Bioinspired Carbonized Polymer Microspheres for Full-Color Whispering Gallery Mode Emission for White Light Emission, Unclonable Anticounterfeiting, and Chemical Sensing Applications.

Light-element-based fluorescent materials, colloidal graphene quantum dots, and carbon dots (CDs) have sparked an immense amount of scientific interest in the past decade. However, a significant challenge in practical applications has emerged concerning the development of solid-state fluorescence (SSF) materials. This study addresses this knowledge gap by exploring the unexplored photonic facets of C-based solid-state microphotonic emitters. The proposed synthesis approach focuses on carbonized polymer microspheres (CPMs) instead of conventional nanodots. These microspheres exhibit remarkable SSF spanning the entire visible spectrum from blue to red. The highly spherical shape of CPMs imparts built-in photonic properties in addition to its intrinsic CD-based attributes. Leveraging their excitation-dependent photoluminescence property, these microspheres exhibit amplified spontaneous emission, assisted by the whispering gallery mode resonance across the visible spectral region. Remarkably, unlike conventional semiconductor quantum dots or dye-doped microresonators, this single microstructure showcases adaptable resonant emission without structural/chemical modifications. This distinctive attribute enables a plethora of applications, including microcavity-assisted energy transfer for white light emission, highly sensitive chemical sensing, and secure encrypted anticounterfeiting measures. This interdisciplinary approach, integrating photonics and chemistry, provides a robust solution for light-element-based SSF with inherent photonic functionality and wide-ranging applications.

High entropy alloying strategy for accomplishing quintuple-nanoparticles grafted carbon towards exceptional high-performance overall seawater splitting.

High entropy alloys (HEAs), a novel class of material, have been explored in terms of their excellent mechanical properties. Seawater electrolysis is a step towards sustainable production of carbon-neutral fuels such as H2, O2, and industrially demanding Cl2. Herein, we report a practically viable FeCoNiMnCr HEA nanoparticles system grafted on a conductive carbon matrix for promising seawater electrolysis. The comprehensive kinetics analysis of the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and chlorine evolution reaction (CER) confirms the effectiveness of our system. As an electrocatalyst, HEAs grafted on carbon black show trifunctionality with promising kinetics, selectivity and enduring performance, towards seawater splitting. We optimize high entropy alloy decorated/grafted carbon black (HEACB) catalysts, studying their synthesis temperature to scrutinize the effect of alloy formation variation on the catalysis efficacy. During the catalysis, selectivity between two mutually competing reactions, CER and OER, in the electrochemical catalysis of seawater is controlled by the reaction media pH. We employ Mott-Schottky measurements to probe the band structure of the intrinsically induced metal-semiconductor junction in the HEACB catalyst, where the carrier density and flat band potential are optimized. The HEACB sample provides promising results towards overall seawater electrolysis with a net half-cell potential of about 1.65 V with good stability, which strongly implies its broad practical applicability.

Interfacial Electron Transfer Strategy to Improve the Hydrogen Evolution Catalysis of CrP Heterostructure.

Though several Pt-free hydrogen evolution reaction (HER) catalysts have been reported, their employment for industry is challenging. Here, a facile pyrolysis method to obtain phase-pure CrP nanoparticles supported on N, P dual-doped carbon (CrP/NPC) is reported to be tuned toward industrial HER. Interestingly, CrP/NPC exhibits excellent HER activity that requires an overpotential of 34 mV to attain a current density of 10 mA cm-2 , which is only 1 mV positive to commercial Pt/C and a potential of 55 mV to achieve a current density of 200 mA cm-2 which is better than Pt/C. In addition, the long-term durability of CrP/NPC is far superior to Pt/C due to the strong interaction between CrP and C support, restricting any agglomeration or leaching. Density functional theory (DFT) calculations suggest that electronic modulation at the interface (CrP/NPC) optimizes the hydrogen adsorption energy. The Cr-Cr bridge site with required density of states near the Fermi level is found to be the active site. Overall, this report provides a practical scheme to synthesize rarely investigated CrP based materials along with a computational mechanistic guideline for electrocatalysis that can be utilized to explore other phosphides for various applications.

