Robust Oxygen Reduction Reaction Research Articles

Tuning the structure and properties of carbon cloth by FeCl3intercalation for efficient two-electron oxygen reduction catalysis.

The advancement of various energy conversion and storage technologies hinges on the development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR). In this study, we report the enhancement of carbon cloth (CC) for robust ORR through an FeCl3intercalation reaction. Utilizing a thermal annealing method, FeCl3was intercalated into the graphite structure on the surface of CC, resulting in the creation of numerous defects and the incorporation of Fe species. These newly introduced defects play a pivotal role in activating the ORR via a two-electron pathway. The presence of Fe species further stabilizes the catalytic activity, leading to efficient and stable ORR performance. Our findings highlight the significance of defect engineering and Fe species incorporation in carbon-based materials for improved ORR catalysis and pave the way for the development of advanced electrocatalysts for energy-related applications.

Protection of Fe Single‐Atoms by Fe Clusters for Chlorine‐Resistant Oxygen Reduction Reaction

AbstractDirect seawater zinc‐air batteries (S‐ZABs), with their inherent properties of high energy density, intrinsic safety, and low cost, present a compelling avenue for the development of energy storage technology. However, the presence of chloride ions in seawater poses challenges to their air electrode, resulting in sluggish reaction kinetics and poor stability for the oxygen reduction reaction (ORR). Herein, Fe atomic clusters (ACs) decorated Fe single‐metal atoms (SAs) catalyst (FeSA‐FeAC/NC) is prepared using a plasma treatment strategy. The aberration‐corrected transmission electron microscope images confirm the successful construction of Fe SAs surrounding Fe ACs, which delivers robust ORR activity with a half‐wave potential of 0.886 V in alkaline seawater electrolyte. When utilized as the cathode catalyst in assembled S‐ZABs, the battery demonstrates excellent discharge performance, achieving a peak power density of 222 mW cm−2, which is 2.3 times higher than Pt/C based S‐ZABs. Moreover, density functional theory calculations unveil that the synergy effect between the Fe ACs and SAs not only reduces the spin‐down d‐band center in the Fe SAs, but also efficiently suppresses Cl−1 adsorption on Fe SAs due to their strong Cl−1 absorption ability of the Fe ACs, thereby enhancing both the activity and stability of the catalyst.

Main Group SnN4O Single Sites with Optimized Charge Distribution for Boosting the Oxygen Reduction Reaction.

Transition metal single-atom catalysts (SACs) have been regarded as possible alternatives to platinum-based materials due to their satisfactory performance of the oxygen reduction reaction (ORR). By contrast, main-group metal elements are rarely studied due to their unfavorable surface and electronic states. Herein, a main-group Sn-based SAC with penta-coordinated and asymmetric first-shell ligands is reported as an efficient and robust ORR catalyst. The introduction of the vertical oxygen atom breaks the symmetric charge balance, modulating the binding strength to oxygen intermediates and decreasing the energy barrier for the ORR process. As expected, the prepared Sn SAC exhibits outstanding ORR activity with a high half-wave potential of 0.912 V (vs RHE) and an excellent mass activity of 13.1 A mgSn-1 at 0.850 V (vs RHE), which surpasses that of commercial Pt/C and most reported transition-metal-based SACs. Additionally, the reported Sn SAC shows excellent ORR stability due to the strong interaction between Sn sites and the carbon support with oxygen atom as the bridge. The excellent ORR performance of Sn SAC was also proven by both liquid- and solid-state zinc-air battery (ZAB) measurements, indicating its great potential in practical applications.

An improvement on the electrocatalytic performance of ZIF-67 by in situ self-growing CNTs on surface

Efficient and robust oxygen reduction reaction (ORR) catalysts are essential for the development of high-performance anion-exchange membrane fuel cells (AEMFC). To enhance the electrochemical performance of metal–organic frameworks of cobalt-based zeolite imidazolium skeleton (ZIF-67), this study reported a novel ZIF-67-4@CNT by in situ growing carbon nanotubes (CNTs) on the surface of ZIF-67 via a mild two-step pyrolysis/oxidation treatment. The electrochemical results showed that the as-prepared ZIF-67-4@CNT after CTAB modification exhibited excellent catalytic activity with good stability, with Eonset, E1/2, and Ilimit, respectively were 0.98 V (versus RHE), 0.87 V (versus RHE) and 6.04 mA cm−2@1600 rpm, and a current retention rate of about 94.21% after polarized at 0.80 V for 10 000 s, which were all superior to that of the commercial 20 wt% Pt/C. The excellent ORR catalytic performance was mainly attributed to the large amount of the in situ growing CNTs on the surface, encapsulated with a wide range of valence states of metallic cobalt.

