Excellent ORR Research Articles

Cu-doped CaFeO3 perovskite oxide as oxygen reduction catalyst in air cathode microbial fuel cells

Cathode electrocatalyst is quite critical to realize the application of microbial fuel cells (MFCs). Perovskite oxides have been considered as potential MFCs cathode catalysts to replace Pt/C. Herein, Cu-doped perovskite oxide with a stable porous structure and excellent conductivity was successfully prepared through a sol-gel method. Due to the incorporation of Cu, CaFe0.9Cu0.1O3 has more micropores and a larger surface area, which are more conducive to contact with oxygen. Doping Cu resulted in more Fe3+ in B-site and thus enhanced its binding capability to oxygen molecules. The data from electrochemical test demonstrated that the as-prepared catalyst has good conductivity, high stability, and excellent ORR properties. Compared with Pt/C catalyst, CaFe0.9Cu0.1O3 exhibits a lower overpotential, which had an onset potential of 0.195 V and a half-wave potential of −0.224 V, respectively. CaFe0.9Cu0.1O3 displays an outstanding four-electron pathway for ORR mechanism and demonstrates superiors corrosion resistance and stability. The MFC with CaFe0.9Cu0.1O3 has a greater maximum power density (1090 mW m−3) rather than that of Pt/C cathode (970 mW m−3). This work demonstrated CaFe0.9Cu0.1O3 is an economic and efficient cathodic catalyst for MFCs.

N-doped carbon nanosheets derived from lignin as a novel bifunctional electrocatalyst for rechargeable zinc-air battery

New energy utilization devices have attracted great research interest as a sustainable route for clean energy production. However, the disadvantage of this process is the need to use high-cost precious metal catalysts. Hereby, N-doped carbon nanosheets (LNZ@GC) was prepared by ball milling-carbonization two step strategy using alkali lignin as carbon source and the gas-phase exfoliation with NH4Cl and ZnCl2 as pore-forming agents. We investigative the properties of LNZ@GC series and find that LNZ@GC exhibit the most excellent ORR performances with a half-wave potential up to 0.851 V, outstanding stability and methanol tolerance, which are all superior commercial Pt/C. Furthermore, the rechargeable zinc-air battery assembled by LNZ-800@GC shows excellent performance with a high power density of 841.8 Wh kg−1, a large specific capacity of 750.3 mA h g−1. This work not only provides a general strategy for the preparation of porous N-doped catalysts, but also provides technical support for the design and development of inexpensive catalysts using lignin as a carbon source.

Synthesis of ternary CoZnAl layered double hydroxide and Co-embedded N-doped carbon nanotube hollow polyhedron nanocomposite as a bifunctional material for ORR electrocatalyst and supercapacitor electrode

The construction of non-precious and high-performance nanomaterial is the current hotspot in oxygen reduction reaction and supercapacitor applications. Herein, a novel composite consisting of a three-metal layered double hydroxide (CoZnAl-LDH) and a ZIF-derived carbon base (Co/NCNHP) is proposed, which is fabricated by the hydrothermal synthesis of CoZnAl-LDH and the in situ loading of Co/NCNHP in different ratios of 10, 20, and 30 %. The synthesized nanomaterials were evaluated by various physical and electrochemical tests. The results manifest that the addition of Co/NCNHP with a carbon nanotube hollow polyhedron morphology to the flower-like CoZnAl-LDH had a remarkable impact on its morphology and properties, such that it elevates the surface area, enhances mass and electron transfer, and improves electrical conductivity of the final product. Based on the results, the CoZnAl-LDH@Co/NCNHP 20 % indicated better electrochemical performance than other synthesized samples. This composite offered excellent ORR catalytic activity with an onset potential of −0.043 V vs. Ag/AgCl in alkaline electrolyte, 4-electrons path selectivity (average electron transfer number = 3.69), and high durability. Furthermore, it exhibited a superior capacitance performance of 869.6 F.g−1 at a current density of 1 A.g−1 and superior cycling stability (92.7 % capacitance retention at 2 A.g−1 after 1000 cycles). Therefore, according to the test results, the final as-prepared nanocomposite possesses a desirable electrochemical performance in both ORR and supercapacitor applications.

