Morphology and phase transformation of α-MnO2/MnOOH modulated by N-CDs for efficient electrocatalytic oxygen evolution reaction in alkaline medium

Ensuring food safety by artificial intelligence-enhanced nanosensor arrays

Current analytical methods utilized for food safety inspection requires improvement in terms of their cost-efficiency, speed of detection, and ease of use. Sensor array technology has emerged as a food safety assessment method that applies multiple cross-reactive sensors to identify specific targets via pattern recognition. When the sensor arrays are fabricated with nanomaterials, the binding affinity of analytes to the sensors and the response of sensor arrays can be remarkably enhanced, thereby making the detection process more rapid, sensitive, and accurate. Data analysis is vital in converting the signals from sensor arrays into meaningful information regarding the analytes. As the sensor arrays can generate complex, high-dimensional data in response to analytes, they require the use of machine learning algorithms to reduce the dimensionality of the data to gain more reliable outcomes. Moreover, the advances in handheld smart devices have made it easier to read and analyze the sensor array signals, with the advantages of convenience, portability, and efficiency. While facing some challenges, the integration of artificial intelligence with nanosensor arrays holds promise for enhancing food safety monitoring.

Detection of SARS-CoV-2 S protein based on FRET between carbon quantum dots and gold nanoparticles

The COVID-19 pandemic caused by SARS-CoV-2 virus brings nasty crisis for public health in the world. Until now, the virus has caused multiple infections in many people. Detecting antigen to SARS-CoV-2 is a powerful method for the diagnosis of COVID-19 and is helpful for controlling and stopping the pandemic. Herein, a rapid and quantitative detection method of SARS-CoV-2 spike(S) protein was built based on the fluorescence resonance energy transfer (FRET) phenomenon without complicated steps. In the process of detecting, the carbon quantum dots (CQDs) and gold nanoparticles (AuNPs) act as donor and acceptor. By modifying the SARS-CoV-2 antibodies on the surface of CQDs and AuNPs, we achieved S protein specific detection using the distance-based FRET phenomenon. Through the electric charge regulation, the limit of detection (LOD) is 0.05 ng/mL, the linear range is 0.1-100 ng/mL, and the detection process only takes 12 min. The proposed method exhibits several advantages such as be available for variants (B.1.1.529 and B.1.617.2) and be suitable for human serum, which is of significance for detecting viral in time and prevention the viral transmission.

Controllable Anchoring of Graphitic Carbon Nitride on MnO2 Nanoarchitectures for Oxygen Evolution Electrocatalysis

The design and fabrication of eco-friendly and cost-effective (photo)electrocatalysts for the oxygen evolution reaction (OER) is a key research goal for a proper management of water splitting to address the global energy crisis. In this work, we focus on the preparation of supported MnO2/graphitic carbon nitride (g-CN) OER (photo)electrocatalysts by means of a novel preparation strategy. The proposed route consists of the plasma enhanced-chemical vapor deposition (PE-CVD) of MnO2 nanoarchitectures on porous Ni scaffolds, the anchoring of controllable g-CN amounts by an amenable electrophoretic deposition (EPD) process, and the ultimate thermal treatment in air. The inherent method versatility and flexibility afforded defective MnO2/g-CN nanoarchitectures, featuring a g-CN content and nano-organization tunable as a function of EPD duration and the used carbon nitride precursor. Such a modulation had a direct influence on OER functional performances, which, for the best composite system, corresponded to an overpotential of 430 mV at 10 mA/cm2, a Tafel slope of ≈70 mV/dec, and a turnover frequency of 6.52 × 10-3 s-1, accompanied by a very good time stability. The present outcomes, comparing favorably with previous results on analogous systems, were rationalized on the basis of the formation of type-II MnO2/g-CN heterojunctions, and yield valuable insights into this class of green (photo)electrocatalysts for end uses in solar-to-fuel conversion and water treatment.

