Efficient Oxygen Reduction Reaction Catalysts Research Articles

Fe3O4/N-CNTs derived from hypercrosslinked carbon nanotube as efficient catalyst for ORR in both acid and alkaline electrolytes

The development of efficient and durable transition metal-based electrocatalysts for the oxygen reduction reaction (ORR) is a key step in the commercial application of renewable energy storage and conversion technology. Herein, a novel and convenient strategy was proposed to embed Fe3O4 nanoparticles into nitrogen-doped carbon nanotubes (Fe3O4/N-CNTs) by the Friedel-Crafts alkylation reaction of iron-tetraphenylporphyrin (FeTPP) and subsequent pyrolysis process. The hypercrosslinked FeTPP framework provided more exposed N and Fe3O4 active sites on the CNTs surface, and the feasibility to adjust the Fe contents that had a great influence on the composite structure. Moreover, the Fe3O4/N-CNTs served as a robust catalyst for the ORR in both acid and alkaline media. Compared with 20% Pt/C, Fe3O4/N-CNTs with Fe content of 2.62% exhibited excellent electrochemical performance in terms of positive onset potential (E0 = 0.920 V vs. RHE), half-wave potential (E1/2 = 0.804 V), much better methanol tolerance, and long-term durability. The remarkable performance of Fe3O4/N-CNTs was ascribed to the favorable oxygen adsorption and diffusion, which benefited from its large specific surface area and microporous structure, high reactivity by the exposed graphitic N and oxygen defects, and strong electronic interaction between Fe3O4 and N-doped CNTs.

Carbon doped cobalt nanoparticles stabilized by carbon shell for highly efficient and stable oxygen reduction reaction

The oxygen reduction reaction (ORR) is a key reaction in metal-air batteries and fuel cells. Herein, a novel carbon-doped Co nanoparticle coated with a carbon layer supported on the ordered macroporous titanium oxide (C-doped Co@C@TiO2) is designed as the highly efficient and stable ORR catalysts. The C-doped Co@C@TiO2 achieves the superior catalytic activity with an onset potential of 0.867 V and a limiting current density of −6.59 mA cm−2, which is much lower than the commercial Pt/C (−5.93 mA cm−2). The turnover frequency (TOF) of the C-doped Co@C@TiO2 at the potential of 0.3 V (0.091 s−1) is nearly four times than the commercial Pt/C (0.025 s−1). This outstanding catalytical performance is attributed to the unique C-doped Co layer in Co nanoparticles, which can stable the OOH* and promote the desorption of OH*, and accelerate the catalyst surface regeneration in ORR. Meanwhile, the outer C layer with mesoporous channels can improve the stability and poisoning resistant of the C-doped Co nanoparticles, and the C-doped Co@C@TiO2 still retains 98% of the current density after the reaction for 60 h. It is worth noting that the assembled zinc-air battery with C-doped Co@C@TiO2 as the air cathode exhibits an ultra-high open circuit voltage of 1.51 V and an excellent durability of more than 41.6 days. This work provides one of the most promising non-noble metal-based catalysts for efficient and stable oxygen reduction reaction.

Hybridization of iron phthalocyanine and MoS2 for high-efficiency and durable oxygen reduction reaction

Hybrid catalysts based on iron phthalocyanine (FePc) have raised much attention due to their promising applications in electrocatalytic oxygen reduction reaction (ORR). Various hybridization strategies have been developed for improving their activity and durability. However, the influence of different hybridization strategies on their catalytic performance remains unclear. In this study, FePc was effectively distributed on molybdenum disulfide (MoS2) forming FePc-based hybrid catalysts, namely FePc-MoS2, FePc*-MoS2, and FePc-Py-MoS2, respectively, to disclose the related influence. Through direct hybridization, the stacked and highly dispersed FePc on MoS2 resulted in FePc-MoS2, and FePc*-MoS2, respectively, in which the substrate and FePc are mainly bound through van der Waals interactions. Through covalent hybridization strategy using pyridyl (Py) as a linker, FePc-Py-MoS2 hybrid catalyst was prepared. Experimental and theoretical results disclosed that the linker hybridization of FePc and MoS2 facilitated the exposure of Fe-N4 sites, maintained the intrinsic activity of FePc by forming a more dispersed phase and increased the durability via Fe-N bonding, rendering the FePc-Py-MoS2 an excellent ORR hybrid catalyst. Compared with van der Waals hybridized FePc-MoS2 and FePc*-MoS2 in alkaline media, the linker hybridized FePc-Py-MoS2 showed an obviously enhanced ORR activity with a half-wave potential (E1/2) of 0.88 V vs RHE and an ultralow Tafel slope of 26 mV dec-1. Besides, the FePc-Py-MoS2 exhibited a negligible decay of E1/2 after 50,000 CV cycles for ORR, showing its superior durability. This work gives us more insight into the influence of different hybrid strategies on FePc catalysts and provides further guidance for the development of highly efficient and durable ORR catalysts.

