Electrocatalytic Performance For Oxygen Reduction Research Articles

"One-stone, Two-Birds": Zinc-Rich Metal-Organic Frameworks as Precursors for High-Entropy Zn-Air Battery Electrocatalysts with Hierarchical Pore Structures.

The active sites of inexpensive transition metal electrocatalysts are sparse and singular, thus high-entropy alloys composed of non-precious metals have attracted considerable attention due to their multi-component synergistic effects. However, the facile synthesis of high-entropy alloy composites remains a challenge. Herein, we report a "one-stone, two-birds" method utilizing zinc (Zn)-rich metal-organic frameworks as precursors, by virtue of the low boiling point of Zn (907 °C) and its high volatility in alloys, high-entropy alloy carbon nanocomposite with a layered pore structure was ultimately synthesized. The experimental results demonstrate that the volatilization of zinc can prevent metal agglomeration and contribute to the formation of uniformly dispersed high-entropy alloy nanoparticles at slower pyrolysis and cooling rates. Simultaneously, the volatilization of Zn plays a crucial role in creating the hierarchical porous structure. Compared to the zinc-free HEA/NC-1, the HEA/NC-5 derived from the precursor containing 0.8 Zn exhibit massive micropores and mesopores. The resulting nanocomposites represent a synergistic effect between highly dispersed metal catalytic centers and hierarchical adsorption sites, thus achieving excellent electrocatalytic oxygen reduction performance with low catalyst loading compared to commercial Pt/C. This convenient zinc-rich precursor method can be extended to the production of more high-entropy alloys and various application fields.

Biomass N/P co‐doped porous carbon plates for electrocatalytic oxygen reduction

AbstractNitrogen and phosphorus co‐doped porous carbon plate (NPCP) was prepared by simple pyrolysis carbonization and alkali activation of biomass duckweed NPCP displays the largest specific surface area (SSA) of 2023 m2 g−1, and is rich in pyridine N and P doping, which makes the metal‐free carbon have excellent electrocatalytic oxygen reduction performance. The best NPCP2 shows a half‐wave potential of 0.19 V vs. Ag/AgCl in alkaline electrolyte, and its activity is equivalent to that of commercial platinum carbon (Pt/C). In addition, it shows excellent methanol toxicity resistance and continuous catalytic stability. The experimental results show that the heteroatom doping method obtained by biomass hydroponics has great advantages and great application value in the catalytic field of porous carbon materials.

Self‐Adjustment of Intrinsic Reaction Intermediate on Atomically Dispersed Co2–N6 Binuclear Sites Achieving Boosted Electrocatalytic Oxygen Reduction Performance

AbstractIsolated dual‐atom catalysts (DACs) have sparked enormous research enthusiasm in new energy community due to their great potentials to substitute the state‐of‐the‐art Pt‐based catalysts. Nevertheless, explicitly unraveling the underlying catalytic mechanisms is of critical significance for performance enhancement, yet remains a huge challenge. Herein, the study reports a reliable hard template‐mediated strategy to accomplish the construction of atomically isolated binuclear Co2‐N6 sites stabilized by ultrathin hollow carbon nanospheres (abbreviated as Co2‐DAs@CHNSs). Systematic spectroscopy characterization and theoretic calculations uncover that the Co2‐N6 sites follow a self‐adjusting mechanism caused by the intrinsic OH intermediate. The involvement of the ‐OH energy‐level modifier is found to induce the electron redistribution and alternation of antibonding orbital fillings for the generated Co2‐N6‐OH site, leading to reduced potential‐determining step (PDS) energy barrier, and thus boosted intrinsic activity. Consequently, the well‐managed Co2‐DAs@CHNSs afford outstanding oxygen reduction reaction (ORR) activity with a half‐wave potential of 0.87 V in alkaline electrolyte, overmatching the Pt benchmark. Furthermore, the Co2‐DAs@CHNSs‐assembled aqueous and all‐solid‐state rechargeable zinc–air batteries (ZABs) demonstrate high power density, large specific capacity, and robust stability. The findings offer an innovative avenue to rationally manipulate the electronic structures of active sites for DACs via a powerful self‐ligand modification strategy.