Homogeneous regulation of arranged polymorphic manganese dioxide nanocrystals as cathode materials for high-performance zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have emerged as attractive energy storage devices by virtue of their low cost, high safety and eco-friendliness. However, zinc-ion cathodes are bottlenecked by their vulnerable crystal structures in the process of zinc embedding and significant capacity fading during long-term cycling. Herein, we report the rational and homogeneous regulation of polycrystalline manganese dioxide (MnO₂) nanocrystals as zinc cathodes via a surfactant template-assisted strategy. Benefiting from the homogeneous regulation, MnO₂ nanocrystals with an ordered crystal arrangement, including nanorod-like polyvinylpyrrolidone-manganese dioxide (PVP-MnO₂), nanowire-like sodium dodecyl benzene sulfonate-manganese dioxide and nanodot-like cetyltrimethylammonium bromide-manganese dioxide, are obtained. Among these, the nanorod-like PVP-MnO₂ nanocrystals exhibit stable long-life cycling of 210 mAh g^-1 over 180 cycles at a high rate of 0.3 A g^-1 and with a high capacity retention of 84% over 850 cycles at a high rate of 1 A g^-1. The good performance of this cathode significantly results from the facile charge and mass transfer at the interface between the electrode and electrolyte, featuring the crystal stability and uniform morphology of the arranged MnO₂ nanocrystals. This work provides crucial insights into the development of advanced MnO₂ cathodes for low-cost and high-performance rechargeable aqueous zinc-ion batteries.

Mo doping and Se vacancy engineering for boosting electrocatalytic water oxidation by regulating the electronic structure of self-supported Co9Se8@NiSe

Oxygen evolution reactions (OERs) are regarded as the rate-determining step of electrocatalytic overall water splitting, which endow OER electrocatalysts with the advantages of high activity, low cost, good conductivity, and excellent stability. Herein, a facile H₂O₂-assisted etching method is proposed for the fabrication of Mo-doped ultrathin Co₉Se₈@NiSe/NF-X heterojunctions with rich Se vacancies to boost electrocatalytic water oxidation. After step-by-step electronic structure modulation by Mo doping and Se vacancy engineering, the self-standing Mo-Co₉Se₈@NiSe/NF-60 heterojunctions deliver a current density of 50 mA cm^-2 with an overpotential of 343 mV and a cell voltage of only 1.87 V at 50 mA cm^-2 for overall water splitting in 1.0 M KOH. Our study opens up the possibility of realizing step-by-step electronic structure modulation of nonprecious OER electrocatalysts via heteroatom doping and vacancy engineering.

Enhanced the synergistic degradation effect between active hydroxyl and reactive oxygen species for indoor formaldehyde based on platinum atoms modified MnOOH/MnO2 catalyst

Maintaining high activity during prolonged catalysis is always the pursuit in catalytic degradation of organic pollutants. For indoor formaldehyde (HCHO) degradation, the accumulation of intermediates is the major factor limiting the conversion of HCHO to final product CO₂ (HCHO-to-CO₂ conversion) and long-lasting catalysis. Herein, a three-dimensional radialized nanostructure catalyst self-assembled by MnOOH/MnO₂ nanosheets anchored with Pt single atoms (Pt_SA-MnOOH/MnO₂ with a trace platinum loading amount of 0.09%) is developed by thermally assisted two-step electrochemical method, which achieves enhanced CO₂ production in catalytic HCHO degradation at the room temperature by the collaborative action of active hydroxyl (OH*) and active oxygen species (O₂*). By boosting intermediates' decomposing, the catalyst implements real-time HCHO-to-CO₂ conversion (∼85.7%) and long-term continuous HCHO removal (∼98%) during 100 h in a 15 ppm HCHO atmosphere at 25 °C under a weight hourly space velocity of 30000 mL/g_cat∙h. Density functional theory calculation shows that the formation energy of O₂* from O₂ over Pt_SA-MnOOH/MnO₂ is nearly half lower than that over Pt-MnO₂ catalyst. And decomposing accumulated intermediates gives the credit to OH* species sustainably generated by the combined action of MnOOH and O₂*. The synergistic action between Pt_SA and MnOOH contributes to the continuous production of O₂* and OH* for enhancing CO₂ production in indoor catalytic formaldehyde degradation.

