Excellent Bifunctional Activity Research Articles

FeN4S1 Single-Atom Sites Anchored on Three-Dimensional Porous Carbon for Highly Efficient and Durable Oxygen Electrocatalysis.

Precisely designing asymmetric active centers and exploring their electronic regulation effects to prepare efficient bifunctional single-atom catalysts (SACs) is important for boosting the practical applications of zinc-air batteries (ZABs). Herein, an effective strategy has been developed by introducing an axial S atom to the FeN4 active center, simultaneously assisted by pyrolyzing the graphene oxide (GO) sheathed zeolitic-imidazolate framework-8 (ZIF8) composite and constructing a three-dimensional (3D) porous framework with abundant FeN4S1 moieties. This structure can accelerate the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics owing to the modulated electronic redistribution and d-band center with a reduced energy barrier. The optimal S-Fe-NC/rGO showcases a lower voltage gap (ΔE) of 0.64 V between both the ORR and OER half-wave potentials at 10 mA cm-2, highlighting the excellent bifunctional activities. The assembled S-Fe-NC/rGO rechargeable liquid ZABs deliver a power density of 154.05 mW·cm-2 and a desirable durability of >900 h. More importantly, the corresponding flexible solid-state ZABs exhibit considerable foldability.

Innovative Air Cathode with Ni-Doped Cobalt Sulfide in Highly Ordered Macroporous Carbon Matrix for Rechargeable Zn-Air Battery.

To realize the practical application of rechargeable Zn-Air batteries (ZABs), it is imperative to develop a non-noble metal-based electrocatalyst with high electrochemical performance for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Ni-doped Co9S8 nanoparticles dispersed on an inverse opal-structured N, S co-doped carbon matrix (IO─NixCo9-xS8@NSC) as a bifunctional electrocatalyst is presented. The unique 3D porous structure, arranged in an inverse opal pattern, provides a large active surface area. Also, the conductive carbon substrate ensures the homogeneous dispersion of NixCo9-xS8 nanocrystals, preventing aggregation and increasing the exposure of active sites. The introduction of heteroatom dopants into the Co9S8 structure generates defect sites and enhances surface polarity, thereby improving electrocatalytic performance in alkaline solutions. Consequently, the IO─NixCo9-xS8@NSC shows excellent bifunctional activity with a high half-wave potential of 0.926V for ORR and a low overpotential of 289mV at 10mA cm-2 for OER. Moreover, the rechargeable ZAB assembled with prepared electrocatalyst exhibits a higher specific capacity (768 mAh gZn -1), peak power density (180.2mW cm-2), and outstanding stability (over 160h) compared to precious metal-based electrocatalyst.

Architecting double-shelled hollow carbon nanocages embedded bimetallic sites as bifunctional oxygen electrocatalyst for zinc-air batteries

Rational design of complex hollow nanostructures offers a great opportunity to construct various functional nanostructures. A novel in situ disassembly-polymerization-pyrolysis approach was developed to synthesize atomically dispersed Fe single atoms (Fe SAs) and tiny Co nanoparticles (Co NPs) binary sites embedded in double-shelled hollow carbon nanocages (Co NPs/Fe SAs DSCNs) without removing excess templates. The Co NPs/Fe SAs DSCNs displayed excellent bifunctional activity, boosting the realistic rechargeable zinc-air batteries with high efficiency, long-term durability, and reversibility, which is comparable to noble metal catalysts (Pt/C and RuO2). The enhanced catalytic activity should be attributed to as well as the strong interactions between Fe SAs and Co NPs with the nitrogen-doped carbon matrix, the exposure of more active sites, and the high-flux mass transportation. In addition, the confinement effect between the double C-N shells prevented the aggregation and corrosion of metal atoms, thus improving the durability of the Co NPs/Fe SAs DSCNs, further highlighting the structural advantages of carbon nanoreactor. This work provides guidance for further rational design and preparation of complex hollow structure materials with advanced bifunctional air cathodes.

