Prussian Blue Analogues Research Articles

A phase transition coordinated monoclinic Fe-based Prussian blue for high-performance sodium-ion battery cathode

Prussian blue analogs (PBAs) are ideal cathode materials for sodium-ion batteries (SIBs) owing to their cost-effectiveness, good low-temperature performance, and facile synthesis process. Nevertheless, their actual capacity and cycling stability limit practical application. Herein, a new chelating agent, sodium tartrate, is proposed to synthesize high-quality Fe-based Prussian blue (HQ-NFF) with enhanced Na content and a stable structure through chelation effect-assisted co-precipitation. The crystal structure of HQ-NFF undergoes a phase transition to a Na-rich monoclinic phase after full discharge, leading to improved capacity and cycling stability. The HQ-NFF cathode exhibits an ultra-high capacity of 160.8 mAh g−1 and a capacity of 146.1 mAh g−1 at 2 C, with a capacity retention of 75.3 % after 150 cycles. Moreover, a 3D-printed HQ-NFF cathode with an areal loading of 7.88 mg cm−2, delivers a high areal capacity of 0.969 mAh cm−2 and good rate capability.

Highly efficient removal of trace thallium from surface water by Co@Fe Prussian blue analogue coated membrane

Super trace thallium(I) (Tl+) is still highly toxic and its removal from surface water is challenging. Here, we developed a new adsorptive membrane by immobilizing bimetal (cobalt and iron) Prussian blue analogues (Co@Fe-PBAs) on a polytetrafluoroethylene microporous membrane (Co@Fe-PBAs-M). The prepared membrane displayed precise adsorption of trace Tl+ (50 μg/L) from complex water. A variety of interfering factors, such as water pH, competitive adsorption of positive ions (Na+ and K+) and negative ions (CO32– and PO43-), natural organic matters (e.g., fulvic acid and bovine serum albumin) were evaluated during Tl removal. The composite membrane showed high removal efficiency (over 80 %) during long-term dynamic membrane separation of surface water containing super trace Tl+ (<2.0 μg/L), breaking through the adsorption limitation in ultralow concentration of Tl+. The unique bimetal electron transfer of Co@Fe-PBAs-M reinforced the adsorptive performance to Tl+ through dual ion exchange and intercalation. In the treatment of real Pearl River water containing 0.5 μg/L of Tl+, our membrane effectively reduced the Tl+ concentration to 0.04 μg/L during 6-h continuous separation, which was far below the required level for drinking water (i.e., 0.1 μg/L). This work offers a promising solution for safe drinking water by remedying ultralow Tl+ contaminated surface water.

ZnFe(PBA)@Ti3C2Tx nanohybrid-based highly sensitive non-enzymatic electrochemical sensor for the detection of glucose in human sweat

The ZnFe prussian blue analogue [ZnFe(PBA)] was infused with Ti3C2Tx (MXene) denoted as ZnFe(PBA)@Ti3C2Tx and was prepared by an in-situ sonication method to use as a non-enzymatic screen printed electrode sensor. The advantage of non-enzymatic sensors is their excellent sensitivity, rapid detection, low cost and simple design. The synthesized ZnFe(PBA)@Ti3C2Tx was characterized for its physical and chemical characterization by XRD, Raman, XPS, EDAX, and FESEM analysis. It possessed multiple functionalized layers and a cubic structure in the nanohybrid. Further, the sensor was investigated by using electroanalytical studies such as cyclic voltammetry and chronoamperometry analysis. The enhanced surface area with a cubic structure of ZnFe(PBA) and the excellent electrical response of Ti3C2 nanosheet support the advancement of a non-enzymatic electrochemical glucose sensor with improved sensitivity of 973.42 µA mM−1 cm−2 with the limit of detection (LOD) of 3.036 µM (S/N = 3) and linear detection range (LDR) from 0.01 to 1 mM.

