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

当p-型GaN阴极在电解质溶液中用紫外光照射时，在零偏压下析氢，尽管在照射期间析氢速率和光电流都降低。自发析氢表明p-GaN的导带边高于H+的还原电位（aq）。从产生的氢的体积与从Pt阳极行进到p-GaN阴极的电子量之间的关系，在中性Na 2SO 4电解质溶液中，从p-GaN阴极的导带注入的电子与H+（aq）的反应效率大于70%。结果，通过考虑p-GaN的入射光子-电流效率，在340 nm的波长下，降解前的氢生成的总量子效率估计为4-6%。我们还通过循环伏安法研究了InGaN和电解质溶液之间的电子输运，并与Pt，TiO 2/FTO（氟掺杂氧化锡玻璃）进行了比较。在Pt和TiO 2/FTO电极上发生了H2→ 2 H + +2 e的正、逆反应。而在GaN和In_（0.12）Ga_（0.88）N电极中，只发生了H_2 → 2 H ~（++）2 e的正向反应，没有观察到H_2 → 2 H ~（++）2 e的储备反应。这些结果表明GaN和In_（0.12）Ga_（0.88）N具有比H ~+（aq）在水中的还原电位更高的导带边电位。在405 nm可见光照射下，在Na_2SO_4溶液中观察到p-In_（0. 12）Ga_（0. 88）N电极的阴极光电流，并通过散射光强度监测原位检测到电极表面的H_2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.