Cathodic Oxygen Research Articles

Simultaneously Geometrical and Electronic Modulation of L10-PtZn by Trace Ge Boosts High-performance Oxygen Reduction Reaction.

Developing a highly active, durable, and low-platinum-based electrocatalyst for the cathodic oxygen reduction reaction (ORR) is for breaking the bottleneck of large-scale applications of proton exchange membrane fuel cells (PEMFCs). Herein, ultrafine PtZn intermetallic nanoparticles with low Pt-loading and trace germanium (Ge) involvement confined in the nitrogen-doped porous carbon (Ge-L10-PtZn@N-C) are reported. The Ge-L10-PtZn@N-C exhibit superior ORR activity with a mass activity of 3.04 A mg-1 Pt and specific activity of 4.69mA cm-2, ≈12.2- and 10.2-times improvement compared to the commercial Pt/C (20%) at 0.90V in 0.1m KOH. The cathodic catalyst Ge-L10-PtZn@N-C assembled in the PEMFC shows encouraging peak power densities of 316.5 (at 0.86V) and 417.2mW cm-2 (at 0.91V) in alkaline and acidic fuel-cell, respectively. The combination of experiment and density functional theory calculations (DFT) results robustly reveal that the participation of trace Ge can not only trigger a "growth site locking effect" to effectively inhibit nanoparticle growth, bring miniature nanoparticles, enhance dispersion uniformity, and achieve the exposure of the more electrochemical active site, but also effectively modulates the electronic structure, hence optimizing the adsorption/desorption of the oxygen intermediates.

Protecting Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode with SrSn0.8Sc0.2O3-δ proton conductor for protonic ceramic fuel cells

Improving chemical stability and performance is desirable for protonic ceramic cathodes (PCFCs). In this study, the proton conductor SrSn0.8Sc0.2O3-δ (SSSc) is used to couple the classically unstable Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cathode to increase the chemical stability of the composite cathode. Compared to the conventional BSCF + BaCe0.7Zr0.1Y0.2O3-δ (BCZY) composite cathode, the new BSCF + SSSc cathode demonstrates enhanced chemical stability. This is a result of the superior chemical stability of SSSc, which protects BSCF. Moreover, the formation of oxygen vacancies is easier at the BSCF/SSSc interface than at the BSCF/BCZY interface, thereby enhancing the cathode oxygen reduction reaction (ORR) activity. The closer proximity of the O p-band center to the Fermi level in BSCF + SSSc compared to BSCF + BCZY further validates the higher ORR activity of the BSCF + SSSc cathode. The peak power density of the PCFC with BSCF + SSSc cathode, which reaches 1404 mW cm−2 at 700 °C, is significantly greater than that with BSCF + BCZY cathode. The protection of SSSc to BSCF is also reflected in the fuel cell's long-term operation, as the BSCF + SSSc cell operates without detectable degradations for more than 150 h, whereas the BSCF + BCZY cell exhibits observable degradation. These findings indicate that utilizing the SSSc proton conductor to couple the cathode material is a feasible and effective strategy for producing the composite cathode with high chemical stability and superior electrochemical performance for PCFCs.

Activating doped graphene surface by cobalt-rich sulfide encapsulation toward oxygen reduction electrocatalysis

Similar to proton exchange membrane fuel cell, anion-exchange membrane fuel cell is also a significant energy conversion device for achieving the utilization of clean hydrogen energy. However, the cathodic alkaline oxygen reduction reaction (ORR) is kinetically not favored and usually requires platinum-group metal (PGM) catalysts such as Pt/C to reduce the overpotential. The major challenge in using PGM-free catalysts for ORR is their low efficiency and poor stability, which urgently demands new concepts and strategies to address this issue. Herein, we controllably manufactured a N, S-co doped graphene encapsulating uniform cobalt-rich sulfides (Co8FeS8@NSG) by a universal synthesis strategy. After encapsulation, electron transfer from the encapsulated cobalt-rich sulfides to the doped graphene was greatly promoted, which effectively optimizes the electronic structure of the doped graphene, thereby enhancing the ORR activity of the doped graphene surface. Consequently, the Co8FeS8@NSG exhibits enhanced ORR activity with a higher half-wave potential of 0.868 V (versus reversible hydrogen electrode, vs. RHE) when compared with pure NSG (0.765 V vs. RHE). Density functional theory calculations further confirm that the construction of interface for NSG encapsulating cobalt-rich sulfides could conspicuously elevate the ORR activity through slightly positively-charged C active site and thus simultaneously enhancing electronic conductivity.