Smartphone-based electrochemical sensing of propyl gallate in food samples by employing NiFe-Oxide decorated flexible laser-induced graphene electrode

Flexible graphene electronics utilizing laser-induced graphene (LIG) technology offer an efficient, cost-effective, and mask-free approach to produce graphene in a single step. LIG can be directly patterned on polyimide films, impacting their surface properties, chemical composition, and electrical conductivity. However, the electrochemical performance of standalone LIG is limited. To address this, the study enhances LIG by synthesizing nickel-iron Prussian blue analogues through co-precipitation and calcination, forming porous NiFe-Oxide, which is subsequently deposited onto the LIG surface via a facile physical deposition method. The porous NiFe-Oxide@LIG electrode material demonstrates excellent electrochemical sensing capabilities due to its high conductivity, improved surface area, enhanced active sites, and superior electrocatalytic performance for detecting the antioxidant propyl gallate (PG). This porous NiFe-Oxide@LIG electrode material features a linear detection range (0.5–5 μM), low detection limit (0.01 μM), high sensitivity (17.12 μAμM−1cm−2), and strong selectivity for PG. Additionally, it offers high reproducibility and repeatability, evidenced by the low relative standard deviation values of 2.61 % and 1.96 %, respectively. The practicality of the proposed sensor was validated using food samples, integrated into a smartphone-based sensing device, achieving satisfactory recovery rates above 79.2 %. This smartphone-based sensor enables effective onsite food quality and safety monitoring.

Dendrite‐Free Zn Anode Modified with Prussian Blue Analog for Ultra Long‐Life Zn‐Ion Capacitors

AbstractThe main challenge for aqueous zinc‐ion capacitors is the low stability of zinc anode. In this study, a Prussian blue analog (PBA) has been coated on the surface of zinc foil to create an inorganic protective layer. This layer features a three‐dimensional open microporous structure, which not only endows it with excellent pseudocapacitive properties but also serves as an effective barrier against dendrite growth. The presence of PBA coating can increase the nucleation point of zinc ions and provide a low‐energy barrier for the rapid migration of zinc ions. Hence, the PBA@Zn ||PBA@Zn symmetric cell exhibits exceptional cycling stability, enduring over 1400 h of operation at a current density of 1 mA cm−2 and a capacity of 1 mAh cm−2. The PBA@Zn||AC capacitor demonstrated a discharge capacity of 46.23 mAh g−1 after 10 000 cycles at a current density of 1 A g−1, with a capacity retention of 92.41%, whereas the discharge capacity of Zn||AC capacitor is only 16.02 mAh g−1, with a capacity retention of 23.13%. The PBA@Zn||AC capacitor exhibited remarkable endurance and stability, retaining a substantial discharge capacity of 32.7 mAh g−1 after 10 000 cycles at 10 A g−1. Density Functional Theory (DFT) calculations also show that PBA has a strong interaction with Zn and exhibits superior zincophilic ability. This study reports industrially applicable low‐cost Prussian blue analogs as artificial interfacial protective layers for improving the cycling stability of zinc anode with a low‐energy barrier for rapid migration of zinc ions especially at high current density.

P-functionalization of Ni Fe − Electrocatalysts from Prussian blue analogue for enhanced anode in anion exchange membrane water electrolysers

Efficient hydrogen generation from water-splitting is widely acknowledged as a priority route to promote the hydrogen economy. Anion exchange membrane water electrolyzers (AEMWE) offer multiple advantages in improving performance and minimizing the cost limitations of current electrolysis technologies. However, the persistence of issues related to the limited electrocatalytic activity of such materials and their poor stability under operating conditions makes developing highly active, stable, platinum-group-metal-free electrocatalysts for oxygen evolution reaction (OER) necessary.We report the development of Prussian blue analogues (PBA)-derived NiFe-based electrocatalysts through a mild aqueous phase precipitation method, followed by thermal stabilization and phosphorus doping. The formation of the NiFe-PBA-precursor with a framework nanocubic Ni(II)[Fe(III)(CN)6]2/3 structure was confirmed by X-ray diffraction, scanning electron microscopy, and inductively coupled plasma analysis. The NiFe-PBA-precursor was subjected to thermal stabilization and phosphorus doping to provide the material with enhanced OER catalytic activity and stability. The existence of OER active sites based on NiFe and NiFeP has been revealed by transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical characterization in a three-electrode cell configuration in a 1 M KOH electrolyte. NiFe-PBA and NiFeP-PBA were assembled at the anode side of an AEMWE, resulting in an excellent electrochemical performance both in terms of current density at 2.0 V using 1 M KOH (1.21 A cm−2) and durability, outperforming the benchmark catalyst.

