Bifunctional Activity Research Articles

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.

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.

Electrocatalytic properties of transition metal vanadates (T = Ti, Cr, Mn, & Fe) for overall water splitting

In this work, first row transition metal vanadates (TMVs), including titanium vanadate (TiV), chromium vanadate (CrV), manganese vanadate (MnV), and iron vanadate (FeV), were synthesized and investigated their electrocatalytic performance for the alkaline water splitting. The prepared TMVs showed easy electron transfer characteristics and tunable band structures, and among these TMVs, the synthesized FeV demonstrated the best electrocatalytic bifunctional activities for both HER (η100 = 375 mV) and OER (η100 = 260 mV) with a significant electronic and morphological stability over 100 h operation. The examination of electronic structure revealed that the balanced catalyst-intermediate interaction through optimum d-p orbital hybridization in FeV, adhering to the Sabater principle, vouched for such facile redox reaction. The structural stability might be attributed to the synergism between iron and vanadate as the multivalent Fe adjusted the shift in vanadium coordination when the oxidation state of Vn+ (n = 3–5) changed. Moreover, the two-electrode system of FeV || FeV in a single electrolyzer demonstrated superior cell voltage100 of 1.86 V in comparison to commercial Pt/C || IrO2 electrodes (1.91 V). This work offers facile perspective to produce TMVs as the efficient electrocatalysts for green synthesis of fuel gases.

Bifunctional heterostructured nitrogen-doped carbon-layer-loaded NiSe2-FeSe2 electrocatalyst for efficient water splitting

Developing high-performance, eco-friendly bifunctional electrocatalysts is crucial to popularizing water electrolysis for hydrogen production, but it still presents major challenges. Here, we develop a composite material with NiSe2-FeSe2 heterostructure loaded on N-doped carbon layers by utilizing the metal-organic framework as a sacrificial template (NiSe2-FeSe2/NC). According to microstructural studies, direct contact between NiSe2 and FeSe2 induces charge transfer and enhances conductivity, while sensible arraying of NiSe2-FeSe2/NC nanosheets fully exposes active sites and protects catalysts from violent reaction processes. The NiSe2-FeSe2/NC heterostructured catalysts show excellent bifunctional catalytic activity for hydrogen and oxygen evolution reactions, with overpotentials of 54 and 232 mV at 10 mA cm−2, respectively. Moreover, NiSe2-FeSe2/NC also retains superiority in a two-electrode system, needing lower voltage to drive the overall water splitting at 10 mA cm−2 (1.53 V) than Pt/C||RuO2 as well as long-term stability. This work introduces a novel concept for developing state-of-the-art non-noble metal catalysts for hydrogen production and new insights into interface engineering.

First principles study of V2CT2-based MXenes materials in oxygen reduction and oxygen evolution reactions

The development of bifunctional ORR/OER electrocatalysts with low cost, high activity and sustainable cycle plays an important role in improving the performance of new green energy storage and conversion devices to alleviate the energy crisis and environmental pollution. As a graphene-like two-dimensional inorganic layered compound with unique electrochemistry, MXenes materials have attracted more and more attention in the field of electrocatalytic applications. In this paper, based on the first-principles calculation method based on density functional theory (DFT) and quantum mechanics, an effective scheme for designing efficient ORR/OER bifunctional electrocatalysts by introducing Pd/Pt single atoms to regulate the electronic structure of V2CT2 (T = O, F) is proposed. Firstly, we discussed the stability of the designed series of single-atom catalysts by calculating the formation energy, binding energy and molecular dynamics simulation. Secondly, by comparing the theoretical overpotentials of these single-atom catalysts for ORR and OER, we found that among the designed SACs, V2CO2-Pd, V2CF2-Pd and V2CO2-VO-Pt are catalysts with good bifunctional catalytic activity for ORR/OER. Our work provides some guidance for the application of MXenes materials in the field of electrocatalysis.

Enhanced electrochemical performance of ZrTe-Mn2O3 nanocomposite electrocatalyst for HER and OER in alkaline medium

Electrochemical energy conversion in renewable-energy technologies relies on the OER and HER towards next-generation fuels. Herein, we have coupled zirconia telluride (ZrTe) and manganese oxide (Mn2O3) nanosheets heterointerfaces by a facile hydrothermal method, which are engineered on stainless steel substrate (ZrTe-Mn2O3/SS). The physical properties, including crystallinity, phase purity, morphology, conductivity, and chemical interacted states of the developed composite, are systematically investigated by XRD, HRTEM, I-V, and XPS. The XPS observation showed unique redox properties of hydrogen peroxide species on the ZrTe-Mn2O3 catalyst and the oxidation state of Zr and Mn that was more easily changed in the ZrTe-Mn2O3 electrocatalyst compared with the pristine catalysts. The very decent electrochemical performance of the catalyst activation step (Mn3+→Mn4+ and Zr2+→Zr4+ oxidations) observed from electrochemical cyclic voltammetry (CV) and linear sweep voltammetry (LSV) studies that are tested in the alkaline environment. Concerning higher bifunctional activity for ZrTe-Mn2O3, the current density of 10 mA cm−2 is revealed only at a lower overpotential of 244 mV and Tafel slope of 48 mV/dec toward better OER. At the same time, composite material also exhibited a minimal overpotential of 61 mV toward HER to attain 100 mA/cm2. It was also found that introducing a connection of ZrTe with Mn2O3 improves the precise surface area and exposes more multi-active sites for easy transfer of electrons. In addition, it maintains excellent long-term stability for almost 110 hrs through chronoamperometry, which leads to no activity loss and further represents higher OER/HER activity in industrial applications. We conclusively demonstrate that the first-time reported research provides valuable insights attributed to the defective structure, porous nature, and covalently bridging between atomic-level heterogeneous interfaces, favouring rapid electron transfer process activation for continuously produced O2 and H2 gas bubbles.

