Superior Oxygen Reduction Performance Research Articles

Sublimation Transformation Synthesis of Dual-Atom Fe Catalysts for Efficient Oxygen Reduction Reaction.

Dual-atom catalysts (DACs) have garnered significant interest due to their remarkable catalytic reactivity. However, achieving atomically precise control in the fabrication of DACs remains a major challenge. Herein, we developed a straightforward and direct sublimation transformation synthesis strategy for dual-atom Fe catalysts (Fe2/NC) by utilizing in situ generated Fe2Cl6(g) dimers from FeCl3(s). The structure of Fe2/NC was investigated by aberration-corrected transmission electron microscopy and X-ray absorption fine structure (XAFS) spectroscopy. As-obtained Fe2/NC, with a Fe-Fe distance of 0.3 nm inherited from Fe2Cl6, displayed superior oxygen reduction performance with a half-wave potential of 0.90 V (vs. RHE), surpassing commercial Pt/C catalysts, Fe single-atom catalyst (Fe1/NC), and its counterpart with a common and shorter Fe-Fe distance of ~0.25 nm (Fe2/NC-S). Density functional theory (DFT) calculations and microkinetic analysis revealed the extended Fe-Fe distance in Fe2/NC is crucial for the O2 adsorption on catalytic sites and facilitating the subsequent protonation process, thereby boosting catalytic performance. This work not only introduces a new approach for fabricating atomically precise DACs, but also offers a deeper understanding of the intermetallic distance effect on dual-site catalysis.

Sublimation Transformation Synthesis of Dual‐Atom Fe Catalysts for Efficient Oxygen Reduction Reaction

Dual‐atom catalysts (DACs) have garnered significant interest due to their remarkable catalytic reactivity. However, achieving atomically precise control in the fabrication of DACs remains a major challenge. Herein, we developed a straightforward and direct sublimation transformation synthesis strategy for dual‐atom Fe catalysts (Fe2/NC) by utilizing in situ generated Fe2Cl6(g) dimers from FeCl3(s). The structure of Fe2/NC was investigated by aberration‐corrected transmission electron microscopy and X‐ray absorption fine structure (XAFS) spectroscopy. As‐obtained Fe2/NC, with a Fe–Fe distance of 0.3 nm inherited from Fe2Cl6, displayed superior oxygen reduction performance with a half‐wave potential of 0.90 V (vs. RHE), surpassing commercial Pt/C catalysts, Fe single‐atom catalyst (Fe1/NC), and its counterpart with a common and shorter Fe–Fe distance of ~0.25 nm (Fe2/NC‐S). Density functional theory (DFT) calculations and microkinetic analysis revealed the extended Fe–Fe distance in Fe2/NC is crucial for the O2 adsorption on catalytic sites and facilitating the subsequent protonation process, thereby boosting catalytic performance. This work not only introduces a new approach for fabricating atomically precise DACs, but also offers a deeper understanding of the intermetallic distance effect on dual‐site catalysis.

2D arrays of hollow carbon nanoboxes: outward contraction-induced hollowing mechanism in Fe-N-C catalysts.

Maximizing the utilization efficiency of monatomic Fe sites in Fe-N-C catalysts poses a significant challenge for their commercial applications. Herein, a structural and electronic dual-modulation is achieved on a Fe-N-C catalyst to substantially enhance its catalytic performance. We develop a facile multi-component ice-templating co-assembly (MIC) strategy to construct two-dimensional (2D) arrays of monatomic Fe-anchored hollow carbon nanoboxes (Fe-HCBA) via a novel dual-outward interfacial contraction hollowing mechanism. The pore engineering not only enlarges the physical surface area and pore volume but also doubles the electrochemically active specific surface area. Additionally, the unique 2D carbon array structure reduces interfacial resistance and promotes electron/mass transfer. Consequently, the Fe-HCBA catalysts exhibit superior oxygen reduction performance with a six-fold enhancement in both mass activity (1.84 A cm-2) and turnover frequency (0.048 e- site-1 s-1), compared to microporous Fe-N-C catalysts. Moreover, the incorporation of phosphorus further enhances the total electrocatalytic performance by three times by regulating the electron structure of Fe-N4 sites. Benefitting from these outstanding characteristics, the optimal 2D P/Fe-HCBA catalyst exhibits great applicability in rechargeable liquid- and solid-state zinc-air batteries with peak power densities of 186 and 44.5 mW cm-2, respectively.