Carboxylate-assisted ZIF-derived Co nanoclusters anchoring hierarchically porous carbon as high-efficient zinc-air batteries cathode catalysts

Metal and nitrogen-doped carbon (M-N-C) catalysts are generally considered to be ideal substitutes for platinum-based noble metal oxygen reduction catalysts. Owing to the significant Fenton effect of the Fe element and the subsequent instability, the Fenton-free Co-based N–C catalyst should perform better in ORR. Pyrolysis of metal-organic frameworks (MOFs) is commonly used to make Co-based N–C catalysts. Still, most of the MOF-derived catalysts reported so far have a microporous structure, which results in hindered mass transfer and partial Co-Nx active sites that cannot function as catalysis. Herein, Co nanoclusters (NCs) with high loading (7.96 wt%) were prepared on hierarchically porous carbon substrates via a carboxylate-assisted strategy. The mesoporous structure of Co nanoclusters/nitrogen-doped hierarchically porous carbon (Co NCs/HPNC) can facilitate mass transport. The smaller size Co nanoclusters can increase the contact area between the carbon matrix and Co-Nx active sites to effectively expose more active centers and increase the density of Co-Nx active sites. A synergistic effect of the two can greatly improve ORR results. Surprisingly, the Co NCs/HPNC catalyst shows excellent ORR activity under alkaline conditions, and Co NCs/HPNC has a better half-wave potential (0.88 V vs. 0.84 V) compared with 20 wt% Pt/C. And it only loses 5% of its current density after 36,000 s of operation, which is significantly less than Pt/C (20%). Furthermore, Co NCs/HPNC battery have a greater open-circuit potential, power density, and specific capacity than Pt/C-based zinc-air batteries (1.51 V, 109.6 mW cm−2, 818.1 mAh gZn−1 vs. 1.46 V, 92.4 mW cm−2, 716.8 mAh gZn−1). This discovery paves the way for high-efficiency electrocatalysts with hierarchically porous architectures and a large number of metal loads to be developed.

Square-Pyramidal Fe-N4 with Defect-Modulated O-Coordination: Two-Tier Electronic Structure Fine-Tuning for Enhanced Oxygen Reduction

Engineering the structure of molecularly dispersed 3d-transition metal phthalocyanines is emerging as an effective avenue for developing low-cost and efficient atomically dispersed catalysts (ADC). The strategy of using axial coordination to adjust the electronic structure of the M-N4 active site is effective for improving the performance of the catalysts, but the question to be asked is how to go beyond that. In this study, we propose and demonstrate a two-tier electronic modulation strategy, for the first time using carbon defects to regulate the tuning power of O-coordination, which in turn provides a more desirable electronic modulation on the Fe center of FePc, as compared to that of bare O-coordination. Such FePc-O-defect ADC was achieved using a one-step wet-ball-milling process with ethylene glycol as liquid media. The mechanochemically constructed active site is a square-pyramidal Fe-N4, with the Fe atom located out of the N4-plane towards an axially coordinated O that is singly bonded to graphene at vacancy defects.The resulting FePc-O-defect ADC with defect-modulated O-coordination exhibits excellent ORR activity in alkaline media, in terms of E1/2 and mass-specific activity. Compared to the baseline with bare O-coordination whose performance is already among the best reported nonprecious metal electrocatalysts, the defect-modulated O-coordination further enhanced the halfwave potential and doubled the kinetic current density. Combining with theoretical investigations, we elucidate how defect-modulated O-coordination would adjust the electronicand geometric structures of the Fe center and thus affect the electrocatalytic ORR. Also, resolving the structural configuration of bilayer catalysts with axial coordination is very challenging. The existed literature on bilayer catalyst, which either relies on 2D FT-EXAFS fitting analysis or simply assumes a bilayer configuration to work on, is in our opinion far from unambiguous structural determination. In this study, we differentiate our work from the existed literature, through a systematic structural determination process by comparing the experimentalXANES with the simulated ones, based on various structural models predicted by DFT calculations. Such analysis is especially necessary for catalysts with a 3D atomistic arrangement, but only a handful of studies have used this step of analysis (e.g., Nature Catalysis 1, 63-72(2018)). We believe that our study presents significant advances regarding the atomistic structure of bilayer catalysts with complex axial coordination.Overall, this work demonstrates a conceptually advanced two-tier electronic modulation strategy, through defect-modulated O-coordination, to further optimize the electronic structure of the Fe center in FePc toward ORR. The concept can be extended to modulate the electrocatalytic properties of molecular catalysts toward other electrochemical processes. Moreover, our catalysts were prepared at room temperature using an industrially available ball milling process. Such a facile pyrolysis-free synthetic approach is ready for scaleup with potentially 100 % usage of the FePc and graphene precursors.

