Statistical Design-Guided Synthesis of Nanoarchitectonics of High-Performance NiFeMoN Electrocatalyst through Facile One-Step Magnetron Sputtering.

This study presents an innovative, statistically-guided magnetron sputtering technique for creating nanoarchitectonics of high-performing, NiFeMoN electrocatalysts for oxygen evolution reaction (OER) in water splitting. Using a central composite face-centered (CCF) design, 13 experimental conditions are identified that enable precise optimization of synthesis parameters through response surface methodology (RSM), confirmed by analysis of variance (ANOVA). The statistical analysis highlighted a interaction between Mo% and N% in the nanostructured NiFeMoN and found optimizing values at 31.35% Mo and 47.12% N. The NiFeMoN catalyst demonstrated superior performance with a low overpotential of 216 mV at 10 mA cm-2 and remarkable stability over seven days, attributed to the modifications in electronic structure and the creation of new active sites through Mo and N additions. Furthermore, the NiFeMoN coating, when used as a protective layer for a Si photoanode in 1 m KOH, achieved an applied-bias photon-to-current efficiency (ABPE) of 5.2%, maintaining stability for 76 h. These advancements underscore the profound potential of employing statistical design for optimizing synthesis parameters of intricate catalyst materials via magnetron sputtering, paving the way for accelerated advancements in water splitting technologies and also in other energy conversion systems, such as nitrogen reduction and CO2 conversion.

Ferri-hydrite: A Novel Electron-Selective Contact Layer for InP Photovoltaic and Photoelectrochemical Cells.

Solar energy conversion devices with charge-selective contacts are attracting significant research interest as a cost-effective alternative to homojunction counterparts. This study presents a novel approach for fabricating high-performance solar cells based on InP heterojunctions using a solution-processed ferri-hydrite (Fh) electron-selective contact (ESC). The champion cell efficiency of 16.6% is achieved, which is a significant improvement over those from previous studies using other solution-processed ESC materials. X-ray photoelectron spectroscopy measurements showed that the low conduction band offset at the Fh-InP interface facilitated selective transport of photogenerated electrons from InP. Moreover, the Fh electron-selective contact layer provided an excellent photoelectrochemical half-cell water reduction efficiency of 8.4%. The Fh layer not only selectively extracts photogenerated electrons from InP but also simultaneously serves as a surface protection layer, improving the cell's long-term stability. These results demonstrate the potential of Fh as a low-cost and easily fabricated material for use in high-efficiency photovoltaic and photoelectrochemical devices. Our findings pave the way for further improvements in the efficiency of InP heterojunction solar cells by addressing the losses incurred in the cells.

Large-area epitaxial growth of InAs nanowires and thin films on hexagonal boron nitride by metal organic chemical vapor deposition.

Large-area epitaxial growth of III-V nanowires and thin films on van der Waals substrates is key to developing flexible optoelectronic devices. In our study, large-area InAs nanowires and planar structures are grown on hexagonal boron nitride templates using metal organic chemical vapor deposition method without any catalyst or pre-treatments. The effect of basic growth parameters on nanowire yield and thin film morphology is investigated. Under optimised growth conditions, a high nanowire density of 2.1×109cm-2is achieved. A novel growth strategy to achieve uniform InAs thin film on h-BN/SiO2/Si substrate is introduced. The approach involves controlling the growth process to suppress the nucleation and growth of InAs nanowires, while promoting the radial growth of nano-islands formed on the h-BN surface. A uniform polycrystalline InAs thin film is thus obtained over a large area with a dominant zinc-blende phase. The film exhibits near-band-edge emission at room temperature and a relatively high Hall mobility of 399 cm-2/(Vs). This work suggests a promising path for the direct growth of large-area, low-temperature III-V thin films on van der Waals substrates.

Protocol on the fabrication of monocrystalline thin semiconductor via crack-assisted layer exfoliation technique for photoelectrochemical water-splitting.

