Dynamic evolution processes in electrocatalysis: structure evolution, characterization and regulation

Linkages Chemistry of Covalent Organic Frameworks in Photocatalysis and Electrocatalysis

Covalent organic frameworks (COFs) have emerged as promising candidates for electrocatalysis and photocatalysis applications due to their structurally ordered architectures and tunable physicochemical properties. In COFs, organic building blocks are linked via covalent bonds, and the structural and electronic characteristics of COFs are critically governed by their linkage chemistry. These linkages influence essential material attributes including surface area, crystallinity, hydrophobicity, chemical stability, and the optoelectronic behavior (e.g., photoelectron separation efficiency, electron conductivity, and reductive activity), which collectively determine catalytic performance in energy conversion systems. A systematic understanding of linkage engineering in COFs not only advances synthetic methodologies but also provides innovative solutions to global energy and environmental challenges, thereby accelerating the development of sustainable technologies for clean energy production and environmental remediation.

Harnessing Multimetallic Effects via Metal-Phenolic Networks: Feasible On-Surface Assembly and Direct Use as Electrocatalysts

Multimetallic electrodes are gaining significant attention due to their ability to offer diverse electronic configurations and local lattice distortions, optimizing interactions with reactants and intermediates. Metal-phenolic networks (MPNs) present a promising solution by incorporating a wide range of metals and ligands to enhance specific electrochemical reactions. Despite their potential, on-substrate synthesis and direct application of MPNs in electrocatalysis have been limited. This study introduces an elegant, feasible strategy for on-substrate synthesis of MPNs and direct application as the oxygen evolution reaction (OER) catalyst without post-treatment and systematically evaluates the metal ion effect leveraging a multimetallic doping strategy. Notably, the trimetallic complex performs unambiguously better than the bimetallic and monometallic counterparts. TA-CoNiFe@NF demonstrated superior OER performance, with an impressive overpotential of 215 mV at 10 mA·cm-2, a Tafel slope of 37.3 mV·dec-1, and excellent stability over 100 h. The computational results illustrate the effect of metal ion doping on the OER mechanism. We demonstrate that phenolic ligands in MPNs offer unique benefits compared to MOFs, alloys, or oxide hybrids, enabling facile on-surface coordination and versatile metal incorporation. This effective, facile approach to multimetallic tuning paves the way for high-performance electrocatalyst designs and synthesis.

Synthesis of helical carbon nanotubes wrapped around Ni2P1-xOx nanoparticle-incorporated carbon nanoribbons as an efficient electrocatalyst for the hydrogen evolution reaction

Helical CNTs wrapped around Ni2P1-xOx nanoparticle-incorporated carbon nanoribbons were prepared by nickel-catalysis and phosphatization. The obtained highly conductive nanocomposite with an active Ni-O-P structure and appropriate Gibbs free energy for adsorbing protons was applied as an advanced electrocatalyst for the HER and delivered comparable electrocatalytic performance to commercial Pt/C in acidic solution.

Theoretical study of ammonia synthesis catalysed by trimetallic clusters with or without a sumanene support

DFT calculations were utilized to explore the electrocatalytic nitrogen reduction reaction (NRR) mechanisms catalyzed by trimetallic clusters M3 (M = Ti, Zr, V, and Nb), both unsupported and supported by bowl-shaped sumanene. The substrate enhanced N2 adsorption and activation but hindered hydrogenation due to more negative adsorption energies. The substrate promoted hydrogenation of nitrogen, reducing the interference of the hydrogen evolution reaction (HER) and enhancing the NRR selectivity. Three fundamental and three mixed pathways were investigated, and the rate-determining step (RDS) was identified for each pathway. Through a consecutive pathway, V3 exhibits the best catalytic performance with the free energy change of the RDS (ΔGRDS) as 0.82 eV, while the optimal supported catalyst, Nb3 supported on sumanene, has a ΔGRDS of 1.43 eV. The introduction of the substrate generally increased ΔGRDS by 0.3-0.8 eV. The substrate can effectively regulate the distance between metal atoms and reduce the change in geometric structures of M3 clusters during the reaction process, thereby enhancing the structural stability of the active sites in the NRR process. The substrate can reduce the reactivity differences among catalysts with different metal types. This so-called blurring effect allows cheap metals to partially replace noble metals while maintaining catalyst performance. A linear correlation between charge changes on M3 or M3 together with the substrate and ΔG was observed, providing a potential method for optimizing the catalyst performance and designing new catalysts.