Nitrogen-deficient g-C3N4 compounded with NiCo2S4 (NiCo2S4@ND-CN) as a bifunctional electrocatalyst for boosting the activity of Li-O2 batteries

The bifunctional electrocatalytic material that has a catalytic effect on oxygen reduction (ORR) and oxygen evolution reactions (OER) is effective to reduce the development bottleneck of Li-O2 batteries. Herein, g-C3N4 was denitrogenated to obtain the nitrogen-deficient graphitic carbon nitride (noted as ND-CN) to improve its intrinsic conductivity while retaining part of the nitrogen active sites, and a transition metal composite electrocatalyst NiCo2S4@ND-CN (noted as NCS@ND-CN) was synthesized using a facile hydrothermal method. The porous structure of ND-CN provides a large specific surface area, which is conducive to exposing more active sites. In addition, the synergistic effect between the double transition metal and ND-CN improves the electrocatalytic activity of the catalyst. As expected, NCS@ND-CN shows excellent OER (low overpotential of 294 mV at 10 mA cm−2 in 1.0 M KOH solution) and ORR (half-wave potential of 0.84 V) activities. Remarkably, the Li-O2 battery assembled with NCS@ND-CN exhibits an improved overpotential of 1.01 V, a high discharge capacity of 9660 mAh g−1 at 100 mA g−1 and a long-term cycle stability under a restricted capacity of 1000 mAh g−1 at 100 mA g−1.

Coupling nano-Fe3O4 with oxygen vacancies on a hypercrosslinked iron porphyrin-coated ZIF-8 as a high-efficiency oxygen reduction reaction electrocatalyst

In this study, a novel and highly efficient ORR catalyst is designed via the pyrolysis of zeolitic imidazole framework-8 (ZIF-8) under the protection of hypercrosslinked iron porphyrins. Fe3O4 nanoparticles with oxygen vacancies are formed in situ and promoting catalytic efficiency. Benefiting from the synergistic effect among the Fe3O4 and ZIF-8 skeleton, the hybrid catalyst exhibits excellent ORR activity even surpassing commercial Pt/C. The pyrolyzation temperature is studied in detail and determined to be a crucial parameter for ORR performance. Nano-Fe3O4, which has high catalytic efficiency, is formed in situ at 800 ℃. Amorphous iron is formed at 600 ℃ and 700 ℃, and zero-valent iron is formed at 900 ℃. The content of oxygen vacancies, Fe–N, and graphite–N, which are beneficial to the ORR reaction, are all reached to a maximum at 800 ℃. This study provides a new approach to design highly active Fe3O4-based electrocatalytic materials.

CoN nanoparticles anchored on ultra-thin N-doped graphene as the oxygen reduction electrocatalyst for highly stable zinc-air batteries

Transition metal nitrides anchored on carbon as oxygen reduction catalysts are widely used in zinc-air batteries. However, the size of transition metal nitrides and the thickness of carbon substrate are often difficultly controlled. Herein, the CoN nanoparticle anchored on ultra-thin nitrogen-doped graphene electrocatalyst (CoN/UNG) was synthesized by the combination strategy of the coordination of 1, 10-phenanthroline with the intercalation effect of polyethylene imine. Polyethylene imine can intercalate into layers of graphene and block the heaping of graphene to achieve ultra-thin nanosheet structures. Lone-pair electrons on nitrogen atoms of 1, 10-phenanthroline can bond to Co2+ to form the Co−N coordination, then confine the aggregation of Co atoms. Finally, small-sized CoN nanoparticles were successfully anchored on ultra-thin nitrogen-doped graphene. The CoN/UNG has a half-wave potential of 0.87 V vs. RHE with excellent electrochemical ORR performance and high stability. The power density of CoN/UNG-based zinc-air battery is 149.3 mW cm−2; the specific capacity is 917.2 mAh g−1 and the cycle stability is 350 h. The new combination strategy is conducive to the rational design of small-sized transition metal nitrides anchored ultra-thin nitrogen-doped graphene catalysts to boost the application of zinc-air batteries.