Inter-site structural heterogeneity induction of single atom Fe catalysts for robust oxygen reduction

Metal-nitrogen-carbon catalysts with hierarchically dispersed porosity are deemed as efficient geometry for oxygen reduction reaction (ORR). However, catalytic performance determined by individual and interacting sites originating from structural heterogeneity is particularly elusive and yet remains to be understood. Here, an efficient hierarchically porous Fe single atom catalyst (Fe SAs-HP) is prepared with Fe atoms densely resided at micropores and mesopores. Fe SAs-HP exhibits robust ORR performance with half-wave potential of 0.94 V and turnover frequency of 5.99 e−1s−1site−1 at 0.80 V. Theoretical simulations unravel a structural heterogeneity induced optimization, where mesoporous Fe-N4 acts as real active centers as a result of long-range electron regulation by adjacent microporous sites, facilitating O2 activation and desorption of key intermediate *OH. Multilevel operando characterization results identify active Fe sites undergo a dynamic evolution from basic Fe-N4 to active Fe-N3 under working conditions. Our findings reveal the structural origin of enhanced intrinsic activity for hierarchically porous Fe-N4 sites.

N-Decorated Main-Group MgAl2O4 Spinel: Unlocking Exceptional Oxygen Reduction Activity for Zn-Air Batteries.

The development of economical and efficient oxygen reduction reaction (ORR) catalysts is crucial to accelerate the widespread application rhythm of aqueous rechargeable zinc-air batteries (ZABs). Here, a strategy is reported that the modification of the binding energy for reaction intermediates by the axial N-group converts the inactive spinel MgAl2O4 into the active motif of MgAl2O4-N. It is found that the introduction of N species can effectively optimize the electronic configuration of MgAl2O4, thereby significantly reducing the adsorption strength of *OH and boosting the reaction process. This main-group MgAl2O4-N catalyst exhibits a high ORR activity in a broad pH range from acidic and alkaline environments. The aqueous ZABs assembled with MgAl2O4-N shows a peak power density of 158.5mWcm-2, the long-term cyclability over 2000h and the high stability in the temperature range from -10 to 50°C, outperforming the commercial Pt/C in terms of activity and stability. This work not only serves as a significant candidate for the robust ORR electrocatalysts of aqueous ZABs, but also paves a new route for the effective reutilization of waste Mg alloys.

Integrating sulfur-doped atomically dispersed FeNx sites with small-sized Fe3C nanoparticles for PEMFCs and beyond

Developing highly efficient and robust oxygen reduction reaction (ORR) catalysts with low cost is essential to accelerate their widespread application in proton exchange membrane fuel cells (PEMFCs) and metal–air batteries.

Bimetallic niobium-iron oxynitride as a highly active catalyst towards the oxygen reduction reaction in acidic media

Developing cost-effective acidic oxygen reduction reaction (ORR) catalysts with high performance is of great significance for proton exchange membrane fuel cells (PEMFCs) but very challenging. Transition-metal oxynitrides have high tolerance to harsh acidic media due to their excellent corrosion resistance, but they suffer from low acidic ORR activity. Here we report the discovery of a carbon-supported bimetallic niobium-iron oxynitride as a highly active and robust ORR catalyst in acidic media. This catalyst shows much higher ORR activity than its monometallic niobium oxynitride counterpart and exhibits a record high ORR activity among transition-metal oxynitrides, with an optimal ORR half-wave potential of 0.75 V vs. RHE, approaching those of atomically dispersed metal-N-C materials. It is revealed that the optimal catalyst has two types of Fe species with low oxidation state and two additional oxygen adsorption sites with high reactivity in comparison to its monometallic niobium oxynitride counterpart, therefore resulting in its remarkable ORR activity. Our work provides a new direction to explore efficient acidic ORR catalysts with low costs.

Functionalized nitrogen doping induced manganese oxyhydroxide rooted in manganese sesquioxide rod for robust oxygen reduction electrocatalysis

