Efficient Oxygen Reduction Reaction Catalysts Research Articles

Asymmetric cobalt porphyrins for oxygen reduction reactions: Boosted catalytic activity by the use of triphenylamine

Asymmetric metalloporphyrins have been rarely investigated in oxygen reduction reaction (ORR), which is probably due to the remaining unclear structural effects on electrocatalytic performance and the low synthetic yields. A remarkable feature of these molecules is their inherent large dipole moments, which can benefit the charge separation and electron density modification. Here we synthesize two asymmetric molecules A-Cb-CoPor and A-TPA-CoPor by substituting one of the meso-positions with carbazole and triphenylamine (TPA) derivatives, respectively, to coat on carbon black as ORR electrocatalysts. Density functional theory calculations suggest the well separation of electron density on the cobalt porphyrins. The electrochemical performances of the composites are performed in acid with comparing to a symmetric Co porphyrin-coated catalyst CoPor1/C. A-TPA-CoPor/C attains better ORR activity and selectivity than A-Cb-CoPor/C due to the structural merits of TPA unit. However, an identical electron transfer number of 3.6 is obtained by A-TPA-CoPor/C and CoPor1/C, which is possibly a trade-off result of the use of TPA from its structural advantage and deleterious electron-donating ability. Impressively, both asymmetric porphyrin-based composites exhibit greater limiting current densities than CoPor1/C, which mainly originates from the reduced charge transfer resistance as suggested by the impedance measurements. Our work demonstrates the promise of the asymmetric molecular approach as a viable strategy for efficient ORR catalysts.

Versatile hyper-cross-linked polymer derived porous carbon nanotubes with tailored selectivity for oxygen reduction reaction

Exploring metal-free, highly active and durable electrocatalysts with tunable selectivity toward oxygen reduction reaction (ORR) still remains a standing challenge. Herein, porous carbon nanotubes derived from a self-supporting hyper-cross-linked polymer with tailored selectivity for efficient ORR are reported. The sulfur-containing tubular polymer provides a versatile platform to fabricate diverse heteroatom doped porous carbon nanotubes. Attributed to the porous tubular morphology, abundant dopants and defects, the N-doped porous carbon nanotubes through pyrolysis under Ar-NH3 show excellent 4e− ORR performance with a half-wave potential (E1/2) of 0.85 V. It also has superior stability and methanol tolerance. Meanwhile, the O, S co-doped porous carbon nanotubes through oxygen plasma treatment show enhanced 2e− ORR performance with a selectivity up to 85.4%, which is probably ascribed to the more C=O and COOH species introduced in the carbon matrix. This work not only provides a useful strategy to design and prepare efficient ORR catalysts, but also paves the avenue for the facile tailoring of selectivity in ORR process.

Novel highly active and selective Co[sbnd]N[sbnd]S[sbnd]C efficient ORR catalyst derived from in-situ egg gel pyrolysis

Exploring the influence of various heteroatoms on MNxC and developing novel synthetic MNC of strategies are great significance to improve the efficiency of continuable energy transformation and storage technologies. In this work, an economic and environmental in-situ doping synthesis scheme for extensible synthesis Co, N and S doped multiple porous-structure carbon (Co-NSEC) using egg gel as carbon precursor was reported. The Co-NSEC were certified to possess multiple porous structure, large surface area and uniform Co distribution. Moreover, systematic characterization results and electrochemical study revealed that thiophene sulfur could enhance Co-Nx oxygen reduction reaction (ORR) catalytic ability. The Co-NSEC catalysts exhibit excellent ORR performance akin to Pt/C (onset potential 0.947 V vs RHE, half-wave potential 0.842 V vs RHE, limiting current density 5.70 mA cm−2) and better alcohol resistance and durability in alkaline solutions. The Co-NSEC electrocatalysts are promising as Pt replacement and are desired to be applied in the aspect of fuel cells.