Pt/Pd Decorate MOFs Derived Co-N-C Materials as High-Performance Catalysts for Oxygen Reduction Reaction

We report here, a strategy to prepare Pt/Pd nanoparticles decorated with Co-N-C materials, where Co-N-C was obtained via pyrolysis of ZIF-67 directly. As-prepared Pt/Pd/Co-N-C catalysts showed excellent ORR performance, offered with a higher limit current density (6.6 mA cm−2) and similar half-wave potential positive (E1/2 = 0.84 V) compared with commercial Pt/C. In addition to an ORR activity, it also exhibits robust durability. The current density of Pt/Pd/Co-N-C decreased by only 9% after adding methanol, and a 10% current density loss was obtained after continuous testing at 36,000 s.

Bimetallic FeCo−N−C Catalyst for Efficient Oxygen Reduction Reaction

AbstractOxygen reduction reaction (ORR) is being deeply studied because of its significance in energy storage and conversion. It is an urgent and challenging task to explore low‐cost ORR catalysts with excellent activity and outstanding long‐term stability. Herein, we report an efficient bimetallic FeCo catalyst based on nitrogen‐doped carbon (FeCo−NC) for ORR by pyrolysis of FeCo‐1,10‐phenanthroline complexes (FeCo‐phen) supported on ZIF‐8. The as‐synthesized FeCo−NC catalyst shows excellent ORR activity, improved durability and excellent methanol cross poisoning resistance, which are ascribed to the formation of metal‐N−C active sites, the synergistic effect between Fe and Co, as well as the porous structure.

Host-guest interactions promoted formation of Fe-N4 active site toward efficient oxygen reduction reaction catalysis

FeNC is the most promising material to replace the noble metal catalyst for cathodic oxygen reduction reaction in proton exchange membrane fuel cells (PEMFCs). However, the practical performance of FeNC catalyst is significantly limited by its low active site (Fe-N4) density. Herein, we propose to promote the formation of Fe-N4 active sites in FeNC catalyst by strengthening the interaction of N precursors and Fe precursors during the carbonization synthesis. In our approach, ionic liquid (IL, [EMIM][NTf2]) with high nitrogen content and good thermal stability is caged in the pores of Fe-ZIF-8 through the host–guest interactions. These interactions are critical for the preservation of Fe and N species and formation of active sites during the synthesis. The optimal catalyst developed with this approach (Fe0.05NC/10) has a high density of accessible Fe-N4 sites (1.88*1019 sites g−1). Therefore, in both acidic and alkaline media, Fe0.05NC/10 showed excellent ORR activity comparable to commercial Pt/C catalyst. Moreover, PEMFC performance with a peak power density of 300 mW cm−2 was demonstrated with Fe0.05NC/10 under H2/O2 conditions. The synthetic approach reported herein may be used for tailoring of advanced catalyst with high intrinsic activity.

An organic-inorganic hybrid strategy to fabricate highly dispersed Fe2C in porous N-Doped carbon for oxygen reduction reaction and rechargeable zinc-air battery

Transition metal-based carbon composites have shown great potentials as electrocatalysts due to their abundance and low cost. However, the sintering from the migration and aggregation of metal species during pyrolysis would compromise the catalytic activity or even lead to the deactivation of the catalyst. Herein, taking advantage of polydopamine (PDA) and silane (3-aminopropyltriethoxysilane, APTS), one novel organic-inorganic hybrid strategy was firstly employed to synthesize highly dispersed Fe species embedded in N-doped porous carbon nanosheet (Fe,N–PCN). Thereinto, organic PDA can provide universally robust adhesion, inner porous structure with enlarged surface area can be achieved from inorganic SiO2, the mutual confinement from PDA-derived carbon and SiO2 facilitates the formation of highly dispersed, exposed active sites. Consequently, the newly-prepared Fe,N–PCN displays excellent alkaline ORR activity matching with Pt/C together with better stability and selectivity. Theoretical computations unclose the C atoms close to N (CN) on carbon as active sites with the optimized adsorption/desorption strength towards ORR intermediates, tailored by the interfacial electron transfer between Fe2C and N-doped carbon. Meanwhile, the assembled rechargeable zinc–air battery exhibits large peak power density (119.7 mW cm−2), specific capacity (775 mAh gZn−1) and robust charge-discharge durability (250 h, 1500 cycles), overmatching Pt/C and previously studied Fe-based materials.

