In Situ Precise Tuning of Bimetallic Electronic Effect for Boosting Oxygen Reduction Catalysis

Sharply expanding single-atomically dispersed Fe-N active sites through bidirectional coordination for oxygen reduction

For Fe-NC systems, high-density Fe-N sites are the basis for high-efficiency oxygen reduction reaction (ORR), and P doping can further lower the reaction energy barrier, especially in the form of metal-P bonding. However, limited to the irregular agglomeration of metal atoms at high temperatures, Fe-P bonds and high-density Fe-N cannot be guaranteed simultaneously. Here, to escape the random and violent agglomeration of Fe species during high-temperature carbonization, triphenylphosphine and 2-methylimidazole with a strong metal coordination capability are introduced together to confine Fe growth. With the aid of such bidirectional coordination, the high-density Fe-N site with Fe-P bonds is realized by in situ phosphorylation of Fe in an Fe-NC system (Fe-P-NC) at high temperatures. Impressively, the content of single-atomically dispersed Fe sites for Fe-P-NC dramatically increases from 2.8% to 65.3% compared with that of pure Fe-NC, greatly improving the ORR activity in acidic and alkaline electrolytes. The theoretical calculation results show that the generated Fe2P can simultaneously facilitate the adsorption of intermediates to Fe-N4 sites and the electron transfer, thereby reducing the reaction energy barrier and obtaining superior ORR activity.

Identification of Intersite Distance Effects in Au-Ag Single-Atom Alloy Catalysts Using Single Nanoparticle Collision Electrochemistry

Regulating the atomic density of single-atom alloys (SAAs) promotes the potential to significantly enhance the electrocatalytic activity. However, conventional methods for study on the electrocatalytic performance of SAAs versus the intersite distance demand exhaustive experiments and characterization. Herein, we present a combinatorial synthesis and analysis method to investigate the intersite distance effect of SAA electrocatalysts. We employ single-nanoparticle collision electrochemistry to realize in situ electrodeposition of a precisely tunable Au atomic density onto individual parent Ag nanoparticles, followed by instantaneous electrocatalytic measurement of the newborn Au-Ag SAAs. In this work, the utility of our method is confirmed by the identification of intersite distance effects of Au-Ag SAAs toward the oxygen reduction reaction. When the site distance between two neighboring Au atoms is 1.9 nm, Au-Ag SAAs exhibit optimal activity. This work provides a simple and efficient method for screening other SAA electrocatalysts with ideal intersite distance at the single-nanoparticle level.

Metal nitrides for seawater electrolysis

Electrocatalytic high-throughput seawater electrolysis for hydrogen production is a promising green energy technology that offers possibilities for environmental and energy sustainability. However, large-scale application is limited by the complex composition of seawater, high concentration of Cl- leading to competing reaction, and severe corrosion of electrode materials. In recent years, extensive research has been conducted to address these challenges. Metal nitrides (MNs) with excellent chemical stability and catalytic properties have emerged as ideal electrocatalyst candidates. This review presents the electrode reactions and basic parameters of the seawater splitting process, and summarizes the types and selection principles of conductive substrates with critical analysis of the design principles for seawater electrocatalysts. The focus is on discussing the properties, synthesis, and design strategies of MN-based electrocatalysts. Finally, we provide an outlook for the future development of MNs in the high-throughput seawater electrolysis field and highlight key issues that require further research and optimization.

Temperature-driven evolution of ceria-zirconia-supported AuPd and AuRu bimetallic catalysts under different atmospheres: insights from IL-STEM studies

The evolution of the structure and composition of the system of particles in two Ce0.62Zr0.38O2-supported bimetallic catalysts based on Au and a 4d metal (Ru or Pd) under high temperature conditions and different reducing and oxidizing environments has been followed by means of Identical Location Scanning Transmission Electron Microscopy (IL-STEM). As an alternative to in situ microscopy, this technique offers valuable insights into the structural modifications occurring in chemical environments with the characteristics of a macro-scale reactor. By tracking exactly the same areas on a large number of metallic entities, it has been possible to reveal the influence of particle size and the nature of the redox environment on the temperature-driven mobilization of the different metals involved. Thus, oxidizing environments evidenced a much higher capacity to mobilize the three metals, preferentially Au. Moreover, the typical storage conditions (under air) of catalysts during the prolonged exposure time has been proved to induce significant modifications in these bimetallic systems, even at room temperature. Regardless of the type of redox environment, bimetallic systems showed better thermal resistance, which demonstrates a beneficial effect of the second metal. In summary, IL-STEM is an invaluable and complementary methodology for characterizing heterogeneous catalysts under realistic reaction conditions and is within the reach of most laboratories.