N and P dual heteroatom doped mesoporous hollow carbon as an efficient oxygen reduction reaction catalyst in alkaline electrolyte

Heteroatom is doped in hollow carbon materials could be an excellent approach for enhancing sluggish cathodic oxygen reduction reaction (ORR) in fuel cells. Herein, we proposed a facile one step synthesis of N and P dual heteroatom doped hollow mesoporous carbon sphere (NPHS) derived from dopamine hydrochloride (DA) and phytic acid (PA) precursors is inspected for the same. By altering PA addition time interval and its loading concentration we achieved NPHS with high surface area and excellent sphere morphology. We established that the addition of 0.4 g PA at an interval of 30 h into DA mixture found to be optimum condition for the formation of NPHS-0.4. Such conditions favored formation of high surface area (1120 m2 g−1), better shell thickness (31 nm), enriched pyridinic N, P–C and P–N sites thereby resulted to an exceptional ORR activity. Moreover, electrochemical studies proved that NPHS-0.4 material possess a moderate carrier concentration (2.3 × 1015 cm−3) and flat band potential (0.56 V vs RHE) leads to a positive onset potential (0.97 V), limiting current density (4.7 mA cm−2) by adopting a close to four electron ORR pathway. In addition, it shows a remarkable electrochemical stability and excellent methanol oxidation tolerance than the Pt/C catalyst. Thus, this interesting outcome absolutely provides a platform to develop a new type of active dual doped mesoporous carbon materials for various energy storage/conversion applications.

Hierarchical Core-Shell Co2 N/CoP Embedded in N, P-doped Carbon Nanotubes as Efficient Oxygen Reduction Reaction Catalysts for Zn-air Batteries.

Projecting a cost-effective and highly efficient electrocatalyst for the oxygen reaction reduction (ORR) counts a great deal for Zn-air batteries. Herein, a hierarchical core-shell ORR catalyst (Co2 N/CoP@PNCNTs) is developed by embedding cobalt phosphides and/or cobalt nitrides as the core into N, P-doped carbon nanotubes (PNCNTs) as the shell via one-step carbonization, nitridation, and phosphorization of pyrolyzing Co-MOF precursor. The globally N, P-doped structure of Co2 N/CoP@PNCNTs demonstrates an outstanding electrocatalytic activity in the alkaline solution with the onset and half-wave potentials of 1.07and 0.85V respectively. Moreover, a Zn-air battery assembled from Co2 N/CoP@PNCNTs as the air cathode delivers an open circuit potential of 1.49V, a maximum power density of 151.1mW cm-2 and a specific capacity of 823.8 mAh kg-1 . It is reflected that Co2 N/CoP@PNCNTs provides a long-term durability with a slight decline of 15 h in the chronoamperometry measurement and an excellent charge-discharge stability with negligible voltage decay for 150 h at 10mA cm-2 in Zn-air batteries. The results reveal that Co2 N/CoP@PNCNTs has superiority over most Co-Nx -C or Cox P@C catalysts reported so far. The excellent catalytic properties and stability of Co2 N/CoP@PNCNTs derive from synergistic effects between Co2 N/CoP and mesoporous N, P-doped carbon nanotubes.

