Bifunctional Activity Research Articles

Demystifying Synergistic Multifunctional Electrocatalysis of N-Doped Graphene/WS2 Heterostructure with Single-Atom Catalysts for Water Splitting and Fuel Cells.

As the demand for sustainable energy continues to rise, electrocatalysis has become increasingly prominent in the advancement of clean energy technologies. By scrutinizing the material to function as a multifunctional catalyst, the effectiveness of energy conversion processes is significantly enhanced. This study focuses on harnessing graphene/WS2 van der Waals heterostructures for overall water splitting and fuel cell applications, using transition metals (TMs) from Sc-Zn as single-atom catalysts (SACs). Additionally, the research explores the synergistic effect of nitrogen doping combined with SACs to modify the material into multifunctional catalysts. The stability of all TMs as SACs in the vdW heterostructure (TM@GW) and nitrogen-doped TM@GW (TM@NGW) is validated with negative cohesive and formation energies, and thermodynamic stability is also corroborated with ab initio molecular dynamics (AIMD) analysis at both 300 and 500 K for 5 ps. The observed electrocatalytic performance of TM@GW and TM@NGW depicts that the Ni@NGW system exhibits trifunctional property with the lowest overpotentials {ηHER; ηOER; ηORR = 0.21; 0.42; 0.27 V}. Additionally, the Cr@NGW material displays bifunctional catalytic activity for the OER and ORR, with overpotentials of 0.53 and 0.37 V, respectively. The synergistic effect between N doping and SACs is further studied with the d, p band centers and density of states calculations. Furthermore, the scaling relation between the adsorption of intermediates and reaction kinetics is studied, which validates the coaction of N and SACs in the TM@NGW heterostructure. This study demonstrates that the inclusion of SACs and nitrogen atoms in the GW heterostructure significantly enhances the catalytic performance by approximately 26%, effectively transforming the system into a multifunctional catalyst. These findings emphasize the role of SACs in vdW heterostructures and N doping effects, providing valuable insights to guide the design of advanced catalysts for water splitting and fuel cell applications.

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.

Isolated FeN3 sites anchored hierarchical porous carbon nanoboxes for hydrazine‐assisted rechargeable Zn‐CO2 batteries with ultralow charge voltage

AbstractZn‐CO2 batteries (ZCBs) are promising for CO2 conversion and electric energy release. However, the ZCBs couple the electrochemical CO2 reduction (ECO2R) with the oxygen evolution reaction and competitive hydrogen evolution reaction, which normally causes ultrahigh charge voltage and CO2 conversion efficiency attenuation, thereby resulting in ~90% total power consumption. Herein, isolated FeN3 sites encapsulated in hierarchical porous carbon nanoboxes (Fe‐HPCN, derived from the thermal activation process of ferrocene and polydopamine‐coated cubic ZIF‐8) were proposed for hydrazine‐assisted rechargeable ZCBs based on ECO2R (discharging process: CO2 + 2H+ → CO + H2O) and hydrazine oxidation reaction (HzOR, charging process: N2H4 + 4OH− → N2 + 4H2O + 4e−). The isolated FeN3 endows the HzOR with a lower overpotential and boosts the ECO2R with a 96% CO Faraday efficiency (FECO). Benefitting from the bifunctional ECO2R and HzOR catalytic activities, the homemade hydrazine‐assisted rechargeable ZCBs assembled with the Fe‐HPCN air cathode exhibited an ultralow charge voltage (decreasing by ~1.84 V), excellent CO selectivity (FECO close to 100%), and high 89% energy efficiency. In situ infrared spectroscopy confirmed that Fe‐HPCN can generate rate‐determining *N2 and *CO intermediates during HzOR and ECO2R. This paper proposes FeN3 centers for bifunctional ECO2R/HzOR performance and further presents the pioneering achievements of ECO2R and HzOR for hydrazine‐assisted rechargeable ZCBs.

Fabrication of an Antibacterial/Anticoagulant Dual-Functional Surface for Left Ventricular Assist Devices via Mussel-Inspired Polydopamine Chemistry.

