High-efficiency Oxygen Reduction Reaction Research Articles

MOF-derived three-dimensional porous dodecahedral structured bimetallic Mn/Co-C-N composite for high-performance durable oxygen reduction reaction electrocatalysts.

Investigating high-efficiency oxygen reduction reaction (ORR) catalysts is one of the most effective methods for addressing the sluggish kinetics at the fuel cell cathode. Bimetallic three-dimensional porous materials have garnered significant attention due to their diverse structures, large specific surface area and synergistic catalytic effects. Herein, we synthesized a bimetallic three-dimensional porous dodecahedral structure, Mn/Co-C-N, derived from MOF using a straightforward approach. Experimental reults confirm that the strategic incorporation of Mn enhances the electrocatalytic activity for ORR. Meanwhile, the synergistic effects of Mn and Co, as well as the advantages of the dodecahedral structure for expediting electron transfer, all contribute to the exceptional ORR performance. Arc testing in an alkaline electrolyte reveals that the initial potential (Eonset) and the half-wave potential (E1/2) are 0.89 V and 0.80 V, closely approximating those of commercial Pt/C (20 wt%). Following 10 000 stability test cycles, the half-wave potential exhibits a mere 8 mV change, confirming its remarkable stability.

Carbothermal Reduction-Assisted Synthesis of a Carbon-Supported Highly Dispersed PtSn Nanoalloy for the Oxygen Reduction Reaction.

Exploring high-performance and low-platinum-based electrocatalysts to accelerate the oxygen reduction reaction (ORR) at the air cathode of zinc-air batteries remains crucial. Herein, by combining electroless deposition and carbothermal reduction, a nitrogen-doped carbon-supported highly dispersed PtSn alloy nanocatalyst (PtSn/NC) was prepared for a high-efficiency ORR process. Electrochemical measurements show that PtSn/NC exhibits excellent electrocatalytic ORR activity with a half-wave potential of 0.850 V versus reversible hydrogen electrode (RHE), which is higher than that of commercial Pt/C (0.815 V). The PtSn/NC-based (20 μgPt cm-2) rechargeable Zn-air battery exhibited astonishing performance with a maximum power density of up to 150.1 mW cm-2, as well as excellent rate performance and charge/discharge stability. Physical characterization reveals that carbothermal reduction could compel the transformation of Sn oxide into metallic Sn, which then alloys with the deposited Pt atoms to form the PtSn nanoalloy, in which electrons are transferred from Sn atoms to neighboring Pt atoms, thereby improving the ability of Pt-based active sites to catalyze the ORR process in PtSn/NC by optimizing the unoccupied d-band of Pt atoms. This work provides a reliable and innovative route for the rational design of highly dispersed Pt-based alloy ORR electrocatalysts.

Optimization and regulation of catalytic activity and stability: Pt–Ni diamond-shaped pearl nanochains with core-shell structure as high-efficient oxygen reduction reaction catalysts

The low utilization efficiency and poor stability of carbon-supported Pt nanoparticles (Pt/C) catalyst are two main problems of proton exchange membrane fuel cells (PEMFC), which can improve the catalytic performance by forming alloys and precisely regulating morphology and structures. Here, we introduced a simple and direct method for synthesizing Pt–Ni diamond-shaped pearl nanochains (Pt–Ni DP-NCs) as efficient electrocatalyst for oxygen reduction reaction (ORR). The alloying with Ni could enhance the catalytic activity, but because of leaching out of Ni during the cathodic reaction process, which causes a poor stability. To achieve the optimal point for both high activity and robust stability, a portion of Ni is selectively etched from Pt–Ni DP-NCs precursor in advance. During the process of de-alloying, Pt atoms with high catalytic activity are exposed to the surface of the nanochain after atomic rearrangement, thus obtaining Pt–Ni etched diamond-shaped pearl nanochains (Pt–Ni EDP-NCs) with 1D core-shell structure, which consisted of Pt–Ni as the core and Pt as the shell. Benefitting from the unique 1D core-shell structure and composition, Pt–Ni EDP-NCs-9 (etched for 9 h) exhibits high catalytic activity and robust stability for ORR. The mass activity of the sample Pt–Ni EDP-NCs-9 is 0.43 A/mgPt, which is 1.65 times higher than that of the Pt–Ni DP-NCs (0.26 A/mgPt), and 2.05 times higher than that of commercial Pt/C (0.21 A/mgPt). In addition, the 1D core-shell structure enables Pt–Ni EDP-NCs to be highly stable, which only lost by 8.6% of mass activity after 10,000 long cycles, whereas Pt–Ni DP-NCs suffers from a 34% loss under the same conditions. This work provides a strategic approach for designing efficient Pt-based catalysts that simultaneously modulate activity and stability.

