Hollow Co3O4 Nanosphere Embedded in Carbon Arrays for Stable and Flexible Solid‐State Zinc–Air Batteries

Highly active and durable air cathodes to catalyze both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for rechargeable metal–air batteries. In this work, an efficient bifunctional oxygen catalyst comprising hollow Co₃O₄ nanospheres embedded in nitrogen‐doped carbon nanowall arrays on flexible carbon cloth (NC‐Co₃O₄/CC) is reported. The hierarchical structure is facilely derived from a metal–organic framework precursor. A carbon onion coating constrains the Kirkendall effect to promote the conversion of the Co nanoparticles into irregular hollow oxide nanospheres with a fine scale nanograin structure, which enables promising catalytic properties toward both OER and ORR. The integrated NC‐Co₃O₄/CC can be used as an additive‐free air cathode for flexible all‐solid‐state zinc–air batteries, which present high open circuit potential (1.44 V), high capacity (387.2 mAh g^?1, based on the total mass of Zn and catalysts), excellent cycling stability and mechanical flexibility, significantly outperforming Pt‐ and Ir‐based zinc–air batteries.     

Elucidation of Active Sites on S,N Codoped Carbon Cubes Embedding Co–Fe Carbides toward Reversible Oxygen Conversion in High‐Performance Zinc–Air Batteries

The development of high‐performance but low‐cost catalysts for the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of central importance for realizing the prevailing application of metal–air batteries. Herein a facile route is devised to synthesize S, N codoped carbon cubes embedding Co–Fe carbides by pyrolyzing the Co–Fe Prussian blue analogues (PBA) coated with methionine. Via the strong metal–sulfur interaction, the methionine coating provides a robust sheath to restrain the cubic morphology of PBA upon pyrolysis, which is proved highly beneficial for promoting the specific surface area and active sites exposure, leading to remarkable bifunctionality of ORR and OER comparable to the benchmarks of Pt/C and RuO₂. Further elaborative investigations on the activity origin and postelectrolytic composition unravel that for ORR the high activity is mainly contributed by the S, N codoped carbon shell with the inactive carbide phase converting into carbonate hydroxides. For OER, the embedded Co–Fe carbides transform in situ into layered (hydr)oxides, serving as the actual active sites for promoting water oxidation. Zn–air batteries employing the developed hollow structure as the air cathode catalyst demonstrate superb rechargeability, energy efficiency, as well as portability.     

Bifunctional Transition Metal Hydroxysulfides: Room‐Temperature Sulfurization and Their Applications in Zn–Air Batteries

Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable metal–air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn–air batteries. By simply immersing Co‐based hydroxide precursor into solution with high‐concentration S^2?, transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as‐obtained Co‐based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm^?2 OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half‐wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co₃FeS_1.5(OH)₆ hydroxysulfides are employed in the air electrode for a rechargeable Zn–air battery with a small overpotential of 0.86 V at 20.0 mA cm^?2, a high specific capacity of 898 mAh g^?1, and a long cycling life, which is much better than Pt and Ir‐based electrocatalyst in Zn–air batteries.     

Boosting Bifunctional Oxygen Electrocatalysis with 3D Graphene Aerogel‐Supported Ni/MnO Particles

Electrocatalysts for oxygen‐reduction and oxygen‐evolution reactions (ORR and OER) are crucial for metal–air batteries, where more costly Pt‐ and Ir/Ru‐based materials are the benchmark catalysts for ORR and OER, respectively. Herein, for the first time Ni is combined with MnO species, and a 3D porous graphene aerogel‐supported Ni/MnO (Ni–MnO/rGO aerogel) bifunctional catalyst is prepared via a facile and scalable hydrogel route. The synthetic strategy depends on the formation of a graphene oxide (GO) crosslinked poly(vinyl alcohol) hydrogel that allows for the efficient capture of highly active Ni/MnO particles after pyrolysis. Remarkably, the resulting Ni–MnO/rGO aerogels exhibit superior bifunctional catalytic performance for both ORR and OER in an alkaline electrolyte, which can compete with the previously reported bifunctional electrocatalysts. The MnO mainly contributes to the high activity for the ORR, while metallic Ni is responsible for the excellent OER activity. Moreover, such bifunctional catalyst can endow the homemade Zn–air battery with better power density, specific capacity, and cycling stability than mixed Pt/C + RuO₂ catalysts, demonstrating its potential feasibility in practical application of rechargeable metal–air batteries.     

