Rationally Designed Double-Shell Dodecahedral Microreactors with Efficient Photoelectron Transfer: N-Doped-C-Encapsulated Ultrafine In2 O3 Nanoparticles

Phosphorus-doped nickel cobalt oxide (NiCo2O4) wrapped in 3D hierarchical hollow N-doped carbon nanoflowers as highly efficient bifunctional electrocatalysts for overall water splitting

Properly design and fabricate capable electrocatalysts with 3D hierarchical hollow framework to realize cost-effective and efficacious overall water splitting (OWS) are particularly meaningful for the large-scale arrangement of pivotal energy technology. In this study, P-doped NiCo2O4 nanoparticles encapsulated in N-doped carbon hierarchical hollow nanoflowers (P-NiCo2O4@NCHHNFs) were constructed using the hydrothermal-pyrolysis-phosphorization approach. This fascinating architecture can not merely serve as a conductive pathway for electron transfer, but at the same time effectively inhibited the aggregation and corrosion of the NiCo2O4 nanoparticles. Additionally, the P doping not only regulates electronic structure configuration to boost the intrinsic activity of the catalyst, but also enhance electrochemical surface areas to reveal more accessible active sites. Attributing to these characteristics, the as-prepared P-NiCo2O4@NCHHNFs exhibit preeminent electrocatalytic performance with low overpotentials of 283 mV and 162 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) (at 10 mA cm-2), respectively. Specifically, by using the P-NiCo2O4@NCHHNFs as bifunctional catalysts, a low potential of 1.56 V (at 10 mA cm-2) is sufficient to drive overall water splitting with splendid durability. This study proposed an innovative strategy for the conceiving and fabricating high-performance catalysts via heteroatom-doping.

TiO2 nanotube arrays-based photoelectrocatalyst: Tri-Doping engineering and carbon coating engineering boosting visible activity, and stable hydrogen evolution

The integration of non-metallic doping and carbon coating for TiO2-based photoelectrocatalysts can be recognized as a promising strategy to enhance their hydrogen production performance. To this end, this study explored the carbon coating engineering to induce stable multi-element doping with an aim to develop high-performance TiO2 nanotube array-based photoelectrocatalysts. The resulting structures consisted of carbon-nitrogen-sulfur-tri-doped TiO2 nanotube arrays with a nitrogen-sulfur-codoped carbon coating (CNS-TNTA/NSC). The fabrication process involved a one-step, low-cost strategy of the carbon-coated tridoped reaction confined in vacuum space, utilizing polymer thiourea sealed in a controlled environment. Compared the photocurrent density of CNS-TNTA/NSC with pristine TNTA, the photocurrent enhancement of approximately 18.3-fold under simulated sunlight and a remarkable increase of 32.8-fold under simulated visible light conditions. The enhanced photocatalytic activity under visible light was ascribed to two factors: First, C, N, and S tri-doping and Ti3+ created a diverse array of impurity energy levels within the band gap, which synergistically narrowed the band gap and further enhanced response to the visible light range. Second, the presence of a carbon coating shell doped with N and S can greatly promote electron transfer and efficient electron-hole pair separation. This study could provide significant insights concerning the design of sophisticated photoanodes.

S-induced Phase Change Forming In2 O3 /In2 S3 Heterostructure for Photoelectrochemical Glucose Sensor

In the past several decades, Photoelectrochemical (PEC) sensing still remains a great challenge to design highly-efficient semiconductor photocatalysts via a facile method. It is of much importance to design and synthesize various novel nanostructured sensing materials for further improving the response performance. Herein, we present an In2 O3 /In2 S3 heterostructure obtained by combining microwave assisted hydrothermal method with S-induced phase change, whose energy band and electronic structure could be adjusted by changing the S content. Combining theoretical calculation and spectroscopic techniques, the introduction of sulfur was proved to produce multifunctional interfaces, inducing the change of phase, oxygen vacancies and band gap, which accelerates the separation of photoexcited carriers and reduces their recombination, improving the electronic injection efficiency around the interface of In2 O3 /In2 S3 . As anticipated, an enhanced glucose response performance with a photocurrent of 0.6 mA cm-2 , a linear range of 0.1-1 mM and a detection limit as low as 14.5 μM has been achieved based on the In2 O3 /In2 S3 heterostructure, which is significant superior over its pure In2 O3 and S-doped In2 O3 counterparts. This efficient interfacial strategy may open a new route to manipulate the electrical structure, and energy band structure regulation of sensing material to improve the performance of photoelectrodes for PEC.

