Solvothermal Process Assisted Sensitization of 1D Anodized TiO2 Nanotubes with 0D Cadmium Chalcogenides (CdTe, CdS) for Efficient Solar to Clean Energy Generation

The creation of an n-n heterojunction between TiO2 nanotubes (T_NT) and CdTe nanocrystals (which mostly exist as p-type) is crucial for realizing the benefits of efficient directional charge transport in a photoanode of 1D/0D architecture. The presented one-pot solvothermal approach leverages temperature control to achieve linker-free spatial distribution of CdTe nanocrystals (NCs) on T_NT resulting in highly efficient optical and photoelectrochemical responses. As a result of this positive outcome, a comparative study between the solvothermal approach and the linker mediated approach was performed on water oxidation with CdS NC decorated T_NT. Solvothermally synthesized T_NT/CdS photoelectrode presents ~600% higher value of short-circuit current density (Isc) than that of the plain T_NT (0.95 mA/cm2); in addition, it demonstrates 4.20-fold increased applied-bias-to photoconversion efficiency (ABPE) in comparison with the lone T_NT (0.77%). However, linker mediated T_NT/MPA-CdS photoelectrode exhibits relatively lower value of Isc (2.51 mA/cm2) and ABPE (1.79 %)

Photoassisted Enhancement of the Electrocatalytic Oxidation of Formic Acid on Platinized TiO₂ Nanotubes

A solvothermal method is used to deposit Pt nanoparticles on anodized TiO₂ nanotubes (T_NT). Surface characterization using SEM, EDX, and XRD indicates the formation of polycrystalline TiO₂ nanotubes of 110 ± 10 nm diameter with Pt nanoparticle islands. The application of the T_NT/Pt photoanode has been examined toward simultaneous electrooxidation and photo­(electro)­oxidation of formic acid (HCOOH). Upon UV–vis photoillumination, the T_NT/Pt photoelectrode generates a current density of 72 mA/cm², which is significantly higher (∼39-fold) than that of the T_NT electrode (1.85 mA/cm²). This boosting in the overall current is attributable to the enhanced oxidation of formic acid at the T_NT/Pt-electrolyte interface. Further, a series of cyclic voltammetric (CV) responses, of which each anodic scan is switched to photoillumination at a certain applied bias (i.e., 0.2 V, 0.4 V, etc.), is used to identify the role of T_NT/Pt as a promoter for the photoelectrooxidation of formic acid and understand a carbon monoxide (CO)-free pathway. Chronoamperometric (j/t) measurements demonstrate the evidence of an external bias dependent variation in the time lag during the current stabilization. An analysis of the CV plots and j/t profiles suggests the existence of both the charge-transfer controlled process and the diffusion-controlled process during formic acid photoelectrooxidation

Engineered Solution–Liquid–Solid Growth of a “Treelike” 1D/1D TiO₂ Nanotube-CdSe Nanowire Heterostructure: Photoelectrochemical Conversion of Broad Spectrum of Solar Energy

This work presents a hitherto unreported approach to assemble a 1D oxide-1D chalcogenide heterostructured photoactive film. As a representative system, bismuth (Bi) catalyzed 1D CdSe nanowires are directly grown on anodized 1D TiO₂ nanotube (T_NT). A combination of the reductive successive-ionic-layer-adsorption-reaction (R-SILAR) and the solution–liquid–solid (S-L-S) approach is implemented to fabricate this heterostructured assembly, reported in this 1D/1D form for the first time. XRD, SEM, HRTEM, and elemental mapping are performed to systematically characterize the deposition of bismuth on T_NT and the growth of CdSe nanowires leading to the evolution of the 1D/1D heterostructure. The resulting “treelike” photoactive architecture demonstrates UV–visible light-driven electron–hole pair generation. The photoelectrochemical results highlight: (i) the formation of a stable n–n heterojunction between TiO₂ nanotube and CdSe nanowire, (ii) an excellent correlation between the absorbance vis-à-vis light conversion efficiency (IPCE), and (iii) a photocurrent density of 3.84 mA/cm². This proof-of-concept features the viability of the approach for designing such complex 1D/1D oxide–chalcogenide heterostructures that can be of interest to photovoltaics, photocatalysis, environmental remediation, and sensing

