control step for the redox reactions on the surface of the InxGa1-xN NWs during the water splitting process.

InxGa1-xN有望成为一种新型光催化分解水的制氢材料。本项目拟利用纳米线的尺寸效应，制备带隙可大范围调控的高晶体质量InxGa1-xN纳米线，实现对太阳光全波段的有效吸收和可见光催化分解水制氢。重点研究VLS-CVD法制备InxGa1-xN纳米线的工艺，分析VLS-CVD制备三元InxGa1-xN纳米线的机理，确定不同基底上的VLS-CVD制备关键工艺参数，控制InxGa1-xN纳米线的成分、取向、形貌、和内部晶体缺陷密度。构筑多种金属（半导体）/InxGa1-xN纳米线光催化电极，有效抑制光生电子-空穴的复合，增强光催化分解水的量子转换效率。深入研究纳米线光催化电极的构-性关系，并进一步探明各种关键性结构因素对光催化分解水制氢特性的影响及作用机制。本课题的相关研究对推进我国新一代光催化材料快速发展提供重要的理论指导和技术支撑。

InxGa1-xN材料具有光分解水制氢功能，其带隙可大范围调控，比表面积高，载流子输运快，且对基底的晶格匹配要求低，有望真正实现对太阳光全波段的有效吸收和转化，在解决能源和环境问题方面有着重要的应用前景。本项目首次提出了包括钛和钽在内的新型衬底用于InxGa1-xN纳米线生长，通过对金属钛片和钽片衬底进行预处理，利用VLS-CVD法直接在金属衬底上合成了带隙可调控的高晶体质量InxGa1-xN纳米线，构筑了衬底和InxGa1-xN纳米线能级匹配的两种新型光催化异质结电极：Ti/TiO2-TiN/InxGa1-xN纳米线和Ta/TaN/Ta2N/Ta3N5/InxGa1-xN纳米线，有望改善载流子在基底/纳米线界面的传输特性，促进光生电子-空穴的分离，大幅度提高光催化分解水制氢效率。同时探明了电极的关键性VLS-CVD制备参数：..金属钛片的表面预处理条件为900℃下氮气（200sccm）和氢气 (200sccm)环境下处理半小时，能够获得致密的包含TiN、TiNO0.28、TiO2的中间层。当使用金属镓和铟作为金属源，金镍合金作为催化剂，预处理钛片表面能在温度为700℃、腔压小于260pa的条件下生成InxGa1-xN纳米线； ..金属钽片的表面预处理条件为阳极氧化（H2SO4:H2O:HF=95:4:1，80V ，2分钟）结合高温氨化（950°C并保温2小时），能够获得致密的中间层，其组织包含Ta3N5、TaN、Ta2N三种结构。当衬底温度为800℃、腔压大于2000pa时，采用乙酰丙酮镓和乙酰丙酮铟作为金属源、镍或金镍合金作为催化剂，在预处理的钽片表面上能够生成生长方向为<1¯100>InxGa1-xN纳米线，且InN沿着纳米线生长方向上有富集。