Oxygen Reduction Reaction Stability Research Articles

Active Sites Regulation and Mass Production of a Hierarchically Porous Fe-N-C Catalyst for Zinc-Air Batteries.

Although the iron-nitrogen-carbon (Fe-N-C) catalyst has great potential in zinc-air batteries (ZABs), the insufficient performance and low production of the Fe-N-C catalyst are still the key factors that greatly limit the commercial application. In this study, first, a simple dual melt-salt template method is developed to prepare the hierarchically porous HPFe-N-C catalyst with abundant highly stable Fe-pyridinic-N sites. Then, HPFe-N-C and Fe-phenanthroline are mixed and heated for the mass production of THPFe-N-C with rich highly active Fe-pyrrolic-N sites. Under the synergistic effect of the different active sites, THPFe-N-C exhibits better activity and stability of oxygen reduction reaction (ORR) than Pt/C. Density functional theory is utilized to reveal the changing of the free energy for the ORR process of active sites. COMSOL multiphysics simulations are used to prove that the hierarchically porous THPFe-N-C is beneficial to the O2 mass-transfer process. Therefore, THPFe-N-C shows a better discharge performance and peak power density than Pt/C in the ZABs.

Biomass-derived single atom catalysts with phosphorus-coordinated Fe-N3P configuration for efficient oxygen reduction reaction

Exploiting non-precious metal catalysts with excellent oxygen reduction reaction (ORR) performance for energy devices is paramount essential for the green and sustainable society development. Herein, low-cost, high-performance biomass-derived ORR catalysts with an asymmetric Fe-N3P configuration was prepared by a simple pyrolysis-etching technique, where carboxymethyl cellulose (CMC) was used as the carbon source, urea and 1,10-phenanthroline iron complex (FePhen) as additives, and Na3PO4 as the phosphorus dopant and a pore-forming agent. The CMC-derived FeNPC catalyst displayed a large specific area (BET:1235 m2 g−1) with atomically dispersed Fe-N3P active sites, which exhibited superior ORR activity and stability in alkaline solution (E1/2 = 0.90 V vs. RHE) and Zn-air batteries (Pmax = 149 mW cm−2) to commercial Pt/C catalyst (E1/2 = 0.87 V, Pmax = 118 mW cm−2) under similar experimental conditions. This work provides a feasible and cost-effective route toward highly efficient ORR catalysts and their application to Zn-air batteries for energy conversion.

Ordered Pt3Ni intermetallic compound: A high-performance oxygen reduction reaction catalyst for Zn-air batteries

The development of advanced catalysts for oxygen reduction reaction (ORR) is crucial for Zinc-air batteries (ZABs). In this study, we focus on the controlled synthesis of ordered Pt3Ni intermetallic compounds through impregnation and high-temperature annealing, aiming to enhance the ORR performance for ZABs. The ordered Pt3Ni (denoted as Pt3Ni) and conventional alloy Pt3Ni (denoted as A-Pt3Ni) are synthesized at 600 ℃ and 200 ℃, respectively. Detailed structural characterizations confirm the formation of both ordered and disordered structures. Pt3Ni demonstrates superior ORR catalytic activity and stability compared to A-Pt3Ni and commercial Pt/C catalyst, as evidenced by higher half-wave potentials, lower Tafel slopes, and enhanced electrochemical stability. Furthermore, Pt3Ni exhibits exceptional performance in ZABs, with higher power density, specific capacity, and longer cycle life than its counterparts. These findings highlight the potential of ordered Pt3Ni intermetallic compounds as efficient ORR catalysts in ZABs, offering a promising route for the development of advanced energy conversion and storage systems.

Seed-Mediated Synthesis of High Loading PtCo Intermetallic Compounds Enhanced Catalytic Efficacy and Long-Term Stability for Oxygen Reduction Reaction.