Co-CoF2 heterojunctions encapsulated in N, F co-doped porous carbon as bifunctional oxygen electrocatalysts for Zn-air batteries

We present a rational design of hierarchical porous Co-N x framework with Co-CoF 2 heterojunctions (PCF@CCFCNT) uniformly dispersed in the holes for advanced Zn-air batteries. This multi-scale strategy from structure to active site design delivers a high power density of 184 mW cm −2 , long-term charge/discharge cycling over 1000h in an ambient environment, which demonstrates a high practical application ability. • Porous Co-N x framework with Co-CoF 2 heterojunctionswere successfully fabricated. • The porous structure leads to synergistically optimization of ion, electron, and gas transport. • Co-CoF 2 heterojunctions and Co-N x results in excellent OER and ORR performance. • PCF@CCFCNT-based Zn-air battery presents a long durability and a high peak power density. The structural design and atomic adjustment of the catalyst are the main factors that regulate the intrinsic electrocatalytic activity. Herein, we report a novel and facile strategy of synthesizing three-dimensional porous carbon network by polymer-assisted molding strategy. The porous carbon framework with Co-CoF 2 and carbon nanotubes (PCF@CCFCNT) was directly obtained by the calcination, in which Co-CoF 2 heterojunctions uniformly dispersed in the interconnected holes. Benefiting from the special hierarchical porous morphology, the dual-function catalytic activity of Co-CoF 2 heterojunctions and existence of Co-N x species, the as-obtained PCF@CCFCNT composites exhibit excellent performance in the oxygen evolution reaction (η = 300 mV@10 mA cm −2 ), as well as outstanding oxygen reduction reaction performance in alkaline medium (E 1/2 = 0.852 V, vs RHE). Moreover, as an air electrode in Zn-air batteries (ZABs), PCF@CCFCNT demonstrates a large peak power density of 184 mW cm −2 and superior long-term stability, which is much more stable than the one consisting of commercial Pt/C. This finding not only shows a simple composite design to achieve high-performance ZABs but also may stimulate the rapid development of 3D hierarchical porous electrocatalysts for advanced energy technologies.

Engineering Gd2O3-Ni heterostructure for efficient oxygen reduction electrocatalysis via the electronic reconfiguration and adsorption optimization of intermediates

• A simple yet effective sol gel strategy to form Gd 2 O 3 -Ni/CNT hybrids. • Gd 2 O 3 -Ni/CNT endows excellent ORR performance. • Superior property is resulted from the electronic reconfiguration of Gd 2 O 3 and Ni. • The as-prepared electrode exhibits high power density and capacity in ZAB. A 3D nano-aerogel electrocatalyst is produced based on metal Ni combined with Gd 2 O 3 species through a facile hydrogel route. The synthetic method hinges on the fabrication of oxidized carbon nanotubes (OCNTs) crosslinked poly (vinyl alcohol) to form hydrogel, which permits effective catch of highly active Gd 2 O 3 /Ni particles after pyrolysis. The designed Gd 2 O 3 -Ni heterostructure on carbon nanotubes (Gd 2 O 3 -Ni/CNT) is highly efficient for oxygen reduction electrocatalysis. It is found that the half-wave potential (E 1/2 ) of Gd 2 O 3 -Ni/CNT is nearly 190 mV positive than that of Ni/CNT and even surpasses the commercial Pt/C. The superior performance is resulted from the electronic reconfiguration between Gd 2 O 3 and Ni in the heterostructure, which further optimized the adsorption of intermediates to balance the binding of OOH* and OH* on the surface of Gd 2 O 3 -Ni and break the OOH*–OH* scaling relation. Finally, the assembled zinc-air battery with Gd 2 O 3 -Ni/CNT as electrocatalyst achieves high capacity.