Infections and thrombosis remain unsolved problems for implanted cardiovascular devices, such as left ventricular assist devices. Hence, the development of surfaces with improved blood compatibility and antimicrobial properties is imperative to reduce complications after artificial heart implantation. In this work, we report a novel approach to fabricate multifunctional surfaces for left ventricular transplanted ventricular assist devices (LVADs) by immobilizing nitric oxide (NO) generation catalysts and heparin and reducing silver nanoparticles in situ. The general view, structure, and chemical compositions of the pure/modified surfaces were characterized using digital imaging, scanning electron microscope (SEM), atomic force microscope (AFM), water contact angle (WCA), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP). All of the results demonstrated that the AgNPs and heparin were successfully immobilized on the surface. The Cu ions and NO release experimental results showed that the immobilized copper ions could catalyze the production of NO from S-nitrosothiols within the biological system. Meanwhile, due to the synergistic anticoagulant effect of NO and surface-immobilized heparin, the fabricated modified surfaces exhibited antiplatelet adhesion activities and good hemocompatibility. Finally, the antimicrobial activity of the samples was evaluated by Escherichia coli and Staphylococcus aureus, and cytocompatibility was measured using human umbilical vein endothelial cells (HUVECs). The results demonstrated that silver nanoparticles (AgNPs) immobilized by surface reduction reaction did not cause any significant inhibition of cell proliferation while providing stable and effective antimicrobial properties. We envision that this simple surface modification strategy with bifunctional activities of antimicrobial and anticoagulant will find widespread use in clinically used indwelling left ventricular assist devices.

Heterointerfacial engineering of N,P-doped carbon nanosheets supported Co/Co2P nanoparticles for boosting oxygen reduction and oxygen evolution reactions towards rechargeable Zn-air battery

Transition metal phosphides (TMPs) with high electrocatalytic activity for the oxygen evolution reaction (OER) are reckoned as a substitution of precious group metals catalysts in rechargeable Zn-air battery. In this work, Co/Co2P heterojunction nanoparticles supported N,P-doped carbon nanosheets (Co/Co2P@NPCNS) were designed and prepared via a facile one-step molten salt-assisted pyrolysis process. Density function theory calculations reveal that the heterogeneous interactions of Co/Co2P effectively enhance the bifunctional electrocatalytic activity for oxygen reduction reaction (ORR) and OER. The synergistic interaction between the Co/Co2P heterojunction nanoparticles with highly exposed active sites and excellent catalytic activity and the two-dimensional doped carbon nanosheets with high conductivity contributes to Co/Co2P@NPCNS exhibiting preeminent bifunctional ORR/OER activity and stability with a high half-wave potential for ORR (0.87 V), a low overpotential for OER (302 mV at 10 mA cm−2) and a low potential gap (0.66 V). The homemade rechargeable Zn-air battery performs high peak power density (187 mW cm−2) and exceptional endurance. This heterogeneous interface tactic of integrating TMPs with heteroatom-doped carbon materials may shed light on the research and development of non-precious metal electrocatalysts.

Substrate specificity and kinetic mechanism of 3-hydroxy-Δ5-C27-steroid oxidoreductase

Cholesterol is a key sterol whose homeostasis is primarily maintained through bile acid metabolism. Proper bile acid formation is vital for nutrient and fat-soluble vitamin absorption and emulsification of lipids. Synthesis of bile acids occurs through two main pathways, both of which rely on 3-hydroxy-5-C27 steroid oxidoreductase (HSD3B7) to begin epimerization of the 3β hydroxyl of cholesterol into its active 3α conformation. In this sequence HSD3B7 catalyzes the dehydrogenation of the 3β-hydroxy group followed by isomerization of the Δ5-cholestene-3-one. These reactions are some of the many steps that transform cholesterol for either storage or secretion. HSD3B7 has distinct activity from other 3β-HSD family members leaving significant gaps in our understanding of its mode of catalysis and substrate specificity. Additionally, the role of HSD3B7 in health and disease positions it as a metabolic vulnerability that could be harnessed as a therapeutic target. To this end, we evaluated the mechanism of HSD3B7 catalysis and reveal that HSD3B7 displays activity towards diverse 7α-hydroxylated oxysterols. HSD3B7 retains its catalytic efficiency towards these substrates, suggesting that its substrate binding pocket can withstand changes in polarity upon alterations to this hydrocarbon tail. Experiments aimed at determining substrate order are consistent with HSD3B7 catalyzing a sequential ordered bi bi reaction mechanism with the binding of NAD+ followed by 7α-hydroxycholesterol to form a central complex. HSD3B7 bifunctional activity is dependent on membrane localization through a putative membrane-associated helix giving insight into potential regulation of enzyme activity. We found strong binding of the NADH product thought to activate the isomerization reaction. Homology models of HSD3B7 reveal a potential substrate pocket that allows for oxysterol binding and mutagenesis was utilized to support this model. Together these studies offer an understanding of substrate specificity and kinetic mechanism of HSD3B7 which can be exploited for future drug development.

