Palladium Nanoparticles Hardwired in Carbon Nanoreactors Enable Continually Increasing Electrocatalytic Activity During the Hydrogen Evolution Reaction

Defect Engineered Ru-CoMOF@MoS2 Heterointerface Facilitate Water Oxidation Process

Catalyst design plays a critical role in ensuring sustainable and effective energy conversion. Electrocatalytic materials need to be able to control active sites and introduce defects in both acidic and alkaline electrolytes. Furthermore, producing efficient catalysts with a distinct surface structure advances our comprehension of the mechanism. Here, a defect-engineered heterointerface of ruthenium doped cobalt metal organic frame (Ru-CoMOF) core confined in MoS2 is reported. A tailored design approach at room temperature was used to induce defects and form an electron transfer interface that enhanced the electrocatalytic performance. The Ru-CoMOF@MoS2 heterointerface obtains a geometrical current density of 10 mA-2 by providing hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at small overpotentials of 240 and 289 mV, respectively. Density functional theory simulation shows that the Co-site maximizes the evolution of hydrogen intermediate energy for adsorption and enhances HER, while the Ru-site, on the other hand, is where OER happens. The heterointerface provides a channel for electron transfer and promotes reactions at the solid-liquid interface. The Ru-CoMOF@MoS2 model exhibits improved OER and HER efficiency, indicating that it could be a valuable material for the production of water-alkaline and acidic catalysts.

In Situ Transformation of Tin Microparticles to Nanoparticles on Nanotextured Carbon Support Boosts the Efficiency of the Electrochemical CO2 Reduction

Developing sustainable, efficient catalysts for the electrocatalytic reduction of CO2 to valuable products remains a crucial challenge. Our research demonstrates that combining tin with nanostructured carbon support leads to a dynamic interface promoting the transformation of microparticles to nanoparticles directly during the reaction, significantly increasing the formate production up to 5.0 mol h-1 g-1, while maintaining nearly 100% selectivity. Correlative electrochemistry-electron microscopy analysis revealed that the catalyst undergoes an in situ self-optimization during CO2 electroreduction. It has been found that changes in the catalyst are caused by the breakdown of Sn particles driven by electrochemical reactions. The process of pulverization typically results in a decrease in the catalytic activity. However, when Sn particles are pulverized and reach approximately 3 nm in size on the surface of the nanotextured carbon support, the efficiency of the catalyst is maximized. This enhancement occurs because the in situ-formed Sn nanoparticles exhibit better compatibility with the nanotextured support. As a result, the number of electrocatalytically active sites significantly increases, leading to a reduction in charge transfer resistance by more than 2-fold and an improvement in reaction kinetics, which is evidenced by changes in the rate-determining step. Collectively, these factors contribute to a 3.6-fold increase in the catalyst's activity while maintaining its selectivity for formate production.

Evolution of amorphous ruthenium nanoclusters into stepped truncated nano-pyramids on graphitic surfaces boosts hydrogen production from ammonia

Atomic-scale changes can significantly impact heterogeneous catalysis, yet their atomic mechanisms are challenging to establish using conventional analysis methods. By using identical location scanning transmission electron microscopy (IL-STEM), which provides quantitative information at the single-particle level, we investigated the mechanisms of atomic evolution of Ru nanoclusters during the ammonia decomposition reaction. Nanometre-sized disordered nanoclusters transform into truncated nano-pyramids with stepped edges, leading to increased hydrogen production from ammonia. IL-STEM imaging demonstrated coalescence and Ostwald ripening as mechanisms of nanocluster pyramidalization during the activation stage, with coalescence becoming the primary mechanism under the reaction conditions. Single Ru atoms, a co-product of the catalyst activation, become absorbed by the nano-pyramids, improving their atomic ordering. Ru nano-pyramids with a 2-3 nm2 footprint consisting of 3-5 atomic layers, ensure the maximum concentration of active sites necessary for the rate-determining step. Importantly, the growth of truncated pyramids typically does not exceed a footprint of approximately 4 nm2 even after 12 hours of the reaction, indicating their high stability and explaining ruthenium's superior activity on nanotextured graphitic carbon compared to other support materials. The structural evolution of nanometer-sized metal clusters with a large fraction of surface atoms is qualitatively different from traditional several-nm nanoparticles, where surface atoms are a minority, and it offers a blueprint for the design of active and sustainable catalysts necessary for hydrogen production from ammonia, which is becoming one of the critical reactions for net-zero technologies.

Direct formation of copper nanoparticles from atoms at graphitic step edges lowers overpotential and improves selectivity of electrocatalytic CO2 reduction

A key strategy for minimizing our reliance on precious metals is to increase the fraction of surface atoms and improve the metal-support interface. In this work, we employ a solvent/ligand/counterion-free method to deposit copper in the atomic form directly onto a nanotextured surface of graphitized carbon nanofibers (GNFs). Our results demonstrate that under these conditions, copper atoms coalesce into nanoparticles securely anchored to the graphitic step edges, limiting their growth to 2-5 nm. The resultant hybrid Cu/GNF material displays high selectivity in the CO2 reduction reaction (CO2RR) for formate production with a faradaic efficiency of ~94% at -0.38 V vs RHE and a high turnover frequency of 2.78 × 106 h-1. The Cu nanoparticles adhered to the graphitic step edges significantly enhance electron transfer to CO2. Long-term CO2RR tests coupled with atomic-scale elucidation of changes in Cu/GNF reveal nanoparticles coarsening, and a simultaneous increase in the fraction of single Cu atoms. These changes in the catalyst structure make the onset of the CO2 reduction potential more negative, leading to less formate production at -0.38 V vs RHE, correlating with a less efficient competition of CO2 with H2O for adsorption on single Cu atoms on the graphitic surfaces, revealed by density functional theory calculations.

Electrocatalytic activity for proton reduction by a covalent non-metal graphene-fullerene hybrid

A non-metal covalent hybrid of fullerene and graphene was synthesized in one step via fluorographene chemistry. Its electrocatalytic performance for the hydrogen evolution reaction and durability was ascribed to intrahybrid charge-transfer phenomena, exploiting the electron-accepting properties of C60 and the high conductivity and large surface area of graphene.

Electrochemistry of redox-active molecules confined within narrow carbon nanotubes

Confinement of molecules within nanocontainers can be a powerful tool for controlling the states of guest-molecules, tuning properties of host-nanocontainers and triggering the emergence of synergistic properties within the host-guest systems. Among nanocontainers, single-walled carbon nanotubes - atomically thin cylinders of carbon, with typical diameters below 2 nm and lengths reaching macroscopic dimensions - are ideal hosts for a variety of materials, including inorganic crystals, and organic, inorganic and organometallic molecules. The extremely high aspect ratio of carbon nanotubes is complemented by their functional properties, such as exceptionally high electrical conductivity and thermal, chemical and electrochemical stability, making carbon nanotubes ideal connectors between guest-molecules and macroscopic electrodes. The idea of harnessing nanotubes both as nanocontainers and nanoelectrodes has led to the incorporation of redox-active species entrapped within nanotube cavities where the host-nanotubes may serve as conduits of electrons to/from the guest-molecules, whilst restricting the molecular positions, orientations, and local environment around the redox centres. This review gives a contemporary overview of the status of molecular redox chemistry within ultra-narrow carbon nanotubes (nanotubes with diameters approaching molecular dimensions) highlighting the opportunities, pitfalls, and gaps in understanding of electrochemistry in confinement, including the role of nanotube diameter, size and shape of guest-molecules, type of electrolyte, solvent and other experimental conditions.