An Iron-Decorated Carbon Aerogel for Rechargeable Flow and Flexible Zn–Air Batteries

Mechanically stable and foldable air cathodes with exceptional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities are key components of wearable metal–air batteries. Herein, a directional freeze-casting and annealing approach is reported for the construction of a 3D honeycomb nanostructured, N,P-doped carbon aerogel incorporating in situ grown FeP/Fe₂O₃ nanoparticles as the cathode in a flexible Zn–air battery (ZAB). The aqueous rechargeable Zn–air batteries assembled with this carbon aerogel exhibit a remarkable specific capacity of 648 mAh g⁻¹ at a current density of 20 mA cm⁻² with a good long-term durability, outperforming those assembled with commercial Pt/C+RuO₂ catalyst. Furthermore, such a foldable carbon aerogel with directional channels can serve as a freestanding air cathode for flexible solid-state Zn–air batteries without the use of carbon paper/cloth and additives, giving a specific capacity of 676 mAh g⁻¹ and an energy density of 517 Wh kg⁻¹ at 5 mA cm⁻² together with good cycling stability. This work offers a new strategy to design and synthesize highly effective bifunctional air cathodes to be applied in electrochemical energy devices.     

Kinetically Stable Oxide Overlayers on Mo3P Nanoparticles Enabling Lithium–Air Batteries with Low Overpotentials and Long Cycle Life

The main drawbacks of today's state-of-the-art lithium–air (Li–air) batteries are their low energy efficiency and limited cycle life due to the lack of earth-abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo₃P) nanoparticles with an exceptional activity—ORR and OER current densities of 7.21 and 6.85 mA cm⁻² at 2.0 and 4.2 V versus Li/Li⁺, respectively—in an oxygen-saturated non-aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance—Tafel slopes of 35 and 38 mV dec⁻¹ for ORR and OER, respectively—resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li–air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo₃P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials.     

Novel MOF‐Derived Co@N‐C Bifunctional Catalysts for Highly Efficient Zn–Air Batteries and Water Splitting

Metal–organic frameworks (MOFs) and MOF‐derived materials have recently attracted considerable interest as alternatives to noble‐metal electrocatalysts. Herein, the rational design and synthesis of a new class of Co@N‐C materials (C‐MOF‐C2‐T) from a pair of enantiotopic chiral 3D MOFs by pyrolysis at temperature T is reported. The newly developed C‐MOF‐C2‐900 with a unique 3D hierarchical rodlike structure, consisting of homogeneously distributed cobalt nanoparticles encapsulated by partially graphitized N‐doped carbon rings along the rod length, exhibits higher electrocatalytic activities for oxygen reduction and oxygen evolution reactions (ORR and OER) than that of commercial Pt/C and RuO₂, respectively. Primary Zn–air batteries based on C‐MOF‐900 for the oxygen reduction reaction (ORR) operated at a discharge potential of 1.30 V with a specific capacity of 741 mA h g_Zn^–1 under 10 mA cm^–2. Rechargeable Zn–air batteries based on C‐MOF‐C2‐900 as an ORR and OER bifunctional catalyst exhibit initial charge and discharge potentials at 1.81 and 1.28 V (2 mA cm^–2), along with an excellent cycling stability with no increase in polarization even after 120 h – outperform their counterparts based on noble‐metal‐based air electrodes. The resultant rechargeable Zn–air batteries are used to efficiently power electrochemical water‐splitting systems, demonstrating promising potential as integrated green energy systems for practical applications.     