Threefold Impact on Reaction Coordinate Mapping of Zirconium Based Tri‐Chalcogenide Pseudo‐Monolayers as Emerging Ultrathin Catalysts for Water Splitting

AbstractThe continuous quest of finding optimum catalysts for photo‐electrocatalytic (PEC) water splitting has been revolving around 2D ultrathin materials because of the fact of exploiting both the surface area. In this work, a threefold impact is envisaged route to enhance the activity both in terms of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the emerging Zirconium Tri‐sulfides (ZrS3) based pseudo‐monolayers. Due to the unique and distinct electronic properties of the tri‐chalcogenide systems as compared to the di‐chalcogenide counterpart of Zirconium, one could afford to explore the implications of not only single‐atom functionalization and vacancy defect, but also the external strain to expedite the bifunctional catalytic activity in this promising material. Rigorous electronic structure calculations have been performed for the mentioned threefold effect on not only the band‐edge alignment, but going beyond to it by further constructing the reaction coordinate mapping corresponding to HER and OER mechanism. The repercussion of external strain in addition to the single atom functionalization and vacancy defect on the adsorption free energies of the prime intermediates of HER and OER reaction has been further correlated with the work function variation in this pseudo‐monolayer system.

FeCo Bimetallic ZIF Derivatives decorated with CoFe-LDH to Promote Bifunctional Oxygen Electrocatalysis Activation.

Reasonably screening the targeted oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) constituents and constructing high-efficiency and stabilized ORR/OER bifunctional electrocatalysts are pivotal for the advancement of rechargeable zinc-air batteries (ZABs). Here, CoFe layered double hydroxide (CoFe-LDH) nanosheets are deposited on nitrogen-doped graphite-carbon polyhedra with FeCo alloy nanoparticles (FeCo/LDH-NGCP). Due to the synergic effect between FeCo-NGCP, CoFe-LDH and FeCo/LDH-NGCP, the electrocatalyst with the abundant and accessible active sites can provide good charge/mass transfer, and thus shows wonderful ORR and OER bifunctional electrocatalytic performance. In ORR tests, FeCo/LDH-NGCP catalyst displays larger half-wave potential (E1/2, 0.89 V vs. 0.85 V), higher limiting current density (JL, 5.91 mA/cm2 vs. 5.14 mA/cm2) and better stability than commercial Pt/C. As for OER, FeCo/LDH-NGCP possesses a smaller overpotential (η) of 299.6 mV at a current density of 10 mA/cm2 and more durable stability than commercial RuO2 (330.6 mV). Furthermore, in ZAB tests, the cycling stability of ZAB-FeCo/LDH-NGCP (over 470 h) outperforms the ZAB-Pt/C+RuO2 (92 h) with commercial electrocatalyst (Pt/C+RuO2). Therefore, the FeCo/LDH-NGCP catalyst offers a new perspective to construct ZABs bifunctional catalysts and their commercial application in ZABs.

Unveiling the Electrocatalytic Activity of Bifunctional Iron‐Niobium Double Perovskites for Overall Water Splitting: A‐Site Cation Influence