Recent advances in fuel cell reaction electrocatalysis based on porous noble metal nanocatalysts

As the center of fuel cells, electrocatalysts play a crucial role in determining the conversion efficiency from chemical energy to electrical energy. Therefore, the development of advanced electrocatalysts with both high activity and stability is significant but challenging. Active site, mass transport, and charge transfer are three central factors influencing the catalytic performance of electrocatalysts. Endowed with rich available surface active sites, facilitated electron transfer and mass diffusion channels, and highly active components, porous noble metal nanomaterials are widely considered as promising electrocatalysts toward fuel cell-related reactions. The past decade has witnessed great achievements in the design and fabrication of advanced porous noble metal nanocatalysts in the field of electrocatalytic fuel oxidation reaction (FOR) and oxygen reduction reaction (ORR). Herein, the recent research advances regarding porous noble metal nanocatalysts for fuel cell-related reactions are reviewed. In the discussions, the inherent structural features of porous noble metal nanostructures for electrocatalytic reactions, advanced synthetic strategies for the fabrication of porous noble metal nanostructures, and the structure-performance relationships are also provided.

Boosting oxygen evolution of layered double hydroxide through electronic coupling with ultralow noble metal doping

Electrocatalytic water oxidation is a rate-determining step in the water splitting process; however, its efficiency is significantly hampered by the limitations of cost-effective electrocatalysts. Here, an advanced Co(OH)₂ electrocatalyst with ultralow iridium (Ir) doping is developed to enable outstanding oxygen evolution reaction (OER) properties; that is, in a 1 M KOH medium, an overpotential of only 262 mV is required to achieve a current density of 10 mA cm^-2, and a small Tafel slope of 66.9 mV dec^-1 is achieved, which is markedly superior to that of the commercial IrO₂ catalyst (301 mV@10 mA cm^-2; 66.9 mV dec^-1). Through the combination of experimental data and a mechanism study, it is disclosed that the high intrinsic OER activity results from the synergistic electron coupling of oxidized Ir and Co(OH)₂, which significantly moderate the adsorption energy of the intermediates. Moreover, we have also synthesized Ru-Co(OH)₂ nanosheets and demonstrated the universal syntheses of Ir-doped CoM (M = Ni, Fe, Mn, and Zn) layered double hydroxides (LDHs).

Recent Advances in Seawater Electrolysis

Hydrogen energy, as a clean and renewable energy, has attracted much attention in recent years. Water electrolysis via the hydrogen evolution reaction at the cathode coupled with the oxygen evolution reaction at the anode is a promising method to produce hydrogen. Given the shortage of freshwater resources on the planet, the direct use of seawater as an electrolyte for hydrogen production has become a hot research topic. Direct use of seawater as the electrolyte for water electrolysis can reduce the cost of hydrogen production due to the great abundance and wide availability. In recent years, various high-efficiency electrocatalysts have made great progress in seawater splitting and have shown great potential. This review introduces the mechanisms and challenges of seawater splitting and summarizes the recent progress of various electrocatalysts used for hydrogen and oxygen evolution reaction in seawater electrolysis in recent years. Finally, the challenges and future opportunities of seawater electrolysis for hydrogen and oxygen production are presented.

CO2-assisted synthesis of crystalline/amorphous NiFe-MOF heterostructure for high-efficiency electrocatalytic water oxidation

Modulating the crystalline phase and structure of metal organic frameworks (MOFs) for superior electrocatalytic oxygen evolution reaction (OER) performance is a significant but challenging topic. Herein, a facile CO2-assisted strategy...