Dual-atom Fe(II,III)N2(µ2-N)2Cu(I,II)N moieties anchored on porous N-doped carbon driving high-efficiency oxygen reduction reaction

Atomically distributed iron electrocatalyst is valid for oxygen reduction reaction (ORR). However, accurate regulation of the structure improving its intrinsic activity is a challenge. Herein, a dual-atom catalyst FeCu-NC with atomically distributed Fe and Cu co-anchored on porous N-doped carbon is obtained. The FeN4 and CuN3 couple sites bridged by two nitrogen atoms, exist as Fe(II,III)N2(µ2-N)2Cu(I,II)N moieties with the metal distance of ∼2.5 Å in the structure of FeCu-NC. The synergistic effect of Fe and Cu dual-atom reducing the dissociation energy of *OOH intermediate, allows an optimized 4e- ORR reaction pathway. The FeCu-NC exhibits high-efficiency ORR activity with the half-wave potential (E1/2) of 0.889 V (vs RHE) and outstanding stability without obvious decay for the E1/2 after 10,000 cycles. The FeCu-NC based Zn-air battery presents large specific capacity of 795 mAh g−1 and energy density of 998 Wh kg−1 as well as high charge-discharge cycling stability superior to the Pt/C.

Application of vertically ordered polyaniline nanofibers in enhancing the ORR activity of Pt catalysis

Pt-based nanocatalysts supported on carbon materials have exhibited remarkable catalytic activity in the oxygen reduction reaction (ORR). However, these catalysts still encounter challenges such as low utilization efficiency, weak binding strength with substrate and proneness to detachment from it. Consequently, we explore the potential application of electron-rich polymer as carrier in high efficiency ORR catalysts, the uniformly distributed Pt-PANI catalyst is successfully synthesized by taking advantage of ion-exchange property of polyaniline (PANI). As an emerging catalyst for ORR, Pt-PANI shows excellent ORR performance in acidic solution, the vertically aligned PANI nanoarrays accelerate the ion diffusion in electrolyte and promote the charge transfer at the interface, improving the catalytic activity of low-loading Pt-based catalyst. In short, this work provides a novel alternative beyond conventional carbonaceous materials for the selection of carriers for Pt-based catalyst.

Tuning the Pyridine Units in Vinylene-Linked Covalent Organic Frameworks Boosting 2e- Oxygen Reduction Reaction.

The N-doped carbon materials are supposed to be the efficient oxygen reduction reaction (ORR) catalysts with the undefined N-doped carbon ring groups. It is essential to well define the role of the nitrogen atoms of these carbon structures in active behavior. Even though, the covalent organic frameworks (COFs) with precise structures are well developed, but unable to exclude the polar linkages influence. This study presents a series of pyridine-containing COFs linked via nonpolar carbon-carbon double bonds (C = C). Their catalytic activity and selectivity for 2e- ORR are successfully modulated by locating the embedded pyridine nitrogen in the backbones through the linking modes of pyridine moieties within the frameworks. Such phenomena can be attributed to their different binding abilities toward O2, leading to the different binding strength of the intermediate OH* to the catalytic sites, also verified by the theoretical calculation. This work provides us a new insight to design high-efficiency ORR catalysts through the exact location of pyridine nitrogen.

Boosting the oxygen reduction reaction activity of dual-atom catalysts on N-doped graphene by regulating the N coordination environment.

