Electrocatalytic Performance For Oxygen Reduction Reaction Research Articles

Enhancing Oxygen Reduction Reaction Electrocatalytic Performance of Nickel‐Nitrogen‐Carbon Catalysts through Coordination Environment Engineering†

Comprehensive SummarySingle‐atom catalysts (SACs) have attracted significant attention due to their high atomic utilization and tunable coordination environment. However, the catalytic mechanisms related to the active center and coordination environment remain unclear. In this study, we systematically investigated the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalytic activities of NiN4, NiN3, NiN3H2, NiN4X, NiN3X, and NiN3H2X (X denotes axial ligand) through density functional theory (DFT) calculations. This study unveils two distinct reaction pathways for ORR and OER, involving proton‐electron pairs adsorbed from both the solution and the catalyst surface. The overpotential is the key parameter to evaluate the catalytic performance when proton‐electron pairs are adsorbed from the solution. NiN3 and NiN3H2 show promise as pH‐universal bifunctional electrocatalysts for both ORR and OER. On the other hand, when proton‐electron pairs are adsorbed from the catalyst surface, the reaction energy barrier becomes the crucial metric for assessing catalytic activity. Our investigation reveals that NiN3H2 consistently exhibits optimal ORR activity across a wide pH range, regardless of the source of proton‐electron pair (solvent or catalyst surface).

FeCo Bimetallic ZIF Derivatives decorated with CoFe-LDH to Promote Bifunctional Oxygen Electrocatalysis Activation.

Reasonably screening the targeted oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) constituents and constructing high-efficiency and stabilized ORR/OER bifunctional electrocatalysts are pivotal for the advancement of rechargeable zinc-air batteries (ZABs). Here, CoFe layered double hydroxide (CoFe-LDH) nanosheets are deposited on nitrogen-doped graphite-carbon polyhedra with FeCo alloy nanoparticles (FeCo/LDH-NGCP). Due to the synergic effect between FeCo-NGCP, CoFe-LDH and FeCo/LDH-NGCP, the electrocatalyst with the abundant and accessible active sites can provide good charge/mass transfer, and thus shows wonderful ORR and OER bifunctional electrocatalytic performance. In ORR tests, FeCo/LDH-NGCP catalyst displays larger half-wave potential (E1/2, 0.89 V vs. 0.85 V), higher limiting current density (JL, 5.91 mA/cm2 vs. 5.14 mA/cm2) and better stability than commercial Pt/C. As for OER, FeCo/LDH-NGCP possesses a smaller overpotential (η) of 299.6 mV at a current density of 10 mA/cm2 and more durable stability than commercial RuO2 (330.6 mV). Furthermore, in ZAB tests, the cycling stability of ZAB-FeCo/LDH-NGCP (over 470 h) outperforms the ZAB-Pt/C+RuO2 (92 h) with commercial electrocatalyst (Pt/C+RuO2). Therefore, the FeCo/LDH-NGCP catalyst offers a new perspective to construct ZABs bifunctional catalysts and their commercial application in ZABs.

Weakening O-Intermediates Adsorption Strength Over the Pd Metallene via Lewis-Acidic Site Modulation for Enhanced Oxygen Reduction.

The reasonable design and modulation of the electronic properties of Pd metallene are acknowledged as a promising avenue for enhancing the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs), yet they remain a formidable challenge. Herein, a thin-sheet structure of Zr-doped Pd metallene (PdZr metallene) with abundant defects is proposed using a facile wet-chemical approach for efficient and highly durable ORR electrocatalysis. Multiple microstructural analyses uncover that orchestrated electronic and oxophilic regulation of PdZr metallene via Lewis-acidic Zr site modulation could concurrently optimize the electronic configuration of Pd, downshift the d-band center of Pd, and, thus, promote the intrinsic activity. Benefiting from the unique two-dimensional morphology and electronic structure optimization facilitated by the Zr coupling effect, the resultant PdZr metallene demonstrates significantly enhanced ORR electrocatalytic performance in basic solutions, with a high half-wave potential (E1/2) of 0.87 V and commendable stability for 30 000 s, surpassing those of Pd metallene and various advanced Pd-based catalysts reported in the literature. Encouragingly, the PdZr metallene-based AEMFC achieves an increased maximum power density (90.4 mW cm-2) and impressive robustness over 12 h in an alkaline environment, manifesting the practical application of PdZr metallene in AEMFCs. This study showcases the applicability of PdZr metallene via Lewis acid site regulation for fabricating highly active electrocatalysts for high-performance AEMFCs.