Interface engineering of polyaniline-functionalized porous Pd metallene for alkaline oxygen reduction reaction

Engineering the interface between two-dimensional materials and polymers is of great importance to improve their catalytic performance for oxygen reduction reaction (ORR). Hence, polyaniline (PANI)-functionalized porous Pd metallene (Pd@PANI metallene) is prepared via a two-step strategy. Due to the ultrathin porous nanosheets and interfacial structure, the Pd@PANI metallene possesses sufficient active sites and optimized electronic structure, which exhibits superior oxygen reduction performance in alkaline electrolyte. The mass and specific activities for Pd@PANI metallene are measured to 1.79 A mgPd−1 and 2.96 mA cm−2, which are 11.9 and 9.30 times those of Pt/C (0.15 A mgPd−1 and 0.32 mA cm−2), respectively. Additionally, the ORR performance and morphology of Pd@PANI metallene can be maintained after long-term stability testing, making it an excellent ORR catalyst. This work provides an effective interface engineering strategy to construct efficient two-dimensional ORR electrocatalysts to improve the performance.

Boosting Oxygen Reduction Activity of Manganese Oxide Through Strain Effect Caused By Ion Insertion

AbstractTransition‐metal oxides with a strain effect have attracted immense interest as cathode materials for fuel cells. However, owing to the introduction of heterostructures, substrates, or a large number of defects during the synthesis of strain‐bearing catalysts, not only is the structure–activity relationship complicated but also their performance is mediocre. In this study, a mode of strain introduction is reported. Transition‐metal ions with different electronegativities are intercalated into the cryptomelane‐type manganese oxide octahedral molecular sieves (OMS‐2) structure with K ions as the template, resulting in the octahedral structural distortion of MnO6 and producing strains of different degrees. Experimental studies reveal that Ni‐OMS‐2 with a high compressive strain (4.12%) exhibits superior oxygen reduction performance with a half‐wave potential (0.825 V vs RHE) greater than those of other reported manganese‐based oxides. This result is related to the increase in the covalence of MnO6 octahedral configuration and shifting down of the eg band center caused by the higher compression strain. This research avoids the introduction of new chemical bonds in the main structure, weakens the effect of eg electron filling number, and emphasizes the pure strain effect. This concept can be extended to other transition‐metal‐oxide catalysts.

Facile synthesis of nitrogen, phosphorus and sulfur tri-doped carbon nanosheets as efficient oxygen electrocatalyst for rechargeable Zn-air batteries

The rechargeable Zn-air battery plays vital roles in renewable energy storage and conversion, but the scarcity of highly efficient air cathode electrocatalysts severely hampers its commercial popularizing. Heteroatoms-doped carbon materials have attracted many interests, because the resulted dopants synergistic effect always brings about extraordinary electrocatalytic activities. Herein, a simple pyrolysis strategy of thiourea, phytic acid and graphene oxide was developed to prepare N, P and S tri-doped carbon nanosheets, featuring sheet structure with specific surface area of 479 m2 g−1 and sufficient dopants (3.78 at% N, 7.97 at% P, and 1.36 at% S). Benefiting from the dominated graphitic and pyridinic N moieties, as well as abundant P-C and S-C functional groups, all of which are desired active species for oxygen electrochemistry, the synthesized tri-doped carbon nanosheets exhibit superior oxygen reduction performance and enhanced oxygen evolution activity in alkaline electrolyte. As the air cathode electrocatalysts for rechargeable Zn-air batteries, the decreased charge–discharge potential gaps and robust cycling stability are observed, even superior to those of noble-metal Pt/C benchmarks. The interconnected porous architecture with high surface area, multiple active species, and significant electric conductivity capability are considered as main factors for the enhanced electrochemical activities of this tri-doped carbon material.

Unraveling the synergistic effect of defects and interfacial electronic structure modulation of pealike CoFe@Fe3N to achieve superior oxygen reduction performance

Engineering of defect and interface are two effective strategies to regulate the electronic structure and electrocatalytic activities. However, integrated the synergistic effect of carbon/oxygen defects and interfacial effects into spinel derivatives to dramatically improve the electrocatalytic property has not been studied up till now. Herein, a CoFe@Fe3N hybrid embedded into N-doped carbon nanotube has been prepared by heat-treatment of CoFe2O4 using a simple chemical vapor deposition method. Impressively, the as-prepared CoFe@Fe3N-CNT catalyst manifests a prominent stability and catalytic performance towards the oxygen reduction reaction (ORR), as demonstrated by an ultrahigh half-wave potential (E1/2) of 0.936 V, which is the best ORR spinel-based catalysts. Furthermore, it was assembled into a rechargeable ZAB, which showed a high-power density of 173.6 mW cm−2 and an open circuit voltage of 1.534 V. The enhanced electrochemical performances are primarily due to the synergistic effect of carbon-oxygen double defects and interfacial electronic structure modulation.