Enhanced nitrogen doping on porous carbon via confining-pyrolysis method for electrocatalytic oxygen reduction

Reasonable design and development of N-doped carbon materials by post-treatment of porous carbon with melamine is an effective route to preparing low-cost and high-performance electrocatalysts toward oxygen reduction reaction. Nevertheless, melamine derivatives have been observed to rapidly escape during pyrolysis, resulting in the undesirable loss of nitrogen atoms and catalytic activity. Here, a confining-pyrolysis method was proposed to accumulate melamine in the micropores of porous carbon to prepare the object N-doped carbon material with an enhanced nitrogen doping. Because the melamine accumulated in the micropores of porous carbon, the object N-doped carbon material shows a significant enhancement in N-atom content, graphitization degree, mesopore volume, electrochemical active surface area and hydrophobic surface. Density functional theory calculations and electrocatalytic tests demonstrate that the object N-doped carbon material delivers a good electrocatalytic oxygen reduction performance. The N-doped carbon electrode displayed a close half-wave potential for alkaline ORR compared to the commercial Pt/C electrocatalyst and showed an excellent cycling stability and methanol tolerance. This work provides a cost-effective method to prepare carbon-based ORR electrocatalyst for energy devices.

Boosted Electrocatalytic Oxygen Reduction Performance of Porous Co-NC Catalysts by the Coexistence of Abundant Co–N4 and g-N Sites

Boosted Electrocatalytic Oxygen Reduction Performance of Porous Co-NC Catalysts by the Coexistence of Abundant Co–N₄ and g-N Sites

Open-Mouthed Hollow Carbons: Systematic Studies as Cobalt- and Nitrogen-Doped Carbon Electrocatalysts for Oxygen Reduction Reaction.

Although hollow carbon structures have been extensively studied in recent years, their interior surfaces are not fully utilized due to the lack of fluent porous channels in the closed shell walls. This study presents a tailored design of open-mouthed particles hollow cobalt/nitrogen-doped carbon with mesoporous shells (OMH-Co/NC), which exhibits sufficient accessibility and electroactivity on both the inner and outer surfaces. By leveraging the self-conglobation effect of metal sulfate in methanol, a raspberry-structured Zn/Co-ZIF (R-Zn/Co-ZIF) precursor is obtained, which is further carbonized to fabricate the OMH-Co/NC. In-depth electrochemical investigations demonstrate that the introduction of open pores can enhance mass transfer and improve the utilization of the inner active sites. Benefiting from its unique structure, the resulting OMH-Co/NC exhibits exceptional electrocatalytic oxygen reduction performance, achieving a half-wave potential of 0.865V and demonstrating excellent durability.

Enhanced Electrocatalytic Oxygen Reduction Performance of Differently Optimized S,N Heteroatom Dual-Doped Carbon-Encapsulated Iron Carbide–Carbon (Fe3C@C-SN) Nanostructures

Enhanced Electrocatalytic Oxygen Reduction Performance of Differently Optimized S,N Heteroatom Dual-Doped Carbon-Encapsulated Iron Carbide–Carbon (Fe₃C@C-SN) Nanostructures

Two-Dimensional Polyphosphazene Nanosheet-Derived N,P Doubly Doped Carbon Nanotubes for Electrocatalytic Oxygen Reduction

