Concentrated Solar Light Photoelectrochemical Water Splitting for Stable and High-Yield Hydrogen Production

Abstract

Photoelectrochemical water splitting is a promising technique for converting solar energy into low-cost and eco-friendly H₂ fuel. However, the production rate of H₂ is limited by the insufficient number of photogenerated charge carriers in the conventional photoelectrodes under 1 sun (100 mW cm^-2) light. Concentrated solar light irradiation can overcome the issue of low yield, but it leads to a new challenge of stability because the accelerated reaction alters the surface chemical composition of photoelectrodes. Here, it is demonstrated that loading Pt nanoparticles (NPs) on single crystalline GaN nanowires (NWs) grown on n⁺-p Si photoelectrode operates efficiently and stably under concentrated solar light. Although a large number of Pt NPs detach during the initial reaction due to H₂ gas bubbling, some Pt NPs which have an epitaxial relation with GaN NWs remain stably anchored. In addition, the stability of the photoelectrode further improves by redepositing Pt NPs on the reacted Pt/GaN surface, which results in maintaining onset potential >0.5 V versus reversible hydrogen electrode and photocurrent density >60 mA cm^-2 for over 1500 h. The heterointerface between Pt cocatalysts and single crystalline GaN nanostructures shows great potential in designing an efficient and stable photoelectrode for high-yield solar to H₂ conversion.

Keywords: concentrated solar light; hydrogen evolution; photoelectrochemical water splitting; stability.

Figure 1

a) Tilt‐view SEM image of Pt‐loaded GaN nanowires / n⁺‐p Si photoelectrode. b) Plots of saturated current density (J_saturation), onset potential (V_onset), and saturation potential (V_saturation) with light intensity. c) Photocurrent density at 0 V_RHE (J₀) and d) V_onset for Pt/GaN/Si and GaN/Si measured as a function of time under 1 sun and 6.4 sun light.

Figure 2

AR‐XPS analysis of Pt/GaN/Si and GaN/Si before and after reaction for 24 h under 6.4 sun light. Relative surface atomic ratio of a) Pt/GaN/Si and b) GaN/Si. XPS spectra of c) Ga 3d, d) O 1s, and e) Pt 4f.

Figure 3

a) Low‐magnification HAADF‐STEM image and b) EDS elemental map of Pt/GaN/Si before the reaction. c) HAADF‐STEM image after 24 h reaction under 6.4 sun light. d) High‐resolution STEM image of Pt/GaN interface and inverse Fourier‐filtered image by masking Pt (111). Dislocations in Pt NPs are indicated in a green mark. e) Plots of d‐spacing of three Pt NPs in Figure 4d and Figure S19a (Supporting Information). f) Schematic lattice alignment at the Pt/GaN interface.

Figure 4

a) Schematic illustration of surface modification during the PEC HER. Surface adsorbed Pt NPs on GaN or GaO_x surface are removed while lattice‐matched Pt NPs on GaN are strongly anchored on the surface. Pt redeposition on the HER‐reacted Pt/GaN provides more stabilized Pt NPs. LSV curves of a) pristine Pt/GaN/Si (0 – 24 h) and b) after 5^th Pt redeposition (216 – 288 h). Plots of d) J_ph at 0 V_RHE and e) V_onset of Pt/GaN/Si over reaction time. The stability was tested over 1500 h.