Iron carbide/nitrogen-doped carbon core-shell nanostrctures: Solution-free synthesis and superior oxygen reduction performance

Core-shell Fe3C@NC nanostructures constructed by Fe3C core encapsulated in N-doped carbon nanotubes (FFCN-MP4000) is designed and readily prepared via a facile and economical solid-state chemical route. By controlling the proportion of C and N in the starting materials, the composition of FeNC core-shell nanotubes was optimized, then provided more possible active sites as electrocatalysts, exhibited superior oxygen reduction performance. Onset potential (Eonset) of 0.96 V versus reversible hydrogen electrode (RHE) and half-wave potential (E1/2) of 0.83 V vs RHE was obtained in 0.1 M KOH, which are comparable to those of the commercial Pt/C catalyst (Eonset = 0.98 V, E1/2 = 0.84 V vs RHE). Notably, the limited current density for FFCN-MP4000 can reach to 6.6 mA cm−2, and it efficiently catalyzes 4-electron reduction of oxygen (n = 3.98) with a hydrogen peroxide yield of below 2.2%. In addition, the methanol tolerance and durability are even superior to commercial Pt/C catalyst. This work provides a facile and economical strategy for the feasible design of oxygen reduction reaction (ORR) electrocatalyst with high activity and low cost in alternative commercial Pt/C electrocatalyst.

Enhancement mechanism of sulfur dopants on the catalytic activity of N and P co-doped three-dimensional hierarchically porous carbon as a metal-free oxygen reduction electrocatalyst

A sulfur, nitrogen and phosphorus ternary-doped cattle-bone-derived hierarchically porous carbon metal-free electrocatalyst was synthesized, exhibiting superior oxygen reduction performance compared to Pt/C.

Out-of-plane FeII–N4 moiety modified Fe–N co-doped porous carbons as high-performance electrocatalysts for the oxygen reduction reaction

A Fe–N–C electrocatalyst with active FeII–N4 sites was synthesized exhibiting superior oxygen reduction performance in both alkaline and acidic electrolytes.

Nitrogen and phosphorus co-doped hierarchically porous carbons derived from cattle bones as efficient metal-free electrocatalysts for the oxygen reduction reaction

Nitrogen and phosphorus co-doped cattle-bone-derived hierarchically porous carbon metal-free electrocatalysts were synthesized exhibiting superior oxygen reduction performance than Pt/C.

N-doped crumpled graphene: bottom-up synthesis and its superior oxygen reduction performance

The crumpled graphene (CrG) was fabricated by applying defluorination of polyvinylidenefluoride (PVDF) on highly curved surface of CaC2 particle through bottom-up synthetic strategy. The limited reaction depth between PVDF and CaC2 leads to the formation of CrG with thin layer (3−6 layer graphene) and reasonable high specific surface area (~324.8 m2 g−1). CrG with N incorporation (N-CrG) was applied as electrode material for reducing oxygen (i.e., oxygen reduction reaction, ORR) in alkaline, showing close onset potential to that of Pt/C and better mass-diffusion behavior. Surprisingly, with increased mass loading of catalysts, N-CrG exhibits steady current increase while Pt/C shows clear current plateau. Meanwhile, the N-CrG sample reveals high cycling stability and tolerance to contaminant, demonstrating its high potential for practical applications. Additionally, the bottom-up synthetic pathway to CrG via polymer dehalogenation on solid alkaline may find more applications which require controlled morphology and thickness of deposited thin graphitic carbon layers.

Supramolecular polymers-derived nonmetal N, S-codoped carbon nanosheets for efficient oxygen reduction reaction

Hydrogen-bonded supramolecular polymer-derived nonmetal N and S codoped carbon nanosheets show superior oxygen reduction performance.

A new C=C embedded porphyrin sheet with superior oxygen reduction performance

C2 is a well-known pseudo-oxygen unit with an electron affinity of 3.4 eV. We show that it can exhibit metal-ion like behavior when embedded in a porphyrin sheet and form a metal-free two-dimensional material with superior oxygen reduction performance. Here, the positively charged C=C units are highly active for oxygen reduction reaction (ORR) via dissociation pathways with a small energy barrier of 0.09 eV, much smaller than that of other non-platinum group metal (non-PGM) ORR catalysts. Using a microkinetics-based model, we calculated the partial current density to be 3.0 mA/cm2 at 0.65 V vs. a standard hydrogen electrode (SHE), which is comparable to that of the state-of-the-art Pt/C catalyst. We further confirm that the C=C embedded porphyrin sheet is dynamically and thermally stable with a quasi-direct band gap of 1.14 eV. The superior catalytic performance and geometric stability make the metal-free C=C porphyrin sheet ideal for fuel cell applications.