A Co-catalyst-Loaded Ta3N5 Photoanode with a High Solar Photocurrent for Water Splitting upon Facile Removal of the Surface Layer
A Co-catalyst-Loaded Ta3N5 Photoanode with a High Solar Photocurrent for Water Splitting upon Facile Removal of the Surface Layer
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具有高太阳光电流的负载助催化剂的 Ta3N5 光阳极，可轻松去除表面层以实现水分解
DOI：
10.1002/anie.201305350
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发表时间：
2013-10-11
影响因子：
16.6
通讯作者：
Zou, Zhigang
中科院分区：
文献类型：
--
作者：
Li, Mingxue;Luo, Wenjun;Zou, Zhigang
化石燃料的大量消耗造成了能源短缺和严重的环境问题，限制了社会的可持续发展。太阳能是世界上最丰富的可再生能源。然而，太阳能由于其能量密度低，分布不均匀，辐射不连续，需要以化学能的形式储存。氢被认为是未来一种有前途的清洁能源载体。[1]太阳能水分解产生氢气和氧气，同时，氢气可以与氧气在燃料电池中重新结合产生水，并将储存的化学能释放为电能。这种能源循环将是一个理想的零碳排放过程。自从Fujishima和本田最初在1972年报道了基于TiO 2的光电化学电池可以用于将水分解为氢气和氧气以来，在过去的四十年中，人们进行了深入的研究以提高光电化学电池的性能。然而，由于TiO 2固有的宽带隙，太阳能转换效率仍然较低。[3]为了获得高的转换效率，有必要探索一些带隙较窄的材料。理论上，需要1.23 V的偏压将水分解为氢和氧。如果考虑到过电位和电阻损失（约0.6 V），则单个材料分裂水将需要至少1.8 eV的带隙，这与肖克利-奎塞尔极限的太阳能使用的最佳带隙（1.2-1.4 eV）不匹配。[4]pn光电化学电池是克服双光子吸收限制的非常理想的方法。[5，6]在该电池中，n型光电阳极（用于水氧化）直接连接到p型光电阴极（用于质子还原）。因此，通过组装两种窄带隙材料可以获得更高的光电压。另一方面，pn光电化学电池中的光电流由具有较低光电流的光电极决定。到目前为止，已经开发出几种具有高太阳光电流（几十mA cm ↑ [2]）的p型半导体光电阴极。[7-10]我们和其他研究人员也研究了一些有前途的可见光响应光阳极材料，如WO 3，[11，12] BiVO 4，[13-15] Fe 2 O3，[16，17]和Ta 3 N5，[18-24]。虽然不同的方法，包括离子掺杂、[13，17]形态控制、[11，24]异质结、[8，9，12，25]和颗粒颈缩[19，26]已被用于改善光电阳极的性能，但所有这些光电阳极都表现出低得多的太阳光电流（低于4 mAcmV 2）[12，13，16，24]，这是pn光电化学电池中水裂解的瓶颈。因此，寻找高效的光阳极是太阳能水分解制氢的关键步骤。Ta 3 N5具有合适的带隙（2.1eV）和能带位置，被认为是一种有前途的无偏压太阳能水分解光阳极。Ta箔的热氧化和氮化是制备Ta 3 N5的非常方便和可重复的方法，[18，21]但通过这种方法制备的Ta 3 N5光电极显示出比通过其他方法制备的样品低得多的性能。[19在本研究中，我们采用改进的热氧化氮化法制备了Ta 3 N5光电极，发现Ta 3 N5光电极效率低的主要原因是样品表面钝化层中光生载流子的严重复合。我们在Ta 3 N5光阳极上通过简单的热或机械方法获得了在1.23 V下5.5 mAcmAh 2的高太阳光电流，与参比氢电极（RHE）相比。
The consumption of fossil fuels creates energy shortage and serious environmental issues, which limit the sustainable development of the society. Solar energy is the most abundant renewable energy in the world. However, solar energy needs to be stored as chemical energy because of its low energy density, uneven distribution, and discontinuous radiation. Hydrogen is considered as a promising clean energy carrier for the future.[1] Solar water splitting produces hydrogen and oxygen, meanwhile, hydrogen can recombine with oxygen to produce water in a fuel cell and release the stored chemical energy to electricity. This energy cycle will be an ideal zerocarbon emission process. Since Fujishima and Honda originally reported that a TiO2-based photoelectrochemical cell could be used to split water into hydrogen and oxygen in 1972,[2] intensive research has been done to improve the performance of the photoelectrochemical cell in the past forty years. However, the solar energy conversion efficiency is still low because of the intrinsic wide band gap of TiO2.[3] It is necessary to explore some materials with narrower band gaps for high conversion efficiency. In theory, a bias of 1.23 V is needed to split water into hydrogen and oxygen. If overpotential and resistance loss (about 0.6 V) are taken into account, a band gap with at least 1.8 eV will be necessary for a single material to split water, which does not match the optimum band gap (1.2–1.4 eV) for solar energy use by the Shockley-Queisser limit.[4] A pn photoelectrochemical cell is a highly desirable approach to overcome the limit by two-photon absorption.[5, 6] In this cell, a n-type photoanode (for water oxidation) is directly connected to a p-type photocathode (for proton reduction). Thus, a higher photovoltage can be obtained by assembling the two narrow-band-gap materials. On the other hand, photocurrent in a pn photoelectrochemical cell is determined by the photoelectrode with the lower photocurrent. To date, several p-type semiconductor photocathodes with high solar photocurrent (dozens of mA cmÀ2) have been developed.[7–10] Some promising visible-light-responsive photoanode materials, such as WO3,[11, 12] BiVO4,[13–15] Fe2O3,[16, 17] and Ta3N5,[18–24] have also been studied by us and other researchers. Though different methods, including ions doping,[13, 17] morphology control,[11, 24] heterojunction,[8, 9, 12, 25] and particle necking [19, 26] have been used to improve the performance of a photoanode, all of these photoanodes exhibit a much lower solar photocurrent (lower than 4 mAcmÀ2)[12, 13, 16, 24] than the photocathodes, which is a bottleneck for water splitting in a pn photoelectrochemical cell. Therefore, finding an efficient photoanode is a key step in solar water splitting for hydrogen production. Ta3N5 has a suitable band gap (2.1 eV) and band position, which is considered as a promising photoanode for solar water splitting without a bias. Thermal oxidation and nitridation of a Ta foil is a very convenient and reproduceable method for preparation of Ta3N5,[18, 21] but the Ta3N5 photoelectrodes produced by this method indicated much lower performance than those of the samples prepared by other methods.[19, 20, 24] In this study, we prepared the Ta3N5 photoelectrodes by a modified thermal oxidation and nitridation method and found that the low efficiency of the Ta3N5 photoanode mainly from serious recombination of photogenerated carriers in the surface passivation layer of the sample. We obtained a high solar photocurrent of 5.5 mAcmÀ2 at 1.23 V versus the reference hydrogen electrode (RHE) on the Ta3N5 photoanode by facile thermal or mechanical …