Development of Bifunctional Electrocatalyst for Overall Water Electrolysis: Vanadium and Phosphorus Dual-Doping Strategy on Ni3S2 Nanoneedle

Along with the rapid consumption of fossil fuels and serious environmental pollution, the development of renewable and clean energy has been receiving a lot of attention recently. Among the various renewable energy sources, hydrogen (H2) is considered as most promising substance in future energy society owing to its high gravimetric energy density and environmental friendliness. Electrochemical water electrolysis system is powerful strategy for high-purity hydrogen production without emission of any pollutants. It consists of two electrocatalytic reactions: oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, the practical efficiency of water electrolysis is limited due to the intrinsically sluggish reaction kinetics of OER and HER. To date, the precious metal-based electrocatalysts such as RuO2 and Pt/C for OER and HER, respectively, were employed as state-of-the-art electrocatalyst to enhance the performance of water electrolysis. However, due to the high expense, mono-functionality, and unsatisfactory stability of the precious metal-based materials, research on bifunctional electrocatalysts with low cost and high activity has become an urgent topic. To date, numerous scientific endeavors have been dedicated to the advancement of highly efficient non-noble metal-based bifunctional electrocatalysts such as transition metal oxides, hydroxides, sulfides, carbides, nitrides, and phosphides. Among these, Ni3S2 has emerged as a particularly promising electrocatalyst for water splitting, garnering substantial attention owing to its high electric conductivity, rich redox property, abundance in the Earth's crust, and environmentally friendly characteristics. Nevertheless, the electrocatalytic activity of Ni3S2 lags behind that of noble metal counterparts. Therefore, elaborate modification of Ni3S2 catalyst should be conducted to further improve its intrinsic activity toward OER and HER. Among the various strategies, heteroatom doping into Ni3S2 structure could be adopted as powerful technique for enhancement of electrocatalytic performance. The homogeneously incorporated dopants not only generate lattice disorders but elaborately modulate the surface electronic property. Specifically, high-valent cation dopants such as vanadium and molybdenum can effectively mediate the change of chemical states of Ni active sites during the step-wise electrocatalytic procedure. Meanwhile, additionally introduced anion dopants, which have lower electronegativity compared with sulfur, can reduce the electron trapping phenomenon induced by excessive electron transfer from nickel to sulfur. Inspired by above features, we synthesized V and P co-doped Ni3S2 nanoneedles directly grown on nickel foam (V-Ni3S2-P/NF) through facile two-step preparation method. First, V doped Ni3S2 nanoneedles were homogeneously grown on NF (V-Ni3S2/NF) by hydrothermal process without use of nickel precursor. The vanadium ions promote the nucleation of Ni3S2 species and lead the preferential growth toward 1D direction during the hydrothermal reaction. After that, the V-Ni3S2/NF was annealed in the tube furnace with the NaH2PO2 as a phosphorus precursor under the Ar flow. Under the mild annealing condition, the PH3 gases generated from thermal decomposition of NaH2PO2 reacted with the V-Ni3S2 species. Consequently, the V-Ni3S2 was partially phosphidated into V-Ni3S2-P throughout anion exchange process. As a result, the V-Ni3S2-P/NF electrocatalyst exhibited excellent bifunctional activity toward both OER and HER compared with mono-doped and un-doped counterparts and precious metal-based electrocatalysts. Furthermore, the outstanding electrocatalytic performance of V-Ni3S2-P/NF was well-maintained over the 100 h of continuous operation under alkaline condition. This study will contribute to the development of efficient and cost-effective electrocatalysts for future energy conversion and storage technologies.

Sandwiched heterostructure of NiFe2O4/TiO2 nanocrystals and MXene nanosheets for highly active oxygen electrocatalyst in rechargeable zinc-air batteries

