Improved Photoelectrochemical Performance by Polyoxometalate-Modified CuBi2O4/Mg-CuBi2O4 Homojunction Photocathode
方文诚 1刘东 1张莹 1冯浩 1李强1
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作者信息
1. 南京理工大学,能源与动力工程学院,电子设备热控制工信部重点实验室,南京 210094
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摘要
CuBi2O4作为最有前景的光阴极材料之一,其理论光电流密度可达20 mA∙cm-2.然而,在实际光电化学反应中,由于光生载流子复合严重,实际的光电流密度相较于理论值仍然存在显著差异.一般而言,光电化学性能在很大程度上依赖于光生载流子的高效分离和传输,以及快速的反应动力学.本文中,我们提出了一种多金属氧酸盐(多酸)修饰的CuBi2O4/Mg-CuBi2O4同质结光阴极.系统考虑了光阴极体相和界面的载流子传输:首先,通过CuBi2O4/Mg-CuBi2O4同质结中所构造的内建电场实现光生电子和空穴的定向转移;另外,多酸助催化剂Ag6[P2W18O62](AgP2W18)在反应过程中可被还原,进而可被用作质子存储载体,可在抑制载流子复合的同时促进界面光电化学反应.这种协同作用可在促进体相-界面载流子传输的同时解决界面缓慢反应动力学这一瓶颈.结果表明,本文所提出的光阴极实现了出色的光电化学性能,在0.3 V vs.RHE时,光电流密度达-0.64 mA∙cm-2;而在使用H2O2电子牺牲剂后,相同电位下的光电流密度进一步提升到-3 mA∙cm-2.本文所提出的光阴极与已有研究工作中报道的最佳结果相比,具有相当的光电化学活性,证明了其在实际应用中的巨大潜力.
Abstract
Photoelectrochemical water splitting using semiconductor materials is one of the most promising methods for converting solar energy into chemical energy.Among the commonly used semiconductors,p-type CuBi2O4 is considered one of the most suitable photocathode materials and can allow a theoretical photocurrent density of about 20 mA·cm-2 for photoelectrochemical water splitting.However,due to severe charge carrier recombination,the obtained photocurrent density is much lower than the theoretical value.Highly efficient photoelectrochemical performance relies on fast charge carrier separation and transport,and prompt reaction kinetics.In this study,we report the development of a polyoxometalate-modified CuBi2O4/Mg-CuBi2O4 homojunction photocathode to improve both the bulk and interfacial charge carrier transport in the photocathode.For the bulk of the photocathode,the built-in electric field originating from the CuBi2O4/Mg-CuBi2O4 homojunction promotes the migration of photo-excited electrons on the conduction band from pure CuBi2O4 to Mg-doped CuBi2O4.Additionally,the electric field facilitates the transfer of holes from the valence band of Mg-doped CuBi2O4 to pure CuBi2O4.This directional transfer of both photo-excited electrons and holes plays a significant role in promoting separation and suppressing the recombination of the charge carriers.On the surface of the photocathode,the reduced polyoxometalate co-catalyst Ag6[P2W18O62](AgP2W18)was used as a proton sponge to accelerate surface reaction kinetics and suppress carrier recombination.These synergistic effects improved the photo-generated charge carrier transfer and reaction kinetics.As a result,the novel photocathode displayed excellent photoelectrochemical properties,and the photocurrent density was observed to be-0.64 mA·cm-2 at 0.3 V vs.RHE,which is better than that of-0.39 mA·cm-2 for a pure photocathode.Furthermore,the novel photocathode had an applied bias photon-to-current efficiency(ABPE)higher than 0.19%at 0.3 V vs.RHE.In contrast,the pure photocathode had an ABPE of～0.12%under the same conditions.Additionally,when H2O2 was used as an electron scavenger,the photocurrent density was-3 mA·cm-2 at 0.3 V vs.RHE,which is an improvement of approximately 1.5 times compared to the pure photocathode.Furthermore,the charge separation and charge injection efficiency of the novel photocathode were significantly improved compared with the pure photocathode.The experimental results conclusively indicate that the formation of the CuBi2O4/Mg-CuBi2O4 homojunction and AgP2W18 modification played a significant role in the improved performance of the CuBi2O4 photocathode.The performance of the novel photocathode was comparable with the results reported in previous studies,demonstrating its promising potential in real applications.
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