Tetraphenolphthalein Cobalt(II) Phthalocyanine Polymer Modified with Multiwalled Carbon Nanotubes as an Efficient Catalyst for the Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the main reaction at the cathode of a fuel cell that utilizes Pt/C as the benchmark catalyst. Due to sluggish activity, high cost, rare abundance, and durability issues, Pt/C must be replaced by nonprecious, stable, and easily synthesizable materials. This work involves the synthesis of novel, simple, low-cost, and environmentally friendly phenolphthalein-bearing cobalt(II) phthalocyanine polymer, poly(CoIITPpPc) dyad, as an efficient catalyst for ORR. The results of analytical characterizations reveal the formation of the poly(CoIITPpPc) polymer in the pure state. To further enhance the catalytic response of poly(CoIITPpPc), a hybrid composite is prepared using poly(CoIITPpPc) and multiwalled carbon nanotubes (MWCNTs) that increase the surface area and conductivity. The poly(CoIITPpPc) and hybrid composite are separately deposited on the electrode surfaces. The electron microscopy images confirm the uniform distribution of the poly(CoIITPpPc) molecules on the electrode surface and MWCNTs. The poly(CoIITPpPc) and hybrid composite electrodes are evaluated for ORR, and the hybrid composite exhibits better onset potential at 0.803 V versus reversible hydrogen reference electrode for ORR according to linear sweep voltammograms (LSVs). The obtained data are superior compared to those of other carbon-based redox-active materials reported previously and nearer to those of the benchmark catalyst (Pt/C). The rotating disc electrode measurement of the hybrid composite electrode confirms the total number of electrons involved in ORR to be four. Furthermore, the hybrid composite electrode exhibits an excellent stability for 100 LSV scans. The synergistic effect of poly(CoIITPpPc) and MWCNTs leads to the surprisingly high ORR activity due to the improved surface area, conductivity, and interfacial confined surface.

Conductive oxide support design and synergistic engineering of bimetallic high-performance electrocatalyst for oxygen reduction reaction

The exploration of oxygen reduction reaction (ORR) catalysts with high electrochemical activity and durability is vital for many energy conversion systems. Herein, an efficient ORR electrocatalyst consisting of highly active Co/W bimetallic nanoclusters supported by conductive and robust N-doped titanium monoxide with three-dimensional ordered macroporous architecture (3DOM Co/W@N-TiO) was developed. The 3DOM N-TiO support with rich oxygen vacancies not only offers a high surface area and conductivity but also facilitates the anchoring of Co/W nanoclusters via strong metal-support interaction, endowing the catalysts with excellent catalytic activity and durability performance. Density functional theory calculations demonstrate that there exists a synthetic effect between the binary Co/W nanocluster, which was originated from electron transfer between W and Co, promoting the ORR kinetics and thermodynamics. Benefited from these features, the catalyst displays excellent ORR performance with a half-wave potential (E1/2) of 0.84 V vs. RHE, competitive with that of benchmark Pt/C. The 3DOM Co/W@N-TiO powered zinc-air batteries achieve high power density of 168 mW cm−2 and specific capacity of 792 mAh g−1 exceeding that driven by Pt/C. This work provides an effective strategy for the development of efficient and durable ORR catalysts through conductive oxide support design and the synergistic engineering of binary metals, demonstrating its promising potentials in energy conversion systems.

Metal-free catalyst for efficient pH-universal oxygen reduction electrocatalysis in microbial fuel cell

• A metal-free and efficient pH-universal ORR catalyst is prepared by simple pyrolysis. • ZIF-8#1000 exhibited ORR electrocatalytic activity, compared with that of 20% Pt/C. • ZIF-8#1000 showed high-performance in air–cathode MFCs. • Three single-chamber MFCs in series can light a light-emitting diode. Developing and utilization of clean and renewable energy is the key to alleviate energy crisis and environmental problems. As a biomass energy utilization, microbial fuel cell (MFC) suffers from low power generation performance caused by the sluggish electronic transfer kinetics of cathodic oxygen reduction reaction (ORR). It is of significance to develop efficient ORR catalysts to get a commercial-scale version in fuel cells. ZIF-8 was usually joined other metal elements (Pt, Fe, Co and etc) to improve ORR catalytic ability. Unfortunately, these catalysts are unstable under acidic conditions. Therefore, it is of great significance to develop an efficient pH-universal ORR catalyst. Herein, a kind of metal-free and efficient pH-universal ORR catalyst are fabricated via a simple method. The catalyst (ZIF-8#1000) exhibits excellent pH-universal ORR electrocatalytic activity and high-performance in single-chamber MFC (distinct output voltage 780 mV and maximum power density 600 mW m −2 ), comparable to those of 20% Pt/C. Interestingly, three single-chamber MFCs in series can light a light-emitting diode. Thus, the as-prepared ZIF-8#1000 has the potential to be alternative of Pt-based ORR catalysts.