Recent advancements in zinc-air batteries (ZABs) emphasize the need for efficient and sustainable oxygen electrocatalysts. Central to these efforts are metal-organic frameworks (MOFs), renowned for their bifunctional oxygen electrocatalytic capabilities. However, MOFs and their derivatives often exhibit subpar electrical conductivity and stability. Addressing this, we introduce an innovative approach involving MOFs-derived NiFe2O4/TiO2 nanocrystals sandwiched between 2D MXene nanosheets. This hybrid structure, NiFe2O4/TiO2@NC/Ti3C2, successfully enhances conductivity and active site accessibility, thereby enhancing oxygen reduction (ORR) and evolution (OER) reactions. The NiFe2O4/TiO2@Ti3C2–2 hybrid demonstrates excellent bifunctional activity, characterized by a notable ORR's half-wave potential of 0.846 V and an OER's onset potential of 1.5 V with a potential gap (ΔE) of 0.75 V. When employed in a ZAB, the battery achieves a peak power density of 164 mW cm−2 and maintains cycling stability for over 500 h at 10 mA cm−2. Beyond serving as conductive scaffolds, Ti3C2 MXene nanosheets have a vital role in preserving surface areas of the NiFe2O4/TiO2@NC materials. This study not only highlights a successful strategy for improving oxygen reactions in ZABs but also opens up new opportunities for the development of advanced MOF@MXene catalysts in energy conversion applications.

Sulfur doping induces internal polarization field in NiFe-LDH for bifunctioanl HER/OER and overall water/simulated seawater splitting

With the development of renewable energy technologies, electrochemical water splitting has been proven to be an effective strategy for energy conversion. Especially, exploring a bifunctional material for electrochemical water splitting devices is vital. Herein, a bifunctional sulfur-doped NiFe-LDH (NFS) through one-step chemical oxidation-assisted etching route was successfully synthesized at room temperature. Moreover, the effects of the component of the etching solution and etching time on the catalytic performance were systematically investigated, so as to explore the optimal synthetic route. The resulted NFS catalyst depicted obvious nanosheets based 3D open structure, which was demonstrated to provide abundant electrochemical active sites, facilitate the rapid diffusion of ions and improve the electrical conductivity as well as the catalytic stability. Electrochemical tests showed that the overpotential of the as-prepared catalyst was 256 mV for OER and 171 mV for HER at 10 mA cm−2 in 1 M KOH solution, which exhibited excellent bifunctional activity. Furthermore, the electrolyzer was assembled using as-prepared catalyst as both the anode and cathode, which expressed good stability either in 1 M KOH (1.67 V@10 mA cm−2) or in alkaline simulated seawater (1.84 V@10 mA cm−2). To better elucidate the crucial role of sulfur doping in the NFS catalyst to boost HER and OER, both theory and poisoning experiment had been proceeded and verified. All in all, the NFS catalyst with excellent bifunctional activity was synthesized by one-step chemical oxidation-assisted etching route at room temperature, which was promising as candidate to be used in commercial water splitting.

Bifunctional oxidase-peroxidase mimicking Fe–Ce MOF on paper-based analytical devices to intensify luminol chemiluminescence: Application for measuring different sugars with a smartphone readout

This study presents a potent paper-based analytical device (PAD) for quantifying various sugars using an innovative bi-nanozyme made from a 2-dimensional Fe/Ce metal-organic framework (FeCe-BTC). The MOF showed excellent bifunctional peroxidase-oxidase activities, efficiently catalyzing luminol's chemiluminescence (CL) reaction. As a peroxidase-like nanozyme, FeCe-BTC could facilitate the dissociation of hydrogen peroxide (H2O2) into hydroxyl radicals, which then oxidize luminol. Additionally, it was also discovered that when reacting with H2O2, the MOF turns into a mixed-valence MOF, and acts as an oxidase nanozyme. This activity is caused by the generated Ce4+ ions in the structure of MOF that can directly oxidize luminol. The MOF was directly synthesized on the PAD and cascaded with specific natural enzymes to establish simple, rapid, and selective CL sensors for the measurement of different sugars. A cell phone was also used to record light intensities, which were then correlated to the analyte concentration. The designed PAD showed a wide linear range of 0.1–10 mM for glucose, fructose, and sucrose, with detection limits of 0.03, 0.04, and 0.04 mM, respectively. It showed satisfactory results in food and biological samples with recovery values ranging from 95.8 to 102.4 %, which makes it a promising candidate for point-of-care (POC) testing for food control and medicinal purposes.