The rational synthesis of hybrid catalysts with diverse electrocatalytically active components for robust oxygen reduction reaction (ORR) is highly desirable for the development of sustainable metal-air batteries. By using melamine as nitrogen and hydrogen precursors, herein, melamine pyrolysis-induced functionalized nitrogen doping was adopted for the construction of nitrogen doped manganese oxides (N-MnOx Rs), which consists of manganese oxyhydroxide (MnOOH) rooted in manganese sesquioxide (Mn2O3) rod, as a robust ORR electrocatalyst. Systematic studies have found that a suitable mass ratio of melamine to β-MnO2 rods is necessary for the formation of electrocatalytically MnOOH and Mn2O3. The representative N-MnOx Rs exhibits the nano structure consisting of interconnected nonorods, nanowires, and nanoparticles, which not only increases the exposure of more active sites but also enhances microstructure stability. Moreover, the nitrogen doping creates high content of oxygen vacancies, which accelerates electron transmission/transfer of N-MnOx Rs. As a result, the optimal N-MnOx Rs exhibits impressive ORR catalytic performance in a homemade ZAB. The N-MnOx Rs driven ZAB (176.6 mW cm-2; 811 mAh g-1) delivers a high peak power density and large discharging capacitance comparable to Pt/C driven one (178.1 mW cm-2; 800 mAh g-1), displaying a promising application potential. This work provides a functionalized nitrogen doping strategy for rational construction of robust hybrid electrocatalysts for energy conversion.

Anion effect on oxygen reduction reaction activity of nitrogen doped carbon nanotube encapsulated cobalt nanoparticles

In this work, we report the diverse cobalt precursors for the synthesis of nitrogen doped carbon nanotubes encapsulated Co nanoparticles (Co@NCNT) as oxygen reduction reaction (ORR) electrocatalyst to verify the anion effect. The X-ray photoelectron spectroscopy (XPS) test indicates that more pyridinic and pyrrolic N species coordinate with Co atoms for cobalt chloride (CoCl2) due to more defective sites on NCNT etched by chlorine compared to the counterparts of cobalt nitrate (Co(NO3)2), cobalt acetate (Co(Ac)2) and cobalt triacetoacetate (Co(acac)2). With higher content of Co–Npyridinic+pyrrolic structures, Co@NCNT-Cl exhibits a robust ORR performance highlighted by half-wave potential of 880 mV vs. RHE, corresponding to a 4-fold better kinetic current density than commercial Pt/C. The superior catalytic activity toward ORR originates from more Co–Npyridinic+pyrrolic structures efficiently hydrogenated the adsorbed O2 to *OOH intermediate; additionally, its low binding strength with *OOH allows the mobility to metallic Co for splitting to generate O* species. Thus, a relay ORR catalysis is noticed for Co@NCNT-Cl. The assembled rechargeable zinc-air battery (ZAB) reaches a power density of 152 mW cm−2 sustained for 500 h, superior to Pt/C-IrO2. Moreover, the all-solid-state ZAB delivers a maximum power density of 54 mW cm−2 and maintains for 30 h.

Spin state modulation on dual Fe center by adjacent Ni sites enabling the boosted activities and ultra-long stability in Zn-air batteries

Breakthrough in developing cost-effective Fe-based catalysts with superior oxygen reduction reaction (ORR) activities and ultra-long-term stability for application in Zn-air batteries (ZABs) remain a priority but still full of challenges. Herein, the neighboring NiN4 single-metal-atom and Fe2N5 dual-metal-atoms on the N-doped hollow carbon sphere (Fe/Ni-NHCS) were deliberately constructed as the efficient and robust ORR catalyst for ZABs. Both theory calculations and magnetic measurements demonstrate that the introduction of NiN4 provides a significant role on optimizing the electron spin state of Fe2N5 sites and reducing the energy barrier for the adsorption and conversion of the oxygen-containing intermediates, enabling the Fe/Ni-NHCS with excellent ORR performance and ultralow byproduct HO2− yield (0.5%). Impressively, the ZABs driven by Fe/Ni-NHCS exhibit unprecedented long-term rechargeable stability over 1200 h. This work paves a new venue to manipulate the spin state of active sites for simultaneously achieving superior catalytic activities and ultra-long-term stability in energy conversion technologies.

Molecular Engineering of Noble Metal Aerogels Boosting Electrocatalytic Oxygen Reduction

AbstractDeveloping robust oxygen reduction reaction (ORR) electrocatalysts with high activity and durability remains great challenging while noble metal aerogels (NMAs) hold great potential because of their hierarchically porous morphology, excellent activity, and self‐supported characteristic. Herein, a general molecular engineering strategy to synthesize molecule‐noble metal aerogels (M‐NMAs) via 3D assembly of metal nanoparticles (e.g., Pt, Pd, Au, Ag, and PtPd NPs) induced by metalloporphyrin as cross‐linkers is reported. Due to the well synergy of NMAs and porphyrin molecule in creating the facile reaction pathway for ORR catalysis, these M‐NMAs demonstrate boosted ORR activity and durability in different electrolytes. Particularly, the best PtPd‐based M‐NMA delivers 1.47 A mgPt−1 and 2.13 mA cm−2 in mass and specific activities, which are 11.3 and 14.2 times higher than those of the commercial Pt/C catalyst, respectively. Thus, this work not only provides a simple and universal functional engineering approach of NMAs with catalytic molecules, but also opens an avenue of the rational design for superior ORR electrocatalysts.