Enhanced durability of Pd/CeO2-C via metal-support interaction for oxygen reduction reaction.

It is a challenge to improve the long-term durability of Pd-based electrocatalysts for oxygen reduction reaction (ORR) in fuel cells. Herein, Pd/CeO2-C-T (T= 800 °C, 900 °C and 1000 °C) hybrid catalysts with metal-support interaction are prepared from Ce-based metal organic framework precursor. Abundant tiny CeO2nanoclusters are produced to form nanorod structures with uniformly distributed carbon through a calcination process. Meanwhile, both carbon and CeO2nanoclusters have good contact with the following deposited surfactant-free Pd nanoclusters. Benefited from the large specific surface area, good conductivity and structure integrity, Pd/CeO2-C-900 exhibits the best electrocatalytic ORR performance: onset potential of 0.968 V and half-wave potential of 0.857 V, outperforming those obtained on Pd/C counterpart. In addition, the half-wave potential only shifts 7 mV after 6000 cycles of accelerated durability testing, demonstrating robust durability.

Carbon dot intercalated MXene with an excellent oxygen reduction reaction electrocatalytic performance

Carbon dot intercalated MXene with an excellent oxygen reduction reaction electrocatalytic performance

Investigation of the Chemical Changes from N-Doped Graphene and MOF to N-G/MOF Composites for the Enhancement of Electrocatalytic Properties

N-doped graphene (N-G) materials showed high potential as electrocatalysts for oxygen reduction reaction (ORR) in electrochemical energy systems and increasingly gaining ground as alternatives to the expensive and degradation-prone Platinum Group Metal (PGM)-based electrocatalysts. Numerous studies demonstrated that as N-G materials are integrated with Metal-Organic Frameworks (MOFs), the N-G/MOF composites exhibited higher electrocatalytic activities than the individual precursors; on several occasions, even higher than the PGM-based ones. In this essence, it is crucial to analyze and understand the chemical changes that occur through the integration of N-G and MOF, as these changes play key roles in enhancing electrocatalytic properties of the materials by introducing different electrochemically active sites. To investigate such chemical changes, we have synthesized an N-G/MOF composite by integrating an N-G with ZIF-8 (which is the most studied member of the MOF family) following a facile mechanochemical wet ball milling process. In the electrochemical characterization, the N-G/MOF composite performed better than N-G and ZIF-8 for ORR catalysis by generating a higher cathodic current density.Multiple samples of N-G, ZIF-8, and N-G/MOF composite were analyzed by X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy to detect the changes in elemental ratios, chemical bonds, and chemical functional groups from the precursors (N-G and ZIF-8) to the N-G/MOF composite. An increase in the elemental Nitrogen (N) ratio was observed in N-G/MOF compared to its precursors; which signifies an increased N-doping ratio in the material which is advantageous for ORR catalysis. The XPS C 1s spectra of N-G/MOF shifted to a higher binding energy (~1eV) compared to the precursors indicating an overall increase in the oxidation states of Carbon (C) atoms in the material which could facilitate oxygen molecules’ adsorption better on these sites at the beginning of ORR process. Comparing the analyzed XPS N 1s spectra revealed an increased relative ratio of the Pyridinic-N functional group in N-G/MOF, which also partly justifies the composite’s enhanced ORR electrocatalytic performance. FTIR analysis revealed interactions between methyl groups (-CH3) of ZIF-8 with oxygen functional groups (i.e. -OH) of N-G while forming the N-G/MOF composite. Besides, a transition from methyl groups (-CH3) to methylene group ( >CH2) was evident during the synthesis, increasing charge density near those C atoms of the N-G/MOF which can as well be advantageous for ORR electrocatalysis. The combined impact of these chemical alterations from N-G and ZIF-8 to N-G/MOF yielded a synergistic effect, elucidating its superior electrocatalytic properties. The findings of this experimental investigation provide insights into the chemical reasons for the enhancement of electrocatalytic properties of N-G/MOF composites; and hereby offer guidance to the design and optimization endeavors of novel catalysts with N-G and MOF materials for diverse electrochemical applications.