Thin semiconductors attract huge interest due to their cost-effective, flexible, lightweight, and semi-transparent properties. Here, we present a protocol on the preparation of thin semiconductor via controlled crack-assisted layer exfoliation technique. The protocol details the fabrication procedure for producing thin monocrystalline semiconductors with thicknesses in the range of a few tens of micrometers from thick donor substrates. In addition, we describe proof-of-concept application of the thin semiconductors for photoelectrochemical water-splitting to produce hydrogen fuel. For complete details on the use and execution of this protocol, please refer to Lee et al. (2021).

Thin silicon via crack-assisted layer exfoliation for photoelectrochemical water splitting.

Silicon (Si) has been widely investigated as a feasible material for photoelectrochemical (PEC) water splitting. Compared to thick wafer-based Si, thin Si (<50 µm thickness) could concurrently minimize the material usage allowing the development of cost-effective and flexible photoelectrodes for integrable PEC cells. This work presents the design and fabrication of thin Si using crack-assisted layer exfoliation method through detailed optical simulations and a systematic investigation of the exfoliation method. Thin free-standing Si photoanodes with sub-50 µm thickness are demonstrated by incorporating a nickel oxide (NiOx) thin film as oxygen evolution catalyst, light-trapping surface structure, and a rear-pn+ junction, to generate a photo-current density of 23.43 mA/cm2 with an onset potential of 1.2 V (vs. RHE). Our work offers a general approach for the development of efficient and cost-effective photoelectrodes with Si films with important implications for flexible and wearable Si-based photovoltaics and (opto)electronic devices.

Solution Processing of Topochemically Converted Layered WO3 for Multifunctional Applications.

Solution processing of nanomaterials is a promising technique for use in various applications owing to its simplicity and scalability. However, the studies on liquid-phase exfoliation (LPE) of tungsten oxide (WO3 ) are limited, unlike others, by a lack of commercial availability of bulk WO3 with layered structures. Herein, a one-step topochemical synthesis approach to obtain bulk layered WO3 from commercially available layered tungsten disulfide (WS2 ) by optimizing various parameters like reaction time and temperature is reported. Detailed microscopic and spectroscopic techniques confirmed the conversion process. Further, LPE was carried out on topochemically converted bulk layered WO3 in 22 different solvents; among the solvents studied, the propan-2-ol/water (1 : 1) co-solvent system appeared to be the best. This indicates that the possible values of surface tension and Hansen solubility parameters for bulk WO3 could be close to that of the co-solvent system. The obtained WO3 dispersions in a low-boiling-point solvent enable thin films of various thickness to be fabricated by using spray coating. The obtained thin films were used as active materials in supercapacitors without any conductive additives/binders and exhibited an areal capacitance of 31.7 mF cm-2 at 5 mV s-1 . Photo-electrochemical measurements revealed that these thin films can also be used as photoanodes for photo-electrochemical water oxidation.

Exfoliation in a low boiling point solvent and electrochemical applications of MoO3.

MoO3 is a versatile two-dimensional transition metal oxide having applications in areas such as energy storage devices, electronic devices and catalysis. To efficiently utilize the properties of MoO3 arising from its two-dimensional nature exfoliation is necessary. In this work, the exfoliation of MoO3 is carried out in 2-butanone for the first time. The achieved concentration of the dispersion is about 0.57 mg·mL-1 with a yield of 5.7%, which are the highest values reported to date. These high values of concentration and yield can be attributed to a favorable matching of energies involved in exfoliation and stabilization of MoO3 nanosheets in 2-butanone. Interestingly, the MoO3 dispersion in 2-butanone retains its intrinsic nature even after exposure to sunlight for 24 h. The composites of MoO3 nanosheets were used as an electrode material for supercapacitors and showed a high specific capacitance of 201 F·g-1 in a three-electrode configuration at a scan rate of 50 mV·s-1.