Development of low-cost and high-efficiency oxygen reduction reaction (ORR) catalysts is of significance for fuel cells and metal-air batteries. Here, by regulating the N environment, a series of dual-atom embedded N5-coordinated graphene catalysts, namely M1M2N5 (M1, M2 = Fe, Co, and Ni), were constructed and systematically investigated by DFT calculations. The results reveal that all M1M2N5 configurations are structurally and thermodynamically stable. The strong adsorption of *OH hinders the proceeding of ORR on the surface of M1M2N5, but M1M2N5(OH2) complexes are formed to improve their catalytic activity. In particular, FeNiN5(OH2) and CoNiN5(OH2) with the overpotentials of 0.33 and 0.41 V, respectively, possess superior ORR catalytic activity. This superiority should be attributed to the reduced occupation of d-orbitals of Fe and Co atoms in the Fermi level and the apparent shift of dyz and dz2 orbitals of Ni atoms towards the Fermi level after adsorbing *OH, thus regulating the active sites and exhibiting appropriate adsorption strength for reaction intermediates. This work provides significant insight into the ORR mechanism and theoretical guidance for the discovery and design of low-cost and high-efficiency graphene-based dual-atom ORR catalysts.

A twisted carbonaceous nanotube as the air-electrode for flexible Zn-Air batteries.

Exploring electrocatalysts with high-efficiency oxygen reduction reaction (ORR) is significant for practical applications of fuel cells and metal-air batteries. In this work, a twisted core@shell material has been prepared with helical polypyrrole nanotubes (HPPys) as the core and coordination polymers (CPs) as the shell. After the pyrolysis process, a dense twisted carbon layer was formed by the reaction of CP and HPPy at its interface under Ar. The derived twisted carbonaceous nanotube exhibits good performance in both electrocatalytic ORR and OER. When used as the air-electrode in a flexible Zn-air battery, the battery shows good performance and stability.

A lignin–derived N-doped carbon-supported iron-based nanocomposite as high-efficiency oxygen reduction reaction electrocatalyst

Fuel cells are a promising renewable energy technology that depend heavily on noble metal Pt-based catalysts, particularly for the oxygen reduction reaction (ORR). The discovery of new, efficient non-precious metal ORR catalysts is critical for the continued development of cost-effective, high-performance fuel cells. The synthesized carbon material showed excellent electrocatalytic activity for the ORR, with half-wave potential (E1/2) and limiting current density (JL) of 0.88 V and 5.10 mA·cm−2 in alkaline electrolyte, respectively. The material has a Tafel slope of (65 mV dec−1), which is close to commercial Pt/C catalysts (60 mV dec−1). Moreover, the prepared materials exhibited excellent performance when assembled as cathodes for zinc-air batteries. The power density reached 110.02 mW cm−2 and the theoretical specific capacity was 801.21 mAh g−1, which was higher than that of the Pt/C catalyst (751.19 mAh g−1). In this study, with the assistance of Mg5(CO3)4(OH)2·4H2O, we introduce an innovative approach to synthesize advanced carbon materials, achieving precise control over the material's structure and properties. This research bridges a crucial gap in material science, with potential applications in renewable energy technologies, particularly in enhancing catalysts for fuel cells.

Concave Structural Carbon Co-Doped with Iron Atom Pairs and Nitrogen as Ultra-High Performance Catalyst Toward Oxygen Reduction.

It is crucial to rationally design and synthesize atomic-scale transition metal-doped carbon catalysts with high electrocatalytic activity to achieve a high-efficient oxygen reduction reaction (ORR). Herein, an electrocatalyst comprised of Fe-Fe dual atom pairs and N-doped concave carbon are reported (N-CC@Fe DA) that achieves ultrahigh electrocatalytic ORR activity. The catalyst is prepared by a gaseous doping approach, with zeolitic imidazolate framework-8 (ZIF-8) as the carbon framework precursor and cyclopentadienyliron dicarbonyl dimer as the Fe-Fe atom pair precursor. The catalyst exhibits high cathodic ORR catalytic performance in an alkaline Zn/air battery and proton exchange membrane fuel cell (PEMFC), yielding peak power densities of 241 mW cm-2 and 724mWcm-2, respectively, compared to 127 mW cm-2 and 1.20Wcm-2 with conventional Pt/C catalysts as cathodes. The presence of Fe atom pairs coordinate with N atoms is revealed by X-ray photoelectron spectroscopy(XPS) and X-ray absorption spectroscopy (XAS) analysis, and Density Functional Theory (DFT) calculation results show that the Fe-Fe pair structure is beneficial for adsorbing oxygen molecules, activating the O─O bond, and desorbing OH* intermediates formed during oxygen reduction, resulting in a more efficient oxygen reaction. The findings may provide a new pathway for preparing ultra-high-performance doped carbon catalysts with Fe-Fe atom pair structures.