Two-dimensional (2D) covalent organic polymers (COPs) featuring large surface areas and exposed active sites are desirable in the modification of electrode materials for electrochemical reactions. However, the rigid and planar conformation of 2D COPs limits the wrap of one-dimensional electrodes. Herein, we have proposed a molecular strategy to regulate in situ encapsulation of carbon nanotubes (CNTs) with 2D polyphosphazene. The stoichiometric control over the nucleophilic substitution reaction between hexachlorocyclophosphazene and amines allows for the oriented evolution around the surface of CNTs. The formed COP sheath is an ultrathin and uniform coating without granular deposition. Upon carbonization, the well-defined core/shell CNT composite was converted into the N,P-codoped carbon, exhibiting outstanding electrocatalytic oxygen reduction performance with a diffusion-limiting current density of 5.4 mA cm–2 and an electron transfer number of 3.97. The improved electrocatalytic activity originates from a high content of active N,P-containing catalytic sites uniformly distributed on porous carbon. This study provides a viable strategy to develop functional composite materials by modulating the flexibility of 2D COPs for 1D substrates, contributing to broad applicability.

Impact of Different Lignin Sources on Nitrogen-Doped Porous Carbon toward the Electrocatalytic Oxygen Reduction Reaction.

Lignin is an ideal carbon source material, and lignin-based carbon materials have been widely used in electrochemical energy storage, catalysis, and other fields. To investigate the effects of different lignin sources on the performance of electrocatalytic oxygen reduction, different lignin-based nitrogen-doped porous carbon catalysts were prepared using enzymolytic lignin (EL), alkaline lignin (AL) and dealkaline lignin (DL) as carbon sources and melamine as a nitrogen source. The surface functional groups and thermal degradation properties of the three lignin samples were characterized, and the specific surface area, pore distribution, crystal structure, defect degree, N content, and configuration of the prepared carbon-based catalysts were also analyzed. The electrocatalytic results showed that the electrocatalytic oxygen reduction performance of the three lignin-based carbon catalysts was different, and the catalytic performance of N-DLC was poor, while the electrocatalytic performance of N-ELC was similar to that of N-ALC, both of which were excellent. The half-wave potential (E1/2) of N-ELC was 0.82 V, reaching more than 95% of the catalytic performance of commercial Pt/C (E1/2 = 0.86 V) and proving that EL can be used as an excellent carbon-based electrocatalyst material, similar to AL.

Preparation of multistage microporous and mesoporous nitrogen-doped carbon nanospheres and study on electrocatalytic oxygen reduction

Non-metallic carbon-based catalysts are one of the most promising catalysts for electrocatalytic oxygen reduction (ORR). However, the controlled synthesis of the pore structures of carbon-based catalysts and the determination of catalytic sites still remains to be further explored. Based on this, two nitrogen-doped carbon-based catalysts with microporous and mesoporous structures were prepared in this paper. The two catalysts had different pore structures and nitrogen-doped species. The experimental results showed that the carbon-based catalyst (PC-NH3) rich in microporous structure and pyridine nitrogen doping had better catalytic performance, the electrocatalytic oxygen reduction performance of the catalyst was comparable to that of the platinum catalyst, and it had excellent methanol resistance and stability. This study provided important guidance for the application of porous carbon materials in oxygen reduction.

Boosting electrocatalytic oxygen reduction performance of Co[sbnd]N[sbnd]C catalysts on Ti3C2 MXene by the synergistic effect with oxygen vacancy-rich TiO2

Construction of multiphase nanocomposites is an effective way to develop high performance oxygen reduction catalysts. Herein, Ti3C2 MXene supported CoNC and oxygen vacancy-rich TiO2 (ov-TiO2) composite catalyst (CoNC/TiO2-Ti3C2) is prepared by coordination and polymerization of dopamine and Co2+ on the surface of Ti3C2 nanosheets and subsequent heating treatment. The oxygen vacancies on the surface of TiO2 nanoparticles can stabilize the CoNC catalysts as well as promote the oxygen reduction reaction (ORR) on them. Therefore, CoNC/TiO2-Ti3C2 exhibits good ORR activity and durability, even better than the commercial Pt/C catalyst. In contrast, Ti3C2 supported CoNC catalyst without ov-TiO2 (CoNC/Ti3C2) shows decreased ORR activity, indicating the significance of the synergistic effect of CoNC and ov-TiO2. In a practical application, CoNC/TiO2-Ti3C2 exhibits a large power density (155.3 mW cm−2) and extraordinary long-term rechargeability as the air cathode for Zn-air batteries. This strategy of in-situ growth of cocatalysts on Ti3C2 MXene provides a new way for the preparation of high-performance non-noble metal catalysts.