Strong interactions through the highly polar “Early–Late” metal–metal bonds enable single–atom catalysts good durability and superior bifunctional ORR/OER activity

Simultaneously enhancing the durability and catalytic performance of metal-nitrogen-carbon (M−Nx−C) single–atom catalysts is critical to boost oxygen electrocatalysis for energy conversion and storage, yet it remains a grand challenge. Herein, through the combination of early and late metals, we proposed to enhance the stability and tune the catalytic activity of M−Nx−C SACs in oxygen electrocatalysis by their strong interaction with the M2′C–type MXene substrate. Our density functional theory (DFT) computations revealed that the strong interaction between “early-late” metal–metal bonds significantly improves thermal and electrochemical stability. Due to considerable charge transfer and shift of the d-band center, the electronic properties of these SACs can be extensively modified, thereby optimizing their adsorption strength with oxygenated intermediates and achieving eight promising bifunctional catalysts for ORR/OER with low overpotentials. More importantly, the constant-potential analysis demonstrated the excellent bifunctional activity of SACs supported on MXene substrate across a broad pH range, especially in strongly alkaline media with record-low overpotentials. Further machine learning analysis shows that the d-band center, the charge of the active site, and the work function of the formed heterojunctions are critical to revealing the ORR/OER activity origin. Our results underscore the vast potential of strong interactions between different metal species in enhancing the durability and catalytic performance of SACs.

Facile synthesis of Co-Cu metal organic framework as efficient non-noble bifunctional electrocatalysts for overall water splitting

The rapid development of superior, highly stable, alkaline-medium-compatible, and nonprecious earth-abundant bifunctional electrocatalysts has garnered significant research interest. This interest aims to replace the costliest noble metals (Pt, Ir/IrO2, and Ru/RuO2) in renewable and green energy technologies for overall water splitting. However, there are still important limitations, such as lower stability and higher energy consumption. In this work, we report the synthesis of Cu-Co metal-organic frameworks (MOFs) as a bifunctional electrocatalyst using a simple chemical precipitation technique. Especially, when 11.5 mM of Co is combined with Cu MOF, it exhibits excellent bifunctional activity for overall water splitting with a lower overpotential of 0.21 V (OER) and -0.71 V (HER) at a current density of 10 mA cm−2, which exhibits nearly several times more enhancement than that of pristine Cu and Co MOFs in a 1 M KOH electrolyte solution. The Tafel slope value of 130 mV/dec and the lower charge transfer resistance, along with relatively high stability for up to 12 h at the onset potential of OER and HER, are observed for the 11.5 mM Cu-Co MOF electrocatalyst. The present results open an alternative pathway for developing a novel design of highly efficient and scalable bifunctional electrocatalysts for overall water splitting.

Controlled synthesis of Co3O4@CoP heterostructured nanoarrays as efficient electrocatalysts in alkaline seawater and urea

How to prepare clean energy has always been a problem to be solved by the modern green chemical industry. Compared with the electrolysis of water to produce hydrogen, electrolysis of seawater for raw material requirements are lower and more widely used. However, the lacks of maturity of the technology, the high cost and the generation of harmful gases such as chlorine in the electrocatalytic process have hindered the development of this process. This study demonstrates a construction of heterogeneous structure based on Co ions as an efficient multifunctional catalyst for overall seawater splitting and urea oxidation. This hybrid structure can combine nanosheets and nanowires, thus exposing the catalyst to more active sites and shortening the ion diffusion path. Comparing the hybrid structure with the single structure, Co3O4@CoP exhibits excellent multifunctional catalytic activity in alkaline seawater and urea. In the oxygen evolution reaction, the working potential is only 1.60 V and 1.70 V at a current density of 50 mA/cm2 and 100 mA/cm2. And in the hydrogen evolution reaction, the working potential was only −0.16 V at a current density of −10 mA/cm2, demonstrating excellent bifunctional activity. On this basis, the catalyst also demonstrated excellent activity for urea oxidation reaction in alkaline environment, with an operating potential of only 1.28 V at a current density of 10 mA/cm2. And the durability of this catalyst is good, it can keep 5 mA/cm2 for 12 h under the constant voltage of 1.45 V, but the initial potential falls off too fast, and there is a decline in performance, which is closely related to the corrosion of Cl- present in seawater. It was shown by density functional theory (DFT) that hierarchical nanostructures can increase the transfer rate of reaction intermediates and the water adsorption energy. At the end of this study, by comparing single nanostructures with hybrid nanostructures, it can be reasonably conjectured that the accompanying increase in the number the heterostructure is resistant to Cl- corrosion in seawater.