Self-Assembled TMD Nanoparticles on N-Doped Carbon Nanostructures for Oxygen Reduction Reaction and Electrochemical Oxygen Sensing Thereof.

Here, we report on a universal carbothermal reduction strategy for the synthesis of well-dispersed WS2 nanoparticles (∼1.7 nm) supported on a N-doped carbon (NxC) nanostructure and the electrocatalytic activity toward oxygen reduction reaction (ORR). Bulk WS2 powder (2 µm) is the source for WS2 nanoparticles, and dicyandiamide is the source for NxC and carbothermal reduction. Interestingly, WS2/NxC serves the purpose of innovative and robust active sites for ORR through an efficient four-electron transfer process with excellent durability. Remarkably, WS2/NxC suppresses the peroxide generation due to the dominating inner-sphere electron transfer mechanism where the direct adsorption of the desolvated O2 molecule on the electroactive centers takes place. The mass activity (at 0.4 and 0.85 V vs RHE) of WS2/NxC outperforms the previously reported transition metal based electrocatalysts. The study further establishes a correlation between the work function and the ORR activity. We have also exploited WS2/NxC for electrochemical oxygen sensing, and there exists a direct correlation between oxygen sensing and ORR as both depend on the oxygen adsorption ability. Finally, the carbothermal reduction strategy has been extended for the synthesis of other TMDs/NxC such as MoS2/NxC, MoSe2/NxC, and WSe2/NxC.

Robust Visible-Blind Wearable Infrared Sensor Based on IrP2 Nanoparticle-Embedded Few-Layer Graphene and the Effect of Photogating.

It is challenging to realize a visible-blind infrared photodetector as the materials that absorb infrared light also absorb visible light. Here, we report the synthesis of IrP2 nanoparticle-embedded few-layer graphene by one-step solid-state pyrolysis and its application in visible-blind infrared sensing. A linear photodetector device was fabricated by drop casting IrP2 nanoparticle-embedded few-layer graphene onto a flexible PET substrate with two gold electrodes separated by ∼16 µm. The photoconductive gain was found to be as high as ∼145% with response and decay times of ∼0.4 and ∼2.8 s, respectively, under 1550 nm irradiation of 800 mW cm-2. The room-temperature responsivity was ∼1.81 A W-1 at 80 mW cm-2 and ∼0.54 A W-1 at a high incident power of ∼2200 mW cm-2 under a bias of 1 V. Interestingly, the device showed response even in the long-wavelength infrared region, but no response was found under visible light. The embedded IrP2 nanoparticles act as trap centers inducing photogating in the device, and the average trap state energy was estimated to be ∼16.5 ± 1.5 meV from the temperature-dependent photocurrent studies. The device was found to be immune to air exposure and bending, suggestive of use a a wearable sensor.

Review on recent progress in metal-organic framework-based materials for fabricating electrochemical glucose sensors.

Diabetes is a type of disease that threatens human health, which can be diagnosed based on the level of glucose in the blood. Recently, various MOF-based materials have been developed as efficient electrochemical glucose sensors because of their tunable pore channels, large specific surface area well dispersed metallic active sites, etc. In this review, the significance of glucose detection and the advantages of MOF-based materials for this application are primarily discussed. Then, the application of MOF-based materials can be categorized into two types of glucose sensors: enzymatic biosensors and non-enzymatic sensors. Finally, insights into the current research challenges and future breakthrough possibilities regarding electrochemical glucose sensors are considered.

Atomic Arrangement Modulation in CoFe Nanoparticles Encapsulated in N-Doped Carbon Nanostructures for Efficient Oxygen Reduction Reaction.