Enhancement of the OER Kinetics of the Less-Explored α-MnO2 via Nickel Doping Approaches in Alkaline Medium

Development of a low-cost transition metal-based catalyst for water splitting is of prime importance for generating green hydrogen on an industrial scale. Recently, various transition metal-based oxides, hydroxides, sulfides, and other chalcogenide-based materials have been synthesized for developing a suitable anode material for the oxygen evolution reaction (OER). Among the various transition metal-based catalysts, their oxides have received much consideration for OER, especially in lower pH condition, and MnO₂ is one of the oxides that have widely been used for the same. The large variation in the structural disorder of MnO₂ and internal resistance at the electrode-electrolyte interfaces have limited its large-scale application. By considering the above limitations of MnO₂, here in this work, we have designed Ni-doped MnO₂ via a simple wet-chemical synthetic route, which has been successfully applied for OER application in 0.1 M KOH solution. Doping of various quantities of Ni into the MnO₂ lattices improved the OER properties, and for achieving 10 mA/cm² current density, the Ni-doped MnO₂ containing 0.02 M of Ni²⁺ ions (coined as MnO₂-Ni_0.002(M)) demands only 445 mV overpotential, whereas the bare MnO₂ required 610 mV overpotential. It has been proposed that the incorporation of nickel ions into the MnO₂ lattices leads to an electron transfer from the Ni³⁺ ions to Mn⁴⁺, which in turn facilitates the Jahn-Teller distortion in the Mn-O octahedral unit. This electron transfer and the creation of a structural disorder in the Mn sites result in the improvization of the OER properties of the MnO₂ materials.

Electromagnetic Interference Shielding Effectiveness of Room Temperature Fabricated Manganese Dioxide/Carbon Dots Nanocomposites

The present work is focused on the fabrication of manganese dioxide/carbon dots (MnO₂/CDs) nanocomposites at room temperature in situ co-participation method in an aqueous medium and characterized. Our study showed that the concentration of CDs controls the morphology of MnO₂/CDs nanocomposite and also acted as a reducing agent to convert potassium permanganate (KMnO₄) to MnO₂. Subsequently, nanoflowers, quasi-spherical particles, broken, and interconnected chain type of morphology was observed by adding dispersion of 0.5, 1.0, 1.5, and 2.0 ml CDs in acetone to 1 mmol KMnO₄ aqueous solution in the corresponding MnO₂/CDs-0.5, MnO₂/CDs-1.0, MnO₂/CDs-1.5, and MnO₂/CDs-2.0 composites, respectively. A plausible mechanism on the transformation of morphology of MnO₂/CDs with CDs concentration is also provided. Further, the present work also focused for the first time on the application in the electromagnetic interference (EMI) shielding of MnO₂/CD nanocomposites due to the high dielectric and conductivity. Interestingly, MnO₂/CDs-2.0 (nanochains) exhibited the highest total EMI shielding efficiency (SE_T) of ~39.4 dB following reflection as dominant shielding mechanism due to the high aspect ratio, highest conductivity, high dielectric loss, and impendence mismatch.

Novel dual-template molecular imprinted electrochemical sensor for simultaneous detection of CA and TPH based on peanut twin-like NiFe2O4/CoFe2O4/NCDs nanospheres: Fabrication, application and DFT theoretical study

Hollow peanut-shaped NiFe₂O₄/CoFe₂O₄ twinned nano-spherical shell composite materials have interconnected electron channels and excellent electrochemical performance, which prompted the use of this unique spatial structure to fabricate efficient electrochemical sensors. In this work, N-doped carbon dots (NCDs) incorporated into magnetic NiFe₂O₄/CoFe₂O₄ nanoparticle shell (NiFe₂O₄/CoFe₂O₄/NCDs) modified glassy carbon electrode (GCE) was applied to construct a dual-template molecularly imprinted polymer (MIP) based electrochemistry sensor (NiFe₂O₄/CoFe₂O₄/NCDs/MIP/GCE) for the simultaneous detection of catechin (CA) and theophylline (TPH). MIP was fabricated by an in-situ electrochemical polymerization strategy based on the theoretical exploration and density functional theory (DFT) computer directional simulation to screen out the optimal functional monomer (L-arginine) and the optimal ratio between the dual template molecules (CA and TPH) and functional monomer. The materials were characterized by SEM, TEM, XRD, XPS, and TGA. Besides, electron binding energy, binding constant, and imprinting factor were investigated. With the optimal conditions, the proposed electrochemical dual detection system showed outstanding analytical performance for the simultaneous sensing of CA and TPH, with an ultralow detection limit (LOD, S/N = 3) of 1.3 nM for CA in 0.01-1 μM (R² = 0.9956) and 1-50 μM (R² = 0.9928), as well as a LOD of 20.0 nM for TPH in the linear range of 0.1-100 μM (R² = 0.9939), respectively. Also, the selectivity and anti-interference performances of the fabricated sensor were performed by differential pulse voltammetry and chronoamperometry, and successfully detected the analyte from tea drinks and human urine samples with the recovery rates ranging from 98.22% to 104.76% and relative standard deviations (RSD) were 1.19%-3.81%, demonstrated the sensor has excellent stability, repeatability, and reproducibility, which paves the way for other platforms to use this nanomaterial for the detection of antioxidant in the filed food safety.