Organo-mediator enabled electrochemical transformations

Electrochemistry has emerged as a powerful means to facilitate redox transformations in modern chemical synthesis. This review focuses on organo-mediators that facilitate electrochemical reactions via outer-sphere electron transfer (ET) between active mediators and substrates, offering advantages over direct electrolysis due to their availability, ease of modification, and simple post-processing. They prevent overoxidation/reduction, enhance selectivity, and mitigate electrode passivation during the electrosynthesis. By modifying the structure of organo-mediators, those with tunable redox potentials enable electrosynthesis and avoid metal residues in the final products, making them promising for further application in synthetic chemistry, particularly in pharmacochemistry, where the maximum allowed level of the metal residue in synthetic samples is extremely strict. This review highlights the recent advancements in this rapidly growing area within the past two decades, including the electrochemical organo-mediated oxidation (EOMO) and electrochemical organo-mediated reduction (EOMR) events. The organo-mediator enabled electrochemical transformations are discussed according to the reaction type, which has been categorized into oxidation and reduction organic mediators.

Electrochemical Scanning Microwave Microscopy Reveals Ion Intercalation Dynamics and Maps Active Sites in 2D Catalyst

The accelerated demand for electrochemical energy storage urges the need for new, sustainable, and lightweight materials able to store high energy densities rapidly and efficiently. Development of these functional materials requires specialized techniques that can provide a close insight into the electrochemical properties at the nanoscale. For this reason, the electrochemical scanning microwave microscopy (EC-SMM) enabling local measurement of electrochemical properties with nanometer spatial resolution and sensitivity down to atto-Ampere electrochemical currents is introduced. Its power is demonstrated by studying NiCo-layered double hydroxide flakes, revealing active site locations and providing atomistic insights into the catalytic process. EC-SMM's spatial resolution of 16 ± 1 nm allows detailed analysis of edge effects in this 2D material, including localized electrochemical impedance spectroscopy and cyclic voltammetry. Coupled with advanced numerical modeling of diffusion and migration dynamics at the material interface, the findings elucidate the previously hypothesized processes responsible for localized enhancements in electrochemical activity, while pinpointing essential parameters for tuning the thermodynamics of ion intercalation and optimizing surface adsorption.

Dynamic surface reconstruction engineers interfacial water structure for efficient alkaline hydrogen oxidation

Investigating the dynamic evolution of the catalyst and regulating the structure of interfacial water molecules participating in the hydrogen oxidation reaction (HOR) are essential for developing highly efficient electrocatalysts toward the practical application of anion exchange membrane fuel cells. Herein, we report an efficient strategy to activate hexagonal close-packed PtSe catalyst through in situ reconstruction that undergoes dynamic Se leaching and phase transition during linear sweep voltammetry cycles. The obtained Pt-Se catalyst presents as a surface Se atom-modified face-centered-cubic Pt-based nanocatalyst, and it exhibited remarkable catalytic performance in the alkaline HOR, showing an intrinsic activity of 0.552 mA cm-2 (j 0,s) and a mass activity of 1.084 mA μg-1 (j k,m @ 50 mV). The experimental results, including in situ surface-enhanced infrared absorption spectroscopy and density functional theory calculations suggest that the accumulated electrons on the surface-decorated Se of Pt-Se can induce the regulation of the interfacial water structure between the electrode and electrolyte surface in the electric double-layer region. Consequently, the migration of OH- species from the electrolyte to the catalyst surface can be apparently accelerated within this disordered water network, which together with the optimized intermediate thermodynamic binding energies, contribute to the enhanced alkaline HOR activity.

Assembly and Valence Modulation of Ordered Bimetallic MOFs for Highly Efficient Electrocatalytic Water Oxidation

Metal synergy can enhance the catalytic performance, and a prefabricated solid precursor can guide the ordered embedding, of secondary metal source ions for the rapid synthesis of bimetallic organic frameworks (MM'-MOFs) with a stoichiometric ratio of 1:1. In this paper, Co-MOF-1D containing well-defined binding sites was synthesized by mechanical ball milling, which was used as a template for the induced introduction of Fe ions to successfully assemble the ordered bimetallic Co1Fe1-MOF-74@2 (where @2 denotes template-directed synthesis of MOF-74). Its electrocatalytic performance is superior to that of the conventional one-step-synthesized Co1Fe1-MOF-74@1 (where @1 denotes one-step synthesis of MOF-74), and the ratio of the two metal sources, Co and Fe, is close to 1:1. Meanwhile, the iron valence states (FeII and FeIII) in Co1Fe1-MOF-74@2 were further regulated to obtain the electrocatalytic materials Co1Fe1(II)-MOF-74@2 and Co1Fe1(III)-MOF-74@2. The electrochemical performance test results confirm that Co1Fe1(II)-MOF-74@2 regulated by valence state has a better catalytic performance than Co1Fe1(III)-MOF-74@2 in the oxygen evolution reaction (OER) process. This phenomenon is related to the gradual increase in the valence state of Fe ions in Co1Fe1(II)-MOF-74@2, which promotes the continuous improvement in the performance of the MOF before reaching the optimal steady state and makes the OER performance reach the optimum when the FeII/FeIII mixed-valence state reaches a certain proportion. This provides a new idea for the directed synthesis and optimization of highly efficient catalysts.