A Deep Dive into the Study of Nitrogen-Doped Carbons As Electrocatalysts for the Oxygen Reduction Reaction Via a Design of Experiments Approach

Porous nitrogen (N)-doped carbons derived from earth-abundant precursors and exhibiting tunable properties hold promise as low-cost, high-performance electrode materials for energy storage and conversion applications. As metal-free electrocatalysts for the oxygen reduction reaction (ORR) at the cathode in hydrogen fuel cells, N-doped carbons have shown selectivity and performance rivaling that of Pt/C. Alternatively, other N-doped carbons have also demonstrated low overpotentials and high selectivity for the 2-electron pathway of the ORR for the production of hydrogen peroxide. The activity and selectivity of these doped carbons are thought to result from their N-content, N-motifs, and/or porosity. However, the extent to which each of these variables impacts electrocatalytic ORR performance and whether there is an interactive effect between N-content, porous structure, etc. remains unclear. Herein, by implementing a design of experiments approach, the synthesis-structure-function relationship for N-doped carbons prepared via molten salt templating was elucidated to reveal how synthetic handles tune material properties which, in turn, determine electrocatalytic performance. Specifically, the wt% of N precursor and the synthesis temperature were found to have the most significant effect on the N-content and N-motif composition of the resulting N-doped carbons. Regarding porosity, larger surface areas and micropore volumes were realized for the carbons prepared with a larger wt% of N precursor. It was found that surface areas upwards of 300 m2/g were required to see any substantial activity (e.g. half-wave potential greater than 0.7 V vs RHE, effective electron transfer number > 3.4). Only after a threshold surface area was achieved were effects from N-content and N-motifs notable on performance and selectivity.

CoNi-N/P-Doped Carbon Nanotubes as Catalysts for Efficient Oxygen Reduction Reaction.

Transition metals (TMs) supported by heteroatom-doped carbon materials are considered to be the potential alternatives to the Pt/C catalyst owing to their low cost, outstanding electrocatalytic efficiency, and excellent electrochemical durability. In this paper, N/P-doped carbon nanotube (CNT) (N/P-CNT)-supported monometallic (Co, Ni) and bimetallic (CoNi) catalysts were synthesized by one-step pyrolysis using diammonium hydrogen phosphate, 2-methylimidazole and organometallic salts as precursors, and the CNT as the catalyst carrier; the effects of transition TM types and pyrolysis temperature (Tp) on the microstructure and electrochemical properties were explored. The analysis exhibited that the CoNi bimetallic catalyst was superior to both Co and Ni monometallic catalysts, and the catalysts pyrolyzed at 900 °C exhibited a better graphitization degree. The optimal CoNi-N/P-CNT-900 displayed remarkable oxygen reduction reaction electrocatalytic performance with a half-wave potential (E1/2) of 0.86 V and excellent methanol tolerance and stability. Moreover, the Zn-air battery coated with CoNi-N/P-CNT-900 demonstrated a larger open circuit voltage of 1.577 V, a larger peak power density of 212.89 mW cm-2 at 357.8 mA cm-2, as well as a higher specific capacity of 799 mA h gZn-1, superior to that of the Pt/C catalyst (1.492 V, 96.04 mW cm-2 at 216.8 mA cm-2, 735 mA h gZn-1), showing outstanding practical value. This study is expected to promote the commercialization of the electrocatalysts.