Precise synthetic control of exclusive ligand effect boosts oxygen reduction catalysis

Ligand effect, induced by charge transfer between catalytic surface and substrate in core/shell structure, was widely proved to benefit Pt-catalyzed oxygen reduction reaction by tuning the position of d-band center of Pt theoretically. However, ligand effect is always convoluted by strain effect in real core/shell nanostructure; therefore, it remains experimentally unknown whether and how much the ligand effect solely contributes electrocatalytic activity improvements. Herein, we report precise synthesis of a kind of Pd3Ru1/Pt core/shell nanoplates with exclusive ligand effect for oxygen reduction reaction. Layer-by-layer growth of Pt overlayers onto Pd3Ru1 nanoplates can guarantee no lattice mismatch between core and shell because the well-designed Pd3Ru1 has the same lattice parameters as Pt. Electron transfer, due to the exclusive ligand effect, from Pd3Ru1 to Pt leads to a downshift of d-band center of Pt. The optimal Pd3Ru1/Pt1-2L nanoplates achieve excellent activity and stability for oxygen reduction reaction in alkaline/acid electrolyte.

Modulating Charges of Dual Sites in Multivariate Metal-Organic Frameworks for Boosting Selective Aerobic Epoxidation of Alkenes

Selective aerobic epoxidation of alkenes without any additives is of great industrial importance but still challenging because the competitive side reactions including C═C bond cleavage and isomerization are difficult to avoid. Here, we show fabricating Cu(I) single sites in pristine multivariate metal-organic frameworks (known as CuCo-MOF-74) via partial reduction of Cu(II) to Cu(I) ions during solvothermal reaction. Impressively, CuCo-MOF-74 is characteristic with single Cu(I), Cu(II), and Co(II) sites, and they exhibit the substantially enhanced selectivity of styrene oxide up to 87.6% using air as an oxidant at almost complete conversion of styrene, ∼25.8% selectivity increased over Co-MOF-74, as well as good catalytic stability. Contrast experiments and theoretical calculation indicate that Cu(I) sites contribute to the substantially enhanced selectivity of epoxides catalyzed by Co(II) sites. The adsorption of two O₂ molecules on dual Co(II) and Cu(I) sites is favorable, and the projected density of state of the Co-3d orbital is closer to the Fermi level by modulating with Cu(I) sites for promoting the activation of O₂ compared with dual-site Cu(II) and Co(II) and Co(II) and Co(II), thus contributing to the epoxidation of the C═C bond. When other kinds of alkenes are used as substrates, the excellent selectivity of various epoxides is also achieved over CuCo-MOF-74. We also prove the universality of fabricating Cu(I) sites in other MOF-74 with various divalent metal nodes.

Regulating Reversible Oxygen Electrocatalysis by Built-in Electric Field of Heterojunction Electrocatalyst with Modified d-Band

Developing bifunctional catalysts for oxygen electrochemical reactions is essential for high-performance electrochemical energy devices. Here, a Mott-Schottky heterojunction composed of porous cobalt-nitrogen-carbon (Co-N-C) polyhedra containing abundant metal-phosphides for reversible oxygen electrocatalysis is reported. As a demonstration, this catalyst shows excellent activity in the oxygen electrocatalysis and thus delivers outstanding performance in rechargeable zinc-air batteries (ZABs). The built-in electric field in the Mott-Schottky heterojunction can promote electron transfer in oxygen electrocatalysis. More importantly, an appropriate d-band center of the heterojunction catalyst also endows oxygen intermediates with a balanced adsorption/desorption capability, thus enhancing oxygen electrocatalysis and consequently improving the performance of ZABs. The work demonstrates an important design principle for preparing efficient multifunctional catalysts in energy conversion technologies.

Alloying as a Strategy to Boost the Stability of Copper Nanocatalysts during the Electrochemical CO2 Reduction Reaction

Copper nanocatalysts are among the most promising candidates to drive the electrochemical CO₂ reduction reaction (CO₂RR). However, the stability of such catalysts during operation is sub-optimal, and improving this aspect of catalyst behavior remains a challenge. Here, we synthesize well-defined and tunable CuGa nanoparticles (NPs) and demonstrate that alloying Cu with Ga considerably improves the stability of the nanocatalysts. In particular, we discover that CuGa NPs containing 17 at. % Ga preserve most of their CO₂RR activity for at least 20 h while Cu NPs of the same size reconstruct and lose their CO₂RR activity within 2 h. Various characterization techniques, including X-ray photoelectron spectroscopy and operando X-ray absorption spectroscopy, suggest that the addition of Ga suppresses Cu oxidation at open-circuit potential (ocp) and induces significant electronic interactions between Ga and Cu. Thus, we explain the observed stabilization of the Cu by Ga as a result of the higher oxophilicity and lower electronegativity of Ga, which reduce the propensity of Cu to oxidize at ocp and enhance the bond strength in the alloyed nanocatalysts. In addition to addressing one of the major challenges in CO₂RR, this study proposes a strategy to generate NPs that are stable under a reducing reaction environment.

