Polyaniline/Carbon Dots Composite as a Highly Efficient Metal-Free Dual-Functional Photoassisted Electrocatalyst for Overall Water Splitting

Engineering cobalt nickel oxide nanowires embedded in tungsten disulfide/reduced graphene oxide hybrid composites for supercapacitor applications and overall water-splitting reactions

This paper presents the fabrication of hierarchical hollow 3D nanowires-like cobalt nickel oxide nanowires (NWs) embedded in tungsten disulfide/reduced graphene oxide hybrid (CoNiO2@WS2/rGO) composite through a facile hydrothermal process.The interaction between the 3D hollow WS2/rGO skeleton network and the well-defined CoNiO2 NWs enabled the remarkable electrochemical supercapacitor performances constructed with an enriched specific capacity (515C/g at 0.5 A/g) and superior cycling solidity (97.5 %). Asymmetric device assembled engaging the CoNiO2@WS2/rGO composite displayed a 236F/g specific capacitance at 1 A/g with ∼74 Wh/kg energy density at 2.4 kW/kg power density along with a high cycling stability (95.2 %). Furthermore, CoNiO2@WS2/rGO composite possessed bundles of pores with strong interfacial connection, and this enabled a large accessible surface area on the nanowires and facilitated the release of gas bubbles, resulting in excellent oxygen evolution and hydrogen evolution kinetics with a small overpotential (η10=195 and 33 mV, respectively). Assembled CoNiO2@WS2/rGO (+/-) electrolyzer achieved a current density of 10 mAcm-2 at a minimal cell voltageof 1.43 with long-span strength. Additionally, theoretical computation studies confirmed that the exceptional catalytic efficacy of the fabricated catalyst could be attributed to the transfer of charge from WS2/rGO to CONiO2 NWs.

Synthesis and Characterization of Polyaniline/Carbon Nanodots: Electrochemical Sensing of Alcohols for Freshness Monitoring for Application as Packaging Materials

The increasing demand for innovative, sustainable, and functional food packaging solutions has led to the exploration of polyaniline (PANI) and carbon nanodots (CNDs) as promising materials for smart packaging. This study investigates the potential of PANI/CND composites for electrochemical sensing of alcohols, a key indicator of spoilage in food products. By leveraging the unique properties of PANI, a conducting polymer, and the fluorescence and electrochemical activity of CNDs, we propose a dual-function smart packaging material capable of real-time monitoring of alcohol levels, which are often released during the fermentation or degradation of food. The integration of PANI with CNDs enhances the material's sensitivity and stability, offering a cost-effective, environmentally friendly, and responsive solution for freshness and spoilage detection. The electrochemical sensing mechanism allows for rapid, non-destructive testing, providing consumers and food producers with an efficient tool to assess product quality and safety. This work paves the way for the development of intelligent packaging systems that can not only detect spoilage but also actively contribute to food preservation, reducing waste and improving food safety.

p-n-Type LaCoO3/NiFe LDH Heterostructures for Enhanced Photogenerated Carrier-Assisted Electrocatalytic Oxygen Evolution Reaction

The oxygen evolution reaction (OER) poses a significant kinetic challenge for various critical energy conversion and storage technologies including electrocatalytic water splitting and metal-air batteries. In this study, a LaCoO3/NiFe layered double hydroxide (LDH) catalyst was synthesized through the in situ growth of n-type NiFe LDH on the surface of the p-type LaCoO3 semiconductor, resulting in a p-n heterostructure for a photogenerated carrier-assisted electrocatalytic OER (PCA-eOER). The alignment of their band structures facilitates the formation of an internal electric field at the heterojunction interface, which promotes the creation of oxygen vacancies and enhances electron transport. Under illumination, the expanded visible-light absorption range and built-in electric field work synergistically to improve the generation and separation of photogenerated carriers. Meanwhile, the accumulation of photogenerated holes on the surface of NiFe LDH results in an enhancement in the concentration of high-valent active metal sites, resulting in a boost in the PCA-eOER efficiency. The LaCoO3/NiFe LDH has achieved an overpotential of 260 mV at the current density of 10 mA cm-2, 50 mV lower than in the absence of illumination. In addition, LaCoO3/NiFe LDH was assembled into an alkaline water electrolyzer and zinc-air batteries (ZABs), showing excellent practical application capability. We explored the application of LaCoO3 in a PCA-eOER, which provides a concept for designing PCA-eOER catalysts and advancing the development of perovskite-based catalysts for clean energy conversion technology.