Hierarchical flower-like FeCo-LDH/GO@montmorillonite composite for efficient catalysis of oxygen reduction

Due to the high swelling capacity and large surface area, montmorillonite (MMT) has been proven a good platform for the fabrication of efficient oxygen reduction reaction (ORR) catalysts. In this work, the composite of CoFe layered double hydroxide (CoFe-LDH), graphene oxide (GO) and MMT was synthesized via a facile co-precipitation method. The characterization with X-ray diffraction spectroscopy (XRD) and scanning electron microscopy (SEM) indicates that the prepared FeCo-LDH/GO@MMT contains no impurities and exhibits a hierarchical flower-like microstructure. Further investigation shows that FeCo-LDH/GO@MMT possesses excellent ORR activity with 4e-route selectivity, suggesting the synergistic effect between CoFe-LDH, GO and MMT.

Pd@SmMn2O5 as an Efficient Oxygen Reduction Reaction Catalyst via Triggering the Synergistic Effect between Dual Crystal Fields in Mullite

Pd@SmMn₂O₅ as an Efficient Oxygen Reduction Reaction Catalyst via Triggering the Synergistic Effect between Dual Crystal Fields in Mullite

The design of single iron atoms dispersed with nitrogen coordination environment electrocatalyst for zinc -air battery

The oxygen reduction reaction (ORR) is crucial to the development of fuel cell and metal-air battery. Metals with atomic-level dispersion has been considered as the effective nano-technologies to promote the activity and stability of catalysts for ORR. Herein, we designed Fe/N-doped porous carbon (Fe-NPC) as efficient ORR catalysts in both alkaline and acid electrolyte through a simplified one-pot method. The Fe species were atomically dispersed in the synthesized materials by FeN4C10 moieties and exhibited excellent electrocatalytic performance. Experimental and theoretical results showed that Fe–N4 sites existed in Fe-NPC endowed it with high intrinsic catalytic activity for ORR. When utilized as air electrode catalyst in Zn-air battery, Fe-NPC material achieved a maximum power density (126.0 mW cm−2) and could operate steadily for over 11 h. This work presents a simplified strategy in the design and synthesis of sing-atom catalysts electrocatalysts with high activity and stability, paving the way for the mass production and mechanistic studies of catalysts in reality.

Precise and controllable tandem strategy triggering boosted oxygen reduction activity

The development of efficient and cost-effective metal-free electrocatalysts for oxygen reduction reaction (ORR) has become crucial for electrochemical energy systems. However, reasonably validating and precisely regulating the active sites for designing optimized materials are still challenging. Herein, we report a precise and controllable tandem strategy to boost the ORR activity based on metal-free covalent organic frameworks (MFCOFs) comprising imine-N, thiophene-S, or triazine-N. Among these MFCOFs, post-tandem BTT-TAT-COF structure displayed a more positive catalytic capability and excellent electrochemical stability, indicating that the synergistic catalysis of multiple active sites induced the ORR catalytic activity through the conjugated skeleton of the structure. Density-functional theory calculations suggest that the series-connected backbone contained highly effective electrocatalytic active centers and provided synergistic catalysis. More importantly, this strategy highlights new opportunities for the advancement of efficient COF-based metal-free ORR catalysts.