Unveiling the potential of ultra-low load Co on porous carbon-rich SiCN(O) fibre mats towards oxygen electrocatalysis in alkaline medium

The development of efficient and cost-effective catalysts for the oxygen electrocatalysis is crucial for advancing renewable energy technologies, such as fuel cells, electrolyzers and metal-air batteries. Herein, we report the high efficiency of Co nanoclusters generated on porous silicon oxycarbonitride (SiCN(O)) fibre mats towards Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in alkaline medium. Porous SiCN(O) ceramic fibrous supports were synthesized via electrospinning of a blend of oligosilazane Durazane 1800, polyacrylonitrile and polystyrene followed by an appropriate heat-treatment. Co nanoparticles with a remarkably low mass loading (4 wt%) were immobilized on the SiCN(O) fibres for efficient bifunctional catalytic activity towards OER/ORR. The catalysts exhibited ORR activity (onset potential (E0) of 0.83 V vs. RHE) and excellent stability (80 h) in alkaline medium. Concomitantly, the catalyst required only 1.67 V to drive a current density of 10 mA cm−2 in 1 M KOH for OER.

The application of Co3S4@NCNT/NCHS with excellent bifunctional catalytic activity in aqueous and flexible Zn-air batteries

In this work, we prepared a hybrid structure Co3S4@NCNT/NCHS using SiO2 nanospheres as a template. The structure is supported by hollow carbon spheres (NCHS), which are coated by Co3S4 nanoparticles and cross-linked N-doped carbon nanotubes. The combination of Co3S4 with N-doped carbon material significantly improves the electrocatalytic activity. In addition, the presence of N-doped carbon nanotubes induces more defects, which can regulate the electronic configuration of the material and improve its electrical conductivity. Therefore, Co3S4@NCNT/NCHS has good catalytic performance. At 10 mA cm−2, the OER overpotential of Co3S4@NCNT/NCHS is only 230 mV, which is lower than that of the commercial catalyst RuO2, and the ORR half-wave potential can reach 0.80 V. In the battery discharge test, Co3S4@NCNT/NCHS based ZABs can discharge continuously for 71.5 h, the specific capacity of 790.12 mA h g−1, power density of 113.09 m W cm−2, better than Pt/C+RuO2 battery. When the current density is 3 mA cm−2, ZABs assembled with Co3S4@NCNT/NCHS as catalyst can maintain a voltage gap of 0.62 V to 0.63 V within 300 h without significant change. When the current density is increased to 5 mA cm−2, ZABs based on Co3S4@NCNT/NCHS can be stably cycled for 300 h at a voltage gap between 0.80 V and 0.82 V.

Manipulating the Electronic Properties of an Fe Single Atom Catalyst via Secondary Coordination Sphere Engineering to Provide Enhanced Oxygen Electrocatalytic Activity in Zinc-Air Batteries.

Oxygen reduction and evolution reactions are two key processes in electrochemical energy conversion technologies. Synthesis of nonprecious metal, carbon-based electrocatalysts with high oxygen bifunctional activity and stability is a crucial, yet challenging step to achieving electrochemical energy conversion. Here, an approach to address this issue: synthesis of an atomically dispersed Fe electrocatalyst (Fe1/NCP) over a porous, defect-containing nitrogen-doped carbon support, is described. Through incorporation of a phosphorus atom into the second coordination sphere of iron, the activity and durability boundaries of this catalyst are pushed to an unprecedented level in alkaline environments, such as those found in a zinc-air battery. The rationale is to delicately incorporate P heteroatoms and defects close to the central metal sites (FeN4P1-OH) in order to break the local symmetry of the electronic distribution. This enables suitable binding strength with oxygenated intermediates. In situ characterizations and theoretical studies demonstrate that these synergetic interactions are responsible for high bifunctional activity and stability. These intrinsic advantages of Fe1/NCP enable a potential gap of a mere 0.65V and a high power density of 263.8mWcm-2 when incorporated into a zinc-air battery. These findings underscore the importance of design principles to access high-performance electrocatalysts for green energy technologies.