Water Flow-Driven Coupling Process of Anodic Oxygen Evolution and Cathodic Oxygen Activation for Water Decontamination and Prevention of Chlorinated Byproducts.

Electrochemical advanced oxidation process (EAOP) is a promising technology for decentralized water decontamination but is subject to parasitic anodic oxygen evolution and formation of toxic chlorinated byproducts in the presence of Cl-. To address this issue, we developed a novel electrolytic process by water flow-driven coupling of anodic oxygen evolution reaction (OER) and cathodic molecular oxygen activation (MOA). When water flows from anode to cathode, O2 produced from OER is carried by water through convection, followed by being activated by atomic hydrogen (H*) on Pd cathode to produce •OH. The water flow-driven OER/MOA process enables the anode to be polarized at low potential (1.7 V vs SHE) that is lower than that of conventional EAOP whose •OH is produced from direct water oxidation (>2.3 V vs SHE). At a flow rate of 30 mL min-1, the process could achieve 94.8% removal of 2,4-dichlorophenol (2,4-DCP) and 71.5% removal of chemical oxygen demand (COD) within 45 min at an anode potential of 1.7 V vs SHE and cathode potential of -0.5 V vs SHE. To achieve the comparable 2,4-DCP removal performance, 4.3-fold higher energy consumption was needed for the conventional EAOP with titanium suboxide anode (anode potential of 2.9 V vs SHE), but current efficiency declined by 3.5 folds. Unlike conventional EAOP, chlorate and perchlorate were not detected in the OER/MOA process, because low anode potential <2.0 V vs SHE was thermodynamically unfavorable for the formation of chlorinated byproducts by anodic oxidation, indicated by theoretical calculations and experimental data. This study provides a proof-in-concept demonstration of water flow-driven OER/MOA process, representing a paradigm shift of electrochemical technology for water decontamination and prevention of chlorinated byproducts, making electrochemical water decontamination more efficient, more economic, and more sustainable.

Hierarchically Porous, N, P‐Co‐Doped Carbon Structures with Embedded Pt Particles as Effective Electrocatalysts for the Oxygen Reduction Reaction

AbstractThe proton exchange membrane fuel cell now ranks as one of the best alternatives to fossil fuels. Two optimization techniques that have stirred up a lot of controversy include reducing the amount of precious metal Pt catalysts and boosting the kinetics of the cathodic oxygen reduction reaction (ORR). Herein, “template‐etching” method is used to create N−P co‐doped low‐Pt catalysts with hierarchical porous carbon nanospheres (Pt/NPC). The P atoms′ valence electrons, which serve to attach the Pt to the equally disseminated N atoms, further disperse the Pt inside the carbon nanospheres. As a result, the Pt is able to modify the electronic structure and alter the d‐band center, which raises the intrinsic ORR activity. The hierarchical porous structure of the carbon nanospheres, created by the phytic acid activation of the pores, can expose more active sites and efficiently enhance the transfer of oxygen and electrons, increasing the catalytic efficiency. The catalysts synthesized using this method had great stability, 9.87 wt % Pt concentration, and half‐wave potential of 0.832 V for acidic intermediates and 0.855 V for alkaline intermediates. Because of its entire pH ORR catalytic capabilities, this catalyst exhibits tremendous application potential for replacing conventional Pt/C catalysts.

