Nanostructuring Bridges Semiconductor–Cocatalyst Interfacial Electron Transfer: Realizing Light-Intensity-Independent Energy Utilization and Efficient Sunlight-Driven Photocatalysis

Abstract

Despite thermodynamic feasibility, the high activation energy originating from potential barriers and trap states kinetically prevents the interfacial transfer of electrons from semiconductor nanostructures to reduction cocatalysts, resulting in a lowered utilization of photogenerated charge carriers in photocatalysis. Nanostructuring-induced narrowing of potential barriers offers a rational solution to kinetically facilitate interfacial electron transfer by tunneling. Here, inspired by theoretical simulation, we manage to promote the separation of photogenerated charge carriers by coating the semiconductor nanostructures with a homogeneous interlayer. The low activation energy for interfacial electron transfer endows photocatalysis with nearly constant quantum yields and a quasi-first-order reaction to the incident photons and grants evident superiority over the photocatalyst without interlayers, especially under sunlight. In our demonstrated sunlight-driven hydrogen evolution integrated with benzylamine oxidation, the production rates for both reduction and oxidation half-reactions reach as high as ∼0.77 mmol dm–2 h–1, which are ∼10 times higher than that without an interlayer.

Revealing the Role of Electronic Doping for Developing Cocatalyst-Free Semiconducting Photocatalysts

“…Although the electrocatalytic step is efficient, semiconductor−cocatalyst (SC) interfacial electron transfer that occurs on the decisecond−second time scale is the ratedetermining step in the whole photocatalytic reaction. 12,14,15 Many approaches thus far, such as nanostructuring induced confinement for electron tunneling 16,17 and the creation of surface sites for trap-assisted charge recombination, have been proposed to reduce the activation energy. 14,15 The creation of surface sites can also modify the reactivity of the semiconductor and, 18−20 ideally, replace the role of the cocatalyst by appropriate design.…”

“…This is because the lowering of activation energy kinetically facilitates the transport/transfer of electrons from the interior to the surface catalytically active sites. Besides, when the activation energy is sufficiently low, the influence of incident light intensity on the electronic processes can be minimized and the index in the power-law relation can be approximately unity: 16 with…”

“…The electronic processes for HE can be described by semiconductor–cocatalyst–solution (SCS) interfacial electron transfer. Although the electrocatalytic step is efficient, semiconductor–cocatalyst (SC) interfacial electron transfer that occurs on the decisecond–second time scale is the rate-determining step in the whole photocatalytic reaction. ,, Many approaches thus far, such as nanostructuring induced confinement for electron tunneling , and the creation of surface sites for trap-assisted charge recombination, have been proposed to reduce the activation energy. , The creation of surface sites can also modify the reactivity of the semiconductor and, − ideally, replace the role of the cocatalyst by appropriate design. − Although it seems that this strategy can avoid excess energy dissipation for SC interfacial electron transfer, , optimally the cocatalyst-free photocatalysts usually deliver reaction rates comparable to that of conventional construction . These phenomena indicate that the activation energy for the semiconductor–catalytic site–solution (SCsS) interfacial electron transfer of the HE half-reaction is still high.…”

Revealing the role of surface elementary doping in photocatalysis

“…The recent breakthrough of the near unity monochromatic quantum yield of water splitting greatly encouraged us to explore novel photocatalytic reactions. [1][2][3] Selective organic oxidation, [4][5][6][7] which was previously used to replace oxygen evolution, 8 is promising to integrate with hydrogen evolution (HE). This is because the integrated scheme can increase the value of the reaction and enhance the solar-to-hydrogen efficiency by extending the spectral response.…”

“…By combining eqn (1a) and (1b), the photocatalytic reaction rate ( r ) can be given by: n × r ≈ r iet ≈ k cr · P inc 0.5 + k te · P inc 2 in which n is the number of electron(s) participating in the reaction. Accordingly, the gross quantum yield (GQY) that reflects the utilization of effective photons can be given by: 7 GQY ≈ k cr · P inc −0.5 + k te · P inc Numerically and physically, GQY delivers a U-type curve with the variation of the light intensity and encounters a minimum near sunlight (AM 1.5G, 100 mW cm −2 , Fig. S1 and S2†).…”