Defective nanomaterials for electrocatalysis oxygen reduction reaction.

The difficulties in O2 molecule adsorption/activation, the cleavage of the O-O bond, and the desorption of the reaction intermediates at the surface of the electrodes make the cathodic oxygen reduction reaction (ORR) for fuel cells show extremely sluggish kinetics. Thus, it is important to the exploitation of highly active and stable electrocatalysts for the ORR to promote the performance and commercialization of fuel cells. Many studies have found that the defects affect the electron and the geometrical structure of the catalyst. The catalytic performance is enhanced by constructing defects to optimize the adsorption energy of substrates or intermediates. Unfortunately, still many issues are poorly recognized, such as the effect of defects (types, contents, and locations) in catalytic performance is unclear, and the catalytic mechanism of defective nanomaterials is lacking. In this review, the defective electrocatalysts divided into noble and non-noble metals for the ORR are highlighted and summarized. With the assistance of experimental results and theoretical calculations, the structure-activity relationships between defect engineering and catalytic performance have been clarified. Finally, after a deeper understanding of defect engineering, a rational design for efficient and robust ORR catalysts for PEMFCs is further guided.

Using 2D-Phthalocyanine Metal Organic Framework-Based Catalysts for Oxygen Reduction Reaction in Alkaline Media

Developing high performance electrocatalysts to improve the sluggish kinetics of oxygen reduction reaction (ORR) at the cathode is essential in expanding fuel cell applications. Metal organic frameworks (MOFs), given their high surface area, tunable pore size, and diverse metal choices, are promising candidates to catalyze such a reaction. Herein, we report a family of nine 2D-phthalocyanine MOF-based catalysts for alkaline ORR, where M = Co, Ni, Cu. Structurally, these bimetallic materials have two distinct metal sites, where M1 is a phthalocyanine moiety and M2 is a node, existing as M-N4 moiety. X-ray Diffraction (XRD) shows that all as-prepared MOFs have similar structures and inter-layer spacing. X-ray Photoelectron Spectroscopy (XPS) shows slight shifts in binding energy when the same element is placed in a M1 or M2 site, which indicates that the M1 and M2 sites are chemically distinct.Through cyclic voltammetry we evaluate the role of the metal sites for ORR activity and selectivity in 0.1 M KOH. All materials are active for alkaline ORR, while Ni (M1) – Co (M2) has the best overall kinetic activity performance of - 5 mA cm-2 at 0.7 V vs. RHE. Cu – Cu, on the other hand, is the least active combination under the same testing conditions. Within composition series where M2 = Co, the activity trend for M1 is Ni > Cu ~ Co. From a 2-electron selectivity perspective, M1 = Ni > Cu > Co. From these general trends we hypothesize that Co M2 and Ni M1 sites are essential in promoting 4- and 2-electron selectively, respectively. On average we find a nominal ORR performance trend where M2 = Co > Cu > Ni. Interestingly, we note that the M1 identity also plays a non-linear role in activity and selectivity modulation. Though we identify one of the metal sites (M1 or M2) as the dominating site for activity and/or selectivity, the other site also contributes to the total performance. The density functional theory (DFT) calculation supports our experimental results and finds out that Ni as M1 is highly selective for H2O2 formation whereas Co as M2 shows excellent activity for ORR. Our predicted volcano plot shows that MOF with Ni – Co and Cu – Co combinations at Co active site offering lowest ORR overpotential among all other combinations, which is also in good agreement with experimental findings.By evaluating different metal sites performance through electrochemical testing, we can better understand the active species in the MOF catalytic system. By pairing theory with experiment, we gain active site insight to design new specific enhanced active motifs. We believe that these performance trends can assist in better designing efficient MOF-based ORR catalysts that can lead to advances in clean energy technology for sustainable development.

