Eigh efficiency solar energy conversion by nano-structured InGaN semiconductor photoelectrode

在紫外光照射下，电解质溶液中的p型氮化镓阴极以零偏压析氢，但析氢速率和光电流均降低。自发析氢表明，p-GaN的导带边缘高于H+(aq)的还原电位。从生成氢气的体积与从Pt阳极向p-GaN阴极移动的电子数量的关系可以看出，在中性Na2SO4电解质溶液中，从p-GaN阴极导带注入的电子与H+(aq)的反应效率大于70%。因此，考虑到p-GaN的入射光子电流效率，在340 nm波长下，降解前氢气生成的总量子效率估计为4-6%。我们还利用循环伏安法研究了InGaN与电解质溶液之间的电子传递，并与Pt， Ti02/FTO（氟掺杂氧化锡玻璃）进行了比较。H2→2H+ + 2e的正反反应分别发生在Pt和TiO2/FTO电极上。相比之下，在GaN和In0.12Ga0.88N电极中，只发生正向反应，没有H2→2H+ + 2e的储备反应。这些结果表明，GaN和In0.12Ga0.88N在水中具有比H+ (aq)的还原电位更高的导电带边电位。此外，我们观察了p-In0.12Ga0.88N电极在Na2SO4溶液中405nm可见光照射下的阴极光电流，并通过监测散射光强度原位检测了电极表面的H2气泡。

Hydrogen was evolved at a zero bias when a p-type GaN cathode in an electrolyte solution is irradiated with UV light, although both hydrogen evolution rate and photocurrent decrease during irradiation. Spontaneous hydrogen evolution indicates that the conduction band-edge of p-GaN is above the reduction potential of H+(aq). From the relationship between the volume of generated hydrogen and the amount of electrons traveling from the Pt anode to the p-GaN cathode, the reaction efficiency of electrons injected from the conduction band of the p-GaN cathode with H+(aq) in a neutral Na2SO4 electrolyte solution is larger than 70%. As a result, the overall quantum efficiency for the hydrogen generation before degradation is estimated to be 4-6% at a wavelength of 340 nm by considering the incident photon-to-current efficiency of p-GaN. We also studied the electron transport between InGaN and electrolyte solution by using cyclic voltammetry, compared with Pt, Ti02/FTO (Fluorine-doped Tin Oxide glass). The forward and reverse reactions of H2→2H+ + 2e occurred at Pt and TiO2/FTO electrodes. In contrast, in GaN and In0.12Ga0.88N electrodes, only forward reaction occured and no reserve reaction of H2→2H+ + 2e was observed. These results show that GaN and In0.12Ga0.88N have higher comduction band-edge potentials than the reduction potential of H+ (aq) in water. Moreover, we observed cathodic photocurrent with p-In0.12Ga0.88N electrode under 405nm visible light irradiation in Na2SO4 solution and H2 bubbles on electrode surface were in-situ detected by monitoring the scattered light intensity.