Surface Passivation of GaN Nanowires for Enhanced Photoelectrochemical Water-Splitting

Abstract

Hydrogen production via photoelectrochemical water-splitting is a key source of clean and sustainable energy. The use of one-dimensional nanostructures as photoelectrodes is desirable for photoelectrochemical water-splitting applications due to the ultralarge surface areas, lateral carrier extraction schemes, and superior light-harvesting capabilities. However, the unavoidable surface states of nanostructured materials create additional charge carrier trapping centers and energy barriers at the semiconductor-electrolyte interface, which severely reduce the solar-to-hydrogen conversion efficiency. In this work, we address the issue of surface states in GaN nanowire photoelectrodes by employing a simple and low-cost surface treatment method, which utilizes an organic thiol compound (i.e., 1,2-ethanedithiol). The surface-treated photocathode showed an enhanced photocurrent density of -31 mA/cm at -0.2 V versus RHE with an incident photon-to-current conversion efficiency of 18.3%, whereas untreated nanowires yielded only 8.1% efficiency. Furthermore, the surface passivation provides enhanced photoelectrochemical stability as surface-treated nanowires retained ∼80% of their initial photocurrent value and produced 8000 μmol of gas molecules over 55 h at acidic conditions (pH ∼ 0), whereas the untreated nanowires demonstrated only <4 h of photoelectrochemical stability. These findings shed new light on the importance of surface passivation of nanostructured photoelectrodes for photoelectrochemical applications.

The Design of a New Cobalt Sulfide Nanoparticle Implanted Porous Organic Polymer Nanohybrid as a Smart and Durable Water‐Splitting Photoelectrocatalyst

“…The appearance of as ignificant broad hysteresis loop at high P/P 0 in the N 2 desorption profile of the isotherm could be attributed to the either elastic deformation or swellingo ft he polymeric framework upon the gas adsorption. In order to assess the structural integrity,m olecular connectivity of organic polymeric framework and the presence of different chemical environments of the carbonn uclei 13 Cc ross-polarisation magic-angles pinning (CP-MAS) NMR analysisw as carried out which is presented in Figure 1D.T he chemicals hift with the peak maximal ocated at 127.4 ppm confirmed the presence of ortho (o-) and meta (m-) carbon atoms of aromatic subunits attached with the N-atoms within the polymers. [28] The Brunauer-Emmett-Te ller (BET) surfacea rea of the respective Co 3 O 4 @POP nanohybrid was measured to be 582 m 2 g À1 ,w ith the corresponding total pore volume 0.212 cm 3 g À1 at P/P 0 = 0.999.…”

“…The solar-to-hydrogen (STH) conversion of ap hotocathode can be estimated from the magnitude of photocurrent generated. This crucial observation revealed that chemical stabilityo fo ur catalyst is significantly improved towards air and moisturea fter successful interaction with the N-doped porouso rganic polymer which was not likely to have happened for the CoS 2 /CNT catalysta sr eported by Wang et al [23] In order to investigate chemical and mechanical stabilityo ft he used CoS x @POP catalyst after PEC test, we have characterised the used catalystb ye mploying TEM, 13 CC Ps olid state MAS NMR spectroscopya nd XPS analysis. The HC-STH value of CoS x @POP photocathode (0.485 at 0.155 Vv s. RHE) was found to be the maximum among the studied catalysts whichr eflects its better photonto-hydrogen conversion efficiency over others.…”

“…The HC-STH value of CoS x @POP photocathode (0.485 at 0.155 Vv s. RHE) was found to be the maximum among the studied catalysts whichr eflects its better photonto-hydrogen conversion efficiency over others. 13 CC P MAS NMR studies of the reused catalyst( FigureS5) revealed that the molecular connectivity of organic polymeric frame- work and the presence of different chemical environments of the carbon nuclei in the POP framework have been retained. This positive shift of HC-STH (%) maxima corroborates the decrease of overpotential for the photoelectrochemical water reduction process.…”

“…Solid-state 13 CC PMAS NMR studies were performed using aB ruker Avance III HD 400 MHz NMR spectrometer.T ransmission electron microscope high-annular dark-field scanning (HAADFSTEM) and energy-dispersive X-ray mapping images were obtained with aT ECNAI G2 F20 equipped with an EDX detector.X -ray photoelectron spectroscopy (XPS) was performed on an Omicron nanotech operated at 15 kV and 20 mA with am onochromatic Al Ka X-ray source. High resolution transmission electron microscopy (HR-TEM) images were recorded in aJ EOL JEM 2010 transmission electron microscope with operating voltage 200 kV, equipped with aF EG.…”

“…[8,9] Although platinum (Pt) hasb een widely recommended as ap romising active hydrogene volutionr eaction( HER) catalyst, the higher cost and limited abundance in the earth's crust are big hurdles for practical applications.Aliterature survey demonstrates that numerous research groups have brought into focus the need towardse xploringi norganict ransition metal based non-precious catalysts, including sulfides, selenides, phosphides and others, in pursuit of inexpensive replacements for Pt;a ddressing all the profound challenges including poor stabilityi na cidic electrolyte,l arge band gap andt heir inferiorp erformance. [12] Similarly,G aN nanowire, [13] perylene tetracarboxylic di(propyl imidazole)/ cobalt (PDI-Co) complexi mmobilised on reduced graphene oxide (rGO), [14] CoSe 2 ,N iSe 2 nanocrystals [15] and Au-NPs decorated on 3D branchedZ nO nanowire [16] have also been considered as promising PEC water-splitting catalysts. [10] Ultrathin hematite (a-Fe 2 O 3 )f ilm deposited on at hree-dimensional nanophotonics tructure has been employed as ap otential PEC water-splitting catalystb y Fan et al and they have achieved about three times higher currentd ensity (3.05 mA cm À2 at 1.23 Vv s. reversible hydrogen electrode, RHE compared with the planarp hotoelectrode.…”