Atomically Dispersed Co-Anchored N Rich Graphitic Carbon Network: A Highly Efficient Oxygen Reduction Electro Catalyst

Rational design of non-precious and highly efficient electrocatalyst for oxygen reduction reaction (ORR) is of great importance for sustainable energy exploitation to solve the energy crisis and environmental jeopardy. In this regard herein, we report work function tailored zeolite derived hierarchically porous and active site enrich electrocatalyst for ORR in acidic and alkaline medium. The electrochemical analysis proposes that the optimized electrocatalyst for surface area, porosity and active center density facilitate the electronic transfer from atomic Co to Nitrogen doped carbon framework and, further to antibonding oxygen state. The optimized catalyst shows the high ORR activity, remarkable onset potential (E onset acid- 0.89 V, E onset alkaline – 0.951 V) and large number of active site density (ASD acid -7.84×1023 /g, ASD acid - 1.51×1024 /g) with excellent stability and durability. It is proposed that the high performance of the catalyst is attributed to the reduction in work function (ф ZIF 67- 5.2 to ф optimized- 4.6) as an effect of temperature followed by post ‘acid leaching’ (AL) treatment to alter the surface area of the catalyst. Here, we represent a favorable strategy for highly efficient and durable ORR catalyst. This hybrid structure provides a new perspective to catalyst architectures.

Robust bimetallic metal-organic framework cathode catalyst to boost oxygen reduction reaction in microbial fuel cell

Metal-organic frameworks (MOFs) have emerged as versatile materials for widespread energy and environmental applications due to their intrinsic physical and chemical properties. To this extent, this research is focused on the synthesis of novel amine-functionalized single (Zr) and bimetallic (Zr, Ni) MOF viz. NH2-UiO-66(Zr) and NH2-UiO-66(Zr/Ni), followed by their testing as cathode catalysts to improve oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) for bioenergy recovery from organic wastes. The physical and chemical characterization techniques depicted the successful synthesis of octahedral-shaped MOF nanoparticles with similar structural integrity despite the incorporation of the secondary metal ion. However, electrochemical analyses demonstrated NH2-UiO-66(Zr/Ni) as a better catalyst, achieving a high ORR peak current, low charge transfer resistance, and high diffusion coefficient as compared to both NH2-UiO-66(Zr) and 10% Pt-C catalyzed cathodes. MFC performance evaluation further confirmed the high catalytic activity of NH2-UiO-66(Zr/Ni), allowing to recover a power density (PD) of 0.8 W/m2 at a coulombic efficiency (CE) of 75.4%, outperforming the MFC using 10 % Pt-C catalysed cathode. This study suggests that the NH2-UiO-66(Zr/Ni) can be used as an efficient ORR catalyst for application in large-scale MFCs.

Unravelling the role of interface of CuOx-TiO2 hybrid metal oxide in enhancement of oxygen reduction reaction performance

Energy security and clean energy are of increasing importance given the current scenario. Hence fuel cells and metal-air batteries are gaining significant attention in recent times. However, the major problem associated with these technologies is the sluggish nature of oxygen reduction reaction (ORR) and the expense associated with the catalyst. This study reports nitrogen-doped carbon-supported CuOx/TiO2-based heterostructure (CuOx/TiO2-10 wt%/NC-800) as an efficient, durable, and low-cost ORR catalyst. CuOx/TiO2-10 wt%/NC-800 catalyst is synthesized using a simple hydrothermal method. The ORR experiments are performed in an alkaline medium (0.1 M KOH). The catalyst has excellent ORR activity with onset potential and half-wave potential of 0.90 V and 0.80 V vs. RHE, respectively. It also shows outstanding limiting current density of 5.80 mA cm−2. The catalyst offers excellent stability (with 92% current retention after 24 h) and durability (only 25 mV half-wave potential shift after 2000 CV cycles). The catalyst follows the 4e− transfer process (n = 3.94) with rather nominal amount of hydrogen peroxide formation (3.5%). The enhanced ORR activity is attributed to the strong synergistic effect between CuOx/TiO2 and NC. The unique structure formation also helps to get excellent electronic conductivity, large surface area, appropriate porosity, and desirable interface charge transfer between CuOx and TiO2.