Defective N/S‐Codoped 3D Cheese‐Like Porous Carbon Nanomaterial toward Efficient Oxygen Reduction and Zn–Air Batteries

Developing a facile and cost‐efficient method to synthesize carbon‐based nanomaterials possessing excellent structural and functional properties has become one of the most attractive topics in energy conversion and storage fields. In this study, density functional theory calculation results reveal the origin of high oxygen reduction reaction (ORR) activity predominantly derived from the synergistic effect of intrinsic defects and heteroatom dopants (e.g., N, S) that modulate the bandgap and charge density distribution of carbon matrix. Under the guidance of the first‐principle prediction, by using ultralight biomass waste as precursor of C, N, and S elements, a defect‐rich and N/S dual‐doped cheese‐like porous carbon nanomaterial is successfully designed and constructed. Herein, the intrinsic defects are artfully generated in terms of alkaline and ammonia activation. The electrochemical measurements display that such a material owns a comparable ORR activity (E_1/2 = 0.835 V) to the commercial Pt/C catalyst, along with splendid durability and methanol tolerance in alkali media. Furthermore, as cathode catalyst, it displays a high Zn–air battery performance. The excellent ORR activity of the catalyst can be attributed to its unique 3D porous architecture, abundant intrinsic defects, and high‐content active heteroatom dopants in the carbon matrix.     

“Wiring” Fe‐Nx‐Embedded Porous Carbon Framework onto 1D Nanotubes for Efficient Oxygen Reduction Reaction in Alkaline and Acidic Media

This study presents a novel metal‐organic‐framework‐engaged synthesis route based on porous tellurium nanotubes as a sacrificial template for hierarchically porous 1D carbon nanotubes. Furthermore, an ultrathin Fe‐ion‐containing polydopamine layer has been introduced to generate highly effective FeN_xC active sites into the carbon framework and to induce a high degree of graphitization. The synergistic effects between the hierarchically porous 1D carbon structure and the embedded FeN_xC active sites in the carbon framework manifest in superior catalytic activity toward oxygen reduction reaction (ORR) compared to Pt/C catalyst in both alkaline and acidic media. A rechargeable zinc‐air battery assembled in a decoupled configuration with the nonprecious pCNT@Fe@GL/CNF ORR electrode and Ni‐Fe LDH/NiF oxygen evolution reaction (OER) electrode exhibits charge–discharge overpotentials similar to the counterparts of Pt/C ORR electrode and IrO₂ OER electrode.     

Hierarchical 3D Oxygenated Cobalt Molybdenum Selenide Nanosheets as Robust Trifunctional Catalyst for Water Splitting and Zinc–Air Batteries

The development of hierarchical nanostructures with highly active and durable multifunctional catalysts has a new significance in the context of new energy technologies of water splitting and metal–air batteries. Herein, a strategy is demonstrated to construct a 3D hierarchical oxygenated cobalt molybdenum selenide (O‐Co_1?xMo_xSe₂) series with attractive nanoarchitectures, which are fabricated by a simple and cost‐effective hydrothermal process followed by an exclusive ion‐exchange process. Owing to its highly electroactive sites with numerous nanoporous networks and plentiful oxygen vacancies, the optimal O‐Co_0.5Mo_0.5Se₂ could catalyze the hydrogen evolution reaction and oxygen evolution reaction effectively with a low overpotential of ≈102 and 189 mV, at a current density of 10 mA cm^?2, respectively, and exceptional durability. Most importantly, the O‐Co_0.5Mo_0.5Se₂||O‐Co_0.5Mo_0.5Se₂ water splitting device only entails a voltage of ≈1.53 V at a current density of 10 mA cm^?2, which is much better than benchmark Pt/C||RuO₂ (≈1.56 V). Furthermore, O‐Co_0.5Mo_0.5Se₂ air cathode‐based zinc–air batteries exhibit an excellent power density of 120.28 mW cm^?2 and exceptional cycling stability for 60 h, superior to those of state‐of‐art Pt/C+RuO₂ pair‐based zinc–air batteries. The present study provides a strategy to design hierarchical 3D oxygenated bimetallic selenide‐based multifunctional catalysts for energy conversion and storage systems.     