ZIF‐derived Low‐Cu‐loaded Carbon Catalysts for Oxygen Reduction Reaction

AbstractCu−N−C catalysts with nitrogen‐coordinated copper supported on carbon exhibits good catalytic performance in oxygen reduction reaction (ORR) and is considered as an excellent substitute for Pt catalyst. Achieving high electrocatalytic activity with low amount of copper is critical for improving the performance and reducing the cost of fuel cells. Here, we propose a Cu−NC‐8 catalyst, using zeolitic‐imidazolate‐framework (ZIF), which is rich in N‐coordination, as the precursor. High ‐emperature pyrolysis of the ZIF‐8 provides metal anchored sites in the carbon skeleton, which promotes the construction of Cu−N active centers by the introduced Cu. The N‐coordination also adjust the electron density of the C atoms to promote the adsorption of O2 on the catalyst, which is beneficial to the ORR activity of 4e− pathway. The 2.5 % Cu−NC‐8 electrocatalyst shows high efficiency ORR activity (Eonset=1.0 V and E1/2=0.82 V) and good stability.

Coexisting Fe single atoms and nanoparticles on hierarchically porous carbon for high-efficiency oxygen reduction reaction and Zn-air batteries

Fe single-atom catalysts still suffer from unsatisfactory intrinsic activity and durability for oxygen reduction reaction (ORR). Herein, the coexisting Fe single atoms and nanoparticles on hierarchically porous carbon (denoted as Fe-FeN-C) are prepared via a Zn5(OH)6(CO3)2-assisted pyrolysis strategy. Theoretical calculation reveals that the Fe nanoparticles can optimize the electronic structures and d-band center of Fe active center, hence reducing the reaction energy barrier for enhancing intrinsic activity. The Zn5(OH)6(CO3)2 self-sacrificial template not only can promote the formation of Fe single atoms, but also contributes to the construction of microporous/mesoporous/macroporous structures. Therefore, the obtained Fe-FeN-C exhibits impressive ORR activity with a half-wave potential of 0.921 V, which far exceeds Pt/C. With Fe-FeN-C as the cathode catalyst, the assembled Zn-air batteries delivered a maximum power density of 206 mW cm−2 and a long-cycle life over 400 h.

Regulating Relative Nitrogen Locations of Diazine Functionalized Covalent Organic Frameworks for Overall H2 O2 Photosynthesis.

Nitrogen-heterocycle-based covalent organic frameworks (COFs) are considered promising candidates for the overall photosynthesis of hydrogen peroxide (H2 O2 ). However, the effects of the relative nitrogen locations remain obscured and photocatalytic performances of COFs need to be further improved. Herein, a collection of COFs functionalized by various diazines including pyridazine, pyrimidine, and pyrazine have been judiciously designed and synthesized for photogeneration of H2 O2 without sacrificial agents. Compared with pyrimidine and pyrazine, pyridazine embedded in TpDz tends to stabilize endoperoxide intermediate species, leading toward the more efficient direct 2e- oxygen reduction reaction (ORR) pathway. Benefiting from the effective electron-hole separation, low charge transfer resistance, and high-efficiency ORR pathway, an excellent production rate of 7327 μmol g-1 h-1 and a solar-to-chemical conversion (SCC) value of 0.62 % has been achieved by TpDz, which ranks one of the best COF-based photocatalysts. This work might shed fresh light on the rational design of functional COFs targeting photocatalysts in H2 O2 production.