Water self-purification via electron donation effect of emerging contaminants arousing oxygen activation over ordered carbon-enhanced CoFe quantum dots

The release of emerging contaminants (ECs) into aquatic environments poses a significant risk to global water security. Advanced oxidation processes (AOPs), while effective in removing ECs, are often resource and energy-intensive. Here, we introduce a novel catalyst, CoFe quantum dots embedded in graphene nanowires (CoFeQds@GN-Nws), synthesized through anaerobic polymerization. It uniquely features electron-rich and electron-poor micro-regions on its surface, enabling a self-purification mechanism in wastewater. This is achieved by harnessing the internal energy of wastewater, particularly the bonding energy of pollutants and dissolved oxygen (DO). It demonstrates exceptional efficiency in removing ECs at ambient temperature and pressure without the need for external oxidants, achieving a removal rate of nearly 100.0%. The catalyst's structure-activity relationship reveals that CoFe quantum dots facilitate an unbalanced electron distribution, forming these micro-regions. This leads to a continuous electron-donation effect, where pollutants are effectively cleaved or oxidized. Concurrently, DO is activated into superoxide anions (O2•-), synergistically aiding in pollutant removal. This approach reduces resource and energy demands typically associated with AOPs, marking a sustainable advancement in wastewater treatment technologies.

Carbon Dots as an Electron Acceptor in the ZnIn2S4@MIL-88A Heterojunction for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

In this study, visible-light-responsive carbon dots (CDs)/ZnIn2S4@MIL-88A (C/ZI@ML) photocatalysts were successfully prepared through in situ loading CDs and ZnIn2S4 nanosheets on MIL-88A(Fe) to form a ternary heterojunction. The detailed characterization indicated that the two-dimensional ZnIn2S4 nanosheets were uniformly coated on the surface of MIL-88A(Fe), and ZnIn2S4/MIL-88A(Fe) exhibited enhanced photocatalytic hydrogen production performance (1259.63 μmol h-1 g-1) compared to that of pristine MIL-88A(Fe) and ZnIn2S4 under visible light illumination. After introduction of CDs into ZnIn2S4/MIL-88A(Fe), the C/ZI@ML catalyst remarkably enhanced the photocatalytic activity and the hydrogen evolution rate of 1C/ZI@ML was up to 3609.23 μmol g-1 h-1. The photoinduced charge carriers of C/ZI@ML can be efficiently separated and migrated because of the close contacted interface, synergistic effect, and suitable band structure. In combination with photoelectrochemical experiments and electron paramagnetic resonance spectra, a possible photocatalytic mechanism over C/ZI@ML was proposed. This work demonstrated a facile preparation method for fabricating efficient visible-light-driven heterojunction photocatalysts.

Photoelectrochemical Engineering for Light-Assisted Rechargeable Metal Batteries: Mechanism, Development, and Future

Rechargeable battery devices with high energy density are highly demanded by  our  modern society. The use of metal anodes is extremely attractive for future rechargeable battery devices. However, the notorious metal dendritic and instability of solid electrolyte interface issues pose a series of challenges for metal anodes. Recently, considering the indigestible dynamical behavior of metal anodes, photoelectrochemical engineering of light-assisted metal anodes have been rapidly developed since they efficiently utilize the integration and synergy of oriented crystal engineering and photocatalysis engineering, which provided a potential way to unlock the interface electrochemical mechanism and deposition reaction kinetics of metal anodes. This review starts with the fundamentals of photoelectrochemical engineering and follows with the state-of-art advance of photoelectrochemical engineering for light-assisted rechargeable metal batteries where photoelectrode materials, working principles, types, and practical applications are explained. The last section summarizes the major challenges and some invigorating perspectives for future research on light-assisted rechargeable metal batteries.

Diversity and Tailorability of Photoelectrochemical Properties of Carbon Dots

As a new kind of carbon based functional material, carbon dots (CDs) have sparked much interest in recent years. The tunable structure, composition, and morphology of CDs unlocks opportunities to enable diversity in their photoelectrochemical properties, and thus they show great potential in various applications such as biology, catalysis, sensors, and energy storage. Nevertheless, the related understanding of CDs is insufficient at present due to their inherent complexity of microstructure, which involves the intersection of high polymer, bulk carbon, and quantum dot (QD). A good understanding of the underlying mechanism behind the properties of CDs is still a formidable challenge, requiring the integration of robust knowledge from organic chemistry, materials science, and solid state physics. Within this context, discovering more appealing properties, elucidating fundamental factors that affect the properties and proposing effective engineering strategies that can realize specific functions for CDs are now highly pursued by researchers.At the beginning of this Account, the main features of CDs are introduced, where not only the basic structural, compositional and morphological characteristics but also the rich photoelectrochemical properties are elucidated, among which the band gap, chirality, photoinduced potential, and electron sink effect are particularly emphasized. Furthermore, new analysis techniques including transient photoinduced current (TPC), transient photoinduced voltage (TPV), and machine learning (ML) to reveal the unique properties of CDs are described. Then, several appealing strategies that aim to rationally tailor CDs for oriented applications are highlighted. These regulation strategies are morphology modulation (e.g., developing CDs with new geometrical configuration, controlling the particle size), phase engineering (e.g., altering the phase crystallinity, introducing the foreign atoms), surface functionalization (e.g., grafting various types of functional groups), and interfacial tuning (e.g., building CD-based nanohybrids with well-defined interfaces). Although the fundamental investigation of CDs is relatively undeveloped because of their complexity, this does not hinder their wide application. At the same time, exploring the extensive applications of CDs will promote their in-depth understanding. Finally, the chances for building a CD-centered blueprint for sustainable society are explored and challenges for future research in the field of CDs are proposed as follows: (i) the controllable synthesis of CDs with uniform size; (ii) search for novel CDs with unique structure, morphology, or composition; (iii) quantitative understanding of the property of CDs; (iv) performance enhancement by external forces such as magnetism or heat injection; (v) construction of the dual carbon concept; (vi) further research on different photocatalytic applications. On the whole, this Account may provide meaningful references for the understanding of the microstructure-property correlation as well as the regulation of CDs, thereby promoting their transition from fundamental research to practical application.