A novel chemical approach for synthesizing highly porous graphene analogue and its composite with Ag nanoparticles for efficient electrochemical oxygen reduction

Single-step phase transformation from amorphous to crystalline material avoiding drastic reaction condition is a novel approach in the synthetic and applied materials chemistry research. Both conjugated microporous polymers (CMPs) and graphene/graphene analogues are very demanding materials in the energy research. Depending upon the nature of the graphene material like amorphous, crystalline, functionalized, single-layered and multi-layered, its property and potential application can be largely tuned. In this perspective, 2D carbon allotropes like graphene and its analogues have attracted a huge attention due to their unique electrical, thermal, mechanical, and physico-chemical properties. On the other hand, CMPs are another class of porous nanomaterial synthesized through the polycondensation/coupling of reactive monomeric building units via bottom-up chemistry approach, where extended π-conjugation prevails in the entire organic framework. To the best of our knowledge, herein we first demonstrated a novel methodology for amorphous CMP to crystalline graphene analogue through single step chemical transformation avoiding drastic reaction conditions. For this purpose, we have synthesized a new pyrene-naphthalene based spherical amorphous conjugated microporous polymer, designated as pyrene-naphthalene CMP (PNC), which upon chemical treatment (oxidative C-C coupling reaction) transforms into a highly porous crystalline multilayer porous nanographene sheet-like material pyrene-naphthalene-graphene (PNG). The BET surface area has been drastically enhanced from 600 m2/g for the CMP to 1414 m2/g for this graphene analogue PNG. As analysed by scanning tunnelling spectroscopy (STS), the PNG material has showed atomic level graphitic images with almost zero bandgap, which suggested highly conductive nature for this crystalline graphene analogue. This material has been further explored in the electrochemical oxygen reduction reaction (ORR) by grafting silver nanoparticles (AgNPs) onto the interlayer nanosheets of PNG. The ORR results displayed an admirable half-wave potential (E1/2) and onset potential of 0.78 V and 0.984 V, respectively. The electrocatalyst achieved a very high current density of −0.53 mA cm−2 under the basic electrolyte medium (0.1 M KOH). An efficient ORR catalyst is very demanding towards the fabrication of metal-air batteries as well as fuel cells, which are promising for clean and green energy production.

Cobalt (iron), nitrogen and carbon doped mushroom biochar for high-efficiency oxygen reduction in microbial fuel cell and Zn-air battery

To improve the oxygen reduction reaction (ORR) kinetics in microbial fuel cell (MFC) and Zn-air battery, cobalt (iron), nitrogen and carbon doped mushroom biochar, i.e. CoNC@MC, FeNC@MC and CoFeNC@MC were prepared using metal-organic frameworks and mushroom as the precursors. The catalysts showed a mesopore-dominant structure with abundant Metal-N, Pyridinic-N and Graphitic-N catalytic active sites. Rotating disk electrode tests revealed that FeNC@MC performed the best ORR activity in neutral and alkaline solutions, which followed the four-electron transfer ORR pathway. Acid leaching could further improve the ORR activity of FeNC@MC in neutral conditions. In MFCs, the FeNC@MC and acid-leached FeNC@MC yielded maximum power densities of 1052.5 mW m−2 and 1126.3 mW m−2 respectively. The above catalysts also produced high power densities of 94.0 mW cm−2 and 93.7 mW cm−2 in the Zn-air battery, with high stability and good methanol tolerance. This article provides a new strategy to prepare low-cost and efficient non-noble ORR catalysts for microbial fuel cell and Zn-air battery.