The properties and, hence, the application of materials are dependent on the way their constituent atoms are arranged. Here, we report a facile approach to produce body-centered cubic (bcc) and face-centered cubic (fcc) phases of bimetallic FeCo crystalline nanoparticles embedded into nitrogen-doped carbon nanotubes (NCNTs) with equal loading and almost similar particle size for both crystalline phases by a rational selection of precursors. The two electrocatalysts with similar composition but different crystalline structures of the encapsulated nanoparticles have allowed us, for the first time, to account for the effect of crystal structure on the overall work function of electrocatalysts and the concomitant correlation with the oxygen reduction reaction (ORR). This study unveils that the electrocatalysts with lower work function show lower activation energy to facilitate the ORR. Importantly, the difference between the ORR activation energy on electrocatalysts and their respective work functions are found to be identical (∼0.2 eV). A notable decrease in the ORR activity after acid treatment indicates the significant role of encapsulated FeCo nanoparticles in influencing the oxygen electrochemistry by modulating the material property of overall electrocatalysts.

High-entropy alloys for water oxidation: a new class of electrocatalysts to look out for.

High-entropy alloys (HEAs) with five or more elements can provide near-continuous adsorption energies and can be optimized for superior persistent catalytic activity. This report presents electrochemical water oxidation facilitated by employing graphene and FeCoNiCuCr HEA nanoparticle based composites prepared via the mechanical milling of graphite-metal powders. The composite efficiently facilitates water oxidation with a low overpotential of 330 mV at 10 mA cm-2, and high specific and mass activities (∼143 mA cm-2 and 380 mA mg-1, respectively, at 1.75 V). Importantly, the composites exhibit excellent accelerated cycling stability with ∼99% current retention (after 3250 cycles). The HEA-based composites are anticipated to replace noble/precious metal based traditional electrocatalysts in the future, the use of which is a major obstacle in the technological scalability of electrochemical energy conversion and storage devices.

Energy-Efficient Rational Designing of Multifunctional Nanocomposites by Preferential Anchoring of Metal Ions via Fermi Level Positioning of Carbon Nanostructures.

Despite the availability and dedicated studies on a variety of carbon nanostructures, amorphous carbon is still a preferred support for a wide range of commercially available metal catalysts. In order to shed some light on this, we carried out electroless deposition of metal nanoparticles on various carbon nanostructures such as amorphous carbon (a-C), carbon nanotubes (CNTs), and nitrogen-doped CNTs (NCNTs) under similar experimental conditions. The main objective is to elucidate the preferable deposition on a particular carbon nanostructure, if any, and understand the underlying mechanism. Experimental results unveil preferred electroless deposition of metal nanoparticles on a-C over CNTs and NCNTs. Notably, the deposition is nicely correlated with the position of the Fermi level (EF) with respect to the Mn+ ↔ M0 redox level (E0). Remarkably, EF is found to be in the following order NCNT > CNT > a-C and the smaller gap (E0-EF) favors the faster electron transfer, resulting in the preferential reduction of Mn+, yielding finer nanoparticles on a-C. We believe that this approach can pave the way for designing noble metal-based carbon nanocomposites for a variety of applications, ranging from environmental redemption to electrochemical energy harvesting. As case studies, we have explored the nanocomposites for various catalytic activities and found them to be very competent with recently reported various state-of-the-art electrocatalysts and their commercial counterparts.

Self-Organized Single-Atom Tungsten Supported on the N-Doped Carbon Matrix for Durable Oxygen Reduction.