Materials Research Directions Toward a Green Hydrogen Economy: A Review

A constellation of technologies has been researched with an eye toward enabling a hydrogen economy. Within the research fields of hydrogen production, storage, and utilization in fuel cells, various classes of materials have been developed that target higher efficiencies and utility. This Review examines recent progress in these research fields from the years 2011-2021, exploring the most commonly occurring concepts and the materials directions important to each field. Particular attention has been given to catalyst materials that enable the green production of hydrogen from water, chemical and physical storage systems, and materials used in technical capacities within fuel cells. The quantification of publication and materials trends provides a picture of the current state of development within each node of the hydrogen economy.

Engineering the electronic structure of Ni3FeS with polyaniline for enhanced electrocatalytic performance of overall water splitting

Developing highly efficient and stable electrocatalysts for oxygen evolution reaction is of significant importance for applications in energy conversion and storage. Modulation of electronic structure of catalysts is critical for improving the performance of the resulting electrodes. Here, we report a facile way to engineer the electronic structure of Ni₃FeS by coating a thin polyaniline (PANI) layer for improving electrocatalytic activity for overall water splitting. Experimental investigations unveil that the strong electronic interactions between the lone electron pairs of nitrogen in PANI and d orbitals of iron, nickel in Ni₃FeS result in an electron-rich structure of Ni and Fe, and consequently optimize the adsorption and desorption processes to promote the OER activity. Remarkably, the resulting PANI/Ni₃FeS electrode exhibited much enhanced OER performance with a low overpotential of 143 mV at a current density of 10 mA·cm^-2and good stability. Promisingly, coupled with the reported MoNi₄/MoO₂electrode, the two-electrode electrolyzer achieved a current density of 10 mA·cm^-2with a relatively low potential of 1.55 V, and can generate oxygen and hydrogen bubbles steadily driven by a commercial dry battery, endowed the composite electrocatalyst with high potential for practical applications.

Integrated Bifunctional Electrodes Based on Amorphous Co-Ni-S Nanoflake Arrays with Atomic Dispersity of Active Sites for Overall Water Splitting

Fabrication of amorphous electrocatalysts without noble metals for cost-effective full water splitting is highly desired but remains a substantial challenge. In the present work, we report a facile strategy for exploring integrated bifunctional electrocatalysts based on amorphous cobalt/nickel sulfide nanoflake arrays self-supported on carbon cloth, by tailoring competitive coordination of metal ions between glucose and 2-aminoterephthalic acid. Ultrahigh dispersion of binary metal active sites with balanced atomic distribution enables the optimization of catalytic properties for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in an alkaline solution. The obtained catalyst exhibits remarkably enhanced OER and HER activities as compared with its oxide counterpart and analogues with different Co/Ni ratios. It requires overpotentials of 296 and 192 mV to deliver a current density of 10 mA cm^-2 for the OER and HER, respectively; it retains 96.6 and 96.9% activity after 32 h of OER and 36 h of HER tests at 10 mA cm^-2, respectively. As directly used an anode and a cathode in an alkaline electrolyzer, a low cell voltage of 1.60 V could endow a water splitting current of 10 mA cm^-2, outperforming the benchmark RuO₂ and Pt/C-based electrolyzer at 1.72 V@10 mA cm^-2. The current synthetic strategy may provide more opportunities for the design and direct synthesis of amorphous catalysts for overall water splitting and beyond.

