Avoiding Sabatier's Limitation on Spatially Correlated Pt-Mn Atomic Pair Sites for Oxygen Electroreduction

Boosting oxygen reduction performances in Pd-based metallenes by co-confining interstitial H and p-block single atoms

The efficiency of the oxygen reduction reaction (ORR) is limited by the scaling relationship in the conventional oxygen associative pathway. To break such limitations, we present an approach to effectively activate the oxygen dissociative pathway through co-confining single p-block (In, Sn, Pb) atoms and interstitial H atoms within Pd metallenes, leading to good ORR performance. PdPbHx metallenes exhibit a high mass activity of 1.36 A mg-1 at 0.95 V (vs. RHE), which is 46.9 times higher than that of the benchmark Pt/C. The minimal performance decay after 50,000 potential cycles confirms a good stability. In situ vibrational spectroscopy investigations and theoretical calculations highlight that interstitial H atoms facilitate the direct dissociation of O2 while single Pb atoms enhance O2 adsorption strength. The electroactive PdPbHx metallenes is attributed to the up-shifted Pd-4d orbitals induced by H and Pb atoms. This research supplies critical inspiration for developing highly efficient ORR electrocatalysts.

Restricting Two-Electron Oxygen Reduction via Secondary Coordinated Sulfur Enabling Ultralong-Lifespan Zn-Air Batteries

The direct four-electron oxygen reduction reaction (4e- ORR) critically governs efficiency and lifespan in metal-air batteries and fuel cells, yet selectively suppressing competitive 2e- and stepwise 2e-pathways that generate corrosive hydrogen peroxide remains a major challenge. Herein, we demonstrate the strategic incorporation of secondary coordinated sulfur atoms into transition metal-N-C electrocatalysts to effectively promote direct 4e- ORR and simultaneously suppress undesirable 2e- pathways. Density functional theory (DFT) calculations and operando spectroscopy reveal that enhanced adsorption of key intermediate *OOH facilitates efficient O─O bond cleavage, underpinning altered catalytic selectivity. Importantly, this approach is universally applicable to various carbon-based catalysts, including Co─N@C, Ni─N@C, Mn─N@C, and N@C. Specifically, a sulfur-mediated Co─N/Co@C catalyst, comprising Co─N4 sites and Co nanoparticles, dramatically lowers the 2e- O2-to-H2O2 rate constant to merely 0.05-fold of its original value at 0.78 V. Consequently, Zn-air batteries using Co─N/Co@C-S as cathode exhibits an outstanding peak power density of 220 mW cm-2, remarkable lifespan over 2500 h, and outstanding rate performance from 5 to 50 mA cm-2. This work paves a generalizable route for designing highly active and selective electrocatalysts suitable for advanced long-life energy storage devices.

High-yield synthesis of FeNC as support of PtFe nanoparticles for the oxygen reduction reaction by a green ball milling method

Enhancing catalytic activity, durability and reducing costs are major challenges in commercialization of proton exchange membrane fuel cells (PEMFCs). Non-precious metal catalysts face durability challenges when applied to PEMFCs, while platinum (Pt)-based catalysts are hampered by their high costs and weak interactions with carbon supports, limiting their application in PEMFCs. Combining Pt-based catalysts with iron-nitrogen-carbon (FeNC) supports can improve the oxygen reduction reaction performance. However, traditional preparation methods for FeNC supports, such as liquid-phase and hydrothermal synthesis, are cumbersome and have low yield. Here, we introduce a simple ball-milling method to synthesize FeNC with high yield that achieves a high-surface-area and uniform dispersion of Fe atoms. The FeNC support anchors PtFe nanoparticles at FeNxsites. This enhances support-alloy interactions and suppresses particle aggregation. The obtained catalyst denoted as PtFe/B-FeNC exhibits an exceptional mass activity of 2.57 A mgPt-1at 0.9 V, representing a 12.2-fold increase compared to the commercial Pt/C. There is only 30 mV degradation for the catalyst after 120 k cycles, indicating outstanding stability. This research paves the way for the green synthesis of PtFe/B-FeNC with high yield, facilitating the development of commercial materials for other electrochemical devices.