Electrochemical Grafting of a Pyridinium‐Conjugated Assembly on Graphite for H 2 O 2 Electrochemical Production

Carbon materials have shown great promise as cost-effective electrocatalysts for H 2 O 2 electrochemical production. In this work, we prepare a series of well-defined pyridinium-conjugated graphite sheets via nucleophilic substitution reaction of graphite with pyridine derivatives in anodic oxidation process. A combination of experimental and computational investigations confirm that the pyridine derivatives are electrochemically grafted onto the armchair-type edges of graphitic layers, where the adjacent carbon atoms show the positively charged state by the intramolecular charge transfer. The strong charge delocalization on pyridinium-conjugated graphite sheets can yield the enhanced electrocatalytic performance for oxygen reduction on both of the activity and selectivity (above 97 %) for H 2 O 2 production. Moreover, we find that the yield of H 2 O 2 production is also affected by the H 2 O 2 decomposing capabilities of functional groups on pyridinium. As one kind of pyrolysis-free strategies, the proposed electrochemical grafting can serve as a molecularly precise regulation to develop nitrogen doped carbon materials for more applications.

Wood based quasi-solid-state Zn-air battery with dual honeycomb-like porous carbon and cationic nanocellulose film

Conversion of low-value biomass to hierarchically porous carbon-based materials for oxygen reduction reactions (ORR), without using conventional template methods, is of particular significant for energy storage technology. Herein, dual honeycomb-like porous carbon inspired by multiscale structure of wood was assembled with cationic nanocellulose film into Zn-air battery. Nitrogen-doped hierarchically porous carbon was obtained by a simple two-step process involving alkaline extraction and pyrolysis with NH4Cl. Alkaline extraction was utilized for partially degrading lignin and heterosaccharide from unprocessed wood to create a porous wood with numerous nanopores and 3D loose structure. The inner and outer parts of obtained porous wood were further pore-optimized and doped with NH4Cl by a consequent pyrolysis step. The resulting carbon-based material (AHWC) possessed high specific surface area (1601.8 m2 g−1), well-developed hierarchical porosity, and high N content enabled excellent electrocatalytic oxygen reduction performance. Compared with commercial Pt/C catalysts in KOH electrolyte, AHWC exhibits nearly two times higher kinetic currents in the low overpotential region, comparable number of transferred electrons, and significantly higher operating stability. This carbon-based material also showed an excellent capacity and energy density equal to 792 mA h g−1 and 927 W h kg−1, together with superior long-term durability (200 h at the current density of 10 mA cm−2) when assembled as the active electrode material into a Zn-air battery. Additionally, cationic modified nanocellulose film (C-CNF-M), acting as a solid electrolyte, was assembled with AHWC for a quasi-solid-state Zn-air battery which exhibited excellent specific capacity (672.2 mA h g−1), energy density (644.11 W h kg−1) and cycling stability (500 min at 1 mA cm−2). The AHWC establish a bridge between papermaking and the field of energy storage by green conversion of biomass and fabrication of porous carbon-based materials and cellulose based electrolyte with excellent properties applicable to electrochemical energy devices.

Bulky Thiolate-Protected Silver Nanocluster Ag 213 (Adm-S) 44 Cl 33 with Excellent Electrocatalytic Performance toward Oxygen Reduction

Bulky Thiolate-Protected Silver Nanocluster Ag ₂₁₃ (Adm-S) ₄₄ Cl ₃₃ with Excellent Electrocatalytic Performance toward Oxygen Reduction

Surface functionalization of polyaniline and excellent electrocatalytic performance for oxygen reduction to produce hydrogen peroxide

