Nickel Oxide Particles Catalyze Photochemical Hydrogen Evolution from Water-Nanoscaling Promotes P-Type Character and Minority Carrier Extraction
Nickel Oxide Particles Catalyze Photochemical Hydrogen Evolution from Water-Nanoscaling Promotes P-Type Character and Minority Carrier Extraction
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DOI：
10.1021/acsnano.5b00435
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发表时间：
2015-05-01
期刊：
影响因子：
17.1
通讯作者：
Osterloh, Frank E.
中科院分区：
文献类型：
--
作者：
Nail, Benjamin A.;Fields, Jorie M.;Osterloh, Frank E.
氧化镍（NiO）是一种重要的宽禁带p型半导体，用作染料敏化太阳能电池的空穴传输材料和水氧化电催化剂。在这里，我们证明了该材料的纳米晶体具有增加的p型特征和改善的光催化活性，用于在甲醇作为牺牲电子供体的存在下从水中析氢。通过水热水解硝酸镍，然后在空气中煅烧，合成了NiO纳米晶。晶体具有岩盐结构类型，并采用板状形态（50-90 nm X 10-15 nm）。漫反射吸收光谱表明带隙为3.45 eV，类似于散装NiO。在中性pH下进行光电化学测量，甲基紫精作为电子受体，揭示纳米级和散装NiO的光起始电位（费米能）分别为0.2和0.05 eV（NHE）。通过H2 PtCl 6的光沉积获得的纳米NiO和NiO-Pt复合物分别以0.8和4.5 μ mol H-2 h（-1）的速率催化甲醇水溶液的析氢，而本体NiO和NiO-Pt（20 mg催化剂，300 W白炽灯）的析氢速率为0.5和2.1 μ mol H-2 h（-1）。Au衬底上的NiO和NiO Pt膜的表面光电压谱表明具有30 mV光电压的金属Pt-NiO结促进载流子分离。从Mott Schottky图、吸光度和X射线光电子能谱数据推断，纳米NiO的光催化和光电化学性能的提高是由于少数载流子提取的改善和p型特性的增加。
Nickel(II) oxide (NiO) is an important wide gap p-type semiconductor used as a hole transport material for dye sensitized solar cells and as a water oxidation electrocatalyst. Here we demonstrate that nanocrystals of the material have increased p-type character and improved photocatalytic activity for hydrogen evolution from water in the presence of methanol as sacrificial electron donor. NiO nanocrystals were synthesized by hydrolysis of Ni(II) nitrate under hydrothermal conditions followed by calcination in air. The crystals have the rock salt structure type and adopt a plate-like morphology (50-90 nm x 10-15 nm). Diffuse reflectance absorbance spectra indicate a band gap of 3.45 eV, similar to bulk NiO. Photoelectrochemical measurements were performed at neutral pH with methylviologen as electron acceptor, revealing photo-onset potentials (Fermi energies) of 0.2 and 0.05 eV (NHE) for nanoscale and bulk NiO, respectively. Nano-NiO and NiO-Pt composites obtained by photodepositon of H2PtC16 catalyze hydrogen evolution from aqueous methanol at rates of 0.8 and 4.5 mu mol H-2 h(-1), respectively, compared to 0.5 and 2.1, mu mol H-2 h(-1) for bulk-NiO and NiO-Pt (20 mg of catalyst, 300 W Xe lamp). Surface photovoltage spectroscopy of NiO and NiO Pt films on Au substrates indicate a metal Pt-NiO junction with 30 mV photovoltage that promotes carrier separation. The increased photocatalytic and photoelectrochemical performance of nano-NiO is due to improved minority carrier extraction and increased p-type character, as deduced from Mott Schottky plots, optical absorbance, and X-ray photoelectron spectroscopy data.