Efficient and robust IrW/WO3-x@NC/CP self-standing electrode with low Ir-loading for overall water electrolysis in acidic medium

To further enhance the long-term durability of the cost-effective Ir-based catalysts, some acid-stable oxides are used as supports for acidic OER catalysts. Herein, taking carbon paper (CP) as the substrate, we prepared a self-standing IrW/WO3-x@NC/CP electrode via a layer-by-layer modified method. Among it, N-doped porous C framework not only provides a large specific surface for the attachment of WO3-x, but also makes up for the lack of conductivity of WO3-x and accelerates the electron transport process. The interaction between Ir and W sites in the form of IrW alloy which has generated during the high-temperature calcination and the dispersed Ir in WO3-x matrix improve the intrinsic catalytic activity. And due to the Pt-like effect of W and the tuning role of the electronic structure by the IrW alloy, IrW/WO3-x@NC/CP with an Ir content of only 19.1 µg cm−2 exhibits excellent bifunctional activity in acidic media. To obtain 10 mA cm−2, IrW/WO3-x@NC/CP just needs overpotential of 22 mV (for HER) and 206 mV (for OER) respectively with a mass specific activity of 4.008 A mgIr−1 at 1.55 V. For the whole water splitting, it only requires 1.52 V and 1.70 V to reach 10 mA cm−2 and 100 mA cm−2 respectively, and can operate continuously for over 40 h.

Theoretical investigation of synergistically boosting the anchoring and electrochemical performance of lithiophilic/sulfiphilic transition metal carbides for lithium-sulfur batteries.

Lithium-sulfur (Li-S) battery is one of the most promising next-generation energy-storage systems with a high energy density and low cost. However, their commercial applications face several challenges, such as the shuttle effect caused by the soluble lithium polysulfide (LiPSs) intermediates and the sluggish sulfur redox reaction. In this article, we systematically investigated the anchoring and electrochemical performance of a series of transition metal carbides (TMCs: TiC, VC, ZrC, NbC, HfC, TaC) as cathode materials for Li-S batteries by theoretical calculations. The lithiophilic/sulfiphilic non-polar (001) surfaces of TMCs can offer moderate binding strength with LiPS intermediates, ensuring good performance of sulfur immobilization. These TMCs can also facilitate lithium diffusion, indicating the good rate performance of Li-S batteries. We also demonstrated that the studied TMCs can be classified into two classes according to their catalytic activity for Li2S decomposition which originated from their different electronic structural features. Furthermore, TiC, ZrC, and HfC exhibited excellent bifunctional electrochemical activity through reducing the Gibbs free energy for sulfur reduction reactions (SRRs) and lowering the barrier for Li2S decomposition which facilitates accelerating electrode kinetics and elevating utilization of sulfur. Our results offer a systematic approach to designing and screening non-polar materials for high-performance Li-S batteries, based on the rational electronic structure and lattice match strategy.

FeNi decorated nitrogen-doped hollow carbon spheres as ultra-stable bifunctional oxygen electrocatalyst for rechargeable zinc-air battery with 2.7% decay after 300 hours cycling.

Research on non-noble metal bifunctional electrocatalysts with high efficiency and long-lasting stability is crucial for many energy storage devices such as zinc-air batteries. In this report, nitrogen-doped porous hollow carbon spheres with a size of about 300 nm were fabricated using a modified Stöber method and decorated with an FeNi alloy through a pyrolytic reduction process, resulting in a promising bifunctional electrocatalyst for both the oxygen evolution reaction and oxygen reduction reaction. The as-prepared FeNi@NHCS electrocatalyst exhibits excellent bifunctional activity in KOH electrolyte, attributed to its mesoporous structure, large specific surface area, and the strong coupling between the FeNi nanoalloy and nitrogen-doped carbon carriers. The electrocatalyst demonstrates excellent ORR performance with E1/2 = 0.828 V and OER activity with Ej=10 mA = 1.51 V. A zinc-air battery using FeNi@NHCS as the air electrode achieves an open-circuit voltage of 1.432 V and a maximum power density of 181.8 mW cm-2. After 300 h of galvanostatic charge-discharge cycles, the charge-discharge voltage gap (ΔU) of the battery had only decayed by 2.7%, demonstrating superior cycling stability.