Co-doped Ni-PBA anchored on optimized ZIF-67-derived Co/N-doped hollow carbon framework for high-performance hybrid capacitive deionization

Prussian blue analogues (PBAs) are considered to be a promising electrode material for hybrid capacitive deionization (HCDI) due to their open lattice structure, adjustable composition and high theoretical capacity. Nevertheless, the performance of PBAs in practical applications is limited by their low intrinsic conductivity and structural degradation. Herein, we demonstrate an advanced heterostructure CoNi-PBA@Co/N-HC by anchoring cobalt-doped nickel hexacyanoferrate (CoNi-PBA) on cobalt/nitrogen-doped hollow porous carbon (Co/N-HC) derived from cobalt-based metal–organic frameworks (ZIF-67). Co/N-HC as the conductive growth framework of CoNi-PBA can not only promote the rapid charge transfer and efficient ion diffusion, but also mitigate the structural degradation of CoNi-PBA crystals during ion intercalation/deintercalation. Moreover, the doped Co in CoNi-PBA is derived from Co/N-HC, allowing the heterostructures to form more stable and tighter interconnections. Therefore, the optimal PBA@Co/N-HC300 electrode exhibits reduced equivalent series resistance (Rs 1.10 Ω < Rs (PBA) 1.41 Ω), enhanced ion diffusion rate (DNa+ 2.86 × 10−16 > DNa+(PBA) 4.65 × 10−18) and exceptional electrochemical stability (99 % capacitance retention, 500 times CV tests). Correspondingly, the HCDI cell PBA@Co/N-HC300//Co/N-HC demonstrates good Na+ removal capacity (33.37 mg·g−1), excellent charge efficiency (83.65 %), diminished energy consumption (0.657 kWh kg−1-NaCl) and improved cycle stability (90.8 % capacity retention, 40 cycles).

Confined Element Distribution with Structure-Driven Energy Coupling for Enhanced Prussian Blue Analogue Cathode.

The structural failure of Na2Mn[Fe(CN)6] could not be alleviated with traditional modification strategies through the adjustable composition property of Prussian blue analogues (PBAs), considering that the accumulation and release of stress derived from the MnN6 octahedrons are unilaterally restrained. Herein, a novel application of adjustable composition property, through constructing a coordination competition relationship between chelators and [Fe(CN)6]4- to directionally tune the enrichment of elements, is proposed to restrain structural degradation and induce unconventional energy coupling phenomenon. The non-uniform distribution of elements at the M1 site of PBAs (NFM-PB) is manipulated by the sequentially precipitated Ni, Fe, and Mn according to the Irving-William order. Electrochemically active Fe is operated to accompany Mn, and zero-strain Ni is modulated to enrich at the surface, synergistically mitigating with the enrichment and release of stress and then significantly improving the structural stability. Furthermore, unconventional energy coupling effect, a fusion of the electrochemical behavior between FeLS and MnHS, is triggered by the confined element distribution, leading to the enhanced electrochemical stability and anti-polarization ability. Consequently, the NFM-PB demonstrates superior rate performance and cycling stability. These findings further exploit potentialities of the adjustable composition property and provide new insights into the component design engineering for advanced PBAs.

Reviving Sodium Tunnel Oxide Cathodes Based on Structural Modulation and Sodium Compensation Strategy Toward Practical Sodium-Ion Cylindrical Battery.

As a typical tunnel oxide, Na0.44MnO2 features excellent electrochemical performance and outstanding structural stability, making it a promising cathode for sodium-ion batteries (SIBs). However, it suffers from undesirable challenges such as surface residual alkali, multiple voltage plateaus, and low initial charge specific capacity. Herein, an internal and external synergistic modulation strategy is adopted by replacing part of the Mn with Ti to optimize the bulk phase and construct a Ti-containing epitaxial stabilization layer, resulting in reduced surface residual alkali, excellent Na+ transport kinetics and improved water/air stability. Specifically, the Na0.44Mn0.85Ti0.15O2 using water-soluble carboxymethyl cellulose as a binder can realize a capacity retention rate of 94.30% after 1,000 cycles at 2C, and excellent stability is further verified in kilogram large-up applications. In addition, taking advantage of the rich Na content in Prussian blue analog (PBA), PBA-Na0.44Mn1-xTixO2 composites are designed to compensate for the insufficient Na in the tunnel oxide and are matched with hard carbon to achieve the preparation of coin full cell and 18650 cylindrical battery with satisfactory electrochemical performance. This work enables the application of tunnel oxides cathode for SIBs in 18650 cylindrical batteries for the first time and promotes the commercialization of SIBs.