CuFe nanoparticles coupled Cu–Nx for enhancing oxygen reduction reaction

For the large-scale development of zinc-air batteries (ZABs), designing efficient, and cost-effective oxygen reduction reaction (ORR) electrocatalysts is crucial yet challenging. Herein, CuFe nanoparticles coupled with Cu–Nx active sites co-anchored on 2D nitrogen–doped porous carbon nanosheets (CuFe@Cu–N–C) were obtained by the pyrolysis of Cu–MOF–74, nitrogen source, and ferric salt. The 2D porous carbon structure and the coupling effect between CuFe nanoparticles and Cu–Nx active sites endowed the CuFe@Cu–N–C electrocatalyst with excellent ORR electrocatalytic performance. Consequently, the CuFe@Cu–N–C electrocatalyst exhibited enhanced ORR activity with a higher half–wave potential than Cu–N–C, surpassing even that of the commercial 20 % Pt/C by 21 mV in alkaline media. Additionally, the CuFe@Cu–N–C electrocatalyst exhibited superior ORR stability to commercial 20 % Pt/C. Primary ZABs assembled with the CuFe@Cu–N–C as the cathode ORR electrocatalyst also showed excellent electrochemical properties. The work shows that the prepared CuFe@Cu–N–C electrocatalyst can serve as an ideal alternative to Pt-based catalysts for ZABs.

Linker Mediated Electronic-State Manipulation of Conjugated Organic Polymers Enabling Highly Efficient Oxygen Reduction.

Conjugated polymers with tailorable composition and microarchitecture are propitious for modulating catalytic properties and deciphering inherent structure-performance relationships. Herein, we report a facile linker engineering strategy to manipulate the electronic states of metallophthalocyanine conjugated polymers and uncover the vital role of organic linkers in facilitating electrocatalytic oxygen reduction reaction (ORR). Specifically, a set of cobalt phthalocyanine conjugated polymers (CoPc-CPs) wrapped onto carbon nanotubes (denoted CNTs@CoPc-CPs) are judiciously crafted via in situ assembling square-planar cobalt tetraaminophthalocyanine (CoPc(NH2)4) with different linear aromatic dialdehyde-based organic linkers in the presence of CNTs. Intriguingly, upon varying the electronic characteristic of organic linkers from terephthalaldehyde (TA) to 2,5-thiophenedicarboxaldehyde (TDA) and then to thieno/thiophene-2,5-dicarboxaldehyde (bTDA), their corresponding CNTs@CoPc-CPs exhibit gradually improved electrocatalytic ORR performance. More importantly, theoretical calculations reveal that the charge transfer from CoPc units to electron-withdrawing linkers (i.e., TDA and bTDA) drives the delocalization of Co d-orbital electrons, thereby downshifting the Co d-band energy level. Accordingly, the active Co centers with more positive valence state exhibit optimized binding energy toward ORR-relevant intermediates and thus a balanced adsorption/desorption pathway that endows significant enhancement in electrocatalytic ORR. This work demonstrates a molecular-level engineering route for rationally designing efficient polymer catalysts and gaining insightful understanding of electrocatalytic mechanisms.

Linker Mediated Electronic‐State Manipulation of Conjugated Organic Polymers Enabling Highly Efficient Oxygen Reduction

AbstractConjugated polymers with tailorable composition and microarchitecture are propitious for modulating catalytic properties and deciphering inherent structure‐performance relationships. Herein, we report a facile linker engineering strategy to manipulate the electronic states of metallophthalocyanine conjugated polymers and uncover the vital role of organic linkers in facilitating electrocatalytic oxygen reduction reaction (ORR). Specifically, a set of cobalt phthalocyanine conjugated polymers (CoPc‐CPs) wrapped onto carbon nanotubes (denoted CNTs@CoPc‐CPs) are judiciously crafted via in situ assembling square‐planar cobalt tetraaminophthalocyanine (CoPc(NH2)4) with different linear aromatic dialdehyde‐based organic linkers in the presence of CNTs. Intriguingly, upon varying the electronic characteristic of organic linkers from terephthalaldehyde (TA) to 2,5‐thiophenedicarboxaldehyde (TDA) and then to thieno/thiophene‐2,5‐dicarboxaldehyde (bTDA), their corresponding CNTs@CoPc‐CPs exhibit gradually improved electrocatalytic ORR performance. More importantly, theoretical calculations reveal that the charge transfer from CoPc units to electron‐withdrawing linkers (i.e., TDA and bTDA) drives the delocalization of Co d‐orbital electrons, thereby downshifting the Co d‐band energy level. Accordingly, the active Co centers with more positive valence state exhibit optimized binding energy toward ORR‐relevant intermediates and thus a balanced adsorption/desorption pathway that endows significant enhancement in electrocatalytic ORR. This work demonstrates a molecular‐level engineering route for rationally designing efficient polymer catalysts and gaining insightful understanding of electrocatalytic mechanisms.