Space Confinement to Regulate Ultrafine CoPt Nanoalloy for Reliable Oxygen Reduction Reaction Catalyst in PEMFC.

A Co-based zeolitic imidazolate framework (ZIF-67) derived catalyst with ultrafine CoPt nanoalloy particles is designed via a two-step space confinement method, to achieve a robust oxygen reduction reaction (ORR) performance for proton exchange membrane fuel cell (PEMFC). The core-shell structure of ZIF-67 (core) and SiO2 (shell) is carefully adjusted to inhibit the agglomeration of Co nanoparticles. In the subsequent adsorption-annealing process, the in situ formed graphene shell on the surface of Co nanoparticles further protects metal particles from coalescence, leading to the ultrafine CoPt nanoalloy (average diameter is 2.61nm). Benefitting from the high utilization of Pt metal, the mass activity of CoPt nanoalloy catalyst reaches 681.8mA mgPt -1 at 0.9V versus RHE according to the rotating disk electrode test in 0.1m HClO4 solution. The CoPt nanoalloy-based PEMFC provides a high maximum power density of 2.22W cm-2 (H2 /O2 ) and 0.923W cm-2 (H2 /air). Simultaneously, itshows good stability in the long-time dynamic test at low humidity, due to the robust CoPt@graphene core-shell nanostructure. This work provides a viable strategy for designing Pt-based nanoalloy catalysts with ultrafine metal particles and high stability.

Synergetic N-doped carbon with MoPd alloy for robust oxygen reduction reaction

Synergetic N-doped carbon with MoPd alloy for robust oxygen reduction reaction

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.

Robust Oxygen Reduction Electrocatalysis Enabled by Platinum Rooted on Molybdenum Nitride Microrods.

Robust oxygen reduction electrocatalysis is central to renewable fuel cells and metal-air batteries. Herein, Pt nanoparticles (NPs) rooted on porous molybdenum nitride microrods (Pt/Mo2N MRs) are rationally constructed toward the oxygen reduction reaction (ORR). Owing to the desired composition with strong electronic metal-support interactions (EMSIs) and a porous one-dimensional structure supporting ultrafine NPs, the developed Pt/Mo2N MRs possess much higher ORR mass and specific activities than commercial Pt/C. In situ Raman and density functional theory calculations reveal that the EMSI weakens the adsorption of intermediates over Pt/Mo2N MRs via an associative mechanism. Moreover, the porous Mo2N support stabilizes these high activities. Impressively, a homemade zinc-air battery driven by Pt/Mo2N MRs delivers excellent performance including a peak power density of 167 mW cm-2 and a high rate capability that ranged from 5 to 50 mA cm-2. This work highlights the role of EMSI in promoting robust ORR electrocatalysis, thus providing a promising approach for efficient and robust cathode materials for advanced metal-air batteries.

Deciphering the Role of Substitution in Transition-Metal Phosphorous Trisulfide (100) Surface: A Highly Efficient and Durable Pt-free ORR Electrocatalyst.

The rational design and development of earth-abundant, cost-effective, environmentally benign, and highly robust oxygen reduction reaction (ORR) electrocatalysts can circumvent the obstacles associated with the large-scale commercialization of fuel cells. Here, using first-principles-based density functional theory (DFT), we have computationally screened the potential and feasibility of transition-metal phosphorous trisulfides (TMPS3 ) (100) surfaces as efficient ORR electrocatalyst in acidic fuel cell application. MnPS3 (100) surface emerges to be the best among TMPS3 surfaces with optimal O2 activation resulting in very low overpotential. The study reveals that ORR occurs on the MnPS3 surface via 4e reduction associative pathway where the kinetically rate-determining step (RDS) is the formation of O*+H2 O with an activation barrier of 0.66 eV. Additionally, high CO tolerance and easy desorption of H2 O make MnPS3 a robust catalyst. Substitution in half of the Mn sites of MnPS3 (100) surface with Co considerably enhances the ORR activity. Mn0.5 Co0.5 PS3 (100) surface exhibits an ultralow overpotential of 0.39 V vs RHE switching ORR pathway from associative to dissociative. Spontaneous dissociation of H2 O2 on Mn0.5 Co0.5 PS3 proves 4e reduction pathway excluding 2e one. Electronic structure analysis reveals that pristine MnPS3 (100) surface is a narrow band gap semiconductor which upon Co substitution transforms into a conducting metallic surface enhancing ORR activity. Besides, Mn0.5 Co0.5 PS3 (100) surface obtains the apex of the volcano plot due to its optimal position of the d-band center which further justifies the improved ORR activity. With Pt-like onset potential, facile H2 O desorption ability, and robust dynamic and thermal stability, this CO tolerant Mn0.5 Co0.5 PS3 catalyst can be a potential alternative to Pt with encouraging practical viability.