Recent Advances in Non‐Precious Metal Single‐Atom Electrocatalysts for Oxygen Reduction Reaction in Low‐Temperature Polymer‐Electrolyte Fuel Cells

AbstractFuel cells have emerged as a promising clean electrochemical energy technology with a great potential in various sectors, including transportation and power generation. However, the high cost and scarcity of the noble metals currently used to synthesise electrocatalysts for low‐temperature fuel cells has hindered their widespread commercialisation. In recent decades, the development of non‐precious metal electrocatalysts for the cathodic oxygen reduction reaction (ORR) have gained significant attention. Among those, electrocatalysts with atomically dispersed active sites, referred to as single‐atom catalysts (SACs), are gaining more interest. Nanocarbon materials containing single transition metal atoms coordinated to nitrogen atoms are active electrocatalysts for the ORR in both acidic and alkaline conditions and thus have a great promise to be utilised as non‐precious metal cathode electrocatalysts in low‐temperature fuel cells. This review article provides an overview of the recent advancements in the utilisation of transition metal‐based SACs in proton exchange membrane fuel cells (PEMFCs) and anion exchange membrane fuel cells (AEMFCs). We highlight the main strategies and synthetic approaches for tailoring the properties of SACs to enhance their ORR activity and durability. Based on the already achieved results, it is evident that SACs indeed could be suitable for the cathode of the low‐temperature fuel cells.

Fe&Fe2O3 Dual-Decorated on N-Doped Porous Carbon for Oxygen Reduction Reaction

Catalysts for the cathodic oxygen reduction reaction (ORR) are important in fuel cells. Herein, a class of non-precious metal ORR catalyst, namely Fe&Fe2O3 dual-decorated on N-doped porous carbon (Fe&Fe2O3/NC), is prepared from the pyrolysis of a mixture containing Fe2O3/NC, Fe salt and melamine, followed by acid-leaching, where Fe2O3/NC is firstly synthesized from one-step pyrolyzing the precursors of coal, KOH, melamine and Fe salt. As a result, the Fe&Fe2O3/NC provides a much better ORR catalytic activity with the peak potential (Ep) and half-wave potential (E1/2) of 902 mV and 852 mV, respectively, than these of Fe2O3/NC (824 mV and 768 mV) and close to these of 20 wt% commercial Pt/C (918 mV and 863 mV). Furthermore, the ORR occurred on Fe&Fe2O3/NC follows near a four-electron transfer pathway. It also has a good stability and methanol-resistance. By comparing the structures of Fe2O3/NC and Fe&Fe2O3/NC, the essential roles on improving the ORR catalytic activity are discussed: both the abundant graphitic N active sites and the synergistic effect of Fe and Fe2O3 play important roles. This work not only provides a general guideline for the design and development of non-precious metal-based catalysts for ORR but also enriches the application scope of coal.

In-situ exsolution of PrO2−x nanoparticles boost the performance of traditional Pr0.5Sr0.5MnO3-δ cathode for proton-conducting solid oxide fuel cells

By synthesizing the nominal PrxSr0.5MnO3-δ materials (x=0.5, 0.6, 0.7, 0.8), new Pr0.5Sr0.5MnO3-δ (PSM50)+PrO2-x composite cathodes for proton-conducting solid oxide fuel cells (SOFCs) were developed. The structure analysis and morphology observations verified the exsolution of PrO2-x particles, and the amount of exsolved PrO2-x increased with the amount of Pr in PrxSr0.5MnO3-δ. An H-SOFC with a Pr0.7Sr0.5MnO3-δ (PSM70) cathode enabled the highest reported fuel cell output for H-SOFCs with manganate cathodes. The construction of a PSM50/PrO2 heterostructure interface can reduce the formation energy of oxygen vacancies, hence accelerating the cathode oxygen reduction reaction (ORR) kinetics, as confirmed by oxygen diffusion and surface exchange experiments. The excellent electrochemical performance was combined with its good chemical stability against CO2 and H2O, allowing a stable operation of the cell for over 100 hours, indicating that PSM70, which was in fact PSM50+PrO2-x, was a highly efficient and durable cathode material for H-SOFCs.