Highly bifunctional Rh2P on N,P-codoped carbon for hydrazine oxidation assisted energy-saving hydrogen production.

Highly pure Rh2P nanoparticles on N,P-codoped carbon were synthesized by a simple "mix-and-pyrolyze" method using one kind of low-cost nucleotide as the carbon, nitrogen and phosphorus source, which exhibits excellent bifunctional activity for the hydrogen reduction and hydrazine oxidation reactions, achieving energy-efficient hydrogen production.

Designing Bifunctional Oxygen Electrocatalysts Using Prussian Blue Analogue and Carbon Nanostructure Hybrids: Understanding the Role of Individual Components for Oxygen Reduction and Evolution Reactions

The incorporation and identification of active sites for OER and ORR is required for designing an efficient bifunctional oxygen electrocatalyst for low cost and high activity of electrochemical devices such as metal air batteries and regenerative fuel cells. In this work, we synthesized CoHCF/GO/f-CNT nanocomposite which showed excellent bi-functional activity with a low overvoltage of 0.8 V between the oxygen evolution reaction (E10 mA/cm 2) and the oxygen reduction reaction (E1/2). The specific functions of CoHCF and GO/f-CNT were described using hydrodynamic voltammetry measurements. For comparison, the pristine CoHCF and the composites with multiwalled carbon nanotubes (CoHCF/f-CNT) and graphene oxide (CoHCF/GO) were also synthesized and thoroughly characterised for physico-chemical and electrochemical properties. It was observed that CoHCF itself had poor ORR activity which increased on addition of GO/f-CNT. Electrochemical analysis suggested that CoHCF is primarily responsible for the OER activity in nanocomposites. The carbon nanostructure, due to strong metal support interactions (SMSI) and electrical conductivity helped in maximising the utilization of PBA active sites on the surface along with acting like a co-catalyst for ORR. The nanoscale geometries of the PBA and GO/CNT further enhanced the metal support and charge transfer interactions, thereby enhancing the activity. The findings of this study provide an insight for developing more effective PBA based nanocomposites for bifunctional OER/ORR electrocatalysis.

Investigation of Transition Metal Oxides & Phosphates for Zn-Ion/Zn-Air Batteries