Simultaneous Mapping of Electrocatalytic Activity and Selectivity via Hybrid Scanning Electrochemical Probe Microscopy.

Nanoscale scanning electrochemical probe microscopy started to elucidate the heterogeneity of electrocatalytic activity at electrode surfaces. However, understanding the heterogeneity in product selectivity, another crucial aspect of interfacial reactivity, remains challenging. Herein, we introduce a method combining scanning electrochemical microscopy (SECM) and scanning electrochemical cell microscopy (SECCM) to enable the spatially resolved mapping of both activity and selectivity in electrocatalysis. A dual-channel nanopipette probe was developed: one channel for activity mapping and the other for product detection with a high collection efficiency (>95%) and sensitivity. Simultaneous mapping of activity and selectivity in the oxygen reduction reaction (ORR) is demonstrated. Combined with colocalized crystal orientation mapping, we uncover the local electrocatalytic performance of ORR at different facets on polycrystalline Pt and Au. The high-resolution selectivity mapping enabled by our method with colocalized structural characterization can provide structure-activity-selectivity relationships that are often unavailable in ensemble measurement, holding promise for understanding key structural motifs controlling interfacial reactivity.

Utilizing Carbonaceous Materials Derived from [BMIM][TCM] Ionic Liquid Precursor: Dual Role as Catalysts for Oxygen Reduction Reaction and Adsorbents for Aromatics and CO2.

This work presents the synthesis of N-doped nanoporous carbon materials using the Ionic Liquid (IL) 1-butyl-3-methylimidazolium tricyanomethanide [BMIM][TCM] as a fluidic carbon precursor, employing two carbonization pathways: templated precursor and pyrolysis/activation. Operando monitoring of mass loss during pyrolytic and activation treatments provides insights into chemical processes, including IL decomposition, polycondensation reactions and pore formation. Comparatively low mass reduction rates were observed at all stages. Heat treatments indicated stable pore size and increasing volume/surface area over time. The resulting N-doped carbon structures were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) and adsorbents for gases and organic vapors. Materials from the templated precursor pathway exhibited high electrocatalytic performance in ORR, analyzed using Rotating Ring-Disk electrode (RRDE). Enhanced adsorption of m-xylene was attributed to wide micropores, while satisfactory CO2 adsorption efficiency was linked to specific morphological features and a relatively high content of N-sites within the C-networks. This research contributes valuable insights into the synthesis and applications of N-doped nanoporous carbon materials, highlighting their potential in electrocatalysis and adsorption processes.

Ternary (molybdenum disulfide/graphene)/carbon nanotube nanocomposites assembled via a facile colloidal electrostatic path as electrocatalysts for the oxygen reduction reaction: Composition and nitrogen-doping play a key role in their performance

Nanocomposites have garnered attention for their potential as catalysts in electrochemical reactions vital for technologies like fuel cells, water splitting, and metal-air batteries. This work focuses on developing three-dimensional (3D) nanocomposites through aqueous phase exfoliation, non-covalent functionalization of building blocks with surfactants and polymers, and electrostatic interactions in solution leading to the nanocomposites assembly and organization. By combining molybdenum disulfide (MoS2) layers with graphene nanoplatelets (GnPs) to form a binary 2D composite (MoS2/GnP), and subsequently incorporating multiwalled carbon nanotubes (MWNTs) to create ternary 3D composites, we explore their potential as catalysts for the oxygen reduction reaction (ORR) critical in fuel cells. Characterization techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction elucidate material composition and structure. Our electrochemical studies reveal insights into the kinetics of the reactions and structure–activity relationships. Both the (MoS2/GnP)-to-MWNT mass ratio and nitrogen-doping of GnPs (N-GnPs) play a key role on the electrocatalytic ORR performance. Notably, the (MoS2/N-GnP)/MWNT material, with a 3:1 mass ratio, exhibits the most effective ORR activity. All catalysts demonstrate good long-term stability and methanol crossover tolerance. This facile fabrication method and observed trends offer avenues for optimizing composite electrocatalysts further.