One-step synthesis of thin-carbon-shell-encapsulated binary cobalt chromium nitrides for oxygen reduction reaction

Hydrogen fuel cells are expected to be widely used in transportation and portable power generation. Unfortunately, sluggish cathodic oxygen reduction reaction (ORR) kinetics hamper the commercial application of the fuel cells. The quest for cost effective and highly efficient ORR catalysts is of great importance. Transition metal nitride (TMN) has received widespread attention mainly for its Pt-like characteristics. Here, we propose a new one-step “NH3-free” synthesis of thin-carbon-shell-encapsulated binary cobalt chromium nitrides (Co-CrN@C) using 1,2,4-1H-triazole as the nitrogen/carbon source. The Co-CrN@C exhibits almost ideal four-electron reduction of oxygen and achieves remarkable long-term durability and better methanol tolerance due to high-degree graphitization of the carbon shell. The X-ray photoelectron spectra and the density functional theory calculations unveil the origin of the intrinsic activity of the catalyst and the reaction mechanism. Furthermore, Co-CrN@C exhibits an impressive peak power density (PPD) of 488 mW cm−2, surpassing the 423 mW cm−2 for the Pt/C-driven anion exchange membrane fuel cells. These findings offer an indispensable strategy for rational design of high-efficient and durable non-noble catalysts.

Tailoring the local electron and modulating morphology to enhance the overall water splitting and urea electrolysis of CoMoO4@Cu2S electrocatalyst with superhydrophilicity

Tailoring the local electron and modulating morphology are the effective ways to improve catalytic performance of the electrocatalysts. Herein, oxygen vacancy-rich CoMoO4@Cu2S heterojunction nanorod arrays electrocatalyst was successfully fabricated on copper foam (VO-CoMoO4@Cu2S HNAs/CF) via the simple solvothermal and calcination routes. The unique VO-CoMoO4@Cu2S HNAs/CF possesses extraordinary activities with an ultralow overpotential of 45 and 181 mV for cathodic hydrogen evolution (HER) and anodic oxygen evolution (OER), respectively, and the low potential of 1.32 V for anodic urea oxidation (UOR) at 10 mA cm−2. More impressively, the assembled VO-CoMoO4@Cu2S HNAs/CF(+/−) cell requires merely 1.47 and 1.33 V to reach 10 mA cm−2 with superb durability for 150 h in 1 M KOH without and with urea, respectively. Multiple characterization and the density functional theory (DFT) calculation results show that the outstanding electrocatalytic performance could be mainly attributed to the synergistic effect of the tailoring the local electron and modulating morphology.

Design and Synthesis of Cubic K3-2 x Bax SbSe4 Solid Electrolytes for K-O2 Batteries.

Developing K-ion conducting solid-state electrolytes (SSEs) plays a critical role in the safe implementation of potassium batteries. In this work, a chalcogenide-based potassium ion SSE is reported, K3 SbSe4 , which adopts a trigonal structure at room temperature. Single-crystal structural analysis reveals a trigonal-to-cubic phase transition at the low temperature of 50 °C, which is the lowest among similar compounds and thus provides easy access to the cubic phase. The substitution of barium for potassium in K3 SbSe4 leads to the creation of potassium vacancies, expansion of lattice parameters, and a transformation from a trigonal phase to a cubic phase. As a result, the maximum conductivity of K3-2 x Bax SbSe4 reaches around 0.1 mS cm-1 at 40 °C for K2.2 Ba0.4 SbSe4 , which is over two orders of magnitude higher than that of undoped K3 SbSe4 . This novel SSE is successfully employed in a K-O2 battery operating at room temperature where a polymer-laminated K2.2 Ba0.4 SbSe4 pellet serves as a separator between the oxygen cathode and the potassium metal anode. Effective protection of the K metal anode against corrosion caused by O2 is demonstrated.

