Protection of GaInP₂ Photocathodes by Direct Photoelectrodeposition of MoS_x Thin Films

Abstract

Catalytic MoS x thin films have been directly photoelectrodeposited on GaInP2 photocathodes for stable photoelectrochemical hydrogen generation. Specifically, the MoS x deposition conditions were controlled to obtain 8–10 nm films directly on p-GaInP2 substrates without ancillary protective layers. The films were nominally composed of MoS2, with additional MoO x S y and MoO3 species detected and showed no long-range crystalline order. The as-deposited material showed excellent catalytic activity toward the hydrogen evolution reaction relative to bare p-GaInP2. Notably, no appreciable photocurrent reduction was incurred by the addition of the photoelectrodeposited MoS x catalyst to the GaInP2 photocathode under light-limited operating conditions, highlighting the advantageous optical properties of the film. The MoS x catalyst also imparted enhanced durability toward photoelectrochemical hydrogen evolution in acidic conditions, maintaining nearly 85% of the initial photocurrent after 50 h of electrolysis. In total, this work demonstrates a simple method for producing dual-function catalyst/protective layers directly on high-performance, planar III–V photoelectrodes for photoelectrochemical energy conversion.

Addressing the Stability Gap in Photoelectrochemistry: Molybdenum Disulfide Protective Catalysts for Tandem III–V Unassisted Solar Water Splitting

“…The MoS2/III-V device lasted over five times longer than the PtRu/III-V device, which is consistent with enhanced durability as observed in previous reports comparing MoS2-and PtRucoated GaInP2 photocathodes. 9,11,12 As seen in the microscope images, both the MoS2/III-V and PtRu/III-V devices had similar failure modes, where macroscopic degradation originated at a single point, likely a material growth or post-growth processing defect. This degraded area then rapidly grew to encompass the whole sample, leading to a sudden loss in current.…”

“…Molybdenum disulfide nanomaterials have been shown to stabilize a variety of singlejunction Si and III-V PEC systems, functioning as a hydrogen evolution reaction (HER) catalyst and protection layer. [9][10][11][12][13][14][15] Because of the promising performance in single-junction photocathodes, it is of interest to use MoS2 with tandem semiconductor systems to improve the stability during unassisted solar water splitting.…”

“…Molybdenum disulfide nanomaterials have been shown to stabilize a variety of singlejunction Si and III-V PEC systems, functioning as a hydrogen evolution reaction (HER) catalyst and protection layer. [9][10][11][12][13][14][15] Because of the promising performance in single-junction photocathodes, it is of interest to use MoS2 with tandem semiconductor systems to improve the stability during unassisted solar water splitting.While most III-V-based unassisted water splitting devices to date have incorporated a Ga0.51In0.49P (hereafter GaInP2) (1.8 eV) top cell, device lifetimes have been limited to <100 h. 7,16 GaxIn1-xAsyP1-y (1.7 eV) has shown promise as a PV material and has been paired with a GazIn1-zAs bottom cell (1.1 eV) for efficient tandem PV systems, motivating efforts to incorporate GaxIn1-xAsyP1-y into PEC systems and investigate the stability of this quaternary top cell. [16][17][18][19] The composition of GaxIn1-xAsyP1-y (hereafter GaInAsP), nominally x ~ 0.68 and y ~ 0.34, gives the desired bandgap of 1.7 eV and a lattice constant matching that of GaAs.…”

Understanding Surface Modulation to Improve the Photo/Electrocatalysts for Water Oxidation/Reduction

“…However, the high densities of surface defect states act as trap states on the surface that accept the charge carriers and recombine with the transferred charge carriers on the surface, degrading the efficiency of the device. So, methods to regulate the densities of surface defects, such as introducing passivation layers, oxygen plasma exposure, hydrogen treatments and annealing are required [9,[55][56][57][58]. In addition, we cover the methods for regulating the type of defects and densities of defects in Section 3 in details.…”

Achieving visible light-driven hydrogen evolution at positive bias with a hybrid copper–iron oxide|TiO2-cobaloxime photocathode

“…Other solutions exploit critical elements such as indium and gallium. 11,12 Silicon and III-V semiconductors exhibit limited stability in aqueous solutions and must be thoroughly passivated after HF etching of native oxide layer. 9,10,[13][14][15] Metal oxides hold promises in that prospect.…”