Surface‐Polarity‐Induced Spatial Charge Separation Boosts Photocatalytic Overall Water Splitting on GaN Nanorod Arrays

Abstract

Photocatalytic overall water splitting has been recognized as a promising approach to convert solar energy into hydrogen. However, most of the photocatalysts suffer from low efficiencies mainly because of poor charge separation. Herein, taking a model semiconductor gallium nitride (GaN) as an example, we uncovered that photogenerated electrons and holes can be spatially separated to the nonpolar and polar surfaces of GaN nanorod arrays, which is presumably ascribed to the different surface band bending induced by the surface polarity. The photogenerated charge separation efficiency of GaN can be enhanced significantly from about 8 % to more than 80 % via co‐exposing polar and nonpolar surfaces. Furthermore, spatially assembling reduction and oxidation cocatalysts on the nonpolar and polar surfaces remarkably boosts photocatalytic overall water splitting, with the quantum efficiency increased from 0.9 % for the film photocatalyst to 6.9 % for the nanorod arrays photocatalyst.

Effects of Different Delocalized π-Conjugated Systems Towards the TiO2-Based Hybrid Photocatalysts

“…These results showed that the delocalized π-conjugated system with the amino group is more conducive to photodegradation of MO. It is reported that the electron-donating group can induce HOMO-LUMO electronic transitions that cause a change in the dipole moment, which results in effective separation of photogenerated charges (Belviso et al, 2019; Li et al, 2020 ). Therefore, it is notable that the catalytic efficiency followed the order of NH 2 -Phen/TiO 2 > NO 2 -Phen/TiO 2 > Phen/TiO 2 , which indicates that −NH 2 has a strong electron-donating group than −NO 2 .…”

Dominant Polar Surfaces of Colloidal II–VI Wurtzite Semiconductor Nanocrystals Enabled by Cation Exchange

“…5 The electric fields in the near-surface space charge regions influence the spatial charge distribution by promoting the charge separation and accumulating electrons and holes on the two end surfaces perpendicular to the electric field, [6][7][8][9][10][11] resulting in super photocatalytic activities and enhanced sensitivity, with relevance to a wide range of applications in catalysis, photocatalysis, gas sensing, piezoelectronics and magnetoresistive devices. [12][13][14][15][16][17][18][19] Compared with non-polar surfaces, polar surfaces of nanocrystals usually have higher energy and therefore they are thermodynamically unstable. To minimize the energy of the systems, these polar surfaces tend to diminish and even vanish during the growth process, producing nanocrystals dominated by thermodynamically stable surfaces with low surface energy.…”

Two-dimensional polarized MoTe2/GeS heterojunction with an intrinsic electric field for photocatalytic water-splitting

“…Moreover, the quantum efficiency enhanced dramatically from 0.9% for the GaN thin-lm to 6.9% for the GaN nanorod arrays. 40 Zhang et al also experimentally conrmed that multi-eld coupling in KNbO 3 nanostructures could enhance its catalytic performance owing to the polarizationmodulated built-in electric elds, which effectively separated excited electron/hole pairs. The photocurrent density enhanced obviously from 25% for the nanocube counterpart to 55% for the KNbO 3 nanosheets.…”