Optimization of sodium-ion battery cathode performance by nickel-based Prussian blue epitaxial growth with iron-based Prussian blue core-shell structure

To address the structural defects and poor electrical conductivity of conventional Prussian blue analogues (PBAs) samples, in this study, nickel hexacyanoferrate (NiHCF) and nickel hexacyanoferrate epitaxially grown with iron hexacyanoferrate (Ni@FeHCF-X) series of samples were successfully synthesized by co-precipitation combined with epitaxial growth technique, and their structural and electrochemical properties were systematically characterized. X-ray powder diffractometer (XRD) results show that all the samples maintain a cubic crystal system structure, and the diffraction peaks of the (220) and (400) crystal planes are shifted to a lower angle with the epitaxial growth of ferric hexacyanoferrate (FeHCF). The successful embedding of Fe was confirmed by inductively coupled plasma (ICP) measurement data. Scanning electron microscope (SEM) images show that the samples are in a cubic morphology, and the surfaces gradually become rounded from sharp to rounded with the increase of the Fe content. High-resolution transmission electron microscope (HRTEM) and energy-dispersive spectrometer (EDS) analyses confirm the successful construction of the core-shell structure and the homogeneous distribution of the elements. Electrochemical testing showed that the Ni@FeHCF-X samples exhibited higher specific capacities and superior rate performance compared to NiHCF, particularly the Ni@FeHCF-4 sample, which delivered a high specific capacity of 73.4 mAh·g⁻¹ at a current density of 100 mA·g⁻¹, significantly outperforming the 38.2 mAh·g⁻¹ achieved by NiHCF. Additionally, the capacity retention rate of Ni@FeHCF-4 reached 42.16 %. Electrochemical impedance spectroscopy (EIS) further confirmed the reduced charge transfer resistance and enhanced reversibility of the electrochemical reactions in the Ni@FeHCF-X samples. These results demonstrate that Ni@FeHCF-4 significantly enhances the electrochemical performance of the samples in aqueous sodium-ion battery, providing new insights into the design of cathode materials for sodium-ion batteries.

MOF-on-MOF Derived Co2P/Ni2P Heterostructures for High-Performance Supercapacitors.

Metal-organic frameworks (MOFs) have been widely used as versatile precursors to fabricate functional nanomaterials with well-defined structures for various applications. Herein, the presynthesized Ni-MOF nanosheets were grown on a Ni foam (NF) substrate, which then guided the nucleation and further growth of Prussian blue analogues (PBA) nanocubes to form MOF-on-MOF of the PBA/Ni-MOF film. This film was subsequently converted into a Co2P/Ni2P heterostructure. The NF-supported Co2P/Ni2P composites exhibited excellent supercapacitor performance, delivering a high specific capacity of 5124.2 mF cm-2 at 1 mA cm-2 and a remarkable capacity retention of 80.69% after 3000 cycles at 10 mA cm-2. An asymmetric supercapacitor assembled using Co2P/Ni2P/NF as the cathode and activated carbon as the anode yielded a maximum energy density of 0.34 mWh cm-2 at a power density of 1.50 mW cm-2. The enhanced supercapacitor performance is attributed to the synergistic effects of the Ni2P and Co2P components with multiple valence states as well as the unique hierarchical structure, which provides efficient pathways for electron and ion transport while mitigating volume expansion during energy storage. This synthetic strategy demonstrates an effective approach to fabricate phosphide-based hybrid materials for high-performance supercapacitor applications.