AbstractCapitalizing on the electrochemical conversion of water into hydrogen stands as a pivotal strategy in the global transition toward sustainable energy sources. This study investigates the influence of the A‐site cation type within A2FeNbO6 double perovskites (where A = Ca, Sr, or Ba) on their bifunctional electrocatalytic activities. The electrocatalytic performance is scrutinized in relation to charge transfer resistance, oxygen vacancy concentration, and metal‐oxygen covalency. Among the variants, Sr2FeNbO6 is distinguished as the optimal catalyst, achieving a current density of 10 mA cm⁻2 at overpotentials of 260 mV for the oxygen evolution reaction (OER) and 176 mV for the hydrogen evolution reaction (HER), thus matching the performance of leading metal oxide electrocatalysts. The study reveals pH‐dependent kinetics for Sr2FeNbO6, indicative of a lattice oxygen evolution mechanism for OER. An electrolyzer employing Sr2FeNbO6 electrodes for both the anode and cathode delivers a current density of 10 mA cm⁻2 at an efficient cell voltage of 1.76 V for complete alkaline water splitting, while also demonstrating exceptional stability. These insights advance the understanding of material optimization for electrocatalysis and position Sr2FeNbO6 as a viable catalyst for the sustainable production of hydrogen.

Investigating the bifunctional electrocatalytic activity of nickel oxide/nitrogen-doped reduced graphene oxide nanocomposite for zinc-air battery application

Investigating the bifunctional electrocatalytic activity of nickel oxide/nitrogen-doped reduced graphene oxide nanocomposite for zinc-air battery application

Novel design of hollow carbon nanocage modified with nanotubes as a bifunctional electrocatalyst for high performance Zn–air batteries

Microcavities play a crucial role as microreactors in the transport of molecular/ionic guests and the exposure of active sites, thus significantly influencing the electrocatalytic performance. This study prepares Co/N-codoped hollow carbon (HT-CoN/C) with surface-distributed carbon nanotubes by pyrolysis of PDA-coated Zn/Co bimetallic ZIF (BM-ZIF@PDA). Benefiting from the hierarchical porous structure, high specific surface area (307.17 m2 g−1) and abundant Co clusters, the HT-CoN/C exhibits remarkable bifunctional oxygen electrocatalytic activity with an overpotential of the ORR/OER processes (ΔE = 0.703 V). The density functional theory (DFT) calculations also verify that the configuration of C-coated N-coordinated Co clusters (Co4-Nx) affect the electrocatalytic activity of ORR and OER, illustrating the source of the excellent oxygen electrocatalytic activity of HT-CoN/C. The aqueous rechargeable zinc-air battery (RZAB) using HT-CoN/C as the air electrode is characterized by a superior peak power density (175 mW cm−2), a prolonged cycle life (1230 cycles/410 h at 5.0 mA cm−2) and a high open-circuit voltage (1.47 V). Meanwhile, the flexible solid-state RZAB assembled by the HT-CoN/C also exhibits a higher peak power density (117 mW cm−2) and an excellent bending performance. This work is extremely valuable for the design and synthesis of Co/N co-doped carbon electrocatalysts.

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.

High-Entropy Ag-Ru-Based Electrocatalysts with Dual-Active-Center for Highly Stable Ultra-Low-Temperature Zinc-Air Batteries.

The development of advanced bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is significant for rechargeable zinc-air batteries (ZABs). Herein, a unique dual active center alloying strategy is proposed to achieve the efficient bifunctional oxygen catalysis, and the high entropy effect is further exploited to modulate the structure and performance of the catalysts. The MOF-assisted pyrolysis-replacement-alloying method was employed to construct the CoCuFeAgRu high-entropy alloy (HEA), which are uniformly anchored in porous nitrogen-doped carbon nanosheets. Notably, the obtained HEA catalyst exhibits excellent catalytic performance for both ORR and OER, and a peak power density of 136. 53 mW cm-2 and an energy density of 987.9 mAh gZn -1, surpassing the most of the previously reported bifunctional oxygen electrocatalysts. Moreover, the assembled flexible rechargeable ZAB enables excellent performance even at the ultralow temperature of -40 °C, with an energy density of 601.6 mAh gZn -1 and remarkable cycling stability up to 1,650 hours. Combined experimental and theoretical calculation results reveal that the excellent bifunctional catalytic activity of the HEA catalyst originated from the synergistic effect of the Ag and Ru dual active centers, and the optimization of the electronic structure by alloying effect.