PtM/Mx By (M=Ni, Co, Fe) Heterostructured Nanobundles as Advanced Electrocatalyst for Hydrogen Evolution Reaction

Optimizing the electronic and synergistic effect of hybrid electrocatalysts based on Pt and Pt-based nanocatalysts is of tremendous importance towards a superior hydrogen evolution performance under both acidic and alkaline conditions. However, developing an ideal Pt-based hydrogen evolution reaction (HER) electrocatalyst with moderated electronic structure as well as strong synergistic effect is still a challenge. Herein, we fabricated boron (B)-doped PtNi nanobundles by a two-step method using NaBH₄ as the boron source to obtain PtNi/Ni₄ B₃ heterostructures with well-defined nanointerfaces between PtNi and Ni₄ B₃ , achieving an enhanced catalytic HER performance. Especially, the PtNi/Ni₄ B₃ nanobundles (PtNi/Ni₄ B₃ NBs) can deliver a current density of 10 mA cm^-2 at the overpotential of 14.6 and 26.5 mV under alkaline and acidic media, respectively, as well as outstanding electrochemical stability over 40 h at the current density of 10 mA cm^-2 . Remarkably, this approach is also universal for the syntheses of PtCo/Co₃ B and PtFe/Fe₄₉ B with outstanding electrocatalytic HER performance.

Recent progress in water-splitting electrocatalysis mediated by 2D noble metal materials

Two-dimensional (2D) nanostructures have enabled noble-metal-based nanomaterials to be promising electrocatalysts toward overall water splitting due to their inherent structural advantages, including a high specific surface active area, numerous low-coordinated atoms, and a high density of defects and edges. Moreover, it is also disclosed that the electronic effect and strain effect within 2D nanostructures also benefit the further promotion of the electrocatalytic performance. In this review, we have focused on the recent progress in the fabrication of advanced electrocatalysts based on 2D noble-metal-based nanomaterials toward water splitting electrocatalysis. First, fundamental descriptions about water-splitting mechanisms, some promising engineering strategies, and major challenges in electrochemical water splitting are given. Then, the structural merits of 2D nanostructures for water splitting electrocatalysis are also highlighted, including abundant surface active sites, lattice distortion, abundant surface defects, electronic effects, and strain effects. Additionally, some representative water-splitting electrocatalysts have been discussed in detail to highlight the superiorities of 2D noble-metal-based nanomaterials for electrochemical water splitting. Finally, the underlying challenges and future opportunities for the fabrication of more advanced electrocatalysts for water splitting are also highlighted. We hope that this review article provides guidance for the fabrication of more efficient electrocatalysts for boosting industrial hydrogen production via water splitting.