Atomically ordered intermetallic Pt-based nanoparticles, recognized as advanced electrocatalysts, exhibit superior activity for the oxygen reduction reaction (ORR) in fuel cell cathodes. Nevertheless, the formation of these ordered structures typically necessitates elevated annealing temperatures, which can accelerate particle growth and diminished reactivity. In this study, we synthesized carbon-supported platinum-cobalt intermetallic compounds (PtCo-IMCs) with sub-4 nm particle sizes and uniform distribution. These catalysts, characterized by high platinum content and exceptional ORR activity, are specifically tailored for heavy-duty vehicle (HDV) applications. The PtCo-IMCs exhibited significantly enhanced catalytic performance and durability compared to conventional Pt-based catalysts, utilizing platinum nanoparticles as nucleation sites to promote growth. This method effectively retained smaller particle sizes while achieving a higher degree of ordering and alloying during high-temperature annealing. Optimization of the annealing temperature resulted in peak activity and stability at 800 °C. The mass activity (MA) of the PtCo-800 catalyst was 2.7-fold and 1.8-fold that of the commercial Pt/C and disordered PtCo catalysts, respectively. Additionally, the single cell employing the PtCo-800 catalyst showed a minimal voltage loss of only 27 mV at a current density of 2 A cm-2 after 30,000 cycles of the accelerated durability test (ADT), underscoring its long-term stability.

Emerging Carbon-Based Catalysts for the Oxygen Reduction Reaction: Insights into Mechanisms and Applications

The oxygen reduction reaction (ORR), as a key electrode process in fuel cells and metal-air batteries, plays a pivotal role in advancing clean energy technologies. However, the slow kinetics and high overpotential of the ORR significantly limit the efficiency of these energy devices. Therefore, the development of efficient, stable, and cost-effective ORR catalysts has become a central focus of current research. Carbon-based catalysts, with their excellent conductivity, chemical stability, and tunable structural features, have emerged as promising alternatives to traditional precious metal catalysts. Nevertheless, challenges remain in the design of active sites, the tuning of electronic structures, and the large-scale synthesis of carbon-based catalysts. This review systematically introduces the fundamental mechanisms and key factors influencing the ORR, providing an analysis of the critical variables that affect catalyst performance. Furthermore, it summarizes several common methods for synthesizing carbon-based catalysts, including pyrolysis, deposition, and ball milling. Following this, the review categorizes and discusses the latest advancements in metal-free carbon-based catalysts, single-atom and dual-atom catalysts, as well as metal-based nanoparticle catalysts, with a particular focus on their mechanisms for enhancing the ORR performance. Finally, the current state of research on carbon-based ORR catalysts is summarized, and future development directions are proposed, emphasizing the optimization of active sites, improvements in catalyst stability, and potential strategies for large-scale applications.

Effect of N-Doped Carbon on the Morphology and Oxygen Reduction Reaction (ORR) Activity of a Xerogel-Derived Mn(II)O Electrocatalyst

This work synthesizes a xerogel from a sol–gel synthesis strategy and supports it on N-doped carbon support from spent coffee biomass (Mn(II)O/N-CC, hereafter MnO) as an efficient oxygen reduction reaction (ORR) catalyst in alkaline electrolytes. The effects of N-CC carbon content on MnO nanoparticle size, dispersion, distribution, morphology, and electrochemistry on ORR are discussed. The SEM and TEM measurements show that increasing the N-CC content during the MnO gelation reaction improved MnO dispersion and particle size during thermal treatment, increasing the ORR’s electrochemical active surface area. Several physiochemical and electrochemical characterizations show a clear relationship between N-CC catalysts and ORR activities. The best catalyst, MnO/N-CC-5, had an even distribution of 27 nm MnO nanoparticles on the N-CC support. The MnO/N-CC-5 catalyst had almost identical ORR kinetics and stability to those of the state-of-the-art Pt/C catalyst in 0.1 M KOH electrolytes, losing only 10 mV in half-wave potential after 5000 potential cycles and retaining 96% of current for over 10 h of continuous chronoamperometric stability. By measuring the electrochemical active surface areas of various catalysts by cyclic voltammetry at different scan rates and measuring the double layer capacitance (Cdl) and ECSA, MnO/N-CC-5 catalysts were shown to have enhanced ORR activity. The XPS analysis explains the ORR activity in terms of the Mn3+/Mn4+ ratio, and a mechanism was proposed. These findings suggest that the MnO/N-CC-5 catalyst could be a cathode catalyst in fuel cells, biofuel cells, metal–air batteries, and other energy conversion devices.

