Axial chlorine-induced asymmetric cobalt single-atom coordination fields for boosting oxygen reduction reaction

Abstract

The development of oxygen reduction reaction (ORR) catalysts with high activity, stability, and economic applicability plays a decisive role in reducing expenses and enhancing the discharge performance of seawater-based zinc-air batteries (SWZABs). Co- and Fe-based single-atom catalysts (M-N₄-C) with metal-N₄ structure offer advantages of well-defined active structure and high active site utilizations. However, the oxygen electrocatalytic performance of M-N₄-C remains a formidable challenge due to the highly stable centrosymmetric electronic structure. To overcome the dilemma, we develop a Co-N₄Cl-C with axial coordination of Cl atoms. The axial coordination drags the Co atoms out of the Co-N₄ centrosymmetric configuration. This alters the electronic configuration of Co single-atom sites, resulting in a valence state change from +1.83 to +0.67 and forming a localized negative charge environment. These alternations enhance the electronic orbital overlap between Co single-atom sites and oxygen species, promote the rapid evolution of *OOH intermediates, and inhibit the adsorption of toxic Cl^- ions, ensuring the ORR kinetics and stability. Co-N₄Cl-C exhibits a high oxygen reduction onset potential of 1.05 mV and a half-wave potential of 0.88 mV vs. the reversible hydrogen electrode. The SWZAB, featuring a Co-N₄Cl-C catalyst cathode, Zn anode, and NaCl electrolyte supplemented with KOH, reaches a discharge voltage platform of 1.27 V and a peak power density of 179 mW·cm^-2, even at a current density of 10 mA·cm^-2. This study sheds important light on advancing single-atom catalysts with superior ORR performance and economic viability.

Keywords

Co-N₄-C single-atom catalyst / chlorine axial coordination / electronic structure / oxygen reduction kinetics / seawater-based zinc-air battery

References

[1] Yu J,Zhao CX.Seawater electrolyte-based metal-air batteries: from strategies to applications.Energy Environ Sci2020;13:3253-68

[2] Wang Q,Xiao X.Sustainable zinc-air battery chemistry: advances, challenges and prospects.Chem Soc Rev2023;52:6139-90

[3] Guo Y,Lu J,Deng Y.The concept, structure, and progress of seawater metal-air batteries.Microstructures2023;3:2023038

[4] Zheng L,Xue S.Electrochemical responsive alginate chains rendered sol-to-gel gradient electrolyte towards practical Ah-level zinc metal pouch cell.Angew Chem Int Ed Engl2025;64:e202502103

[5] Ju L,Kou L.Polarization boosted catalysis: progress and outlook.Microstructures2022;2:2022008

[6] Dey S,Chatterjee S,Amanullah SK.Molecular electrocatalysts for the oxygen reduction reaction.Nat Rev Chem2017;1:0098

[7] Zhan Y,He F.Active site switching of Fe-N-C as a chloride-poisoning resistant catalyst for efficient oxygen reduction in seawater-based electrolyte.Chem Eng J2022;443:136456

[8] Zhang J,Gao L,Li M.Stabilizing Pt-based electrocatalysts for oxygen reduction reaction: fundamental understanding and design strategies.Adv Mater2021;33:e2006494

[9] Li Y,Lin Z.Introducing covalent metal-phosphorus bonds into intermetallic platinum-based catalysts for high-performance fuel cells.Renewables2024;2:223-32

[10] Zeng K,Li C.Recent advances in non-noble bifunctional oxygen electrocatalysts toward large-scale production.Adv Funct Mater2020;30:2000503

[11] Osgood H,Xu H,Wu G.Transition metal (Fe, Co, Ni, and Mn) oxides for oxygen reduction and evolution bifunctional catalysts in alkaline media.Nano Today2016;11:601-25

[12] Han X,He Y.Metal air batteries: engineering catalytic active sites on cobalt oxide surface for enhanced oxygen electrocatalysis.Adv Energy Mater2018;8:1870043

[13] Pu Z,Amiinu IS.Transition-metal phosphides: activity origin, energy-related electrocatalysis applications, and synthetic strategies.Adv Funct Materials2020;30:2004009

[14] Tian D,Li K,Kattel S.Density functional theory studies of transition metal carbides and nitrides as electrocatalysts.Chem Soc Rev2021;50:12338-76

[15] Maiti S,Curnan MT,Noh K.Engineering electrocatalyst nanosurfaces to enrich the activity by inducing lattice strain.Energy Environ Sci2021;14:3717-56

[16] Hu X,Wu Z,Li Y.Synthesis of Zr₂ON₂ via a urea-glass route to modulate the bifunctional catalytic activity of NiFe layered double hydroxide in a rechargeable zinc-air battery.J Colloid Interface Sci2024;672:610-7

[17] Poudel MB,Lohani PC,Yoo DJ.Atomic engineering of 3D self-supported bifunctional oxygen electrodes for rechargeable zinc-air batteries and fuel cell applications.Adv Energy Mater2024;14:2400347

[18] He Y,Priest C,Wu G.Atomically dispersed metal-nitrogen-carbon catalysts for fuel cells: advances in catalyst design, electrode performance, and durability improvement.Chem Soc Rev2020;49:3484-524

[19] Yuan LJ,Pan H.Strategies and mechanism for enhancing intrinsic activity of metal-nitrogen-carbon catalysts in electrocatalytic reactions.Renewables2023;1:514-40

[20] Shang H,Dong J.Engineering unsymmetrically coordinated Cu-S₁N₃ single atom sites with enhanced oxygen reduction activity.Nat Commun2020;11:3049 PMCID:PMC7297793