Boosting ORR performance by single atomic divacancy Zn–N3C–C8 sites on ultrathin N-doped carbon nanosheets

Single-atom catalysts (SACs) show great promise to improve the performance of catalysis because of their spatially isolated single-atom sites with unique electronic properties. Herein, we construct single Zn atoms anchored on ultrathin two-dimensional (2D) N-doped carbon nanosheets (Zn–SAs/UNCNS) as an efficient electrocatalyst for oxygen reduction reaction (ORR). The microenvironment of Zn–SAs/UNCNS with super ORR intrinsic activity was identified as the divacancy Zn–N 3 C–C 8 by both experiments and theoretical simulations. Density functional theory (DFT) calculations reveal that the divacancy Zn–N 3 C–C 8 sites exhibit near-Fermi electronic states distinct from those of graphene-enclosed Zn–N 4 –C 10 and divacancy trans -Zn–N 2 C 2 –C 8 sites, which greatly facilitate the ORR process. Furthermore, compared with 3D architecture, the single atomic divacancy Zn–N 3 C–C 8 sites anchored on ultrathin 2D carbon nanosheets show more active site exposure and fast electron transport, which collectively boost the ORR performance, showing a high half-wave potential of 0.91 V versus reversible hydrogen electrode [RHE] and a super turnover frequency (4.99 e − site −1 s −1 ). • The coordination environment of the Zn single-atom catalyst is regulated • Zn–SAs/UNCNS with divacancy Zn–N 3 C–C 8 sites demonstrate high ORR performance • Zn–SAs/UNCNS delivers a maximum primary Zn–air battery power density of 282 mW cm −2 Zn–air batteries are promising next-generation energy-storage devices. A major challenge for further boosting the efficiency of Zn–air batteries is to develop highly efficient and low-cost oxygen reduction reaction (ORR) catalysts. Due to the complexity of screening catalysts, it is of great importance to discover the underlying principles to guide the rational design of cost-effective catalysts. In this work, we identify the coordination environment of the Zn single-atom catalyst with the best ORR performance. By changing the pyrolysis temperature, the relationship between the coordination environment of the Zn single-atom catalyst and ORR activity is discovered. Additionally, we demonstrate the support effect of ultrathin 2D carbon that promotes the active sites’ exposure and electron transport compared with the bulk one. The insights of the coordination environment-activity relationship obtained can guide the further development of efficient and earth-abundant single-atom catalysts for ORR. By anchoring atomically dispersed divacancy Zn–N 3 C–C 8 sites on ultrathin two-dimensional N-doped carbon nanosheets (Zn–SAs/UNCNS), the Zn–SAs/UNCNS exhibits an excellent four-electron oxygen reduction reaction performance with a high half-wave potential of 0.91 V versus RHE and a super turnover frequency (4.99 e − site −1 s −1 ) at 0.90 V (versus RHE).

Electronic Regulation of ZnCo Dual-Atomic Active Sites Entrapped in 1D@2D Hierarchical N-Doped Carbon for Efficient Synergistic Catalysis of Oxygen Reduction in Zn-Air Battery.

Transition metal-based nitrogen-doped carbon (M-Nx -C) is considered as a promising catalyst for the oxygen reduction reaction (ORR) in clean energy storage and conversion devices. Herein, ZnCo dual-atomic sites are incorporated in hierarchical N-doped carbon (HNC), with 1D nanotubes wrapped in 2D nanosheets structure (termed as 1D@2D ZnCo-HNC), via a one-step bio-inspired pyrolysis. The feeding ratio of Zn to Co precursor and pyrolytic temperature are critically modulated to achieve well-defined morphologies of the products, endowing them with the integrated merits of nanotubes and nanosheets as efficient ORR catalysts. Benefiting from the particular structure and electronic regulation of Zn on Co, the ZnCo-Nx dual-atomic system exhibits excellent ORR catalytic characteristics with an onset potential of 1.05V and a half-wave potential of 0.82V. Density functional theory calculations further explain the regulating role of Zn, such that the adjusted Co in ZnCo-Nx sites significantly reduces the energy cost to ultimately facilitate the ORR. Moreover, the Zn-air battery assembled with ZnCo-HNC is capable of delivering the maximum power density of 123.7mW cm-2 and robust stability for 110 h (330 cycles). This method provides a promising strategy for fabricating efficient transition metal-based carbon catalysts for green energy devices.