Co/Co3O4 Heterojunctions Encased in Porous N-Doped Carbon Nanocapsules for High-Performance Cathode of Rechargeable Zinc-Air Batteries.

A long-term goal of rechargeable zinc-air batteries (ZABs) has always been to design bifunctional electrocatalysts that are robust, effective, and affordable for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). It has become a feasible method to construct metal/metal oxide interfaces to achieve superior electrocatalytic performance for ORR and OER by enhanced charge transfer. In this study, Co/Co3O4 heterojunctions were successfully prepared and encased in porous N-doped mesoporous carbon (Co/Co3O4@NC) via a simple condensation-carbonization-etching method. The extensive specific surface area of Co/Co3O4@NC facilitates effective interaction between the electrolyte and the catalyst, thereby enabling sufficient exposure of active sites for the ORR and the OER, consequently enhancing the rate of transport of active species. The well-designed Co/Co3O4@NC delivers superior ORR catalytic activity with a half-wave potential of 0.82 V (vs RHE) and a low overpotential of 347 mV at 10 mA cm-2 for OER in alkaline solution. The power density of Co/Co3O4@NC-based alkaline aqueous ZAB (156.5 mW cm-2) is superior to the commercial Pt/C + IrO2-based alkaline aqueous ZAB, and the cycling stability of ZAB is up to 220 h. In addition, Co/Co3O4@NC-based ZAB shows a high power density (50.1 mW cm-2). The construction of metal/metal oxide heterojunction encased in N-doped mesoporous carbon provides a novel route for the design of bifunctional electrocatalysts for high-performance ZABs.

Solution-Plasma Synthesis and Characterization of Transition Metals and N-Containing Carbon-Carbon Nanotube Composites.

Lithium-air batteries (LABs) have a theoretically high energy density. However, LABs have some issues, such as low energy efficiency, short life cycle, and high overpotential in charge-discharge cycles. To solve these issues electrocatalytic materials were developed for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which significantly affect battery performance. In this study, we aimed to synthesize electrocatalytic N-doped carbon-based composite materials with solution plasma (SP) using Co or Ni as electrodes from organic solvents containing cup-stacked carbon nanotubes (CSCNTs), iron (II) phthalocyanine (FePc), and N-nethyl-2-pyrrolidinone (NMP). The synthesized N-doped carbon-based composite materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). TEM observation and XPS measurements revealed that the synthesized carbon materials contained elemental N, Fe, and electrode-derived Co or Ni, leading to the successful synthesis of N-doped carbon-based composite materials. The electrocatalytic activity for ORR of the synthesized carbon-based composite materials was also evaluated using electrochemical measurements. The electrochemical measurements demonstrated that the electrocatalytic performance for ORR of N-doped carbon-based composite material including Fe and Co showed superiority to that of N-doped carbon-based composite material including Fe and Ni. The difference in the electrocatalytic performance for ORR is discussed regarding the difference in the specific surface area and the presence ratio of chemical bonding species.