[21] Mun Y,Kim K.Versatile strategy for tuning ORR activity of a single Fe-N₄ site by controlling electron-withdrawing/donating properties of a carbon plane.J Am Chem Soc2019;141:6254-62

[22] Liu M,Su H.In situ modulating coordination fields of single-atom cobalt catalyst for enhanced oxygen reduction reaction.Nat Commun2024;15:1675 PMCID:PMC10891135

[23] Grimaud A,Saubanère M.Activation of surface oxygen sites on an iridium-based model catalyst for the oxygen evolution reaction.Nat Energy2016;2:1-10

[24] Wang A,Zhang T.Heterogeneous single-atom catalysis.Nat Rev Chem2018;2:65-81

[25] Zhou AW,Li YD.Hollow microstructural regulation of single-atom catalysts for optimized electrocatalytic performance.Microstructures2022;2:2022005

[26] Wang Z,Wu T,Yu Xia B.Periodic defect boundary-mediated activity of electrocatalytic oxygen reduction reactions of Fe-N-C catalysts.Renewables2024;3:213-9

[27] Wang W,Li P,Chen S.Realizing the 4e^-/2e^- pathway transition of O₂ reduction on Co-N₄-C catalysts by regulating the chemical structures beyond the second coordination shells.ACS Catal2024;14:5961-71

[28] Datye AK.Single atom catalysis poised to transition from an academic curiosity to an industrially relevant technology.Nat Commun2021;12:895 PMCID:PMC7873241

[29] Liu Y,Shan L.Localized negatively charged interfaces for seawater electrolyte-based zinc-air batteries.Adv Funct Materials2025;35:2422874

[30] Yu J,Liu JN,Tang C.Seawater-based electrolyte for zinc-air batteries.GreenChE2020;1:117-23

[31] Yu Q,Liu G.Constructing three-phase heterojunction with 1D/3D hierarchical structure as efficient trifunctional electrocatalyst in alkaline seawater.Adv Funct Materials2022;32:2205767

[32] Wu S,Mao H.Realizing high-efficient oxygen reduction reaction in alkaline seawater by tailoring defect-rich hierarchical heterogeneous assemblies.Appl Catal B-Environ2023;330:122634

[33] Wu S,Mao H.Unraveling the tandem effect of nitrogen configuration promoting oxygen reduction reaction in alkaline seawater.Adv Energy Mater2024;14:2400183

[34] Luo Y,Hu Y.TiN as radical scavenger in Fe-N-C aerogel oxygen reduction catalyst for durable fuel cell.Small2024;20:e2309822

[35] Meng R,Lu Z.An oxygenophilic atomic dispersed Fe-N-C catalyst for lean-oxygen seawater batteries.Adv Energy Mater2021;11:2170085

[36] Zhang J,Zhang Y.Tandem synergetic effect in symbiotic Co catalyst for enhanced oxygen reduction.Chem Eng J2025;505:159687

[37] Zhang W,Wang N.Two-electron redox chemistry via single-atom catalyst for reversible zinc-air batteries.Nat Sustain2024;7:463-73

[38] Wang K,Lei J,Li Y.Modulation of ligand fields in a single-atom site by the molten salt strategy for enhanced oxygen bifunctional activity for zinc-air batteries.ACS Nano2022;16:11944-56

[39] Feng X,Cui Z.Engineering electronic structure of nitrogen-carbon sites by sp³-hybridized carbon and incorporating chlorine to boost oxygen reduction activity.Angew Chem Int Ed Engl2024;63:e202316314

[40] Tian H,Li Z.Disorder-tuned conductivity in amorphous monolayer carbon.Nature2023;615:56-61

[41] Cui J,Liu Z.Carbon-anchoring synthesis of Pt₁Ni₁@Pt/C core-shell catalysts for stable oxygen reduction reaction.Nat Commun2024;15:9458 PMCID:PMC11530681

[42] Zhang H,Li D.Halogen doped graphene quantum dots modulate TDP-43 phase separation and aggregation in the nucleus.Nat Commun2024;15:2980 PMCID:PMC10998863

[43] Huang Y,Hu Z.Solvent-free synthesis of foam board-like CoSe₂ alloy to selectively generate singlet oxygen via peroxymonosulfate activation for sulfadiazine degradation.J Hazard Mater2024;466:133611

[44] Su J,Song Y.Strain enhances the activity of molecular electrocatalysts via carbon nanotube supports.Nat Catal2023;6:818-28

[45] Kumar P,Zeraati AS.High-density cobalt single-atom catalysts for enhanced oxygen evolution reaction.J Am Chem Soc2023;145:8052-63

[46] Ye P,Wang H.Lattice oxygen activation and local electric field enhancement by co-doping Fe and F in CoO nanoneedle arrays for industrial electrocatalytic water oxidation.Nat Commun2024;15:1012 PMCID:PMC10837452

[47] Ding S,Shi Q.Engineering atomic single metal-FeN₄Cl sites with enhanced oxygen-reduction activity for high-performance proton exchange membrane fuel cells.ACS Nano2022;16:15165-74

[48] Liu P,Liang C.Tip-enhanced electric field: a new mechanism promoting mass transfer in oxygen evolution reactions.Adv Mater2021;33:e2007377

[49] Khan MU,Liu Z.Pt₃Co octapods as superior catalysts of CO₂ hydrogenation.Angew Chem Int Ed Engl2016;55:9548-52

[50] Zhang L,Yang Y.Advances on axial coordination design of single-atom catalysts for energy electrocatalysis: a review.Nanomicro Lett2023;15:228 PMCID:PMC10575848

[51] Sabhapathy P,Sabbah A.Axial chlorine induced electron delocalization in atomically dispersed fen4 electrocatalyst for oxygen reduction reaction with improved hydrogen peroxide tolerance.Small2023;19:e2303598