Double Insurance of Continuous Band Structure and N-C Layer Induced Prolonging of Carrier Lifetime to Enhance the Long-Wavelength Visible-Light Catalytic Activity of N-Doped In2O3

Nonmetallic doped metal oxides can be broad in their visible-light-response range. However, the half-filled or isolated impurity state can also be the new recombination center for photogenerated electrons/holes, which seriously influence the photocatalytic activity of the catalyst in the visible-light region. Therefore, how to prolong the photogenerated carrier life of nonmetallic doping metal oxides is the difficult and challenging topic in the field of photocatalysis. In this work, the hexagonal nanosheets assembled by N-doped C (N-C)-coated N-doped In₂O₃ (N-In₂O₃) nanoparticles (N-C/N-In₂O₃ HS) was obtained by simply pyrolyzing the In(2,5-PDC) hexagonal sheets. The N-C/N-In₂O₃ HS catalyst exhibit good photocatalytic activity and cycle stability in the long-wavelength region of visible light (λ = 520 and 595 nm). The effective utilization of long-wavelength visible light for N-C/N-In₂O₃ HS was mainly attributed to the acceptor-donor-acceptor compensation mechanism between the oxygen vacancy (V_O) and substitutional N-doping (N_s) sites, which made the N-C/N-In₂O₃ HS possess a continuous band structure, without the half-filled or isolated impurity state in the band gap, and extended its light absorption edge to 733 nm. The compensation mechanism of nitrogen doping on In₂O₃ can promote the photocatalytic activity under longer-wavelength yellow light (595 nm) irradiation. The N-C layer coated on the N-In₂O₃ nanoparticles acted as a good acceptor of photogenerated electrons, facilitating the effective spatial separation of photogenerated carriers and extend photogenerated carrier lifetimes. The comparative photocatalytic experiments (N-In₂O₃ HS and N-C/N-In₂O₃ HS) show that the presence of N-doped C layer can enhance the photocatalytic efficiency by nearly 10-fold. This double-doping and carbon-coating strategy provided a novel research idea to solve the problem that nonmetal atoms doped metal oxides led to the secondary combination of photogenerated electrons/holes.

Hollow Dodecahedral Structure of In2O3-In2S3 Heterojunction Encapsulated by N-Doped C as an Excellent Visible-Light-Active Photocatalyst for Organic Transformation

The low utilization efficiency in the visible region of the sunlight spectrum and the rapid recombination of photogenerated charge carriers are two crucial drawbacks that suppress the practical usage of metal oxide semiconductors as photocatalysts. In this article, we report a rational design of In₂O₃-In₂S₃ heterojunctions encapsulated by N-doped carbon with a hollow dodecahedral structure (In₂O₃-In₂S₃/N-C HDS), which can effectively handle the two drawbacks of metal oxide semiconductors and behave active for organic transformation under the irradiation of visible light even with long wavelengths. As exemplified by the selective oxidative coupling reaction of amine to imine, the obtained In₂O₃-In₂S₃/N-C HDS as the photocatalyst has exhibited excellent activity and stability. Experimental and density functional theory studies have verified that the excellent performance of In₂O₃-In₂S₃/N-C HDS can be attributed to the synergistic effect of In₂O₃-In₂S₃ heterojunctions, the coating of N-doped carbon, and the hollow porous structure with nanosheets as subunits.