N and S dual-coordinated Fe single-atoms in hierarchically porous hollow nanocarbon for efficient oxygen reduction

Fe-, and N-co-doped carbon (FeNC) electrocatalysts are promising alternatives to Pt-based catalysts for oxygen reduction reaction (ORR); however, simultaneously enhancing their intrinsic activity and exposure of Fe active sites remains challenging. Herein, we report S-modified Fe single-atom catalysts (SACs) anchored on N,S-co-doped hollow porous nanocarbon (Fe/NS-C) for ORR. The unique hollow structure and large surface area of the SACs are favorable for mass/electron transport and exposure of Fe single-atom active sites. The as-prepared Fe/NS-C electrocatalysts display a high-efficiency ORR activity with a half-wave potential of 0.893 V versus the reversible hydrogen electrode and exceed that of the benchmark commercial Pt/C catalyst as well as most reported transition-metal based SACs. Impressively, the Fe/NS-C-based Al-air battery (AAB) displays a high open circuit voltage of 1.48 V, a maximum power density of 140.16 mW cm−2, and satisfactory durability, outperforming commercial Pt/C-based AAB. Furthermore, Fe/NS-C exhibits considerable potential as a cathode catalyst for application in direct methanol fuel cells. Experimental and theoretical calculation results reveal that the excellent ORR performance of Fe/NS-C can be contributed to the highly active FeN3S sites and the unique hollow structure. This work provides new insights into the rational design and synthesis high-performance ORR electrocatalysts for energy conversion and storage devices. of employing ZIF-8 as precursors.

Edge-rich Co/N-doped 3D nanosheet stacked carbon as an efficient dual-function electrocatalyst for rechargeable Zn-air battery

The development of high-efficiency oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) dual-function electrocatalysts based on transition metal and nitrogen co-doped carbon material is vital to the development of rechargeable Zn-air battery. In this work, dual-function oxygen electrocatalysts of 2D graphene-like (NC) and 3D nanosheet stacked carbon (CNC) derived from Zn-based zeolite-like metalorganic frameworks were prepared from the complex of imidazole-4, 5-dicarboxylic acid (4,5-Imdc) with only zinc nitrate (4,5-Imdc-Zn) or zinc and cobalt nitrate (4,5-Imdc-ZnCo). Morphology and catalytic activity of NC and CNC were studied in detail. After high temperature calcination, 4,5-Imdc-Zn developed into a 2D graphene-like structure (NC). While derivative of 4,5-Imdc-ZnCo appears a 3D nanosheet stacked (CNC) structure induced by a “pinning effect” of the existing Co ions. With increased defects, edges and Co-Nx active sites compared to NC, CNC shows more excellent electrocatalytic activity.

Pyrolysis-Free Synthesis of Bimetal Phthalocyanine Covalent Organic Polymers/Ordered Mesoporous Carbon Nanocomposites for an Efficient Oxygen Reduction Reaction

The development of non-noble metal–nitrogen ring complex (M–N–C) catalysts with high activity and stability for the oxygen reduction reaction (ORR) is of great significance. However, M–N–C catalysts are generally prepared from precursors under high-temperature pyrolysis, which leads to complex product structures and makes it difficult to identify the catalytic active center. Herein, we have successfully structured a novel bimetal phthalocyanine covalent organic polymer/ordered mesoporous carbon (CoFe-COP/OMC) electrocatalyst through a pyrolysis-free approach. Due to the well-defined active sites (Fe/CoN4), ordered COP structure, and highly conductive carrier materials, the CoFe-COP/OMC nanocomposite exhibits remarkable ORR electrocatalytic activity with a half-wave potential and initial potential of 0.908 and 0.932 V (vs reversible hydrogen electrode (RHE)), respectively, a limiting current density of 5.35 mA cm–2, and a nearly four-electron reduction pathway. In addition, the acquired hybrid catalysts show excellent methanol resistance and electrochemical stability compared with Pt/C. The outstanding performance confirms that the CoFe-COP/OMC nanocomposite is a promising high-efficiency ORR catalyst for metal–air batteries and fuel cells.

Engineering the electronic structure of isolated manganese sites to improve the oxygen reduction, Zn-air battery and fuel cell performances

Single-atom manganese catalysts possess high stability in the oxygen reduction reaction (ORR) due to their lower Fenton reaction activity. Here, we employ N- and S-co-coordination strategy to modulate the microstructural Mn sites towards high-efficiency ORR. The fabricated Mn-N/S-C catalyst with isolated Mn-N2S2 sites demonstrates a positive half-wave potential of 0.91 V for the ORR. The fabricated zinc–air battery with Mn-N/S-C as the cathode affords a maximal power density of 193 mW cm−2 and superior output stability. Moreover, the maximal power density is increased by 1.53 times compared with S-free Mn-N-C catalyst in anion exchange membrane fuel cells (AEMFCs). Both experimental characterizations and theoretical simulations unveil that the main active sites in the Mn-N/S-C should be Mn-N2S2 moiety embedded into the graphene framework (Mn-N2S2G). Further computational results demonstrate that the S atom doping and asymmetry of structure lead to higher ORR activities of ortho-Mn-N2S2G than Mn-N4G, Mn-N3SG, para-Mn-N2S2G and Mn-NS3G.