Efficient ORR catalysts for zinc-air battery: Biomass-derived ultra-stable Co nanoparticles wrapped with graphitic layers via optimizing electron transfer

The poor stability of non-noble metal catalysts in oxygen reduction reaction (ORR) is a main bottleneck that limits their big-scale application in metal-air batteries. Herein, we construct a chainmail catalyst (Co-NC-AD) with outstanding stability, via the competitive complexation and post absorption strategy, consisting of highly graphitic layers wrapped uniform-size Co nanoparticles (Co-NPs). Experiments combined with density functional theory (DFT) calculations jointly confirmed that the electron transfer occurred from the inner Co-NPs to the external graphitic layers. It facilitated the adsorption process of oxygen molecules and the hybridization of the O-2p and C-1p orbitals, which accelerated the ORR reaction kinetics. Consequently, our prepared Co-NC-AD shows excellent ORR activity, offered with a more positive initial potential (Eonset = 0.95 V) and half-wave potential (E1/2 = 0.86 V). The remarkable stability and resistance of methanol poisoning are merited from the protection effect of stable graphitic layers. In addition, the high electrochemical performance of Co-NC-AD-based zinc-air battery demonstrates their potential for practical applications. Therefore, our work provides new ideas for the design of nano-confined catalysts with high stability and activity.

Hollow structured Zn0.76Co0.24S–Co9S8 composite with two-phase synergistic effect as bifunctional catalysts

It is of great significance to develop efficient and inexpensive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts for the current energy crisis. But this is still a long-term and formidable challenge. In this work, a two-phase synergistic effect between transition metal sulfides is applied in the design of ORR/OER bifunctional catalysts. Co-based zeolite imidazolate framework (MOF) is used as a precursor to prepare the hollow Co 9 S 8 through vulcanization and heat treatment. At the same time, the phase transformation occurs to form some Zn 0.76 Co 0.24 S on surface during the heat treatment due to the Zn-polydopamine coating. The hollow structure Zn 0.76 Co 0.24 S–Co 9 S 8 composite has been verified and promotes the diffusion of reactants and products, and the interaction between two phases greatly promotes the catalytic reactions. The coating of Zn-polydopamine forms uniform carbon layer on surface, enhancing the conductivity of Zn 0.76 Co 0.24 S–Co 9 S 8 composite. The Zn 0.76 Co 0.24 S–Co 9 S 8 composite shows much better performance of ORR and OER compared to any of them. The overpotential of OER at a current density of 10 mA/cm 2 is 330 mV, and the half-wave potential of ORR is 0.83 V. Additionally, the Zn 0.76 Co 0.24 S–Co 9 S 8 composite displays better cyclic stability. The synergistic effect of Zn 0.76 Co 0.24 S and Co 9 S 8 can be considered as the foremost factor for the improvement of catalyst performance, which provides new possibilities for the development of non-precious metal bifunctional catalysts. • Hollow Zn 0.76 Co 0.24 S–Co 9 S 8 composite with carbon coating as bifunctional catalyst. • The uniform carbon coating derived from Zn-polydopamine enhances the conductivity. • The unique hollow structure provides abundant active sites and promotes the diffusion. • The two-phase synergistic effect greatly enhances the ORR and OER performance.

Innovative Fabrication of Pd/Pd4S Based Highly Active Electrocatalysts for ORR in a Primary Zn-Air Battery

On account of their high theoretical energy density and minimal cost, Zn-air batteries have gotten a lot of interest as a viable energy storage technology. However, the problem of a high overpotential at the cathode because of the slow oxygen reduction reaction (ORR) kinetics persists. Developing an efficient cathode ORR catalyst and exceeding in performance in comparison to the existing and widely utilized Pt-based catalysts is still a formidable challenge. Herein, this study focuses on the design of a Pt-free catalyst, precisely, Pd/Pd4S based electrocatalysts to enhance ORR performance of cathode. The simple encapsulated structure containing nitrogen-doped carbon (N-doped C) coated Pd/Pd4S and CeO2 nanoparticles (Pd-Pd4S/CeO2/N-C) fabricated by a practical and trouble-free approach has a powerful electrochemical ability. Pd-Pd4S/CeO2/N-C displays a virtually identical limited current density to the commercial 20% Pt/C catalysts and better durability under alkaline conditions. Moreover, this work involves the subsequent utilization of Pd-Pd4S/CeO2/N-C in a primary Zn-air battery as the air electrode, where it manifested comparable current density and power density at 0.6 V as furnished by the Pt/C catalyst. Along with this, the primary Zn-air battery system comprising Pd-Pd4S/CeO2/N-C exhibited constant discharge comprising several hours, a specific capacity of 748 mAh gZn −1, and stability at 10 mA cm−2.