Rational engineering of atomically scaled metal-nitrogen-carbon (M-N-C) moieties has been the topic of recent research interest because of their potential application as an electrochemical oxygen reduction reaction (ORR) catalyst. Despite numerous efforts on M-N-Cs, attaining both adequate activity and a satisfactory stability simultaneously is a principal issue. Herein, we demonstrated the synthesis of a single-atom tungsten catalyst supported on the N-doped carbon matrix (W-N-C) and its application as an ORR catalyst. W-N-C was synthesized using the economically viable, simple, one-step pyrolysis of dicyandiamide and tungsten(VI) chloride at moderate temperature (700 °C). The synthesis of W-N-C avoids any post acid treatment as it does not require any subsidiary sacrificial metal like Zn and, hence, does not induce any burden associated with chemical waste management. The atomic dispersion of W atoms stabilized by N-doped porous carbon and the formation of WN2C2 were confirmed by high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy. Interestingly, as-synthesized WN2C2 exhibited unprecedented electrocatalytic activity with a half-wave potential of 764 mV vs reversible hydrogen electrode (RHE) as well as significantly enhanced stability (retaining >99% diffusion-limited current density and the loss in activity is 10.5% at 0.84 V after 10,000 potential cycles), which is much better than the stability limit set by the US Department of Energy in an alkaline medium. Overall, the activity of W-N-C surpasses that of Pt/C after 5000 cycles. The excellent stability is believed to be due to the symmetric coordination of the metal active site (W2N2C2).

Inner Sphere Electron Transfer Promotion on Homogeneously Dispersed Fe-Nx Centers for Energy-Efficient Oxygen Reduction Reaction.

The study reports the optimized incorporation of pyridinic nitrogen in nitrogen-doped carbon nanotubes (CNTs) to realize effective Fe-Nx centers throughout the framework. The study unveils nitrogen as a valuable asset to promote the homogeneous dispersion of Fe moieties throughout the CNT framework, which is a necessary component to institute uniform Fe-Nx centers. In addition, pyridinic nitrogen causes disruption in strongly delocalized π-electrons, which impart electron-withdrawing nature in the carbon matrix, resulting in an anodic shift in oxygen reduction reaction (ORR) onset potential (Eonset). The direct interaction of Fe-Nx with O2, as evidenced by poisoning and computational studies, ensures the preferential inner sphere electron transfer mechanism. Despite the alkaline medium, the outer sphere electron transfer mechanism was muted, with suppressed HO2- generation, preferential 4e- reduction pathways, and excellent cyclic stability. The study indicates the dependency of ORR half-wave potential on the electron transfer mechanism. The poisoning study unveils the direct involvement of Fe-Nx electroactive centers in facilitating ORR in alkaline medium. It further indicates a noticable increase (up to ∼25%) in peroxide generation-an unwanted ORR intermediate-and concomitant reduction in average electron transfer no. per oxygen molecule.

Mechanistic Investigation into Efficient Water Oxidation by Co-Ni-Based Hybrid Oxide-Hydroxide Flowers.

Oxides are envisioned as promising catalysts to facilitate water oxidation, and the benign presence of hydroxide moieties can further enhance the catalyst performance. However, the nature of synergy between oxides and hydroxides remains elusive. In this study, we have designed a one-pot solution growth technique for the synthesis of flower-shaped N-doped-C-enveloped NiCo2O4/NixCo(1-x)(OH)y catalysts with varying oxide and hydroxide contents and investigated their water oxidation behavior. The correlation between performance-determining parameters involved in water oxidation, such as the onset potential and overpotential with oxide and/or hydroxide content, oxidation states (oxides), and elemental composition (Co/Ni content), and the possible ways to achieve their optimal values are discussed in detail. Our observations conclude that the onset potential and overpotential are minimal for the hybrid oxide-hydroxide bimetallic system compared with pristine hydroxide or oxide. The optimal hybrid catalyst shows excellent current density, low Tafel slope (82 mV/dec), and low onset potential (281 mV at 2 mA/cm2) and overpotential (348 mV at 10 mA/cm2), besides enduring operational stability in alkaline medium. The low Tafel slope suggests the preferable kinetics for water oxidation, and the poisoning study reveals the direct involvement of metal as active sites. The overall study unveils the synergy in the Co-Ni-based binary transition-metal oxide-hydroxide hybrid, which makes it a potential candidate for water oxidation catalysts, and hence, it is expected that the hybrid will find applications in energy conversion devices, such as electrolyzers.