Adsorption Energy in Oxygen Electrocatalysis

Adsorption energy (AE) of reactive intermediate is currently the most important descriptor for electrochemical reactions (e.g., water electrolysis, hydrogen fuel cell, electrochemical nitrogen fixation, electrochemical carbon dioxide reduction, etc.), which can bridge the gap between catalyst's structure and activity. Tracing the history and evolution of AE can help to understand electrocatalysis and design optimal electrocatalysts. Focusing on oxygen electrocatalysis, this review aims to provide a comprehensive introduction on how AE is selected as the activity descriptor, the intrinsic and empirical relationships related to AE, how AE links the structure and electrocatalytic performance, the approaches to obtain AE, the strategies to improve catalytic activity by modulating AE, the extrinsic influences on AE from the environment, and the methods in circumventing linear scaling relations of AE. An outlook is provided at the end with emphasis on possible future investigation related to the obstacles existing between adsorption energy and electrocatalytic performance.

Pt-Sn alloy shells with tunable composition and structure on Au nanoparticles for boosting ethanol oxidation

Combining the core-shell structure with the optimization of surface composition and structure in the shell is a fantastic strategy to enhance the electrocatalytic performances. Here, we synthesized trimetallic Au@Pt_xSn_y core-shell nanoparticles (NPs) with tunable composition and structure of Pt-Sn alloyed shells. Impressively, the Au@PtSn core-shell NPs with hexagonal PtSn alloyed shells exhibited the highest mass activity and specific activity toward ethanol oxidation reaction (EOR) in alkaline electrolyte, which are 13.0 and 12.7 times higher than those of the commercial Pt/C. In addition, the Au@PtSn core-shell NPs displayed the best stability compared to commercial Pt/C, with only 44.8% loss vs. 86.8% loss in mass activity after 1,000 s due to the stronger anti-poisoning ability for reaction intermediates. The theory calculations reveal that the introduction of Au core and alloying Pt with Sn both endow Pt with an appropriate d-band center, and thus effectively boosting the EOR activity.

Tuning 4f-Center Electron Structure by Schottky Defects for Catalyzing Li Diffusion to Achieve Long-Term Dendrite-Free Lithium Metal Battery

Lithium metal is considered as the most prospective electrode for next-generation energy storage systems due to high capacity and the lowest potential. However, uncontrollable spatial growth of lithium dendrites and the crack of solid electrolyte interphase still hinder its application. Herein, Schottky defects are motivated to tune the 4f-center electronic structures of catalysts to provide active sites to accelerate Li transport kinetics. As experimentally and theoretically confirmed, the electronic density is redistributed and affected by the Schottky defects, offering numerous active catalytic centers with stronger ion diffusion capability to guide the horizontal lithium deposition against dendrite growth. Consequently, the Li electrode with artificial electronic-modulation layer remarkably decreases the barriers of desolvation, nucleation, and diffusion, extends the dendrite-free plating lifespan up to 1200 h, and improves reversible Coulombic efficiency. With a simultaneous catalytic effect on the conversions of sulfur species at the cathodic side, the integrated Li-S full battery exhibits superior rate performance of 653 mA h g^-1 at 5 C, high long-life capacity retention of 81.4% at 3 C, and a high energy density of 2264 W h kg^-1 based on sulfur in a pouch cell, showing the promising potential toward high-safety and long-cycling lithium metal batteries.

Alkynyl ligands-induced growth of ultrathin nanowires arrays

Ligands are almost essential in the synthesis of nanostructures. In this work, we introduce the alkynyl ligands into the synthesis of ultrathin gold (Au) nanowires arrays. The strong binding affinity of the alkynyl ligands enables one-dimensional (1D) growth via the active surface growth mechanism. The scope of the ligand generality was systematically investigated, and the alkynyl ligand-induced nanowire growth processes were compared and contrasted with those involving thiolated ligands. While strong ligands are usually difficult to dissociate from the nanostructure surface and therefore problematic for post-synthetic processing, the alkynyl ligands are readily dissociable, making the alkynyl ligand-stabilized Au nanowires potentially more modifiable and applicable. As a demonstration, direct palladium (Pd) deposition on the Au nanowires was successfully carried out without any ligand exchange process.

A ternary PdNiMo alloy as a bifunctional nanocatalyst for the oxygen reduction reaction and hydrogen evolution reaction

Mo0.2Pd3Ni/NC shows superior electrochemical performances for both ORR and HER due to the charge redistribution among Ni, Pd, and Mo, tuning the electronic structure of Pd.