High‐Entropy Ag‐Ru‐based Electrocatalysts with Dual‐Active‐Center for Highly Stable Ultra‐Low‐Temperature Zinc‐Air Batteries

The development of advanced bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is significant for rechargeable zinc‐air batteries (ZABs). Herein, a unique dual active center alloying strategy is proposed to achieve the efficient bifunctional oxygen catalysis, and the high entropy effect is further exploited to modulate the structure and performance of the catalysts. The MOF‐assisted pyrolysis‐replacement‐alloying method was employed to construct the CoCuFeAgRu high‐entropy alloy (HEA), which are uniformly anchored in porous nitrogen‐doped carbon nanosheets. Notably, the obtained HEA catalyst exhibits excellent catalytic performance for both ORR and OER, and a peak power density of 136. 53 mW cm‐2 and an energy density of 987.9 mAh gZn‐1, surpassing the most of the previously reported bifunctional oxygen electrocatalysts. Moreover, the assembled flexible rechargeable ZAB enables excellent performance even at the ultralow temperature of ‐40°C, with an energy density of 601.6 mAh gZn‐1 and remarkable cycling stability up to 1,650 hours. Combined experimental and theoretical calculation results reveal that the excellent bifunctional catalytic activity of the HEA catalyst originated from the synergistic effect of the Ag and Ru dual active centers, and the optimization of the electronic structure by alloying effect.

Boosting the bifunctional catalytic activity of Co3O4 on silver and nickel substrates for the alkaline oxygen evolution and reduction reactions

Developing an efficient bifunctional catalyst for oxygen reduction (ORR) and evolution reactions (OER) is a crucial step for the wide commercialization of alkaline water electrolyzers. However, a proper assessment and comparison of various catalysts is still challenging due to the different catalyst substrates and loadings. In this work, Co3O4 spinel nanoparticles (NPs) were investigated as a bifunctional catalyst at different substrates of glassy carbon or Ag bulk substrate or Ni particles and with different loadings. For Co3O4 (800 µg cm-2)/Ag electrode, not only the overpotential for ORR was 50 mV lower than the bare Ag electrode, but also the OER overpotential was 40 mV lower than the sole Co3O4. Besides, less than 1% peroxide intermediate was detected during ORR using the rotating ring disc electrode (RRDE) method, suggesting a 4-electron O2 reduction. Tafel slopes of 70 and 60 mV dec‑1 at Co3O4/Ag were obtained for ORR and OER, respectively. The improved bifunctional activity could be attributed to a synergistic effect between Co3O4 and the Ag support. For the loading effect, it is revealed that the number of accessible sites of Ag surface decreases with increasing the Co3O4 loading, as evaluated from lead-underpotential deposition measurements. Interestingly, after running ORR/OER cycles, the surface area increased by 4–6 times. This surface roughening was also confirmed by SEM and EDX. The study was extended to Co3O4+Ni mixed catalyst to validate the effect of the support on this induced synergism. Hence, this work provides a simple route for designing potential effective catalytic interfaces and contributes to unravelling the influence of the substrate and loading on the catalyst activity for water electrolyzers.

High activity of cobalt-atomically dispersed catalyst on mesoporous carbon for rechargeable Zn-air batteries via effective removal of the hard template

The use of oxygen from air in Zn-air batteries requires the smart design of materials with bifunctional activity for oxygen reduction and evolution reactions (ORR/OER), and with a porous structure to facilitate the diffusion of oxygen gas to active sites. Kit-6 template-assisted porous structures have been proposed to this end; however, traditional methods for the removal of Kit-6 templates are highly aggressive and environmentally harmful. In this study, we present the synthesis of a cobalt atomically dispersed catalyst (Co-ADC) with interlayer engineering using mesoporous Kit−6 templates, focusing on two removal strategies: sodium hydroxide (0.5, 1, and 2 M) and hydrofluoric acid (15, 30, and 45 %). Physicochemical results indicated that Co-ADC-containing nanoparticles were obtained using the proposed methodology, while the use of HF promoted the loss of cobalt in the catalyst. During the activity evaluation for the ORR, and it was found that 0.5 M NaOH and HF at 15 % displayed similar activity, which could be related to the effect of carbon material as co-catalyst, but the first enabled a close 4e− pathway, and thus, the Co-ADC presented a ΔEOER-ORR of 640 mV. This optimized ADC displayed improved functionality owing to diffusion improvements by the mesoporous structure, presenting a maximum power density of 130.6 mW cm−2 and 30 % higher specific activity than the Pt + IrO2/C reference material. Rechargeability was evaluated, yielding a ΔV = 0.87 V at 5.175 mA cm−2 with a round-trip efficiency of 57.5 %. Nonetheless, the optimized material presented higher rechargeability, displaying no significant round-trip changes after 100 cycles, while Pt + IrO2/C presented changes due to OER issues after only 48 cycles.