Enhanced electrocatalytic activities of MoO3/rGO nanocomposites for oxygen reduction reaction

AbstractBACKGROUNDThe availability of highly active, low‐cost and stable oxygen reduction reaction (ORR) electrocatalysts remains a barrier to the development of energy techniques. This study presents molybdenum trioxide/reduced graphene oxide (MoO3/rGO) composite as an effective electrocatalytic material for ORR.RESULTSThe nanosized MoO3 particles loaded on rGO as an efficient ORR catalyst was prepared via a two‐step method. The MoO3(0.1)/rGO nanocomposite showed the highest content of Mo6+ and rGO carbon among rGO and MoO3/rGO. The MoO3(0.1)/rGO showed the highest limiting current density of −3.04 mA cm−2 at 0.2 V versus reversible hydrogen electrode, which was comparable to the commercial 10% Pt/C in the present work. The electron transfer number of 2.74 on MoO3(0.1)/rGO indicated ORR selectivity towards the four‐electron pathway was not very high. The electrochemical active surface area of the MoO3(0.1)/rGO nanocomposite was 9.94 cm2, which was about twice the commercial 10% Pt/C. The small Tafel slope of 57.56 mV dec−1 confirms the high ORR activity of the MoO3(0.1)/rGO catalyst. The MoO3(0.1)/rGO also showed good stability under alkaline conditions and better methanol tolerance compared to the commercial 10% Pt/C.CONCLUSIONThe increased activity of the MoO3(0.1)/rGO composite may be attributed to the higher content of Mo6+ and rGO carbon in the catalyst. Performance of the catalysts may be further improved by optimizing the experimental conditions. The synthesized MoO3/rGO composite is a potential alternative electrocatalyst for ORR. © 2022 Society of Chemical Industry (SCI).

A self-assembled nanoflower-like Ni5P4@NiSe2 heterostructure with hierarchical pores triggering high-efficiency electrocatalysis for Li–O2 batteries

The remarkably high theoretical energy densities of Li–O2 batteries have triggered tremendous efforts for next-generation conversion devices. Discovering efficient oxygen reduction reaction and oxygen evolution reaction (ORR/OER) bifunctional catalysts and revealing their internal structure-property relationships are crucial in developing high-performance Li–O2 batteries. Herein, we have prepared a nanoflower-like Ni5P4@NiSe2 heterostructure and employed it as a cathode catalyst for Li–O2 batteries. As expected, the three-dimensional biphasic Ni5P4@NiSe2 nanoflowers facilitated the exposure of adequate active moieties and provide sufficient space to store more discharge products. Moreover, the strong electron redistribution between Ni5P4 and NiSe2 heterojunctions could result in the built-in electric fields, thus greatly facilitating the ORR/OER kinetics. Based on the above merits, the Ni5P4@NiSe2 heterostructure catalyst improved the catalytic performance of Li–O2 batteries and holds great promise in realizing their practical applications as well as inspiration for the design of other catalytic materials.

Facile synthesis of NS@UiO-66 porous carbon for efficient oxygen reduction reaction in microbial fuel cells

Exploiting a facile way to synthesize low-cost and high-performance oxygen reduction reaction (ORR) catalysts is a core issue in microbial fuel cells (MFCs). Hence, a facile and extensible method has been developed to prepare efficient ORR catalysts by using robust UiO-66 as a precursor, modified with melamine and trithiocyanuric via the impregnation method. Benefiting from the hierarchical structure of UiO-66, the NS@UiO-66 has excellent stability, more active sites and improved mass transfer. Significantly, the half-wave potential and the current density of the NS@UiO-66 are 0.546 V vs. RHE and 6.19 mA cm−2 respectively, which is better than that of benchmark Pt/C in neutral conditions. Furthermore, the power density of MFCs assembled with the NS@UiO-66 catalyst is 318.6 ± 2.15 mW m−2. The density functional theory calculation demonstrates that the reaction barrier can be reduced effectively for accelerating the ORR process through the synergistic effect of N and S. The NS@UiO-66, as an ideal candidate to substitute for the commercial Pt/C counterpart, is expected to promote the scaling-up production and application of MFCs due to low-cost elements doping and facilely synthetic method.