The Spin-Selective Channels in Fully-Exposed PtFe Clusters Enable Fast Cathodic Kinetics of Li-O2 Battery

In Li-O2 batteries (LOBs), the electron transfer between triplet O2 and singlet Li2O2 possesses a spin-dependent character but is still neglected, while the spin-conserved electron transfer without losing phase information should guarantee fast kinetics and reduced energy barriers. Here, we provide a paradigm of spin-selective catalysis for LOB that the ferromagnetic quantum spin exchange interactions between Pt and Fe atoms in fully-exposed PtFe clusters filter directional e-spins for spin-conserved electron transfer at Fe-Fe sites. The kinetics of O2/Li2O2 redox reaction is markedly accelerated as predicted by theoretical calculations, showing dramatically decreased relaxation time of the rate determining step for more than one order of magnitude, compared with the Fe clusters without spin-selective behavior. In consequence, the assembled LOB provides ultrahigh energy conversion efficiency of 89.6 % at 100 mA g-1 under a discharge-charge overpotential of only 0.32 V. This work provides new insights into the spin-dependent mechanisms of O2/Li2O2 redox reaction, and the strategy of constructing spin catalysts at atomic level.

Achieving a Thermodynamic Self-Regulation Dynamic Adsorption Mechanism for Ammonia Synthesis through Selective Orbital Coupling

With the continuous pursuing on the improvement of catalytic activity, a catalyst performed exceeding catalytic volcano plots is desired, while it is impeded by the adsorption-energy scaling relations of reaction intermediates. Numerous efforts have been focused on optimizing the initial and final intermediates to circumvent the scaling relations for an improved performance. For a step forward, simultaneously optimizing all intermediates is essential to explore the theoretical maximum of catalytic activity. Herein, we proposed a dynamic adsorption mechanism (DAM) to independently regulate the adsorption configurations of all intermediates of electrochemical nitrogen reduction reaction (NRR). To demonstrate the DAM, a multi-site NbNi3 intermetallic is developed, which enables suitable adsorption energies of different intermediates via modulating orbital coupling mechanisms. As a result, NbNi3 achieves an ultra-low limiting potential of NRR of -0.11 V vs. reversible hydrogen electrode (RHE). Strikingly, the theoretical result is confirmed by a proof-of-concept experiment, wherein the nanoporous NbNi3 electrode exhibits a remarkable NH3 yield rate of 25.89 μg h-1 cm-2 with the Faradaic efficiency of 33.15 % at -0.25 V vs. RHE. Overall, this work brings out a new strategy to avoid the scaling relations, and opens up a promising avenue toward high-efficiency NRR catalysts.

Chlorine Axial Coordination Activated Lanthanum Single Atoms for Efficient Oxygen Electroreduction with Maximum Utilization

Currently, there are still obstacles to rationally designing the ligand fields to activate rare-earth (RE) elements with satisfactory intrinsic electrocatalytic reactivity. Herein, axial coordination strategies and nanostructure design are applied for the construction of La single atoms (La-Cl SAs/NHPC) with satisfactory oxygen reduction reaction (ORR) activity. The nontrivial LaN4Cl2 motifs configuration and the hierarchical porous carbon substrate that facilitates maximized metal atom utilization ensure high half-wave potential (0.91 V) and significant robustness in alkaline media. The aqueous and flexible Zinc-air battery (ZAB) integrating La-Cl SAs/NHPC as the cathode catalyst exhibits a maximum power density of 260.7 and 68.5 mW cm-2, representing one of the most impressive RE-based ORR electrocatalysts to date. Theoretical calculations have demonstrated that the Cl coordination evidently modulate the electronic structures of La sites, which promoted electron transfer efficiency by d-p orbital couplings. With enhanced electroactivity of La sites, the adsorptions of key intermediates are optimized to alleviate the energy barriers of the potential-determining step. Importantly, this preparation strategy is also successfully applied to other REs. This work provides perspectives for near-range electronic structure modulation of RE-SAs based on a nonplanar coordination micro-environment for efficient electrocatalysis.