Potential-driven instability effect of carbon supports for Pt/C electrocatalysts

Proton exchange membrane fuel cell (PEMFC) technology is a crucial approach of achieving clean and efficient power generation. However, prior to its full commercialization, several pressing issues must be addressed, especially the dissolution/degradation of Pt-based electrocatalysts for the cathode oxygen reduction reaction (ORR). This degradation significantly reduces the electrocatalytic activity of the catalysts. In this work, the impact of solid carbon support (Vulcan XC-72 R) and porous carbon support (Ketjenblack EC-300) on the degradation process of Pt/C electrocatalysts was investigated. By utilizing various triangular-wave voltage cycles in accelerated durability testing (ADT) protocols, the experimental findings suggest that a lower upper potential limit (UPL) in ADT tends to promote Pt diffusion and further aggregation, while a higher UPL exacerbates the electrochemical dissolution of Pt. Furthermore, the results indicate that Ketjenblack is more proficient than Vulcan XC-72 R in facilitating Pt redeposition after dissolution, which helps to minimize the loss of Pt under standardized rotating disk-electrode (RDE) aqueous electrolyte ADT conditions.

Pyrazine-linked Iron-coordinated Tetrapyrrole Conjugated Organic Polymer Catalyst with Spatially Proximate Donor-Acceptor Pairs for Oxygen Reduction in Fuel Cells.

Nitrogen-coordinated iron (Fe-N4 ) materials represent the most promising non-noble electrocatalysts for the cathodic oxygen reduction reaction (ORR) of fuel cells. However, molecular-level structure design of Fe-N4 electrocatalyst remains a great challenge. In this study, we develop a novel Fe-N4 conjugated organic polymer (COP) electrocatalyst, which allows for precise design of the Fe-N4 structure, leading to unprecedented ORR performance. At the molecular level, we have successfully organized spatially proximate iron-pyrrole/pyrazine (FePr/Pz) pairs into fully conjugated polymer networks, which in turn endows FePr sites with firmly covalent-bonded matrix, strong d-π electron coupling and highly dense distribution. The resulting pyrazine-linked iron-coordinated tetrapyrrole (Pz-FeTPr) COP electrocatalyst exhibits superior performance compared to most ORR electrocatalysts, with a half-wave potential of 0.933 V and negligible activity decay after 40,000 cycles. When used as the cathode electrocatalyst in a hydroxide exchange membrane fuel cell, the Pz-FeTPr COP achieves a peak power density of ≈210 mW cm-2 . We anticipate the COP based Fe-N4 catalyst design could be an effective strategy to develop high-performance catalyst for facilitating the progress of fuel cells.

Pyrazine‐linked Iron‐coordinated Tetrapyrrole Conjugated Organic Polymer Catalyst with Spatially Proximate Donor‐Acceptor Pairs for Oxygen Reduction in Fuel Cells

AbstractNitrogen‐coordinated iron (Fe−N4) materials represent the most promising non‐noble electrocatalysts for the cathodic oxygen reduction reaction (ORR) of fuel cells. However, molecular‐level structure design of Fe−N4 electrocatalyst remains a great challenge. In this study, we develop a novel Fe−N4 conjugated organic polymer (COP) electrocatalyst, which allows for precise design of the Fe−N4 structure, leading to unprecedented ORR performance. At the molecular level, we have successfully organized spatially proximate iron‐pyrrole/pyrazine (FePr/Pz) pairs into fully conjugated polymer networks, which in turn endows FePr sites with firmly covalent‐bonded matrix, strong d‐π electron coupling and highly dense distribution. The resulting pyrazine‐linked iron‐coordinated tetrapyrrole (Pz−FeTPr) COP electrocatalyst exhibits superior performance compared to most ORR electrocatalysts, with a half‐wave potential of 0.933 V and negligible activity decay after 40,000 cycles. When used as the cathode electrocatalyst in a hydroxide exchange membrane fuel cell, the Pz−FeTPr COP achieves a peak power density of ≈210 mW cm−2. We anticipate the COP based Fe−N4 catalyst design could be an effective strategy to develop high‐performance catalyst for facilitating the progress of fuel cells.