Unique One-Step Strategy for Nonmetallic and Metallic Heteroatom Doped Carbonaceous Materials.

Nonmetallic and metallic heteroatom doped carbonaceous materials have garnered tremendous research attention due to a potential replacement to the precious Pt-group and (Ru, Ir)-oxide based catalysts and are essential part of the next-generation electrode catalysts for fuel cells, electrolyzers, and metal-air batteries. In this regard, we focus on three important categories of carbonaceous material, namely, metal-free heteroatom doped, transition metal heteroatom codoped, and carbon nitride (C3N4) based hybrid materials. Implications of various strategies, using one-step pyrolysis technique have been discussed for the effective design of heteroatom modified carbonaceous electrocatalysts. In this minireview, we outline the richness of one-step strategy for designing electrochemically active heteroatom doped carbon, transition metal-heteroatom codoped carbon, and C3N4 derived hybrid materials in the perspective of electrochemical energy conversion and storage devices. We also outline the future research direction in the development of highly efficient and sustainable electrocatalysts for oxygen electrochemistry. Finally, we wind up the article with the challenges and outlook on heteroatoms and transition metal-heteroatom codoped carbon material as an efficient and low-cost electrocatalysts, thereby promoting the development of this important area.

Pd-coated Ru nanocrystals supported on N-doped graphene as HER and ORR electrocatalysts.

Here, Pd-coated Ru nanocrystals supported on N-doped graphene (Pd-Ru@NG) are obtained via electroless deposition of Pd on Ru nanocrystals. We have demonstrated that Pd boosts the electrocatalytic performance of Pd-Ru@NG towards the hydrogen evolution reaction (HER) and alcohol tolerant oxygen reduction reaction (ORR) as compared to Pt/C.

In Situ Fabrication of a Nickel/Molybdenum Carbide-Anchored N-Doped Graphene/CNT Hybrid: An Efficient (Pre)catalyst for OER and HER.

Despite the recent promise of transition metal carbides as nonprecious catalysts for the hydrogen evolution reaction (HER), their extension to the oxygen evolution reaction (OER) to achieve the goal of overall water splitting remains a significant challenge. Herein, a new Ni/Mo xC (MoC, Mo2C) nanoparticle-supported N-doped graphene/carbon nanotube hybrid (NC) catalyst is developed via a facile, one-step integrated strategy, which can catalyze both the HER and OER in an efficient and robust manner. The catalyst affords low overpotentials of 162 and 328 mV to achieve a current density of 10 mA/cm2 for HER and OER, respectively, in alkaline medium, which either compares favorably or exceeds most of the Mo-based catalysts documented in the literature. It is believed that there is an electronic synergistic effect among Mo xC, Ni, and NC, wherein a tandem electron transfer process (Ni → Mo xC → NC) may be responsible for promoting the HER as well as OER activity. This work opens a new avenue toward the development of multicomponent, highly efficient but inexpensive electrocatalysts for overall water splitting.

Enhanced Solar Light Absorption and Photoelectrochemical Conversion Using TiN Nanoparticle-Incorporated C3N4-C Dot Sheets.

In this work, a promising strategy to increase the broadband solar light absorption was developed by synthesizing a composite of metal-free carbon nitride-carbon dots (C3N4-C dots) and plasmonic titanium nitride (TiN) nanoparticles (NPs) to improve the photoelectrochemical water-splitting performance under simulated solar radiation. Hot-electron injection from plasmonic TiN NPs to C3N4 played a role in photocatalysis, whereas C dots acted as catalysts for the decomposition of H2O2 to O2. The use of C dots also eliminated the need for a sacrificial reagent and prevented catalytic poisoning. By incorporating the TiN NPs and C dots, a sixfold improvement in the catalytic performance of C3N4 was observed. The proposed approach of combining TiN NPs and C dots with C3N4 proved effective in overcoming low optical absorption and charge recombination losses and also widens the spectral window, leading to improved photocatalytic activity.