Development of α‐MnO2 Nanowire with Ni‐ and (Ni, Co)‐Cation Doping as an Efficient Bifunctional Oxygen Evolution and Oxygen Reduction Reaction Catalyst

AbstractManganese oxides (MnO2) with nanowire morphology materials are promising candidates for improving oxygen evolution and oxygen reduction reaction (OER/ORR) performance. In this work, we developed transition metal cation doping strategy into the α‐MnO2 tunnel structure to tune the Mn oxidation states and control the uniform nanowire morphology, crystalline structure to investigate the effect of doping over bifunctional activity. The single Ni2+ cation doping in α‐MnO2 with various loading concentrations resulted in 8Ni−MnO2 exhibiting remarkable OER and ORR activity owing to their excessive concentration of Mn3+ and Mn4+ octahedral sites respectively. Further, Co2+ cation doping in 8Ni−MnO2 leads to an enhanced synergistic effect that significantly improves the fraction of Mn3+ quantity which is confirmed by average oxidation state. For electrochemical OER performance, 8Co−8Ni−MnO2 exhibits a potential of 1.77 V, Tafel slope value of 68 mV dec−1 and lower charge transfer resistance and it is active in ORR with more positive onset potential of 0.90 V, half‐wave potential of 0.80 V, better current density (4.7 mA cm−2) and a four‐electron pathway. Moreover, bifunctional activity (ΔE=EOER@10 mA cm−2 – ORR@E1/2) of 8Co−8Ni−MnO2 demonstrated 0.97 V, indicates an excellent activity in alkaline electrolyte solution.

Boosting Electrochemical Oxygen Reduction Performance of Iron Phthalocyanine through Axial Coordination Sphere Interaction.

Precise regulation of the electronic states of catalytic sites through molecular engineering is highly desired to boost catalytic performance. Herein, a facile strategy was developed to synthesize efficient oxygen reduction reaction (ORR) catalysts, based on mononuclear iron phthalocyanine supported on commercially available multi-walled carbon nanotubes that contain electron-donating functional groups (FePc/CNT-R, with "R" being -NH2 , -OH, or -COOH). These functional groups acted as axial ligands that coordinated to the Fe site, confirmed by X-ray photoelectron spectroscopy and synchrotron-radiation-based X-ray absorption fine structure. Experimental results showed that FePc/CNT-NH2 , with the most electron-donating -NH2 axial ligand, exhibited the highest ORR activity with a positive onset potential (Eonset =1.0 V vs. reversible hydrogen electrode) and half-wave potential (E1/2 =0.92 V). This was better than the state-of-the-art Pt/C catalyst (Eonset =1.00 V and E1/2 =0.85 V) under the same conditions. Overall, the functionalized FePc/CNT-R assemblies showed enhanced ORR performance in comparison to the non-functionalized FePc/CNT assembly. The origin of this behavior was investigated using density functional theory calculations, which demonstrated that the coordination of electron-donating groups to FePc facilitated the adsorption and activation of oxygen. This study not only demonstrates a series of advanced ORR electrocatalysts, but also introduces a feasible strategy for the rational design of highly active electrocatalysts for other proton-coupled electron transfer reactions.

Three-Dimensional Hierarchical Conductive Metal-Organic Frameworks/Nife Layered Double Hydroxide/Carbon Nanofibers: An Efficient Oxygen Reduction Reaction Catalyst for Zn-Air Batteries

Three-Dimensional Hierarchical Conductive Metal-Organic Frameworks/Nife Layered Double Hydroxide/Carbon Nanofibers: An Efficient Oxygen Reduction Reaction Catalyst for Zn-Air Batteries