Atomic-Level Regulation of Cu-Based Electrocatalyst for Enhancing Oxygen Reduction Reaction: From Single Atoms to Polymetallic Active Sites.

The slow kinetics of cathodic oxygen reduction reactions (ORR) in fuel cells and the high cost of commercial Pt-based catalysts limit their large-scale application. Cu-based single-atom catalysts (SACs) have received increasing attention as a promising ORR catalyst due to their high atom utilization, high thermodynamic activity, adjustable electronic structure, and low cost. Herein, the recent research progress of Cu-based catalysts is reviewed from single atom to polymetallic active sites for ORR. First, the design and synthesis method of Cu-based SACs are summarized. Then the atomic-level structure regulation strategy of Cu-based catalyst is proposed to improve the ORR performance. The different ORR catalytic mechanism based on the different Cu active sites is further revealed. Finally, the design principle of high-performance Cu-based SACs is proposed for ORR and the opportunities and challenges are further prospected.

Hofmann-type MOFs derived intermetallic L10-PtFe/NC electrocatalysts for boosting oxygen reduction reaction

Intermetallic electrocatalysts have demonstrated significant potential in facilitating the cathodic oxygen reduction reaction (ORR) in fuel cells with enhanced activity and durability. However, it is still an enormous challenge to the facile synthesis of Pt-based intermetallic catalysts with uniform size and high ordering degree. Here, we innovatively fabricate the core-shell structured L10-PtFe intermetallics with Pt skins supported on N-doped porous carbon matrix through one-step pyrolysis of PtFe Hofmann-type metal-organic frameworks (denoted as L10-PtFe/NC). Under the constraints of the porous structure and cyano-ligand bonding, most Fe atoms are alloyed with Pt to form uniform-ordered PtFe intermetallics, while some Fe atoms are atomically dispersed in the carbon framework to form FeNx moieties. Notably, a series of intermetallic PtFe catalysts with different ordering degrees are successfully constructed by adjusting the pyrolysis temperature, which verified that the increase of ordering degree is beneficial to promote the electrocatalytic performance. In particular, the ordered L10-PtFe/NC-800 exhibits superb ORR activity with both mass and specific activities, which are 2.7-folds higher than those of commercial Pt/C. Moreover, after an accelerated durability test, L10-PtFe/NC-800 retains over 90 % mass activity. This work provides a promising approach for the development of efficient Pt-based intermetallic electrocatalysts for fuel cells.

Illuminating Oxygen Reduction Reaction Kinetics in High Temperature Polymer Electrolyte Membrane Fuel Cells Using EIS

High Temperature Polymer Electrolyte Membrane Fuel Cells (HTPEMFCs) commercialization, is impeded by the sluggish, power intensive and elusive cathodic Oxygen Reduction Reaction (ORR) kinetics. In this work we provide solid experimental evidence that the simple three elementary step Dissociative Adsorption (DA) pathway, with two intermediate species (Oad and OHad), can accurately describe the steady state (IV) and the Electrochemical Impedance Spectra (EIS) response of a HTPEMFC. Deconvoluted EIS outlined the important role of Intrinsic Kinetic Inertia, which dominated both EIS and polarization resistance. The Degree of Rate Control (DRC) analysis, identified the O2(g) dissociative adsorption as the rate limiting step. Finally, Transition State Theory (TST) allowed the extraction and analysis of ORR energetics, demonstrating that the high ORR overpotential losses originate from the combined strength of both kinetically and thermodynamically imposed barriers, due to the high bonding strength of Oad on Pt and the high activation energy of O2(g) adsorption.