A robust asymmetric diatomic electrocatalyst for oxygen reduction reaction in both acidic and alkaline media

Herein, an asymmetric diatomic site oxygen reduction reaction (ORR) electrocatalyst with atomically dispersed Fe and Cu species co-anchored on porous nitrogen-doped polyhedra carbon was successfully prepared through a facile cooperation of post-adsorption and two-step pyrolysis method. Density functional theory (DFT) calculations reveal that the asymmetric FeCu dual atomic site experiences a symmetry destruction of electron transfer due to the existing Cu-N4 sites and thus results in the electron redistribution in FeSACuSA/NC, contributing significantly to the optimization of intermediates adsorption and acceleration of kinetics during ORR process. Attributed to the structural advantages of FeSA-N4&CuSA-N4 sites and highly porous carbon matrix, the FeSACuSA/NC catalyst exhibits excellent electrocatalytic ORR performance with half-wave potentials (E1/2) of 0.86 and 0.88 V versus reversible hydrogen electrode in 0.1 M HClO4 and 0.1 M KOH solutions as well as high durability. Moreover, FeSACuSA/NC-based H2/O2 fuel cell and zinc-air battery present superior performance with high peak power density.

Synergistic effects of hierarchical porous structures and ultra-high pyridine nitrogen doping enhance the oxygen reduction reaction electrocatalytic performance of metal-free laminated lignin-based carbon

Construction of non-metallic biomass-carbon based catalysts for fuel cell air cathode applications has attracted great attention in recent years. In this work, a convenient and clean technique was developed to fabrication nitrogen-doped lignin-based hierarchical porous lamellar carbon (N-LHPC) via lignin as the carbon precursor, melamine/urea as the nitrogen source and ZnC2O4.2H2O as the chemical activator. The N-LHPC has a high specific surface area (491.5 m2 g−1) and macroporous/mesoporous/microporous structures. The nitrogen doping of N-LHPC can reach 16.37 wt%, with a high pyridinic nitrogen content of 41.39 at.%. N-LHPC exhibits a high half-wave potential (0.87 V) and a large limiting current density (5.75 mA cm−2) in 0.1 mol KOH media which is comparable to the commercial Pt/C catalysts. Furthermore, N-LHPC was assembled as air cathode catalyst for Zn-air batteries to evaluate its practical catalytic performance, and the power density was as high as 191 mW cm−2, which was superior to the 20 wt% Pt/C electrocatalyst. This research demonstrates that lignin is a promising carbon source for the fabrication of high catalytic activity and economical electrocatalysts for energy storage systems.

One pot production of Co core/carbon shell materials and their electrocatalytic properties

AbstractThe oxygen reduction reaction (ORR) is a kinetically sluggish reaction because it requires the transfer of four electrons. In this work, one‐pot process involving thermal treatment of Co(II) acetylacetonate is developed. The resulting core–shell material (Co@C‐800) consists of metallic Co cores encapsulated by carbon‐based layered shells. Morphological analysis reveals the core–shell structures, with core particles surrounded by carbon networks. Chemical characterization using various spectroscopic techniques indicates the presence of metallic Co as the major component in Co@C‐800, with minor Co species exhibiting higher oxidation states. Raman spectroscopy confirms the formation of sp2‐hybridized carbon shells. Co@C‐800 displays efficient electrocatalytic ORR performance, evidenced by high onset and half‐wave potentials. The excellent durability and stability of Co@C‐800, demonstrated through resistance to methanol poisoning and cyclic testing, suggest the potential of core–shell materials as a practical electrocatalyst.

Controlled construction of core-shell structured Prussian Blue analogues towards enhanced oxygen reduction.

Metal-organic frameworks-based electrocatalysts have been developed as highly desirable and promising candidates for catalyzing oxygen reduction reaction (ORR), which, however, usually need to be prepared at elevated temperatures and may suffer from the framework collapse in water environment largely preventing its industrial application. Herein, we demonstrate a facile low-temperature ion exchange method to synthesize Mn and Fe co-loaded Prussian blue analogues possessing core-shell structured frameworks and favorable water-tolerance. Among the catalysts prepared, the optimal HMPB-2.6Mn shows a high ORR electrocatalytic performance featuring a half-wave potential of 0.86 V and zinc-air battery power density of 119 mW cm-2, as well as negligible degradation up to 60 h, which are comparable to commercial Pt/C. Such an excellent electrocatalytic performance is attributed to the special core-shell-like structure with Mn concentrated in outer shell, and the synergetic interactions between Mn and Fe, endowing HMPB-Mn with outstanding ORR activity and good stability.