Ni‐Fe Nitride Nanoplates on Nitrogen‐Doped Graphene as a Synergistic Catalyst for Reversible Oxygen Evolution Reaction and Rechargeable Zn‐Air Battery

Obtaining bifunctional electrocatalysts with high activity for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is a main hurdle in the application of rechargeable metal‐air batteries. Earth‐abundant 3d transition metal‐based catalysts have been developed for the OER and ORR; however, most of these are based on oxides, whose insulating nature strongly restricts their catalytic performance. This study describes a metallic Ni‐Fe nitride/nitrogen‐doped graphene hybrid in which 2D Ni‐Fe nitride nanoplates are strongly coupled with the graphene support. Electronic structure of the Ni‐Fe nitride is changed by hybridizing with the nitrogen‐doped graphene. The unique heterostructure of this hybrid catalyst results in very high OER activity with the lowest onset overpotential (150 mV) reported, and good ORR activity comparable to that for commercial Pt/C. The high activity and durability of this bifunctional catalyst are also confirmed in rechargeable zinc‐air batteries that are stable for 180 cycles with an overall overpotential of only 0.77 V at 10 mA^?2.     

Nitrogen,Fluorine, and Boron Ternary Doped Carbon Fibers as Cathode Electrocatalysts for Zinc–Air Batteries

Zinc–air batteries with high‐density energy are promising energy storage devices for the next generation of energy storage technologies. However, the battery performance is highly dependent on the efficiency of oxygen electrocatalyst in the air electrode. Herein, the N, F, and B ternary doped carbon fibers (TD‐CFs) are prepared and exhibited higher catalytic properties via the efficient 4e⁻ transfer mechanism for oxygen reduction in comparison with the single nitrogen doped CFs. More importantly, the primary and rechargeable Zn–air batteries using TD‐CFs as air–cathode catalysts are constructed. When compared to batteries with Pt/C + RuO₂ and Vulcan XC‐72 carbon black catalysts, the TD‐CFs catalyzed batteries exhibit remarkable battery reversibility and stability over long charging/discharging cycles.     

Palladium Enhanced Iron Active Site – An Efficient Dual-Atom Catalyst for Oxygen Electroreduction

Metal–nitrogen–carbon (M–C/N) electrocatalysts have been shown to have satisfactory catalytic activity and long-term durability for the oxygen reduction reaction (ORR). Here, a strategy to prepare a new electrocatalyst (Fe&Pd–C/N) using a unique metal-containing ionic liquid (IL) is exploited, in which Fe & Pd ions are positively charged species atomically dispersed by coordination to the N of the N-doped C substrate, C/N. X-ray absorption fine structure, XPS and aberration-corrected transmission electron microscopy results verified a well-defined dual-atom configuration comprising Fe^+2.x–N₄ coupled Pd²⁺–N₄ sites and well-defined spatial distribution. Electronic control of a coupled Fe–Pd structure produces an electrocatalyst that exhibits superior performance with enhanced activity and durability for the ORR compared to that of commercial Pt/C (20%, Johnson Matthey) in both alkaline and acid media. Density functional theory calculations indicate that Pd atom can enhance the catalytic activity of the Fe active sites adjacent to Pd sites by changing the electronic orbital structure and Bader charge of the Fe centers. The excellent catalytic performance of the Fe&Pd–C/N electrocatalyst is demonstrated in zinc–air batteries and hydrogen–air fuel cells.     

High-Activity Fe3C as pH-Universal Electrocatalyst for Boosting Oxygen Reduction Reaction and Zinc-Air Battery

Transition metal catalysts are regarded as one of promising alternatives to replace traditional Pt-based catalysts for oxygen reduction reaction (ORR). In this work, an efficient ORR catalyst is synthesized by confining Fe₃C nanoparticles into N, S co-doped porous carbon nanosheets (Fe₃C/N,S-CNS) via high-temperature pyrolysis, in which 5-sulfosalicylic acid (SSA) demonstrates as an ideal complexing agent for iron (ΙΙΙ) acetylacetonate while g-C₃N₄ behaves as a nitrogen source. The influence of the pyrolysis temperature on the ORR performance is strictly examined in the controlled experiments. The obtained catalyst exhibits excellent ORR performance (E_1/2 = 0.86 V; E_onset = 0.98 V) in alkaline electrolyte, coupled by exhibiting the superior catalytic activity and stability (E_1/2 = 0.83 V, E_onset = 0.95 V) to Pt/C in acidic media. In parallel, its ORR mechanism is carefully illustrated by the density functional theory (DFT) calculations, especially the role of the incorporated Fe₃C played in the catalytic process. The catalyst-assembled Zn-air battery also exhibits a much higher power density (163 mW cm^–2) and ultralong cyclic stability in the charge–discharge test for 750 h with a gap increase down to 20 mV. This study provides some constructive insights for preparation of advanced ORR catalysts in green energy conversion units correlated systems.     