Solid Contact Microfabricated Electrode for Point-of-Care Electrochemical Determination of a Parasitic Infection Managing Medication Based on a Transducer Layer Prussian Blue Analogue Decorated with Multi-Walled Carbon Nanotubes

Point-of-care diagnostics (POC), often known as on-site testing has evolved as a quick and accurate methodology for analyzing and therapeutic monitoring of drugs. The aim of this study is to provide cost-effective, simple, portable, reliable, and ecofriendly methodology for determination of Tinidazole (TD); potentiometric sensors are found to be an ideal fit for achieving these goals. An advanced microfabricated ion selective electrode is provided employing two-steps procedure. The first is selecting the most selective ionophore for TD determination while the second is to improve the stability and detection limit upon doping the nanoparticles as ion to electron transducer layer between the microfabricated copper electrode and the ion selective media as it can decrease potential drift from 8.0 to ∼1.0 mV h−1. Nernstian potentiometric results were obtained for TD in range of concentration 1.0 × 10−3 to 1.0 × 10−8 M, its slope was −57.43 mV/decade with lower detection limits 2.55 × 10−9 M. Essential values of the adopted sensor are fast and stable response time (9 ± 2 s). The provided potentiometric approach succeeds to asses TD in its pure and pharmaceutical forms, furthermore in different biological fluids with satisfactory results.

Elucidating the role of double-confined effect in hollow MOFs/GO catalytic membrane for deep arsenic pollution treatment

The significance of addressing arsenic contamination is huge, given its widespread environmental impact and detrimental effects on human health. Herein, we developed a double-confined catalytic membrane capable of activating peroxymonosulfate (PMS) by integrating hollow Prussian blue analogues (H-PBA) with a unique void-confinement effect into graphene oxide (GO) laminates. This delicately designed H-PBA/GO membrane displayed 98.8 % p-arsanilic acid (p-ASA) removal with a 9.03 s retention time, surpassing most reported studies. Our experiments underscored that the dual-confined architecture not only drove mass transfer but also bolstered reactant concentration, thereby multiplying catalytic activities. Remarkably, this double-confinement conduced to a sustained dominance of surface-radicals (SO4−) and singlet oxygen (1O2), bolstering p-ASA degradation across a broad pH spectrum and numerous aqueous realms, inclusive of high salinity waters pertinent to desalination pre-treatment processes. Crucially, the H-PBA/GO membrane demonstrated over 90 % degradation of p-ASA and immobilized total As, unfaltering over 80 h of continuous operation. This signified an evolution in membrane technology, promising enhanced and steadfast performance. This innovation bore profound implications for devising double-confined efficacious and robust catalysts, poised to revolutionize advanced wastewater treatment, notably augmenting desalination systems by fortifying pre-treatment and safeguarding reverse osmosis membranes from organic and arsenic fouling.

Additive-Free, In Situ Rapid Repair of Vacancies in Fe[Fe(CN)6] Electrodes for Efficient Capacitive Deionization.

Fe[Fe(CN)6] (FeHCF) is considered a promising material for capacitive deionization-desalination of saline wastewater due to its excellent structure. However, additives are usually introduced during the synthesis of FeHCF in order to avoid [Fe(CN)6]3- vacancy defects filled by ligand water, which can result in the appearance of harmful byproducts and additional water treatment costs. In this study, an additive-free in situ vacancy repair strategy is proposed for the rapid synthesis of high-quality FeHCF in a saturated K3Fe(CN)6 solution. During the process of synthesizing FeHCF in solution, a high concentration of [Fe(CN)6]3- is found to facilitate the binding of Fe3+ to [Fe(CN)6]3- and hinder the hydrolysis and coordination reaction of Fe3+. After undergoing repair, FeHCF4 demonstrates an increased capacity and highly reversible electrochemical performance due to the robust structure. When utilized as Faraday cathodes in hybrid capacitive deionization (HCDI) systems, FeHCF4 exhibits a higher salt removal capacity (65.67 mg g-1) and lower energy consumption (0.68 kWh kg-1-NaCl) compared to unrepaired FeHCF1, while still maintaining excellent cycling performance. This environmentally friendly approach of repairing vacancies serves as a source of inspiration for the advancement of high-performance Prussian Blue analogues as capacitive sodium-removing materials.