We have developed the CNT@PANI-NO electrocatalyst that is significantly different from the conventional electrocatalyst previously reported. • Polyaniline (PANI) can be changed into PANI-NO with the functional group of –NO. • Introducing PANI-NO on the surface of CNT obtains the CNT@PANI-NO. • PANI-NO has promoted selectivity of H 2 O 2 than PANI. • CNT@PANI-NO exhibits excellent electrochemical performance for H 2 O 2 production. Electrochemical two-electron oxygen reduction is an environmental-friendly and promising method to generate H 2 O 2 . However, a great challenge remains to develop more economic and effective electrocatalysts for practical application. Here, we have developed a CNT@PANI-NO electrocatalyst that is significantly different from the conventional electrocatalyst previously reported (such as metal, alloy, carbon materials doped with heteroatoms, metal single-atom catalysts). We firstly find that the polyaniline (PANI) treated by dilute nitric acid can be changed into the PANI-NO product with the functional group of –NO. Then we introduce the PANI-NO on the surface of carboxylated carbon nanotubes to obtain the CNT@PANI-NO nanocomposites, which exhibit excellent electrochemical performance to H 2 O 2 production. The H 2 O 2 selectivity of the typical CNT@PANI-NO is between 87% and 94% at the potential of 0.2–0.68 V (vs. RHE), the faradaic efficiency is close to 95% and the current density is up to 2.9 mA/cm 2 (at 0.3 V) in alkaline condition. The DFT results give the origin of the catalytic activity. This study provides a new idea for the application of polymer in electrocatalysis and a new way to develop the high-performance 2e-ORR electrocatalyst.

Two-Dimensional Metal–Organic Frameworks with Unique Oriented Layers for Oxygen Reduction Reaction: Tailoring the Activity through Exposed Crystal Facets

Two-Dimensional Metal–Organic Frameworks with Unique Oriented Layers for Oxygen Reduction Reaction: Tailoring the Activity through Exposed Crystal Facets

Aminoclay/MWCNT supported spherical Pt nanoclusters with enhanced dual-functional electrocatalytic performance for oxygen reduction and methanol oxidation reactions

The structure–activity-durability relationship of Pt nanoclusters anchored on aminoclay functionalized multi-walled carbon nanotube (Pt/AC-MWCNT) was well corroborated by the correlation between physicochemical properties and electrocatalytic oxygen-reduction (ORR) and methanol oxidation reactions. By TEM and XRD results, the closely-packed small Pt nanoparticles (~2 nm) forming an unique spherical-shaped nanocluster morphology with higher lattice strain (-0.432%) were determined. The dual functionality of Pt/AC-MWCNT has been substantially confirmed from the key electrochemical parameters of mass and specific activities for both ORR (0.223 mA μg−1 and 0.4 mA cm−2) and MOR (1688.8 mA mg−1 and 3.03 mA cm−2). After the accelerated durability test, the higher retention percentage of its initial catalytic activity for both ORR (5000 cycles) and MOR (2000 cycles) confirms the sustained stability of the catalyst. The superior performance of Pt/AC-MWCNT was attributed to, (i) the synergistic effect between Pt nanoclusters and hybrid support, (ii) the electronic effect by compressive lattice strain, and (iii) the shape of Pt nanocluster with tiny particles. Compared to commercial Pt/C (Alfa Aesar) and reported Pt-based nanostructures for ORR and MOR, the Pt/AC-MWNCT has shown promising dual-functional electrocatalytic efficiency.