Density functional theory investigation of the role of Fe doped in boron carbide nanotube as an electro-catalyst for oxygen reduction reaction in fuel cells

A critical issue in enhancing the performance of polymer electrolyte membrane fuel cells (FCs) is the slow kinetics of the cathodic oxygen reduction reaction (ORR). The development of electrocatalysts with selectivity toward the four-electron (4e) pathway and high electrochemical activity to ORR reaction is important for fuel cell applications. Within the present study, it was found that boron carbide nanotube (BC3NT) is an encouraging ORR-EC based on density functional theory computations. In the pristine BC3NT, the neighboring B atoms with positive charges on the surface of the material surface were incapable of providing active sites for the dissociation of O. However, the ORR catalytic activity of BC3NT improved under the ligand effect due to the replacement of Fe atom, where there was a slight over-potential that was similar or lower than that of platinum (111), which demonstrated its superior ORR activity. The results suggest that BC-based materials are considered promising for ORR catalysis and for designing highly efficient ORR-ECs as alternatives to platinum-based catalysts.

Synergistic Effect of Aluminum Lactate and Sodium Molybdate on Freshwater Corrosion of Carbon Steel Under Irradiation

In this study, a corrosion inhibitor suitable for the corrosion inhibition of primary containment vessels at the Fukushima Daiichi Nuclear Power Station is investigated. Considering the internal environment of the primary containment vessels, the corrosion inhibitor should inhibit the freshwater corrosion of carbon steel under irradiation and should not come under effluent standards in Japan. Herein, a corrosion inhibitor was devised by combining Al lactate and Na molybdate that met the above conditions, and its corrosion mechanism was investigated. It was found that 0.75 mM Al lactate and 0.25 mM Na molybdate were the most inhibitive to the corrosion of carbon steel. As Al lactate has never been reported as a corrosion inhibitor for metallic materials, it could be developed as a novel corrosion inhibitor in this study. The corrosion inhibitor inhibited the freshwater corrosion of carbon steel even under gamma irradiation of 200 Gy/h. Al and molybdate ions in the solution formed a metal cation layer on carbon steel with few defects and without iron. This metal cation layer inhibited both the cathodic oxygen reduction reaction and the anodic iron dissolving reaction, thereby enhancing the corrosion protection of carbon steel in freshwater.

Constructing Nitrogen-Doped Carbon Hierarchy Structure Derived from Metal-Organic Framework as High-Performance ORR Cathode Material for Zn-Air Battery.

The development of efficient and low-cost catalysts for cathodic oxygen reduction reaction (ORR) in Zn-air battery (ZAB) is a key factor in reducing costs and achieving industrialization. Here, a novel segregated CoNiPt alloy embedded in N-doped porous carbon with a nanoflowers (NFs)-like hierarchy structure is synthesized through pyrolyzing Hofmann-type metal-organic frameworks (MOFs). The unique hierarchical NFs structure exposes more active sites and facilitates the transportation of reaction intermediates, thus accelerating the reaction kinetics. Impressively, the resulting 15% CoNiPt@C NFs catalyst exhibits outstanding alkaline ORR activity with a half-wave potential of 0.93V, and its mass activity is 7.5 times higher than that of commercial Pt/C catalyst, surpassing state-of-the-art noble metal-based catalysts. Furthermore, the assembled CoNiPt@C+RuO2 ZAB demonstrates a maximum power density of 172mW cm-2 , which is superior to that of commercial Pt/C+RuO2 ZAB. Experimental results reveal that the intrinsic ORR mass activity is attributed to the synergistic interaction between oxygen defects and pyrrolic/graphitic N species, which optimizes the adsorption energy of the intermediate species in the ORR process and greatly enhances catalytic activity. This work provides a practical and feasible strategy for synthesizing cost-effective alkaline ORR catalysts by optimizing the electronic structure of MOF-derived catalysts.