Engineering the Local Atomic Environments of Te-Modulated Fe Single-Atom Catalysts for High-Efficiency O2 Reduction

Atomically dispersed metal-nitrogen-carbon materials (AD-MNCs) are considered the most promising non-precious catalysts for the oxygen reduction reaction (ORR), but it remains a major challenge for simultaneously achieving high intrinsic activity, fast mass transport, and effective utilization of the active sites within a single catalyst. Here, an AD-MNCs consisting of defect-rich Fe-N3 sites dispersed with axially coordinated Te atoms on porous carbon frameworks (Fe1Te1-900) is designed. The local charge densities and energy band structures of the neighboring Fe and Te atoms in FeN3-Te are rearranged to facilitate the catalytic conversion of the O-intermediates. Meanwhile, the negative shift of the d-band center in FeN3-Te reduces the energy barrier limit for effective desorption of the final OH* intermediate. In the electrochemical evaluation, Fe1Te1-900 presents a more positive onset potential and half-wave potentials of 1.03 and 0.89 V versus the reversible hydrogen electrode, respectively. Furthermore, the liquid zinc-air batteries assembled with Fe1Te1-900 exhibited excellent performances compared to commercial Pt/C. This work opens up new ideas for the development of high-performance ORR electrocatalysts for applications in various energy conversion and storage technologies.

Breaking the Mutual-Constraint of Bifunctional Oxygen Electrocatalysis via Direct O─O Coupling on High-Valence Ir Single-Atom on MnOx

Insufficient bifunctional activity of electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the major obstruction to the application of rechargeable metal-air batteries. The primary reason is the mutual constraint of ORR and OER mechanism, involving the same oxygen-containing intermediates and demonstrating the scaling limitations of the adsorption energies. Herein, it is reported a high-valence Ir single atom anchored on manganese oxide (IrSA-MnOx) bifunctional catalyst showing independent pathways for ORR and OER, i.e., associated 4e- pathway on high-valence Ir site for ORR and a novel chemical-activated concerted mechanism for OER, where a distinct spontaneous chemical activation process triggers direct O─O coupling. The IrSA-MnOx therefore delivers outstanding bifunctional activities with remarkably low potential difference (0.635 V) between OER potential at 10 mA cm-2 and ORR half-wave potential in alkaline solution. This work breaks the scaling limitations and provides a new avenue to design efficient and multifunctional electrocatalysts.

Consolidating the Oxygen Reduction with Sub-Polarized Graphitic Fe-N4 Atomic Sites for an Efficient Flexible Zinc-Air Battery

The effectuation of the Zn-air battery (ZAB) is appealing for active and durable catalysts to kinetically drive the sluggish cathodic oxygen reduction reaction (ORR). Atomic metal-Nx-C sites are widely witnessed with Pt-like activity, but their demetalations still severely restrict the durability in ORR. Here we have profiled an ordered hierarchical porous carbon supported Fe-N4 single-atom (FeNC) catalyst by a template derivation method for efficient ORR and flexible ZAB studies. The FeNC structure is observed with a sub-polarized graphitic Fe-N4 coordination with a shortened Fe-N bond for potentially consolidating the ORR, together with the hierarchical porous matrix for kinetical mass transfer. Resultantly, the optimized FeNC catalyst showcases Pt-beyond alkaline ORR activity (E1/2 = 0.95 V) with long-term durability for 100 h, delivering the flexible ZAB device with high power density (251 mW cm-2) and durable cycle life (80 h). This research underscores the criterion in rationalizing active and robust ORR catalysts through metal-nitrogen bond modulation.