Facile synthesis and electrocatalytic performance for oxygen reduction of boron‐doped carbon catalysts on graphene sheets

AbstractBoron‐doped carbon catalysts are synthesized via a liquid‐phase electrodeposition technique using methanol‐containing graphene nucleating agent and B2O3 dopant as the reaction solution. The relationship between boron‐doped content and specific surface area (SSA), as well as their influence on electrocatalytic activity for oxygen reduction reaction, is studied by changing the concentration of B2O3. When the concentrations of B2O3 are 23.94 and 14.36 mol ml–1, respectively, boron‐doped content and SSA reach the peak values of 0.53 at.% and 18.476 m2 g–1. The data of electrochemical tests, such as onset potential of –0.016 V and transferred electron number of 3.74–3.77 in the range of –0.5 to –0.9 V, exhibit that the catalyst with a boron‐doped content of 0.47 at.% and an SSA of 18.476 m2 g–1 has the best electrocatalytic activity in all the synthesized samples. The enhanced electrocatalytic activity is ascribed to a synergistic effect originating from boron‐doped content and SSA, in which the SSA contributes more. The experimental results have important guiding significance to maximize the oxygen reduction activity of catalysts and elucidate that it tends to design and synthesize catalysts with large SSA compared with doping.

Synthesis of N-doped Co@C/CNT materials based on ZIF-67 and their electrocatalytic performance for oxygen reduction

ZIF-67/CNT materials are prepared by using in situ growth method with cobalt nitrate and 2-methylimidazole (2-MI) as raw materials, polyvinyl pyrrolidone (PVP) as complexing agents. A series of N-Co@C/CNT catalysts are prepared through heating ZIF-67/CNT in N2 atmosphere. The effects of additional proportion of CNT on the catalytic performance of N-Co@C/CNT catalysts for oxygen reduction reaction (ORR) are studied. The chemical states of the materials, micro-morphology, elemental composition, and crystalline structure are analyzed by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results show that polyhedral ZIF-67 has grown on the surfaces of CNTs. After heat treatment, ZIF-67/CNT transforms to N-Co@C/CNT. The particle size of Co is 10–20 nm. N-Co@C/CNT-2.6 shows the best catalytic performance for ORR in alkaline solution with the onset potential of 0.94 V, half-wave-potential of 0.83 V, and limiting diffusion current density of 5.6 mA cm−2. The ORR on N-Co@C/CNT proceeds through a four-electron path and the yield of H2O2 is 12%, which is close to Pt/C. N-Co@C/CNT shows higher methanol-tolerant ability than Pt/C. The addition of CNT makes N-Co@C expose more active sites. CNT plays an important role in connecting different N-Co@C particles and enhancing the electron conductivity. The contents of graphitic nitrogen and pyridine nitrogen in N-Co@C/CNT-2.6 catalysts are 15.8% and 38.6%, respectively, which are higher than those in N-Co@C (7% and 34%).

Long-range order, short-range disorder: Engineering one-dimensional flow channel arrays with hierarchically porous reaction interfaces for electrocatalytic reduction of oxygen

Fuel cell performance depends heavily on electrochemical reaction kinetics and mass transport. Rapid kinetics requires high-activity catalysts while good mass transport demands efficient transport domains. Recent fundamental studies in these areas focus more on the improvement in catalyst activity, whereas the importance of mass transport should not be underestimated, which is the focal point of this work. Hierarchical pores are generally considered to be conducive to enhancing reaction kinetics and mass transport, but the degree of order of pore structures has a significant influence over the fuel cell performance. Herein, we introduce the concept of ‘long-range order, short-range disorder’ to design transport domains and reaction interfaces: dispensing with conventional microfabrication techniques, well-ordered, one-dimensional channel arrays are constructed using vascular bundles of natural material, capable of decreasing tortuosity, increasing porosity, optimizing reactant distribution and thus minimizing concentration losses; further, intrinsic biominerals and tissues of organisms existing on the inner and outer walls of channel arrays are harnessed to form hierarchically porous domains, that is, raising the roughness of reaction interfaces by increasing the degree of short-range disorder. The combination of one-dimensional flow channels (long-range order) and hierarchically porous reaction interfaces (short-range disorder), analogous to blood vessels composed of arteries/veins and capillaries, ensures the optimization of mass transport and catalytic kinetics, leading to an electrocatalytic oxygen reduction performance enhancement over a wide array of biomass-derived carbonaceous materials. Accordingly, this work provides inspiration for finding the right balance between mass transport and reaction kinetics from an order perspective.