Modulating the Charge-Transfer Step of a p-n Heterojunction with Nitrogen-Doped Carbon: A Promising Strategy To Improve Photocatalytic Performance

Engineering p-n heterojunctions among metal oxide semiconductors to provide a built-in electric field is an efficient strategy to facilitate the separation of photogenerated electrons and holes and improve their photocatalytic activities. However, the inherent poor conductivity of p-n heterojunctions still limits the charge-transfer step and thus hampers their practical application in photocatalysis. In this work, a nitrogen-doped carbon-coated NiO/TiO₂ p-n (NCNT) heterojunction with hierarchical mesoporous sphere morphology was synthesized by in situ pyrolytic decomposition of nickel-titanium complexes. The NiO/TiO₂ p-n heterojunction in NCNT was fully characterized by several techniques, supported by theoretical calculations and Mott-Schottky plots. On coating with a thin nitrogen-doped carbon layer, the electron transfer of the obtained p-n heterojunction could be significantly enhanced. On account of the favorable structural features of the p-n heterojunction with nitrogen-doped carbon coating and hierarchical mesoporous structure, NCNT exhibited excellent photocatalytic activity toward various reaction systems, including the hydrogen evolution reaction and the visible-light-induced hydroxylation of phenylboronic acids.

Double-shelled hollow rods assembled from nitrogen/sulfur-codoped carbon coated indium oxide nanoparticles as excellent photocatalysts

Excellent catalytic activity, high stability and easy recovery are three key elements for fabricating efficient photocatalysts, while developing a simple method to fabricate such photocatalysts with these three features at the same time is highly challenging. In this study, we successfully synthesized double-shelled hollow rods (DHR) assembled by nitrogen (N) and sulfur (S)-codoped carbon coated indium(III) oxide (In₂O₃) ultra-small nanoparticles (N,S-C/In₂O₃ DHR). N,S-C/In₂O₃ DHR exhibits remarkable photocatalytic activity, high stability and easy recovery for oxidative hydroxylation reaction of arylboronic acid substrates. The catalyst recovery and surface area were well balanced through improved light harvesting, contributed by concurrently enhancing the reflection on the outer porous shell and the diffraction in the inside double-shelled hollow structure, and increased separation rate of photogenerated carriers. Photocatalytic mechanism was investigated to identify the main reactive species in the catalytic reactions. The electron separation and transfer pathway via N,S-codoped graphite/In₂O₃ interface was revealed by theoretical calculations.

While photoredox catalysis presents exciting avenues for molecular transformations, balancing optimal photochemical and materials properties can be challenging. Here, the authors prepare carbon-coated In₂O₃ nanoparticles as recoverable photocatalysts for arylboronic acid oxidative hydroxylation.

Hierarchical NiO@N-Doped Carbon Microspheres with Ultrathin Nanosheet Subunits as Excellent Photocatalysts for Hydrogen Evolution

Achieving highly efficient hierarchical photocatalysts for hydrogen evolution is always challenging. Herein, hierarchical mesoporous NiO@N-doped carbon microspheres (HNINC) are successfully fabricated with ultrathin nanosheet subunits as high-performance photocatalysts for hydrogen evolution. The unique architecture of N-doped carbon layers and hierarchical mesoporous structures from HNINC could effectively facilitate the separation and transfer of photo-induced electron-hole pairs and afford rich active sites for photocatalytic reactions, leading to a significantly higher H₂ production rate than NiO deposited with platinum. Density functional theory calculations reveal that the migration path of the photo-generated electron transfer is from Ni 3d and O 2p hybrid states of NiO to the C 2p state of graphite, while the photo-generated holes locate at Ni 4s and Ni 4p hybrid states of NiO, which is beneficial to improve the separation of photo-generated electron-hole pairs. Gibbs free energy of the intermediate state for hydrogen evolution reaction is calculated to provide a fundamental understanding of the high H₂ production rate of HNINC. This research sheds light on developing novel photocatalysts for efficient hydrogen evolution.