Carbon-coated Fe3C derived from MIL-100 growth on covalent triazine framework in situ as an efficient ORR catalysts

Fe-based N-doped carbon materials have become the most potential electrocatalysts to replace noble metal catalysts in oxygen reduction reaction (ORR) due to their wide availability, affordability, and high catalytic activity. In this study, novel Fe-based Fe3C nanoparticles encapsulated by N-doped mesopores carbon were prepared via a cost-effective method using MIL-100(Fe) growth on CTF as the precursor. Benefit from the compositional and structural synergistic effect of metal and substrate, the highly dispersed core–shell Fe/Fe3C@C catalyst shows excellent ORR activity and stability with an onset potential of 1.016 V and a half-wave potential of 0.831 V, which is comparable with commercial Pt/C. Meanwhile, the interfacial electron transfer between Fe3C nanoparticles and neighboring Fe-N species, as well as the porous carbon architecture, contribute to the excellent ORR performance. The CTF-derived synthetic enhances ORR activity strategy inspires new perspectives to develop Fe-based composites as high-efficiency ORR electrocatalysts.

NaNO3 assisted gelatin-derived multi-level porous carbon aerogel loaded Fe single-atom for high efficient oxygen reduction reaction

In thrall to the low productivity and expensive price of the precious metal catalysts (PMC), it is imminent to develop high-efficient non-noble metal single-atom catalysts (SACs) to replace PMC. However, thermally induced aggregation into nanoparticles and micropores-dominated structures are commonly encountered issues in loading SACs on carbonaceous supports, leading to low exposure ratio of active sites and inadequate mass transference. Herein, we fabricated a series of gelatin-derived carbon-aerogels (GDCAx) to prevent the aggregation of Fe atom and form the hierarchically porous nanonetwork, and thus the Fe SACs (Fe-N-GDCAx) with abundant and hierarchical pores are obtained after pyrolysis. The Fe-N-GDCAx has plentiful accessible Fe-Nx active sites and mass transfer pathways, benefiting to ORR procedure. The optimal sample Fe-N-GDCA0.8 without other gas assisted during annealing (only in argon atmosphere) exhibits exceedingly excellent half-wave potential (E1/2) of 0.93 V (vs. RHE) in 0.1 M KOH. Aqueous zinc-air battery assembled with Fe-N-GDCA0.8 presents ultrahigh specific capacitance of 803.4 mAh gZn−1 (close to 824 mAh gZn−1 theoretical value) and long-term stability. Meanwhile, quasi-solid zinc-air battery has high peak density and specific capacitance of 82.6 mW cm−2 and 713.2 mAh gZn−1 respectively.

Realizing high-efficient oxygen reduction reaction in alkaline seawater by tailoring defect-rich hierarchical heterogeneous assemblies

The development of efficient and stable oxygen reduction reaction (ORR) electrocatalysts in seawater electrolyte is the key to realizing marine resource utilization and expanding metal-air battery applications. Herein, defect-rich Fe-doped Co nanoparticles encapsulated by N-doped hierarchical carbon (D-FeCo@NHC) are rationally designed and synthesized. It is worth mentioning that the Fe doping helps to promote the generation of metal defect and adjust the electronic structure of D-FeCo@NHC. Density functional theory (DFT) demonstrate that the metal defect and carbon defect jointly optimize the d-band center of D-FeCo@NHC. As a result, in alkaline seawater electrolyte, D-FeCo@NHC display a half-wave potential of 0.874 V, and the assembled liquid Zn-air battery exhibit a high peak power density (173 mW cm−2) and ultra-long cycling stability (over 800 h). This work highlights the defect engineering in the construction of seawater-based oxygen reduction electrocatalysts, which provide a significant and promising approach for seawater-based metal-air cathode materials.