Competition for Ion Intercalation in Prussian Blue Analogues as Cathode Materials for Calcium Ion Batteries

With multivalent ion batteries being considered viable post‐lithium energy storage technologies, the last few years have seen increasing interest in intercalation type cathode materials for Ca‐ion batteries (CIBs). Prussian blue analogues (PBAs) display many positive attributes such as open structural framework, large interstitial sites, and versatile transition metal redox activity. The PBA cathodes reported for CIBs often contain K‐ion or Na‐ion due to the syntheses involving the use of potassium or sodium hexacyanoferrate. It has been long overlooked whether the presence of K‐ion or Na‐ion in pristine PBAs could affect the Ca‐ion storage in the PBAs when assessing their CIB performance. Through a combined experimental and computational investigation, this work reports that when K+/Na+ is present in the pristine PBAs, K/Na intercalation is preferred by the PBA structure over Ca intercalation even in the Ca cells. Ca‐ion intercalation can be increased when the K+/Na+ content in the pristine PBAs is reduced, shifting from a K or Na‐dominated intercalation process to a Ca/K or Ca/Na co‐intercalation process. This work consolidates that PBAs are an interesting and versatile intercalation host for several ions, but investigating PBAs as intercalation cathodes requires careful consideration of all ions present in the battery system.

Unveiling the Influence of Water Molecules on the Structural Dynamics of Prussian Blue Analogues.

3D-framework Prussian blue analogues (PBAs) are appealing as a cost-effective, sustainable cathodes for Na-ion batteries. However, the aqueous-based synthesis of PBAs inherently introduces three different forms of water molecules (surface, interstitial and crystal) into the structure. Removal of water molecules causes phase transformation from monoclinic (M) to rhombohedral (R). This work presents the effects of water molecules on the structure before the phase transformation temperature, employing two promising PBA cathodes, Na2Fe[Fe(CN)6]·1.69H2O and Na2Mn[Fe(CN)6]·1.76H2O. Specifically, the water molecules impact the molecular interactions at the local structure and the electrochemical properties. This work has performed calculations on low-vacancy Na2M[Fe(CN)6] PBAs (where M = Mn, Fe, Co, Ni and Cu) to understand the dehydration energy. Employing in situ high-temperature X-ray diffraction and Raman spectroscopy, this work observes that water removal induces negative thermal expansion and stronger interactions between C≡N and Na ions, resulting in biphasic reactions with sluggish kinetics. Additionally, water molecules play a role in maintaining the open 3D tunnels and facilitating a solid-solution like insertion of Na ions. Calculated phonon-Raman spectra provide insights into cyanide group deformations, revealing the interactions between water molecules, alkali-ions, and transition-metal ions. This study enhances the understanding of the relationship among electronic, vibrational, and electrochemical properties.

A(CoFe)(S2)2/CoFe heterostructure constructed in S, N co-doped carbon nanotubes as an efficient oxygen electrocatalyst for zinc-air battery

Transition metal alloys can exhibit synergistic intermetallic effects to obtain high activities for oxygen reduction/evolution reactions (ORR/OER). However, due to the insufficient stability of active sites in alkaline electrolytes, conventional alloy catalysts still do not meet practical needs. Herein, by using polypyrrole tubes and cobalt-iron (CoFe) Prussian blue analogs as precursors, CoFe sulfides is in-situ formed on CoFe alloys to construct (CoFe)(S2)2/CoFe heterostructure in sulfur (S) and nitrogen (N) co-doped carbon nanotubes (CoFe@NCNTs-nS) via a low-temperature sulfidation strategy. The as-marked CoFe@NCNTs-12.5S exhibits a comparable ORR activity (half-wave potential of 0.901 V) to Pt/C (0.903 V) and a superior OER activity (overpotential of 272 mV at 10 mA cm−2) to RuO2 (299 mV). CoFe@NCNTs-12.5S also exhibits ultralow charge transfer resistances (ORR-6.36 Ω and OER-0.21 Ω) and an excellent potential difference of 0.617 V. The sulfidation-induced (CoFe)(S2)2/CoFe heterojunctions can accelerate interfacial charge transfer process. Tubular structure not only disperses the (CoFe)(S2)2/CoFe heterostructure, but also reduces the corrosion of active-sites to enhance catalysis stability. Zinc-air battery with CoFe@NCNTs-12.5S achieves a high specific capacity (718.1 mAh g−1), maintaining a voltage gap of 0.957 V after 400 h. This work reveals the potential of interface engineering for boosting ORR/OER activities of alloys via in-situ heterogenization.