Nonmetal-doping of noble metal-based catalysts for electrocatalysis

In response to the shortage of fossil fuels, efficient electrochemical energy conversion devices are attracting increasing attention, while the limited electrochemical performance and high cost of noble metal-based electrode materials remain a daunting challenge. The electrocatalytic performance of electrode materials is closely bound with their intrinsic electronic/ionic states and crystal structures. Apart from the nanoscale design and conductive composite strategies, heteroatom doping, particularly for nonmetal doping (e.g., hydrogen, boron, sulfur, selenium, phosphorus, and tellurium), is also another effective strategy to greatly promote the intrinsic activity of the electrode materials by tuning their atomic structures. From the perspective of electrocatalytic reactions, the effective atomic structure regulation could induce additional active sites, create rich defects, and optimize the adsorption capability, thereby contributing to the promotion of the electrocatalytic performance of noble metal-based electrocatalysts. Encouraged by the great progress achieved in this field, we have reviewed recent advancements in nonmetal doping for electrocatalytic energy conversion. Specifically, the doping effect on the atomic structure and intrinsic electronic/ionic state is also systematically illustrated and the relationship with the electrocatalytic performance is also investigated. It is believed that this review will provide guidance for the development of more efficient electrocatalysts.

A mild reduction of Co-doped MnO2 to create abundant oxygen vacancies and active sites for enhanced oxygen evolution reaction

Efficient and non-precious-metal-based catalysts (e.g., manganese-based oxides) for the oxygen evolution reaction (OER) remain a substantial challenge. Creation of oxygen vacancies of manganese-based oxides with the aim to enhance their intrinsic activities is rarely reported, and there is a critical requirement for a mild and facile synthesis strategy to create abundant oxygen vacancies on manganese-based oxides. Herein, Co-doped MnO₂ nanowires were reduced by NaBH₄ solution at room temperature; then, MnCo₂O_4.5 nanosheets with abundant oxygen vacancies and active sites were formed on the surface of Co-doped MnO₂ nanowires. Benefiting from the reduction strategy, the fabricated hierarchical Co-doped-MnO₂@MnCo₂O_4.5 nanowire/nanosheet nanocomposites exhibit higher catalytic activity (an overpotential of 250 mV at a current density of 10 mA cm^-2 in 1.0 M KOH solution) than pristine Co-doped MnO₂ nanowires. The calculated TOF of Co-doped-MnO₂@MnCo₂O_4.5 is 0.034 s^-1 at the overpotential of 300 mV, which is 136-fold higher than that of Co-doped-MnO₂. The excellent OER performance was attributed to the synergistic advantages of abundant oxygen vacancies and active sites over the hierarchical nanowire-nanosheet architectures.

MoS2 Decoration Followed by P Inclusion over Ni-Co Bimetallic Metal-Organic Framework-Derived Heterostructures for Water Splitting

Demonstrating a highly efficient non-noble bifunctional catalyst for complete water electrolysis remains challenging because of kinetic limitations and crucial importance for future energy harvesting. Herein, a low-cost, integrated composite of a Ni-Co metal-organic framework decorated with thin MoS₂ nanosheets was synthesized by a simple hydrothermal method followed by carbonization and phosphorization for electrochemical oxygen and hydrogen evolution reactions. Such a composite heterostructure exhibits outstanding performance in the electrocatalysis process with a lower overpotential of 184 mV for the oxygen evolution reaction (OER) and 84 mV for the hydrogen evolution reaction (HER) in 1.0 M KOH and 0.5 M H₂SO₄ electrolytes to reach a current density of 10 mA cm^-2, with a slight Tafel slope of 63 mV dec^-1 for the OER and 96 mV dec^-1 for the HER. The obtained results are far better than those of the commercial benchmark catalyst. Furthermore, online gas chromatography quantifies the amount of hydrogen generation in a symmetric cell as equal to 0.002121 moles with an energy efficiency of about 2.237 mg/kWh. Thus, the composite electrode's remarkable performance is further demonstrated as a potentially viable alternative non-noble electrocatalyst for energy conversion reactions.

