Modified p-GaN Microwells with Vertically Aligned 2D-MoS₂ for Enhanced Photoelectrochemical Water Splitting

Abstract

Photoelectrochemical (PEC) water splitting has been considered as the future technology for storing solar energy in the chemical bonds. However, due to the search of ideal heterostructured materials for photoanode/cathode, the full potential of this technology has not been realized yet. Herein we present, the nanotextured hexagonal microwell of p-GaN [p-GaN­(Et)] synthesized via wet chemical etching route as a photocathode (PC) for PEC water splitting. The p-GaN­(Et) was further modified by interconnected nanowall network of two-dimensional (2D) transition metal dichalcogenide (MoS2) [2D-MoS2/p-GaN­(Et)]. Both PCs were characterized for their morphology, structures, and optical and electronic properties. The overall PEC performance was validated through photocurrent values followed by the amount of hydrogen and oxygen evolution. This combination of 2D-MoS2/p-GaN­(Et) outplayed pristine p-GaN­(Et) by several orders of magnitude in overall PEC performance. The extraordinary stability under a continuous operating condition with 1 sun illumination (100 mW/cm2) provides the much-needed flavor of an efficient photocathode. The optimized photocathode [2D-MoS2/p-GaN­(Et)] shows the highest applied bias photon-to-current conversion efficiency of ∼3.18% with hydrogen evolution rate of 89.56 μmol/h at −0.3 V vs RHE. This wafer-level cost-effective synthesis of 2D-MoS2/GaN heterostructure based PCs opens a new way for large-scale solar–fuel conversion.

Fabrication of Semi-Transparent SrTaO2N Photoanodes with a GaN Underlayer Grown via Atomic Layer Deposition

“…In addition to the mitigation in conductivity, the GaN layer inserted between the SrTaO2N and SiC also sustains hole-blocking effect to alleviate carrier recombination. 25,37,61,62 This effect is similar to a reported SnO2 layer for BiVO4 thin film, and a Lu2O3 film deposited on a BiVO4 photoanode. 63,64 The introduced GaN that can afford holeblocking potential barrier is prone to suppress the backward holes migration from the photoabsorber, due to its deep position on the top of the valance band (Figure 5d).…”

Fabrication of Semi-Transparent SrTaO2N Photoanodes with a GaN Underlayer Grown via Atomic Layer Deposition

“…We have recently introduced a 2 µm GaN layer on sapphire substrates by MOVPE, which was used for SrTaO2N and LaTiO2N thin film deposition 21. Although the fabricated photoanodes demonstrated comparable photocurrent density with the present SrTaO2N thin film, the pronounced cathodic shift of the onset potential and the far smaller thickness of the GaN highlight the significance of the Ga(III) triazenide precursor and ALD technique in producing high-quality GaN conductive layer.In addition to the mitigation in conductivity, the GaN layer inserted between the SrTaO2N and SiC also sustains hole-blocking effect to alleviate carrier recombination 25,37,61,62. This effect is similar to a reported SnO2 layer for BiVO4 thin film, and a Lu2O3 film deposited on a BiVO4 photoanode 63,64.…”

A Water‐Splitting System with a Cobalt (II,III) Oxide Co‐Catalyst‐Loaded Bismuth Vanadate Photoanode Along with an Organo‐Photocathode

“…Water photolysis is known to be the most optimal procedure for acquiring solar hydrogen. Since the discovery of the water splitting system comprising a titanium(IV) dioxide (TiO 2 ) photoanode by Honda and Fujishima, [1] numerous studies on water splitting by both photoelectrochemical and photocatalytic methods have been conducted [2–12] . As a long‐standing issue, the development of active photocatalyst materials, which are able to efficiently utilize the solar spectrum for high output of molecular hydrogen, is required.…”