Engineering solid–liquid-gas interfaces of single-atom cobalt catalyst for enhancing the robust stability of neutral Zn-air batteries under high current density

To simultaneously achieve high power density and robust stability under high current density for neutral Zn-air batteries (ZABs), it is significant yet still remains challenging for the rational design of advanced air–cathode electrocatalyst with fast electron transfer, rapid oxygen/electrolyte transport and timely water removal. Herein, we synthesized the single Co atoms embedded in sandwich-like multimodally porous N-doped dual-carbon architecture (denoted as the NMCS-rGO-Co) via a facile self-assembly method and subsequent pyrolysis strategy. By taking advantage of abundant Co-N4 active sites and the optimized multimodally porous structure, the obtained NMCS-rGO-Co catalyst possesses stable three-phase reaction interfaces (catalysts, electrolyte and oxygen), which could be beneficial to simultaneously achieving fast electron transfer, accelerated oxygen/electrolyte diffusion and timely water removal. In response, the NMCS-rGO-Co catalyst displays excellent ORR performance in neutral electrolyte. More importantly, the NMCS-rGO-Co-based neutral ZABs exhibit the robust stability accompanied with continuously discharging for 36 h under high current density of 50 mA cm−2. This is the first time to rationally design efficient catalysts for achieving the long-term stability of neutral ZABs at high current density from the perspective of constructing stable three-phase interfaces. This work also sheds new lights on the development of neutral ORR catalysts for the application of sustainable energy conversion technologies.

Cobalt oxyhydroxide decorating hollow carbon sphere: A high-efficiency multi-functional material for Li-S batteries and alkaline electrocatalysis

Materials with excellent electrocatalytic properties play an important role in the field of electrochemistry. In this work, a multi-function electrocatalyst of cobalt oxyhydroxide decorating homogeneous porous hollow carbon sphere (CoOOH-PHCS) was designed and fabricated. The CoOOH-PHCS can not only be used as an electrocatalyst to inhibit the shuttle effect in Li-S batteries (LSBs), but also can effectively accelerate the reaction kinetics in oxygen reduction/evolution reactions (ORR/OER). Meanwhile, density functional theory (DFT) calculations were performed to investigate the electrocatalytic activity of the CoOOH-PHCS. Benefiting from the synergy effect of CoOOH and PHCS, the CoOOH-HPC/S electrode exhibits a low capacity decay of 0.04% per cycle in 450 cycles at 1C. Meanwhile, the CoOOH-PHCS demonstrates excellent OER and ORR activity in the alkaline electrolyte. This work explores and reveals the application potential of CoOOH in electrocatalytic field.

Efficient synthesis of Pt3Co/NC alloy catalysts with enhanced durability and activity for the oxygen reduction reaction

Lack of catalytic performance, short life, and high cost are three main problems related to JM-Pt/C catalysts for proton exchange membrane fuel cells. The introduction of cheap transition metals improves catalytic performance while significantly reducing the cost of the catalysts. Here, we report the synthesis of Pt3Co/NC alloy catalysts via coating and pyrolysis treatment. The agglomeration of nanoparticles during the high-temperature alloying process is significantly inhibited by coating with PANI. Remarkably, the obtained Pt3Co/NC alloy catalysts exhibit excellent ORR catalytic performance and structural stability in 0.1 mol/L HClO4. After 30,000 potential cycles, the mass activity and area-specific activity of Pt3Co/NC alloy catalysts are 1.949 and 3.936 times higher, respectively, than that of JM-Pt/C with negligible performance loss. The strong metal-support interaction between N and Pt and the Pt-rich surface restrict the dissolution of Pt and Co, resulting in excellent stability. This synthesis approach provides an effective way to develop active and stable Pt alloy catalysts.