Single atomic cobalt electrocatalyst for efficient oxygen reduction reaction

Robust oxygen reduction reaction (ORR) catalysts are essential for energy storage and conversion devices, but their development remains challenging. Herein, we design a single-atom catalyst featuring isolated Co anchored on nitrogen-doped carbon (Co-SAC/NC) via a highly efficient “plasma-bombing” strategy. With a high loading (up to 2.5 ​wt%), the well-dispersed single Co atoms in Co-SAC/NC give it robust ORR performance in an alkaline medium. It also demonstrates excellent battery performance when implemented as the air-cathode catalyst in a zinc-air battery (ZAB). Theoretical calculations reveal that the Co–N4 moiety experiences an “extraction/recovery” structural evolution during the ORR process, and the reaction's rate-determining step is the formation of OOH∗ (reaction intermediate). This work provides a new strategy for designing robust ORR catalysts for high-performance ZABs and other energy-conversion devices.

FePc nanoclusters modified NiCo layered double hydroxides in parallel with Ti3C2 MXene as a highly efficient and durable bifunctional oxygen electrocatalyst for zinc-air batteries

Boosting the bifunctional oxygen activity of layered double hydroxides (LDHs) is a frontier but challenging issue for metal-air batteries. Herein, an iron phthalocyanine (FePc) nanocluster modified NiCo LDH in parallel with Ti3C2 (FePc-NiCo-LDH/Ti3C2) two-dimensional multilayer structured bifunctional oxygen catalyst is engineered by growing NiCo-LDH in parallel with Ti3C2 followed with adsorbing FePc via electrostatic interaction approach. Thanks to the abundant retained Fe-Nx active sites, the FePc-NiCo-LDH/Ti3C2 catalyzes the oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 80 mV positive compared to Pt/C. Besides, the current density only drops 5% after 33,000 s of chronoamperometry test, confirming the robust ORR stability. On the other hand, there are electronic interactions formed between FePc nanocluster and NiCo-LDH/Ti3C2 which boosts the OER activity as demonstrated by the negatively shifted potential of 89 mV at 10 mA cm−2 versus RuO2. The overall ORR/OER activity makes FePc-NiCo-LDH/Ti3C2 ranking top among the most active analogous samples. The Zn-air battery (ZAB) assembled with FePc-NiCo-LDH/Ti3C2 as air electrode exhibits a peak power density of 148 mW cm−2 and can be charge-discharged continuously for 80 h. This direct engineering ORR/OER active center strategy offers a unique facile direction for the fabrication of oxygen electrode catalysts for renewable clean energy devices.

Construction of abundant Co3O4/Co(OH)2 heterointerfaces as air electrocatalyst for flexible all-solid-state zinc-air batteries

The heterostructure has its distinctive superiority for electrocatalysis ascribed to strain effect at heterointerfaces triggered by the lattice mismatch. Therefore, tailored electronic configurations of active centers, faster electronic conductivity associated with abundant active sites are induced as advantages to boost the relative electrocatalytic activity. Herein, we report the fabrication of Co3O4/Co(OH)2 hetero quantum dots as bifunctional electrocatalyst in rechargeable zinc air batteries (ZABs). To obtain catalytic current density of 10 mA cm−2 in oxygen evolution reaction (OER), Co3O4/Co(OH)2-HQDs only demands 300 mV overpotential, lower than Co(OH)2-QDs and Co3O4-QDs. The boosted OER performance is ascribed to the abundance of oxygen defects in Co3O4/Co(OH)2-HQDs resulting in more Co atoms in low coordination environment favorable for electro-adsorption of OH− species. In addition, a robust oxygen reduction reaction (ORR) catalytic activity is recorded for Co3O4/Co(OH)2-HQDs with half-wave potential of 844 mV vs. RHE. Because of the strong electronic interplay, appreciable stability is attained for Co3O4/Co(OH)2-HQDs. The manufactured aqueous rechargeable ZAB shows 1.4 times higher battery performance than Pt/C-IrO2 noble metal system. Furthermore, the all-solid-state ZAB also performs a considerable power density (57.4 mW cm−2) and its performance is well preserved during the flexibility test demonstrating the potential application in wearable devices.