Photoilluminated Redox-Processed Rh₂P Nanoparticles on Photocathodes for Stable Hydrogen Production in Acidic Environments

While photoelectrochemical (PEC) cells show promise for solar-driven green hydrogen production, exploration of various light-absorbing multilayer coatings has yet to significantly enhance their hydrogen generation efficiency. Acidic conditions can enhance the hydrogen evolution reaction (HER) kinetics and reduce overpotential losses. However, prolonged acidic exposure deactivates noble metal electrocatalysts, hindering their long-term stability. Progress requires addressing catalyst degradation to enable stable, efficient, and acidic PEC cells. Here, we proposed a process design based on the photoilluminated redox deposition (PRoD) approach. We use this to grow crystalline Rh2P nanoparticles (NPs) with a size of 5–10 on 30 nm-thick TiO2, without annealing. Atomically precise reaction control was performed by using several cyclic voltammetry cycles coincident with light irradiation to create a system with optimal catalytic activity. The optimized photocathode, composed of Rh2P/TiO2/Al–ZnO/Cu2O/Sb–Cu2O/ITO, achieved an excellent photocurrent density of 8.2 mA cm–2 at 0 VRHE and a durable water-splitting reaction in a strong acidic solution. Specifically, the Rh2P-loaded photocathode exhibited a 5.3-fold enhancement in mass activity compared to that utilizing just a Rh catalyst. Furthermore, in situ scanning transmission electron microscopy (STEM) was performed to observe the real-time growth process of Rh2P NPs in a liquid cell

Ultrafine Nb₂O₅ Nanocrystal Coating on Reduced Graphene Oxide as Anode Material for High Performance Sodium Ion Battery

Ultrafine niobium oxide nanocrystals/reduced graphene oxide (Nb₂O₅ NCs/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. Nb₂O₅ NCs/rGO was synthesized by controllable hydrolysis of niobium ethoxide and followed by heat treatment at 450 °C in flowing forming gas. Transmission electron microscopy images showed that Nb₂O₅ NCs with average particle size of 3 nm were uniformly deposited on rGO sheets and voids among Nb₂O₅ NCs existed. The architecture of ultrafine Nb₂O₅ NCs anchored on a highly conductive rGO network can not only enhance charge transfer and buffer the volume change during sodiation/desodiation process but also provide more active surface area for sodium ion storage, resulting in superior rate and cycle performance. <i>Ex situ</i> XPS analysis revealed that the sodium ion storage mechanism in Nb₂O₅ could be accompanied by Nb⁵⁺/Nb⁴⁺ redox reaction and the ultrafine Nb₂O₅ NCs provide more surface area to accomplish the redox reaction

Engineering Molybdenum Diselenide and Its Reduced Graphene Oxide Hybrids for Efficient Electrocatalytic Hydrogen Evolution

We report the hydrogen evolution reaction (HER) with molybdenum diselenide (MoSe₂) and its reduced graphene oxide (rGO) hybrids synthesized by a microwave process followed by annealing at 400 °C. The content of GO was varied to understand its role in the electrocatalytic activities. Electrochemical performance of the as-synthesized and the annealed catalysts underscores (i) a requirement of catalytic activation of the as-synthesized samples, (ii) an apparent shift in the onset potential as a result of annealing, and (iii) striking changes in the Tafel slope as well as the overpotential. The results clearly reveal that partially crystalline plain MoSe₂ is more elctroactive in comparison to its annealed counterpart, whereas annealing is advantageous to MoSe₂/rGO. Improved HER performances of the annealed MoSe₂/rGO hydrids arise from the synergistic effect between active MoSe₂ and rGO of improved conductivity. The annealed hybrid of MoSe₂ with rGO designated as MoSe₂/rGO100_400 °C demonstrated an excellent HER activity with a small onset potential of −46 mV vs reversible hydrogen electrode, a smaller Tafel slope (61 mV/dec), and a reduced overpotential of 186 mV at −10 mA/cm². As a result of a convenient synthetic process and the suitable electrocatalytic performance, this study would be beneficial to designing and fabricating other nanomaterials with/without a conductive support for their versatile applications