A strain-engineered self-intercalation Ta9Se12 based bifunctional single atom catalyst for oxygen evolution and reduction reactions

Seeking and designing stable, high-efficiency, and economical bifunctional catalysts for the metal-air battery is challenging but of great significance towards the conversion and storage of renewable energy. In this study, based on first principles calculations, the oxygen evolution (OER) and oxygen reduction reaction (ORR) catalytic performance of different transition-metal (TM) atoms embedded into the surface of the self-intercalation structure Ta9Se12 (TM-Ta9Se12) were evaluated. The results demonstrate that the self-intercalated Ta-layer obviously improves the stability and catalytic activity of the system. Remarkably, Pd-Ta9Se12 under a tensile strain of 3 % was identified as an efficient bifunctional catalyst for OER and ORR with overpotentials of 0.65 and 0.42 V, respectively. Mechanistically, the intercalation structure of Ta9Se12 leads to a charge accumulation in the inner layer. But divertingly, under an external force, the charge in the inner layer will diffuse to the surface. This curious phenomenon can provide the possibility for directional and continuous regulation of the catalytic performance of the catalysts. This work elucidates a new approach for designing high-efficient and stable bifunctional SACs for OER and ORR.

ZIF‐Mediated Anchoring of Co species on N‐doped Carbon Nanorods as an Efficient Cathode Catalyst for Zn‐Air Batteries

Developing efficient oxygen reduction reaction (ORR) catalyst is essential for the practical application of Zn‐air batteries (ZABs). In this contribution, we develop a novel zeolitic imidazolate framework (ZIF)‐mediated strategy to anchor Co species on N‐doped carbon nanorods for efficient ORR. Featuring ultrahigh N‐doping (10.29 at.%), monodisperse Co nanocrystal decoration, and well‐dispersed Co‐Nx functionalization, the obtained Co‐decorated N‐doped carbon nanorods (Co@NCNR) exhibit a decent ORR performance comparable to commercial Pt/C in alkaline media. Aqueous ZABs have been assembled using Co@NCNR as the cathode catalyst. The assembled ZABs manifest high initial open‐circuit voltage as well as high energy density. In addition, the Co@NCNR also demonstrates ideal ORR performance in quasi‐solid‐state ZABs.

One-step complexation and self-template strategy to synthesis bimetal Fe/Mn–N doped interconnected hierarchical porous carbon for enhancing catalytic oxygen reduction reaction

Currently, it is still a challenge in the research of fuel cells and zinc-air battery to use a facile method to prepare efficient and low-cost cathode oxygen reduction reaction (ORR) catalysts to replace the precious metal Pt-based catalyst. Herein, we reported a one-step complexation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) with transition metals (M) and self-template strategy to synthesis an bimetal Fe/Mn–N doped interconnected hierarchical porous carbon material for efficient catalytic ORR. In addition to being a carbon source, EDTA-2Na can very well fix M atoms in the carbon precursory by complexation, which is beneficial for M atoms to be anchored in the carbon structure by N atoms, thus forming the M-Nx catalytic active site. During pyrolysis, meanwhile, Na ions in EDTA-2Na not only acted as self-template to form the interconnected porous structure but also separated M atoms from each other, which also suppressed the aggregation and growth of the M atoms. More importantly, the prepared bimetal Fe/Mn–N doped interconnected hierarchical porous carbon (Fe/Mn–NIHPC) showed better catalytic ORR performance (half-wave potentials of 0.86 V vs. RHE) than those prepared by single metal elements (Fe or Mn). And Fe/Mn–NIHPC also exhibited better catalytic ORR activity and durability, compared with the Pt/C (20 wt%) catalyst.

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.