Development of a photoelectrochemically self-improving Si/GaN photocathode for efficient and durable H2 production

Abstract

Development of an efficient yet durable photoelectrode is of paramount importance for deployment of solar-fuel production. Here, we report the photoelectrochemically self-improving behaviour of a silicon/gallium nitride photocathode active for hydrogen production with a Faradaic efficiency approaching ~100%. By using a correlative approach based on different spectroscopic and microscopic techniques, as well as density functional theory calculations, we provide a mechanistic understanding of the chemical transformation that is the origin of the self-improving behaviour. A thin layer of gallium oxynitride forms on the side walls of the gallium nitride grains, via a partial oxygen substitution at nitrogen sites, and displays a higher density of catalytic sites for the hydrogen-evolving reaction. This work demonstrates that the chemical transformation of gallium nitride into gallium oxynitride leads to sustained operation and enhanced catalytic activity, thus showing promise for oxynitride layers as protective catalytic coatings for hydrogen evolution.

Observation of polarity-switchable photoconductivity in III-nitride/MoSx core-shell nanowires

“…In another word, the OER process still dominates the direction of net photocurrent in bare p-AlGaN/n-GaN nanowire, resulting in a lower but still positive photocurrent under 254 nm illumination. This indicates that modification of the Δ G H of III-nitride nanowire surface may be one of the critical factors in the pursuit of spectrally distinctive photodetection, to realize the wavelength-induced polarity-switchable photoconductivity behavior 20 , 41 , 56 .…”

“…S1. The MBE-grown p-n junction based on III-nitride nanowires enables efficient light absorption and photogenerated charge-carrier extraction, more importantly, they are highly beneficial for exposing high-density catalytic sites for the PEC process, not to mention its superior crystallinity and photoelectric properties [19][20][21] . The schematic illustration of 365 nm photodetection process of bare p-AlGaN/n-GaN nanowires was shown in Fig.…”

“…In particular, owing to their distinctive nature of one-dimensional geometry and large surface-to-volume ratio, III-V nanowire platform offers versatile strategies to manipulate the intrinsic material properties in the pursuit of novel applications while exhibiting new material-wise challenges that do not exist in their bulk form [14][15][16] . For instance, on one hand, such vertical and high-aspect-ratio geometry (1) enables core-shell device architecture in the radial direction which facilitates efficient light absorption and photo-generated charge-carrier extraction for high-efficient photovoltaic or photodetection applications 17,18 , and (2) provides high density of surface sites for artificial photosynthesis or photoelectrochemical photodetection [19][20][21][22] . On the other hand, ultrahigh surface areas naturally induce a high density of surface states 23,24 , which could act as charge trapping centers and harmful to the performance of nanoscale devices.…”

Shining Light on Anion-Mixed Nanocatalysts for Efficient Water Electrolysis: Fundamentals, Progress, and Perspectives

“…The incorporation of nitrogen (N) into oxides opens the facile route of tuning physical and chemical properties [76][77][78]. As N with weaker electronegative and is more polarizable than O, the M-N bond is more covalent than the M-O bond in nature [79].…”

Solar hydrogen production under combined solar light and thermal effect at mid-and-low temperature –experimental and thermodynamic analysis

“…Using a carbon-free energy, like hydrogen etc., is attractive. Many technologies have been researched for hydrogen production by solar energy, such as solar thermochemical water splitting cycles [1], solar photochemical water splitting [2], solar photoelectrochemical water splitting [3] and so on. The thermochemical processes can utilize solar energy in the full spectrum.…”