Negative-charge-functionalized carbon nanodot: a low-cost smart cold emitter.

Cold emission properties of carbon nanodots (CNDs) evaluated using ANSYS Maxwell software are predicted to be size-dependent and then verified experimentally. In order to correlate the electron emission properties with the size of CNDs, the work function values were determined using ultraviolet photoelectron spectroscopy. This is the first report on theoretical calculations based on density functional theory and experimental results that confirm the work function dependency on the charge state of the functional group attached on the particle surface. The smallest CND (2.5 nm) has the highest percentage of negatively charged groups as well as the lowest work function (5.18 eV). The smallest dimension with the lowest work function assures that this sample is the best suited for field emission. It shows excellent field emission properties with a high current density of ∼1.45 mA cm-2 at 2 V µm-1 electric field, turn-on field as low as 0.04 V µm-1, very high field enhancement factor of 2.7 × 105 and high stability. Overall, the zero-dimensional CNDs showed superior field emission activity as compared to the higher dimensional carbon nanomaterials.

An efficient on-board metal-free nanocatalyst for controlled room temperature hydrogen production.

Positively charged functionalized carbon nanodots (CNDs) with a variety of different effective surface areas (ESAs) are synthesized via a cheap and time effective microwave method and applied for the generation of hydrogen via hydrolysis of sodium borohydride. To the best of our knowledge, this is the first report of metal-free controlled hydrogen generation. Our observation is that a positively charged functional group is essential for the hydrolysis for hydrogen production, but the overall activity is found to be enhanced with the ESA. A maximum value of 1066 ml g-1 min-1 as the turnover frequency is obtained which is moderate in comparison to other catalysts. However, the optimum activation energy is found to be 22.01 kJ mol-1 which is comparable to well-known high cost materials like Pt and Ru. All of the samples showed good reusability and 100% conversion even after the 10th cycle. The effect of H+ and OH- is also studied to control the on-board and on-demand hydrogen production ("on-off switching"). It is observed that H2 production decreases inversely with NaOH concentration and ceases completely when 10-1 M NaOH is added. With the addition of HCl, H2 production can be initiated again, which confirms the on/off control over production.

Designing Dual Emissions via Co-doping or Physical Mixing of Individually Doped ZnO and Their Implications in Optical Thermometry.

Here, we report on the novel design of dual emission via defect state engineering in codoped oxide microstructures and its implication in fluorescence intensity ratio (FIR) based optical temperature sensing. Eu- and Er-co-doped ZnO (EuEr:ZnO) microrods prepared by hydrothermal method. The emission peaks corresponding to Eu3+ and Er3+ are observed suggesting dual emission from codoped ZnO. Interestingly, Er3+ peak intensity decreases and that of Eu3+ increases with increase of temperature as is the case of individual doped cases and dual emission is also achieved via phyical mixing of the individual doped ZnO. The opposite trend is due to the electron transfer from the defect levels of host ZnO to Eu3+ and not to Er3+. Overall, our results pave the way in designing dual emission that can be exploited in FIR based temperature sensing. As an example, we probe temperature dependency of congo-red and polyvinyle alcohol (PVA) composite using EuEr:ZnO as optical probe for temperature sensing.

A noble and single source precursor for the synthesis of metal-rich sulphides embedded in an N-doped carbon framework for highly active OER electrocatalysts.

Here, we demonstrate a green and environment-friendly pyrolysis route for the synthesis of metal-rich sulphide embedded in an N-doped carbon (NC) framework in the absence of sulphide ions (S(2-)). The metal-chelate complex (tris(ethylenediamine) metal(ii) sulfate) serves as a new and single source precursor for the synthesis of earth abundant and non-precious hybrid structures such as metal-rich sulphides Co9S8@NC and Ni3S2@NC when M(II) = Co(2+) and Ni(2+) and counter sulphate (SO4(2-)) ions are the source of S. Both the hybrids show superior OER activity as compared to commercial RuO2.