Optimizing Fe-N-C Electrocatalysts for PEMFCs: Influence of Constituents and Pyrolysis on Properties and Performance

Proton exchange membrane fuel cells (PEMFCs) are promising alternative technologies with applications in stationary power systems, vehicles, and portable electronics due to their low temperature operation, fast start-up, and environmental advantages. However, the high cost of platinum-based catalysts, in particular for the oxygen reduction reaction (ORR) of the cathode side, prevents their widespread incorporation. Fe-N-C electrocatalysts have emerged as viable alternatives to platinum. In this study, different precursor components were investigated for the way that they affect the pyrolysis process, which is crucial for tailoring the final catalyst properties. In particular, carbon allotropes such as carbon Vulcan, Ketjenblack, and carbon nanotubes were selected for their unique structures and properties. In addition, various sources of iron (FeCl2, FeCl3, and K[Fe(SCN)4]) were evaluated. The influence of the pyrolysis atmosphere on the resulting Fe-N-C catalyst structures was also assessed. Through an integrated structure and surface chemistry analyses, as well as electrochemical tests with rotating disk electrode experiments in acidic media, the ORR performance and stability of these catalysts were defined. By examining the relationships between carbon sources and iron precursors, this research provides valuable information for the optimization of Fe-N-C catalysts in fuel cell applications.

Carbon-anchoring synthesis of Pt1Ni1@Pt/C core-shell catalysts for stable oxygen reduction reaction

Proton-exchange-membrane fuel cells demand highly efficient catalysts for the oxygen reduction reaction, and core-shell structures are known for maximizing precious metal utilization. Here, we reported a controllable “carbon defect anchoring” strategy to prepare Pt1Ni1@Pt/C core-shell nanoparticles with an average size of ~2.6 nm on an in-situ transformed defective carbon support. The strong Pt–C interaction effectively inhibits nanoparticle migration or aggregation, even after undergoing stability tests over 70,000 potential cycles, resulting in only 1.6% degradation. The stable Pt1Ni1@Pt/C catalysts have high oxygen reduction reaction mass activity and specific activity that reach 1.424 ± 0.019 A/mgPt and 1.554 ± 0.027 mA/cmPt2 at 0.9 V, respectively, attributed to the optimal compressive strain. The experimental results are generally consistent with the theoretical predictions made by our comprehensive microkinetic model which incorporates essential kinetics and thermodynamics of oxygen reduction reaction. The consistent results obtained in our study provide compelling evidence for the high accuracy and reliability of our model. This work highlights the synergy between theory-guided catalyst design and appropriate synthetic methodologies to translate the theory into practice, offering valuable insights for future catalyst development.

Optimizing Activity and Stability in AgCl‐CuO Electrocatalysts: Insights from Different Morphologies for Enhanced ORR Performance

AbstractHighly enduring and methanol‐tolerant electrocatalysts are pertinent to revolutionizing direct methanol fuel cell (DMFC) technologies. Transition‐metal‐based electrocatalysts are anticipated to rank among the remarkable electrocatalysts for boosting the sluggish oxygen reduction reaction (ORR) kinetics. In this study, we report a facile approach to optimize the activity and stability of the AgCl‐CuO systems. The tailored nanoparticle–nanorod (NP–NR) and nanoleaf (NL) like morphologies deliver remarkable bifunctional catalytic performance for oxygen reduction and hydrogen evolution reactions, sustained activity, and comparatively better stability for ORR. A meager shift of only 0.014 and 0.024 V in the half‐wave potential is observed in the NP‐NR and NL structures, respectively, for the ORR even after 2500 cycles. Furthermore, both the AgCl‐CuO composite exhibit an excellent tolerance to methanol.

Nitrogen-doped carbon embedded with heterostructured Co3Fe7-Co5.47N nanoalloys for electrocatalytic oxygen reduction reaction in zinc-air battery

The oxygen reduction reaction (ORR) is the cathodic process in zinc-air batteries, but its sluggish kinetics significantly limit the energy conversion efficiency of these batteries. Therefore, developing high-performance ORR electrocatalysts is essential to support the advancement of zinc-air battery technology. Herein, a nitrogen-doped carbon embedded with heterostructured Co3Fe7-Co5.47N nanoalloys (FeCo@NC-900) was fabricated, and the electrocatalytic ORR activity and stability of FeCo@NC-900 were investigated in alkaline media. The FeCo@NC-900 catalyst exhibited a half-wave potential of 0.84 V, a Tafel slope of 76.06 mV·dec−1, and an electron transfer number (n) of approximately 3.83 for ORR. A rechargeable zinc-air battery was assembled using FeCo@NC-900 as the air cathode, achieving an open-circuit voltage of 1.435 V and a maximum power density of 81 mW cm−2, along with good cycling stability.