Boosted Electrochemical Hydrogen Evolution Activity via the Core-Shell Heterostructure of Nickel Sulfide Nanoframe-Supported Layered Rhenium Disulfide.

The strategic design of a heterostructure catalyst with a core-shell nanoarchitecture is imperative for enhancing the efficiency of the electrocatalytic hydrogen evolution reaction (HER). Herein, the core-shell catalyst comprising the rhenium disulfide nanosheets was vertically integrated onto a hollow nickel sulfide (NiS@ReS2) via coprecipitation and hydrothermal treatment. The morphology involves the sulfurization of a nickel-based Prussian blue analogue, effectively mitigating the aggregation of ReS2 nanosheets and maximizing the exposed active sites. By the synergistic effect of morphological design and heterostructure formation, the overpotential of NiS@ReS2 is 136 mV at 10 mA cm-2 in an alkaline electrolyte, and the rapid kinetics is confirmed by the small Tafel slope and low charge transfer resistance during the HER process. Moreover, the electrocatalytic durability of NiS@ReS2 is elucidated, and the boosted catalytic activity of NiS@ReS2 is confirmed by density functional theory. This study unveils a promising method for advancing ReS2-based electrocatalysts with potential implications for producing hydrogen.

Thermal expansion in Prussian Blue analogs M3[Cr(CN)6]2.nH2O (M = Mn, Fe, Co, Ni)

Thermal expansion in Prussian Blue Analogs (PBAs) M3[Cr(CN)6]2.nH2O (M = Mn, Fe, Co, Ni; n = 10–16) was studied using powder X-ray diffraction (XRD) as a function of temperature in the range 123–298 K. Standard chemical precipitation was used to prepare the materials and they were characterized using standard characterization techniques XRD, X-ray fluorescence (XRF), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. All materials were found to crystallize in the cubic structure with space group Fm3‾m. Strong compositional dependence of thermal expansion is found in this series of PBAs. While Mn3[Cr(CN)6]2.12H2O and Ni3[Cr(CN)6]2.16H2O show positive thermal expansion (PTE) behavior the other two PBAs, Fe3[Cr(CN)6]2.10H2O and Co3[Cr(CN)6]2.14H2O, show strong negative thermal expansion (NTE) behavior with as large coefficient of thermal expansion (CTE) as −19.7 x 10−6 K−1 (for M = Fe) in the temperature range 123–223 K. For the PBAs showing NTE, the magnitude of NTE coefficients can be correlated with the trends for M cation size and cell (or lattice) parameter.

Strategic integration of nickel tellurium oxide and cobalt iron prussian blue analogue into bismuth vanadate for enhanced photoelectrochemical water oxidation

Bismuth vanadate (BVO) with a small band gap and suitable band edges is regarded as one of the promising photocatalysts for water oxidation. However, the short charge-transfer path limits its photocatalytic performance. Establishing a heterojunction and incorporating a co-catalyst are feasible methods to improve the photocatalytic ability of BVO by enhancing carrier transfer rates and reducing in-electrode resistances. In this study, nickel tellurium oxide (NTO) and cobalt iron Prussian blue analogues (CoFePBA) are incorporated into the BVO electrode to respectively develop a heterojunction and decorate co-catalyst for efficiently catalyzing the water oxidation reaction for the first time. Different amounts of CoFePBA are deposited on the NTO/BVO electrode by varying the electrodeposition durations to enhance exited charge generations and maintain high absorbance of incident light. The largest photocurrent density of 6.55 mA/cm2 at 1.23 V versus reversible hydrogen electrode is attained for the optimal CoFePBA/NTO/BVO electrode prepared using an electrodeposition duration of 2 min. Excellent catalytic stability is also achieved, with the photocurrent retention of 91.9% after illuminating the electrode for 5000 s. This study provides blueprints for incorporating novel electrochemically active materials in the BVO system to realize heterojunction and co-catalyst strategies, thereby attaining excellent photocatalytic ability toward water oxidation.