Being a champion in a portable electronics world, lithium-ion batteries (LIBs) are irreplaceable, but the scarcity of Li, high cost, and the inclusion of non-aqueous electrolytes make them relatively perilous and inefficient for grid-scale energy storage. Recently, the blooming aqueous Zn-ion batteries (ZIBs) have emerged as one of the pioneer candidates featuring the inherently safe nature of metallic Zn anode and its unique properties.[1] Vanadium-based compounds show fast ion diffusion and excellent reversible capacity because of their rich valence state of vanadium, facile distortion of V-O polyhedrons, and tuneable composition, which offers an excellent treasure house. Moreover, the different oxidation states of vanadium allow a higher degree of structural change and greater functional flexibility while incorporating multivalent cations into vanadium-based compounds. [2] The present work focuses on one V-based oxide cathode. The cathode, ZnV2O4, synthesized by a simple solid-state route, showed a reversible capacity of around 200 mAh/g at a current density of 500 mA/g. Ex-situ XAS suggested that there is a drastic change in V and Zn local environment, confirming that there is a structural transformation taking place. Further, we have pursued ex-situ TEM where segregation of the conversion product phases was seen, confirmed by the small crystalline domains present at the nanoscale regime. A detailed analysis will be discussed to verify that a phase transformation is happening and is getting amorphized in subsequent cycles using ex-situ TEM and XAS.Also, metal-air batteries are widely discussed and studied because of their high energy density. In this pursuit, highly efficient bifunctional electrocatalysts, non-noble such as Co metal-based phosphates/oxides, have been studied vividly.[3,4] Herein, we present a thorough study of three-dimensional ZnCo2(PO4)2 (ZCP), which showed excellent bifunctional activity compared to the benchmark catalysts, denoting the presence of many catalytically active Co sites in ZCP. The presence of asymmetric edge-sharing CoO5/CoO6 polyhedra enhances the net catalytic activity.[5] ZCP exhibited robust oxygen reduction and evolution (ORR and OER) activity with the onset of 0.87 and 1.50 V vs. RHE for ORR and OER, respectively. The ORR saturated current density for ZCP was 6.38 mA/cm2, close to the 20% Pt/C catalyst benchmark. It also showed an OER exchange current density of 16.7 mA/cm2, closer to RuO2 ( j= 17.6 mA/cm2). This bifunctional electrocatalytic activity will be elaborated using analytical tools and DFT, along with the demonstration of Zn-air batteries. A detailed structural characterization using synchrotron refinement, TEM analysis, magnetic studies, and electrocatalysis performance will be discussed. Reference s : [1] M. Song et al., Adv. Funct. Mater. 2018, 28, 1802564.[2] Yao. Zhang et al., Chem. Front. 2021, 5 744-762.[3] J. L. Jung et al., Energy Environ. Sci. 2016, 9176-183.[4] W. Liu et al., Acc. Chem. Res . 2018,51,1858.[5] A. Baby et al., Chem. Comm. 2020, 56, 8400-8403.

Co9S8-FeCoS2 Two-Phase Nanoparticles Anchored in N, S Co-Doped Honeycomb Carbon Spheres as Highly Efficient Bifunctional Oxygen Catalyst

Transition metal sulfides (TMS) are considered as candidate oxygen redox catalysts (OER/ORR) due to their high catalytic activity and reversible redox performance. The OER/ORR performance for TMS can be further improved through the multi-doped electrochemical active sites provided by the dual-metallic (Co,Fe) and dual-nonmetallic species (N,S). Herein, a Co9S8-FeCoS2 two-phase nanoparticle anchored in N, S co-doped honeycomb carbon sphere ((Co,Fe)S@N,S-HCS) is synthesized by a multistep process template method. It has been found that the (Co,Fe)S@N,S-HCS possesses a mesoporous structure with a highly graphitized carbon along with the key OER active site of Co9S8 and the major ORR active center of FeCoS2. Also, the synergistic effect of Co9S8-FeCoS2 two-phase nanoparticles can further enhance the activity of OER and ORR. The as-prepared (Co,Fe)S@N,S-HCS exhibits excellent bifunctional activity in alkaline media, with an OER overpotential as low as 310 mV at 10 mA cm−2 and good stability, which exceeds (Fe)S@N,S-HCS, (Co)S@N,S-HCS and the noble metal RuO2. Besides, the ORR activity exhibits a half-wave potential of 0.84 V, which exceed the other two single component sulfides and close to the commercial Pt/C. Therefore, this work provides a significant approach to prepare highly efficient and stable dual-TMS heteroatom modified carbon-based OER/ORR bifunctional oxygen catalyst.

Superb Bifunctional Water Electrolysis Activities of Carbon Nanotube-Decorated Lanthanum Hydroxide Nanocomposites