Boosting the Performance and Durability of Fe-N-C Fuel Cell Catalysts via Integrating Mo2C Clusters.

Carbon-supported nitrogen-coordinated iron single-atom (Fe-N-C) catalysts have been regarded among the most promising platinum-group-metal-free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Nevertheless, their limited intrinsic activity and unsatisfactory stability have hindered their practical applications. Here, it is reported that the integration of Mo2C clusters effectively enhances the ORR activity and stability of Fe-N-C catalysts. The composite catalyst of Fe single atoms and Mo2C clusters co-embedded on nitrogen-doped carbon (FeSA/Mo2C-NC) exhibits an excellent ORR activity with a half-wave potential of 0.82V in acidic media and a high peak power density of 0.5W cm-2 in an H2-air PEMFC. Moreover, improved stability is achieved with nearly no decay under H2-air conditions for 80h at 0.4V. Experiments with theoretical calculations elucidate that the etching effect of the phosphomolybdic acid precursor optimizes the pore size distribution of the composite catalyst, thereby exposing more active sites. The Mo2C clusters modulate the electronic configuration of the Fe-N4 sites, optimizing adsorption energy for ORR intermediates and strengthening the Fe-N bond to mitigate demetalation. This work provides valuable insights into the construction of single-atom/nanoaggregate hybrid catalysts for efficient energy-related applications.

Fluorine‐Lodged High‐Valent High‐Entropy Layered Double Hydroxide for Efficient, Long‐Lasting Zinc‐Air Batteries

AbstractEfficient and stable bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts are urgently needed to unlock the full potential of zinc‐air batteries (ZABs). High‐valence oxides (HVOs) and high entropy oxides (HEOs) are suitable candidates for their optimal electronic structures and stability but suffer from demanding synthesis. Here, a low‐cost fluorine‐lodged high‐valent high‐entropy layered double hydroxide (HV‐HE‐LDH) (FeCoNi2F4(OH)4) is conveniently prepared through multi‐ions co‐precipitation, where F− are firmly embedded into the individual hydroxide layers. Spectroscopic detections and theoretical simulations reveal high valent metal cations are obtained in FeCoNi2F4(OH)4, which enlarge the energy band overlap between metal 3d and O 2p, enhancing the electronic conductivity and charge transfer, thus affording high intrinsic OER catalytic activity. More importantly, the strengthened metal‐oxygen (M−O) bonds and stable octahedral geometry (M−O(F)6) in FeCoNi2F4(OH)4 prevent structural reorganization, rendering long‐term catalytic stability. Furthermore, an efficient three‐phase reaction interface with fast oxygen transportation was constructed, significantly improving the ORR activity. ZABs assembled with FeCoNi2F4(OH)4@HCC (hydrophobic carbon cloth) cathodes deliver a top performance with high round‐trip energy efficiency (61.3 % at 10 mA cm−2) and long‐term stability (efficiency remains at 58.8 % after 1050 charge–discharge cycles).

Fluorine-Lodged High-Valent High-Entropy Layered Double Hydroxide for Efficient, Long-Lasting Zinc-Air Batteries.

Efficient and stable bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts are urgently needed to unlock the full potential of zinc-air batteries (ZABs). High-valence oxides (HVOs) and high entropy oxides (HEOs) are suitable candidates for their optimal electronic structures and stability but suffer from demanding synthesis. Here, a low-cost fluorine-lodged high-valent high-entropy layered double hydroxide (HV-HE-LDH) (FeCoNi2F4(OH)4) is conveniently prepared through multi-ions co-precipitation, where F- are firmly embedded into the individual hydroxide layers. Spectroscopic detections and theoretical simulations reveal high valent metal cations are obtained in FeCoNi2F4(OH)4, which enlarge the energy band overlap between metal 3d and O 2p, enhancing the electronic conductivity and charge transfer, thus affording high intrinsic OER catalytic activity. More importantly, the strengthened metal-oxygen (M-O) bonds and stable octahedral geometry (M-O(F)6) in FeCoNi2F4(OH)4 prevent structural reorganization, rendering long-term catalytic stability. Furthermore, an efficient three-phase reaction interface with fast oxygen transportation was constructed, significantly improving the ORR activity. ZABs assembled with FeCoNi2F4(OH)4@HCC (hydrophobic carbon cloth) cathodes deliver a top performance with high round-trip energy efficiency (61.3 % at 10 mA cm-2) and long-term stability (efficiency remains at 58.8 % after 1050 charge-discharge cycles).