Co Nanoislands Rooted on Co–N–C Nanosheets as Efficient Oxygen Electrocatalyst for Zn–Air Batteries

Developing non‐precious‐metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn–air batteries. Co‐based catalysts have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co–N–C nanosheets supported by carbon felts (Co/Co–N–C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self‐template and cobalt source. The synergistic effect of metal Co islands with OER activity and Co–N–C nanosheets with superior ORR performance leads to good bifuctional catalytic performances. Wavelet transform extended X‐ray absorption fine spectroscopy and X‐ray photoelectron spectroscopy certify the formation of Co (mainly Co⁰) and the Co–N–C (mainly Co²⁺ and Co³⁺) structure. As the air‐cathode, the assembled aqueous Zn–air battery exhibits a small charge–discharge voltage gap (0.82 V@10 mA cm^?2) and high power density of 132 mW cm^?2, outperforming the commercial Pt/C catalyst. Additionally, the cable flexible rechargeable Zn–air battery exhibits excellent bendable and durability. Density functional theory calculation is combined with operando X‐ray absorption spectroscopy to further elucidate the active sites of oxygen reactions at the Co/Co–N–C cathode in Zn–air battery.     

Nitrogen‐Doped Co3O4 Mesoporous Nanowire Arrays as an Additive‐Free Air‐Cathode for Flexible Solid‐State Zinc–Air Batteries

The kinetically sluggish rate of oxygen reduction reaction (ORR) on the cathode side is one of the main bottlenecks of zinc‐air batteries (ZABs), and thus the search for an efficient and cost‐effective catalyst for ORR is highly pursued. Co₃O₄ has received ever‐growing interest as a promising ORR catalyst due to the unique advantages of low‐cost, earth abundance and decent catalytic activity. However, owing to the poor conductivity as a result of its semiconducting nature, the ORR activity of the Co₃O₄ catalyst is still far below the expectation. Herein, we report a controllable N‐doping strategy to significantly improve the catalytic activity of Co₃O₄ for ORR and demonstrate these N doped Co₃O₄ nanowires as an additive‐free air‐cathode for flexible solid‐state zinc‐air batteries. The results of experiments and DFT calculations reveal that the catalytic activity is promoted by the N dopant through a combined set of factors, including enhanced electronic conductivity, increased O₂ adsorption strength and improved reaction kinetics. Finally, the assembly of all‐solid‐state ZABs based on the optimized cathode exhibit a high volumetric capacity of 98.1 mAh cm^‐3 and outstanding flexibility. The demonstration of such flexible ZABs provides valuable insights that point the way to the redesign of emerging portable electronics.     

Interfacing Manganese Oxide and Cobalt in Porous Graphitic Carbon Polyhedrons Boosts Oxygen Electrocatalysis for Zn–Air Batteries

Rational design and synthesis of highly active and robust bifunctional non‐noble electrocatalysts for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are urgently required for efficient rechargeable metal–air batteries. Herein, abundant MnO/Co heterointerfaces are engineered in porous graphitic carbon (MnO/Co/PGC) polyhedrons via a facile hydrothermal‐calcination route with a bimetal–organic framework as the precursor. The in situ generated Co nanocrystals not only create well‐defined heterointerfaces with high conductivity to overcome the poor OER activity but also promote the formation of robust graphitic carbon. Owing to the desired composition and formation of the heterostructures, the resulting MnO/Co/PGC exhibits superior activity and stability toward both OER and ORR, which makes it an efficient air cathode for the rechargeable Zn–air battery. Importantly, the homemade Zn–air battery is able to deliver excellent performance including a peak power density of 172 mW cm^?2 and a specific capacity of 872 mAh g^?1, as well as excellent cycling stability (350 cycles), outperforming commercial mixed Pt/C||RuO₂ catalysts. This work highlights the synergy from heterointerfaces in oxygen electrocatalysis, thus providing a promising approach for advanced metal–air cathode materials.     