Bifunctional catalytic activity of anion-doped LaSrCoO4 for oxygen reduction and evolution reactions.

Here, we synthesized Co-based, anion-incorporated‍ ‌R‌u‌d‌d‌l‌e‌s-d‌e‌n‌-‌Popper perovskite electrocatalysts (LaSrCoO4-x X y ) and compared their catalytic performances in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The ORR mechanism with the newly synthesized F-doped LaSrCoO4 catalyst was dominated by a four-electron process, and the number of electrons involved in the reaction increased compared with that for LaSrCoO4. The OER activity of the hydride-doped LaSrCoO4 catalyst was the highest among the LaSrCoO4 system catalysts. Density functional theory calculations revealed that there is a correlation between the Co 3d unoccupied orbital band centre and the OER activity. The addition of anions and substitution of metal sites improved the ORR and OER activities of the catalysts. Our findings confirmed that the addition of heteroatom anions can improve the activity of perovskite-type electrocatalysts, promoting their application in various fields.

Defective wood-based chainmail electrocatalysts boost performances of seawater-medium Zn-air batteries

A high-activity and stable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalyst is critical for seawater-based Zn-air batteries (ZABs). Herein, we report a wood-derived chainmail electrocatalyst containing defective nitrogen-doped carbon nanotubes encapsulating cobalt nanoparticles (Co@D-NCNT/CW) to enhance the ORR/OER activity and stability in seawater medium. During the preparation process, the introduction and removal of Zn increased the defect sites and pyridine N content in the carbon material, modulating charge distribution and influencing the adsorption and activation processes. The highly ordered open channels in Co@D-NCNT/CW promoted mass transfer of reactants and accelerated gas diffusion. The resultant chainmail electrocatalyst exhibited impressive bifunctional ORR and OER activities with an ultra-low gap of 0.67 V in seawater-based alkaline electrolyte. The Co@D-NCNT/CW-assembled seawater-based rechargeable liquid ZABs demonstrated a maximum power density of 245.3 mW cm−2 and a long-term cycling performance over 500 h. The seawater-based all-solid-state ZABs achieved the maximum power density of 48.2 mW cm−2 and stabilized over 30 h. Density functional theory revealed that the presence of defects and pyridine nitrogen in Co@D-NCNT/CW modulated the electronic structure of Co, optimizing the binding affinity of the Co sites with intermediates and weakening Cl− adsorption. This work provides a new approach to preparing high-activity and stable ORR/OER electrocatalyst utilizing wood nanostructures, boosting the development of seawater-based ZABs.

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.

Coordination polymer derived transition metal phosphide/carbon composites for bifunctional oxygen electrocatalyst

Developing nonprecious electrocatalysts with bifunctional performances for oxygen reduction (ORR) and evolution reactions (OER) remains a crucial challenge in rechargeable Zn-air batteries (RZABs). In this study, we report the synthesis of a three-dimensional (3D) porous N, P-doped carbon-wrapped cobalt phosphide composite (Co2P@3DNPC) via direct calcination of a novel organic/inorganic porous coordination polymer by an in-situ phosphating strategy. DFT calculations demonstrate the intricate interactions occurring during the PEI-directed grinding self-assembly process among Co2+, phytic acid (PA), and polyethylenimine (PEI). Specifically, Co2+ ions initially adsorb onto PEI molecules before integrating with PA to form a 3D coordination polymer matrix. As-fabricated Co2P@3DNPC composite exhibits impressive ORR/OER bifunctional performances, with a half-wave potential of 0.78 V and an overpotential of 1.71 V, respectively. Its bifunctional activities enable a power density of 148.5 mW cm–2 in rechargeable ZABs, with remarkable stability (> 480 h) during a discharge-charge cycle. The interconnected porous structure and embedded Co2P nanoparticles optimize the electrode-electrolyte interfacial contact, boosting energy density and cycle life of as-assembled ZABs. This innovative approach paves the way for efficient, cost-effective production of bifunctional electrocatalysts for RZABs.