Dual Fe/I Single-Atom Electrocatalyst for High-Performance Oxygen Reduction and Wide-Temperature Quasi-Solid-State Zn-Air Batteries.

Oxygen reduction reaction (ORR) electrocatalysts are essential for widespread application of quasi-solid-state Zn-air batteries (ZABs), but the well-known Fe-N-C single-atom catalysts (SACs) suffer from low activity and stability because of unfavorable strong adsorption of oxygenated intermediates. Herein, the study synthesizes dual Fe/I single atoms anchored on N-doped carbon nanorods (Fe/I-N-CR) via a metal-organic framework (MOF)-mediated two-step tandem-pyrolysis method. Atomic-level I doping modulates the electronic structure of Fe-Nx centers via the long-range electron delocalization effect. Benefitting from the synergistic effect of dual Fe/I single-atom sites and the structural merits of 1D nanorods, the Fe/I-N-CR catalyst shows excellent ORR activity and stability, superior to Pt/C and Fe or I SACs. When the Fe/I-N-CR is employed as cathode for quasi-solid-state ZABs, a high power density of 197.9mW cm-2 and an ultralong cycling lifespan of 280h at 20mA cm-2 are both achieved, greatly exceeding those of commercial Pt/C+IrO2 (119.1mW cm-2 and 47h). In addition, wide-temperature adaptability and superior stability from -40 to 60 °C are realized for the Fe/I-N-CR-based quasi-solid-state ZABs. This work provides a MOF-mediated two-step tandem-pyrolysis strategy to engineer high-performance dual SACs with metal/nonmetal centers for ORR and sustainable ZABs.

Tuning the structure and properties of carbon cloth by FeCl3intercalation for efficient two-electron oxygen reduction catalysis.

The advancement of various energy conversion and storage technologies hinges on the development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR). In this study, we report the enhancement of carbon cloth (CC) for robust ORR through an FeCl3intercalation reaction. Utilizing a thermal annealing method, FeCl3was intercalated into the graphite structure on the surface of CC, resulting in the creation of numerous defects and the incorporation of Fe species. These newly introduced defects play a pivotal role in activating the ORR via a two-electron pathway. The presence of Fe species further stabilizes the catalytic activity, leading to efficient and stable ORR performance. Our findings highlight the significance of defect engineering and Fe species incorporation in carbon-based materials for improved ORR catalysis and pave the way for the development of advanced electrocatalysts for energy-related applications.

Reaction-driven restructuring of defective PtSe2 into ultrastable catalyst for the oxygen reduction reaction.

PtM (M = S, Se, Te) dichalcogenides are promising two-dimensional materials for electronics, optoelectronics and gas sensors due to their high air stability, tunable bandgap and high carrier mobility. However, their potential as electrocatalysts for the oxygen reduction reaction (ORR) is often underestimated due to their semiconducting properties and limited surface area from van der Waals stacking. Here we show an approach for synthesizing a highly efficient and stable ORR catalyst by restructuring defective platinum diselenide (DEF-PtSe2) through electrochemical cycling in an O2-saturated electrolyte. After 42,000 cycles, DEF-PtSe2 exhibited 1.3 times higher specific activity and 2.6 times higher mass activity compared with a commercial Pt/C electrocatalyst. Even after 126,000 cycles, it maintained superior ORR performance with minimal decay. Quantum mechanical calculations using hybrid density functional theory reveal that the improved performance is due to the synergistic contributions from Pt nanoparticles and the apical active sites on the DEF-PtSe2 surface. This work highlights the potential of DEF-PtSe2 as a durable electrocatalyst for ORR, offering insights into PtM dichalcogenide electrochemistry and the design of advanced catalysts.