Self-Sacrificing Template Synthesis of Carbon Nanosheets Assembled Hollow Spheres with Abundant Active Fe–N4O1 Moieties for Electrocatalytic Oxygen Reduction

Single-atom Fe–N–C (Fe₁–N–C) materials represent the benchmarked electrocatalysts for oxygen reduction reaction (ORR). However, single Fe atoms in the carbon skeletons cannot be fully utilized due to the mass transfer limitation, severely restricting their intrinsic ORR properties. Herein, a self-sacrificing template strategy is developed to fabricate ultrathin nanosheets assembled Fe₁–N–C hollow microspheres (denoted as Fe₁/N-HCMs) by rational carbonization of Fe³⁺ chelating polydopamine coated melamine cyanuric acid complex. The shell of Fe₁/N-HCMs is constructed by ultrathin nanosheets with thickness of only 2 nm, which is supposed to be an ideal platform to isolate and fully expose single metal atoms. Benefiting from unique hierarchical hollow architecture with highly open porous structure, 2 nm-thick ultrathin nanosheet subunits and abundant Fe–N₄O₁ active sites revealed by X-ray absorption fine structure analysis, the Fe₁/N-HCMs exhibit high ORR performance with a positive half-wave potential of 0.88 V versus the reversible hydrogen electrode and robust stability. When served as air-cathode catalysts with ultralow loading mass of 0.25 mg cm⁻², Fe₁/N-HCMs based Zn–air batteries present a maximum power density of 187 mW cm⁻² and discharge specific capacity of 806 mA h g_Zn⁻¹ in primary Zn–air batteries, all exceeding those of commercial Pt/C.     

Strongly Coupled 3D Hybrids of N‐doped Porous Carbon Nanosheet/CoNi Alloy‐Encapsulated Carbon Nanotubes for Enhanced Electrocatalysis

A novel 3D nanoarchitecture comprising in situ‐formed N‐doped CoNi alloy‐encapsulated carbon nanotubes (CoNi‐NCNTs) grown on N‐doped porous carbon nanosheets (NPCNs) is designed and constructed for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). When evaluated as an electrocatalyst for ORR, the hybrid shows efficient catalytic activity, high selectivity, superior durability, and strong tolerance against methanol crossover compared with the commercial Pt/C catalyst. Such good oxygen reduction reaction performance is comparable to most of the previously reported results and the synergistic effect is found to boost the catalytic performance. Moreover, the constructed hybrid exhibits an excellent ORR activity with a current density of 10 mA cm⁻² at 1.59 V and an onset potential of 1.57 V, even beyond the state‐of‐the‐art Ir/C catalyst in alkaline media. The enhancement in electrochemical performance can be attributed to the unique morphology and defect structures, high porosity, good conductive networks, and strongly interacting CoNi‐NCNT and NPCN in the hybrid. These results suggest the possibility for the development of effective nanocarbon electrocatalysts to replace commercial noble metal catalysts for direct use in fuel cells and water splitting devices.     

Strain-Regulated Pt–NiO@Ni Sub-Micron Particles Achieving Bifunctional Electrocatalysis for Zinc–Air Battery

Highly active bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have always been the key factors to affect the performance of zinc–air batteries. However, integrating the independent reaction sites of ORR and OER in a catalyst remains a major challenge. Herein, a collaborative strategy based on defect induction and doping is proposed to prepare the strain-regulated Pt–NiO@Ni sub-micron particles (Pt–NiO@Ni SP). Benefiting from the synergistic effect of tensile strain and Pt-doped, the metallic Ni-based sub-micron particles with tensile strain as the catalyst carriers can effectively optimize the electronic distribution of atomic structures in Pt and NiO on the surface of particles, leading to reduce the energy barrier of intermediates for ORR and OER. Consequently, the Pt–NiO@Ni SP exhibits outstanding bifunctional catalytic activity with the ΔE index of 0.65 V under a low Pt loading, outperforming that of the benchmark Pt/C+IrO₂ catalysts (0.76 V). Impressively, the Pt–NiO@Ni SP-based liquid zinc–air battery develops a high open-circuit potential (1.47 V), excellent energy density (188.2 mW cm⁻²), and favorable cyclic charge–discharge cycling durability (200 h at 20 mA cm⁻²). This work provides an innovative avenue for the rational construction of highly active bifunctional electrocatalysts for practical applications.