Visualization of the Distance-Dependent Synergistic Interaction in Heterogeneous Dual-Site Catalysis

Understanding the characteristics of interfacial hydroxyl (OH) at the solid/liquid electrochemical interface is crucial for deciphering synergistic catalysis. However, it remains challenging to elucidate the influences of spatial distance between interfacial OH and neighboring reactants on reaction kinetics at the atomic level. Herein, we visualize the distance-dependent synergistic interaction in heterogeneous dual-site catalysis by using ex-situ infrared nanospectroscopy and in situ infrared spectroscopy techniques. These spectroscopic techniques achieve direct identification of the spatial distribution of synergistic species and reveal that OH facilitates the reactant deprotonation process depending on site distances in dual-site catalysts. Via modulating Ir-Co pair distances, we find that the dynamic equilibrium between generation and consumption of OH accounts for high-efficiency synergism at the optimized distance of 7.9 Å. At farther or shorter distances, spatial inaccessibility and resistance of OH with intermediates lead to OH accumulation, thereby diminishing the synergistic effect. Hence, a volcano-shaped curve has been established between the spatial distance and mass activity using formic acid oxidation as the probe reaction. This notion could also be extended to oxophilic metals, like Ir-Ru pairs, where volcano curves and dynamic equilibrium further evidence the universal significance of spatial distances.

Sabatier phenomenon in chemoselective gas-sensing reactions induced by Ag cluster coordination

The Sabatier principle in heterogeneous catalysis provides guidance for designing optimal catalysts with the highest activity. We report a new Sabatier phenomenon induced by nanoclusters on different atomic scales in gas-sensitive reactions. We prepared a series of Ag nanocluster catalysts with coordination structures ranging from Ag0 to Ag13 through a surface coordination strategy. When used as catalysts for gas-sensitive reactions, a volcano-type relationship between the coordination number of Ag nanoclusters and gas-sensitive activity emerges, with a summit at a moderate coordination of Ag5. Mechanistic studies show that the efficient adsorption of activated *C2H6O on electron-rich Ag5 clusters is a key factor for the Sabatier phenomenon (adsorption energy from -0.322 eV to -0.663 eV), which leads to highly selective sensing. We found that the catalyst electron-rich surface layer induced by Ag5 clusters serves as a descriptor to explain the structure-activity relationship. Furthermore, due to the well-defined geometric and electronic structures in the Ag5 clusters, the optimized catalyst achieves both maximum activity and selectivity in chemoselective sensing reactions. This study reveals the Sabatier principle and provides insightful guidance for the rational design of more efficient and practical nanocluster catalysts for heterogeneous catalysis.

Fe-Co heteronuclear atom pairs as catalytic sites for efficient oxygen electroreduction

Single-site Fe-N-C catalysts are the most promising Pt-group catalyst alternatives for the oxygen reduction reaction, but their application is impeded by their relatively low activity and unsatisfactory stability as well as production costs. Here, cobalt atoms are introduced into an Fe-N-C catalyst to enhance its catalytic activity by utilizing the synergistic effect between Fe and Co atoms. Meanwhile, phenanthroline is employed as the ligand, which favours stable pyridinic N-coordinated Fe-Co sites. The obtained catalysts exhibit excellent ORR performance with a half-wave potential of 0.892 V and good stability under alkaline conditions. In addition, the excellent ORR activity and durability of FeCo-N-C enabled the constructed zinc-air battery to exhibit a high power density of 247.93 mW cm-2 and a high capacity of 768.59 mA h gZn-1. Moreover, the AEMFC based on FeCo-N-C also achieved a high open circuit voltage (0.95 V) and rated power density (444.7 mW cm-2), surpassing those of many currently reported transition metal-based cathodes. This work emphasizes the feasibility of this non-precious metal catalyst preparation strategy and its practical applicability in fuel cells and metal-air batteries.