Controllable porous perovskite with three-dimensional ordered structure as an efficient oxygen reduction reaction electrocatalyst for flexible aluminum-air battery

Perovskite materials have recently attracted extensive attention since tailoring their chemical compositions has led to remarkable activity toward oxygen reduction reaction. However, the desired electrocatalytic activity is limited by the morphological effect, and lack of methods to achieve large surface area. Herein we report an effective strategy to synthesize three-dimensional ordered macroporous (3DOM) perovskite oxides, where La0.75Sr0.25MnO3 (3DOM LSMO) displays excellent ORR activity and durability with considerable specific surface area (43.1 m2 g-1). The electrochemical results exhibit that the electron transferred numbers (n) is close to 4 and the H2O2 yield (% H2O2) is as low as 10% for 3DOM LSMO, which mainly attributes to comprehensive effect of the reduced Mn valence state, the increased specific surface, and the exposed high activity crystal planes. First-principles study confirms that the lowest overpotential obtained by LSMO is in good agreement with the experimental results. Our work demonstrates perovskite oxides with larger surface area could be advanced oxygen catalysts with wide applications.

Self‑nitrogen-doped carbon materials derived from microalgae by lipid extraction pretreatment: Highly efficient catalyst for the oxygen reduction reaction

Biomass-based nitrogen-doped carbon-based material has gradually become a premising metal alternative catalyst for oxygen reduction reaction due to their broad resources, renewable property, and low cost. However, the efficient nitrogen doping is still restricted by their low content and poor conversion efficiency. In this study, self- nitrogen -doped biomass-based carbon materials with high content of nitrogen (27.8% pyridinic-N and 40.3% graphitic-N) and hierarchical pore structure were prepared via lipid extraction pretreatment. The obtained microalgae residue carbon (MRC) catalyst exhibits superior oxygen reduction reaction performance, in terms of more preferable electrode performance and better stability, higher power density in the microbial fuel cells system compared to that of microalgae carbon (MAC). The onset potential of the MRC is 60 mV higher than that of MAC, and the maximum power density of microbial fuel cells (MFCs) with MRC as cathode catalyst reache 412.85 mW m−2. This can be attributed to the fact of that the lipid extraction was not only beneficial to the nitrogen enhancement and oriented conversion but also be conductive to the structure construction. The synergistic effect between active sites and hierarchical structure endows the catalyst excellent ORR performance and good stability in the MFCs system.

Highly efficient rechargeable Zn-air batteries based on hybrid CNT-grafted, Co/CoS2-Fe embedded, Nitrogen-doped porous carbon Nano-frameworks

Catalysts with embedded and functionalized elements used for the effective control of oxygen-reduction (ORRs) and oxygen-evolution reactions (OERs) are the key to developing high-performance rechargeable Zn–air batteries (ZABs). Here, carbon nanotube-grafted, Co–Fe embedded, nitrogen-doped porous carbon nano-frameworks (CNT–Co–Fe/NC) were synthesized through the carbonization of Fe-doped zeolitic imidazolate frameworks and vulcanization of the CNT–Co–Fe/NC to form CNT–CoS2–Fe/NC. The CNT–CoS2–Fe/NC exhibited a superior OER performance with an overpotential of only 1.637 mV at a current density of 10 mA/cm2 and a Tafel slope of 197 mV/dec (which, for RuO2, is 112 mV/dec), whereas the CNT–Co–Fe/NC showed an excellent ORR performance with a Tafel slope of 71 mV/dec (which, for 20 wt% Pt/C, is 91 mV/dec). A ZAB was developed with a hybrid catalyst of 50 wt% CNT–Co–Fe/NC and 50 wt% CNT–CoS2–Fe/NC in the cathode, and it achieved an excellent specific discharge capacity of 814 mAh/g at 50 mA/cm2, high power density of 245 mW/cm2, and outstanding cycle stability of over 1800 cycles (300 h) at 10 mA/cm2 with a very high retention of 95% and small potential gap of 0.68 V, compared to the corresponding values of 803.7 mAh/g, 215.3 mW/cm2, 900 cycles: retention 92%, and potential gap 0.837 V for 150 h for the ZAB with a hybrid catalyst of Pt/C + RuO2. It is hypothesized that the ZAB with the novel hybrid catalyst exhibits its excellent catalytic activity and durability as a result of the synergistic effect of the catalyst’s embedded heteroatoms and nitrogen–metal/carbon framework that enhances the ORR/OER performance, porous carbon nano-framework that enables rapid diffusion and electrical conduction, and carbon nanotubes that complete the external electrical connection between the catalysts.