Universal MOF-Mediated synthesis of 2D CoNi-based layered triple hydroxides electrocatalyst for efficient oxygen evolution reaction

Developing low-budget, stable, and high-performance electrocatalyst toward oxygen evolution reaction (OER) is of pivotal significance in the fields of energy conversion and storage. Herein, a universal metal organic framework (MOF)-mediated method for the synthesis of two-dimensional (2D) layered triple hydroxides (LTHs) nanosheets with ultrathin nature has been developed. It is interesting to disclose that the CoNi-based LTHs possess better electrochemical catalytic performance, giving superior performance to commercial RuO₂ catalysts. Remarkably, benefitting from the ultrathin nanosheet configuration, optimized electronic structure, and strong synergistic effect, the optimized CoNiFe LTHs nanosheets show excellent OER performance with an ultralow overpotential of 262 mV at a current density of 10 mA cm^-2 and a small Tafel slope of 88.1 mV dec^-1. This work provides a promising avenue to develop low-cost and high-performance layered ternary hydroxide electrocatalysts.

Advances in hydrogen production from electrocatalytic seawater splitting

As one of the most abundant resources on the Earth, seawater is not only a promising electrolyte for industrial hydrogen production through electrolysis, but also of great significance for the refining of edible salt. Despite the great potential for large-scale hydrogen production, the implementation of water electrolysis requires efficient and stable electrocatalysts that can maintain high activity for water splitting without chloride corrosion. Recent years have witnessed great achievements in the development of highly efficient electrocatalysts toward seawater splitting. Starting from the historical background to the most recent achievements, this review will provide insights into the current state, challenges, and future perspectives of hydrogen production through seawater electrolysis. In particular, the mechanisms of overall water splitting, key features of seawater electrolysis, noble-metal-free electrocatalysts for seawater electrolysis and the underlying mechanisms are also highlighted to provide guidance for fabricating more efficient electrocatalysts toward seawater splitting.

A general MOF-intermediated synthesis of hollow CoFe-based trimetallic phosphides composed of ultrathin nanosheets for boosting water oxidation electrocatalysis

Engineering an electrode material for boosting reaction kinetics is highly desired for the oxygen evolution reaction (OER) in the anodic half reaction, and is still a grand challenge for energy conversion technologies. By taking inspiration from the catalytic properties of transition metal phosphides (TMPs) and metal-organic frameworks (MOFs), we herein propose a general MOF-intermediated synthesis of a series of hollow CoFeM (M = Bi, Ni, Mn, Cu, Ce, and Zn) trimetallic phosphides composed of ultrathin nanosheets as advanced electrocatalysts for the OER. A dramatic improvement of electrocatalytic performance toward the OER is observed for hollow CoFeM trimetallic phosphides compared to bimetallic CoFe phosphides. Remarkably, composition-optimized CoFeBiP hollow microspheres could deliver superior electrocatalytic performance, achieving a current density of 10 mA cm^-2 with an overpotential of only 273 mV. Mechanistic investigations reveal that the Bi and P doping effectively optimizes the electronic structure of Co and Fe by charge redistribution, which significantly lowers the adsorption energy of oxygen intermediates. Moreover, the hollow microsphere structures composed of ultrathin nanosheets also enable them to provide rich surface active sites to boost the electrocatalytic OER.

A high-performance voltammetric methodology for the ultra-sensitive detection of riboflavin in food matrices based on graphene oxide-covered hollow MnO2 spheres

A high-performance voltammetric methodology was developed to achieve ultra-sensitive detection of riboflavin, employing an electrode modified by graphene oxide-covered hollow MnO₂ spheres nanocomposite with high catalytic activity, large surface area, and hierarchical layered structure. Under the optimal conditions, the current responses of the oxidation peak located at -0.39 V showed a good linear relationship versus the concentration of riboflavin in the range of 1.0 nM-4.0 μM in acetate buffer (pH 5.4). The limit of detection was determined as 0.26 nM. Moreover, the proposed electrode exhibited high reproducibility (relative standard deviation of 1.7%, n = 10) and excellent stability (97.6% sensitivity within two months), which has been successfully applied to the quantification of riboflavin in complicated food matrices, with results in good accordance with those obtained by chromatography as a reference method, indicating it is an effective sensing platform for ultra-sensitive determination of riboflavin in practical applications.