For highly efficient hydrogen production from electrocatalytic water electrolysis, developing a high-fidelity electrocatalyst is pivotal. Herein, we demonstrated the excellent water-splitting performances of the carbon allotrope-decorated rare earth oxide nanocomposite system, which was composed of lanthanum hydroxide (La(OH)3) and carbon nanotube (CNT). The nanocomposites of CNT-La(OH)3 were fabricated via facile ultrasonication using La(OH)3 nanoparticles and CNT nanofibers, and they exhibited excellent bifunctional water-splitting activities. For the hydrogen evolution reaction, CNT-La(OH)3 showed low values of both overpotential (150 mV) and Tafel slope (113 mV/dec) in 1 M KOH at -10 mA/cm2. Additionally, for the oxygen evolution reaction, CNT-La(OH)3 also displayed small values for their overpotential (310 mV) as well as the Tafel slope (39 mV/dec). Furthermore, both bifunctional hydrogen- and oxygen-evolution reactions were confirmed to be stable in chronopotentiometric tests. From the material characterization and the electrochemical characterization, such excellent bifunctional water electrolysis performances were ascribed to the synergetic effects of hybridization of La(OH)3 (i.e., a large number of electrochemically active sites of 304 cm2) and CNT (i.e., high charge transport conductivity). The results specify that the present CNT-La(OH)3 nanocomposite system possesses ample aptitude as a superior electrocatalyst for next-generation hydrogen production technology.

P-N Heterojunction Embedded CuS/TiO2 Bifunctional Photocatalyst for Synchronous Hydrogen Production and Benzylamine Conversion.

The coupling of photocatalytic hydrogen production and selective oxidation of benzylamine is a topic of significant research interest. However, enhancing the bifunctional photocatalytic activity in this context is still a major challenge. The construction of Z-scheme heterojunctions is an effective strategy to enhance the activity of bifunctional photocatalysts. Herein, a p-n type direct Z-scheme heterojunction CuS/TiO2 is constructed using metal-organic framework (MOF)-derived TiO2 as a substrate. The carrier density is measured by Mott-Schottky under photoexcitation, which confirms that the Z-scheme electron transfer mode of CuS/TiO2 is driven by the diffusion effect caused by the carrier concentration difference. Benefiting from efficient charge separation and transfer, photogenerated electrons, and holes are directedly transferred to active oxidation and reduction sites. CuS/TiO2 also exhibits excellent bifunctional photocatalytic activity without noble metal cocatalysts. Among them, the H2 evolution activity of the CuS/TiO2 is found to be 17.1 and 29.5 times higher than that of TiO2 and CuS, respectively. Additionally, the yields of N-Benzylidenebenzylamine (NBB) are 14.3 and 47.4 times higher than those of TiO2 and CuS, respectively.

Unveiling the origin of activity in RuCoOx-anchored nitrogen-doped carbon electrocatalyst for high-efficiency hydrogen production and hydrazine oxidation using Raman spectroscopy

Hydrazine-assisted water electrolysis has gained much attention nowadays as an energy-saving strategy for the large-scale production of hydrogen fuel. Regardless, the synthesis of highly proficient bifunctional electrocatalysts remains a major challenge. Metal–organic frameworks (MOF) derived electrocatalysts have recently demonstrated excellent bifunctional activity in water electrolysis. Herein, we developed a new type of Ru-MOF on rod-like Co-MOF (Ru/Co-MOF) microstructures via a two-step solvothermal route. Subsequently, the Ru/Co-MOF was used as a precursor and self-template to synthesize an electrocatalytically active RuO2/Co3O4 anchored nitrogen-doped carbon (RuCoOx@NC) composite via a one-pot pyrolysis–oxidation strategy under atmospheric air. The RuCoOx@NC composite showed an ultralow overpotential of 44 mV for the hydrogen evolution reaction and 255 mV for the oxygen evolution reaction at 10 mA cm−2 in a 1 M KOH solution. Besides, the RuCoOx@NC composite exhibited an ultra-small working potential of − 0.040 V (vs. reversible hydrogen electrode (RHE)) for the hydrazine oxidation reaction at 10 mA cm−2 in a 1 M KOH/0.5 M hydrazine solution. The assembled RuCoOx@NC∥RuCoOx@NC membrane-free overall hydrazine splitting electrolyzer only required ultralow cell voltages of 0.063 and 0.505 V to produce 10 and 100 mA cm−2, with remarkable long-term stability, demonstrating its exceptional bifunctional activity. Ex situ Raman spectroscopy results indicate that both Co3O4 and RuO2 species contribute to the electrocatalytic activity of the RuCoOx@NC composite. This work suggests a potential strategy for developing bifunctional electrocatalytic materials for energy-saving hydrogen production to solve future energy demands.