A Janus Platinum/Tin Oxide Heterostructure for Durable Oxygen Reduction Reaction.

Designing efficient and durable electrocatalysts for oxygen reduction reaction (ORR) is essential for proton exchange membrane fuel cells (PEMFCs). Platinum-based catalysts are considered efficient ORR catalysts due to their high activity. However, the degradation of Pt species leads to poor durability of catalysts, limiting their applications in PEMFCs. Herein, a Janus heterostructure is designed for high durability ORR in acidic media. The Janus heterostructure composes of crystalline platinum and cassiterite tin oxide nanoparticles with carbon support (J-Pt@SnO2/C). Based on the synchrotron fine structure analysis and electrochemical investigation, the crystalline reconstruction and charge redistribution at the interface of Janus structure are revealed. The tightly coupled interface could optimize the valance states of Pt and the adsorption/desorption of oxygenated intermediates. As a result, the J-Pt@SnO2/C catalyst possesses distinguishing long-term stability during the accelerated durability test without obvious degradation after 40000 cycles and keeps the majority of activity after 70000 cycles. Meanwhile, the catalyst exhibits outstanding activity with half-wave potential at 0.905V and a mass activity of 0.355AmgPt -1 (2.7 times higher than Pt/C). The approach of the Janus catalyst paves an avenue for designing highly efficient and stable Pt-based ORR catalyst in the future implementation.

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.

Enhanced ORR kinetics and stability through synergy of Pt-Ni clustering and porous N-doped C/Ca aerogel support

The oxygen reduction reaction (ORR) is fundamental in numerous electrochemical energy conversion technologies, necessitating efficient catalysts to enhance reaction kinetics and reduce precious metal usage. This study focuses strategic clustering of Pt-Ni on Calcium Oxide/activated carbon (C/Ca) aerogels. Electrochemical analyses confirmed that incorporating Ni into Pt matrices significantly enhanced ORR activities with Pt25Ni75-C/Ca composition emerged as optimum. A positive shift in half-wave potential (905 mV vs. RHE) and impressive mass activity (72.50 Ag−1 at 85 V) highlight the potential of this composite as a highly effective and stable ORR catalyst. Pt-C/Ca demonstrated performance fluctuation, while Pt25Ni75-C/Ca showed remarkable stability after 40,000 cycles. Furthermore, C/Ca aerogels exhibited a significantly increased BET surface area, and the presence of Pt-Ni/pyridinic-N species on its surface C/Ca aerogel provided supplementary active sites that facilitated the adsorption and reduction of O2 during ORR.

Trifunctional Graphene-Sandwiched Heterojunction-Embedded Layered Lattice Electrocatalyst for High Performance in Zn-Air Battery-Driven Water Splitting.

Zn-air battery (ZAB)-driven water splitting holds great promise as a next-generation energy conversion technology, but its large overpotential, low activity, and poor stability for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) remain obstacles. Here, a trifunctional graphene-sandwiched, heterojunction-embedded layered lattice (G-SHELL) electrocatalyst offering a solution to these challenges are reported. Its hollow core-layered shell morphology promotes ion transport to Co3S4 for OER and graphene-sandwiched MoS2 for ORR/HER, while its heterojunction-induced internal electric fields facilitate electron migration. The structural characteristics of G-SHELL are thoroughly investigated using X-ray absorption spectroscopy. Additionally, atomic-resolution transmission electron microscopy (TEM) images align well with the DFT-relaxed structures and simulated TEM images, further confirming its structure. It exhibits an approximately threefold smaller ORR charge transfer resistance than Pt/C, a lower OER overpotential and Tafel slope than RuO₂, and excellent HER overpotential and Tafel slope, while outlasting noble metals in terms of durability. Ex situ X-ray photoelectron spectroscopy analysis under varying potentials by examining the peak shifts and ratios (Co2+/Co3+ and Mo4+/Mo6+) elucidates electrocatalytic reaction mechanisms. Furthermore, the ZAB with G-SHELL outperforms Pt/C+RuO2 in terms of energy density (797Wh kg-1) and peak power density (275.8mW cm-2), realizing the ZAB-driven water splitting.