Organic Semiconductor/Carbon Dot Composites for Highly Efficient Hydrogen and Hydrogen Peroxide Coproduction from Water Photosplitting

Coproduction of hydrogen (H₂) and hydrogen peroxide (H₂O₂) from water splitting is one of the most promising ways to alleviate the energy crisis and environmental pollution. Here, we first show the synthesis and photocatalytic property of an organic semiconductor (DAnTMS compound) from 9,10-dibromoanthracene and trimethylsilylacetylene. Then, a metal-free photocatalyst of a DAnTMS/carbon dot (DAnTMS/CD) composite was designed and fabricated, which achieved the efficient photocatalytic production of H₂ and H₂O₂ without usage of any organic solvents and sacrificial agents. Under visible light, the DAnTMS/CD composite could produce H₂O₂ with a maximum rate of 396.7 μmol g^-1 h^-1 and H₂ with a maximum rate of 265.0 μmol g^-1 h^-1 in pure water. Transient photovoltage tests showed that CDs changed the interfacial electron transfer kinetics and served as the active site for highly efficient H₂ evolution. This work provided a deep insight into the function of CDs in regulating the catalytic property of organic photocatalysts.

Binder-free Fe-doped NiCo2O4/Ni3S4 hollow heterostructure nanotubes for highly efficient overall water splitting

For overall water splitting, a vital challenge is to design active sites at interfaces. Heterogeneous catalysts with enhanced mass/charge transfer and accelerated adsorption of intermediates have exhibited significantly enhanced activities. Herein, a Fe-doped NiCo₂O₄/Ni₃S₄ heterogeneous electrocatalyst is synthesized for the HER and OER. On account of the synergistic effect of heterostructures, Ni-O-S presents a low overpotential of 29.1 mV (10 mA cm^-2), a relatively small Tafel slope of 53.3 mV dec^-1 for the HER, and 259 mV at a current density of 100 mA cm^-2 (33.1 mV dec^-1) for the OER. What is more, Ni-O-S acts as a binder-free bi-functional electrode in an alkaline electrolyte for overall water splitting, exhibiting a cell voltage of 1.45 V (10 mA cm^-2) with good stability. This work offers an efficient approach for designing stable and high-efficiency heterogeneous electrodes for overall water splitting.

Highly efficient photocatalytic overall water splitting on plasmonic Cu6Sn5/polyaniline nanocomposites

A plasmonic Cu₆Sn₅/polyaniline (Cu₆Sn₅/PANI) nanocomposite was synthesized by chemical reduction and hydrothermal methods. The best photocatalytic overall water splitting performance was achieved by the Cu₆Sn₅/PANI_3wt% composite, which contains 3 wt% PANI, which is approximately three times more than that of pure Cu₆Sn₅. Meanwhile, Cu₆Sn₅/PANI_3wt% exhibited excellent photocatalytic stability for water splitting during the stability investigation. The dramatic promotion of the photocatalytic activity performance can be ascribed to the cocatalyst PANI. The existence of PANI can remarkably promote the separation and transfer efficiency of the photoinduced electron-hole pairs, and therefore enhance the photocatalytic activity. Our results also verify that the photogenerated charge comes from plasmonic Cu₆Sn₅ with the surface plasmon resonance (SPR) effect, which is different from traditional semiconductor-based photocatalysts. This work sheds some light on plasmonic photocatalyst development and provides an alternative pathway for photocatalytic reactions.

Ag-In-Zn-S Quantum Dot-Dominated Interface Kinetics in Ag-In-Zn-S/NiFe LDH Composites toward Efficient Photoassisted Electrocatalytic Water Splitting

Photoassisted electrocatalysis (P-EC) emerges as a rising star for hydrogen production by embedding photoactive species in electrocatalysts, for which the interfacial structure design and charge transfer kinetics of the multifunctional catalysts remain a great challenge. Herein, Zn-AgIn₅S₈ quantum dots (ZAIS QDs) were embedded into 2D NiFe layered double hydroxide nanosheets through a simple hydrothermal treatment to form 0D/2D composite catalysts for P-EC. With evidence from transient photovoltage spectroscopy, we acquired a clear and fundamental understanding on the kinetics of charge extraction time and extraction amount in the 0D/2D heterojunctions that was proved to play a key role in P-EC. Upon light illumination, for HER, the optimized NiFe-ZAIS exhibits obviously reduced overpotentials of 129 and 242 mV at current densities of 10 and 50 mA cm^-2, which are 22 and 33 mV lower than those of dark electrocatalysis, respectively. For OER, the NiFe-ZAIS electrode also shows low overpotentials of 220 and 268 mV at current densities of 10 and 50 mA cm^-2, respectively, under light illumination, which were able to almost double the intrinsic activity. Finally, with NF@NiFe-ZAIS as both the cathode and the anode, the assembled electrolyzer only requires 1.62 V to reach the overall water splitting current density of 10 mA cm^-2 under P-EC. This work provides a useful example for the profound understanding of the design and the kinetics study of multifunctional P-EC catalysts.