Activation of H2O Tailored by Interfacial Electronic States at a Nanoscale Interface for Enhanced Electrocatalytic Hydrogen Evolution

Magnetic Effects in Electrocatalysis Studied with Electrochemical Impedance Spectroscopy: The Cases of Oxygen Reduction and Evolution Reactions on Cobalt Ferrite Electrodes

Recent years have witnessed an intense effort to unravel magnetic field effects in electrocatalysis, as they can enhance the performance of common electrocatalysts. Both experimental and theoretical studies have shown that magnetic fields may affect, among others, the macroscopic spin-orbital ordering, charge transport, bubble release, and electron transfer kinetics. This paper highlights Electrochemical Impedance Spectroscopy (EIS) as a tool to analyze and separate the effects of magnetic field on both the oxygen reduction and evolution reactions at cobalt iron oxide electrodes. The unequivocal existence of magnetic field effects is demonstrated through EIS, which provides additional information useful to individuate the magnetic field effects. In the almost superparamagnetic nanoparticles studied here, while the magnetic field impact is positive for oxygen reduction, it turns out to be negligible in the case of oxygen evolution. In addition, this study reveals new significant insights, including the exceptionally slow relaxation kinetics of the magnetic effects and the significance of magnetic-induced surface modifications. The fact that the effects virtually disappear in the presence of electrolyte cesium ions points to the key role of electrode surface states. This study showcases the potential of EIS to probe the effects of permanent magnetic fields in electrocatalysis.

Role of Water in Green Carbon Science

Within the context of green chemistry, the concept of green carbon science emphasizes carbon balance and recycling to address the challenge of achieving carbon neutrality. The fundamental processes in this field are oxidation and reduction, which often involve simple molecules such as CO2, CO, CH4, CHx, and H2O. Water plays a critical role in nearly all oxidation-reduction processes, and thus, it is a central focus of research in green carbon science. Water can act as a direct source of dihydrogen in reduction reactions or participate in oxidation reactions, frequently involving O-O coupling to produce hydrogen peroxide or dioxygen. At the atomic level, this coupling involves the statistically unfavorable proximity of two atoms, requiring optimization through a catalytic process influenced by two types of factors, as described by the authors. Extrinsic factors are related to geometrical and electronic criteria associated with the catalytic metal, involving its d-orbitals (or bands in the case of zerovalent metals and electrodes). Intrinsic factors are related to the coupling of oxygen atoms via their p-orbitals. At the mesoscopic or microscopic scale, the reaction medium typically consists of mixtures of lipophilic and hydrophilic phases with water, which may exist under supercritical conditions or as suspensions of microdroplets. These reactions predominantly occur at phase interfaces. A comprehensive understanding of the phenomena across these scales could facilitate improvements and even lead to the development of novel conversion processes.

Confined Structural Water Molecules as Alternative Potential Emitters for Bright Photoluminescence of Thiolate-Gold Complexes

The debate about water as an emitter has spanned nearly a century, but how it emits bright colors remains elusive. In this report, using the widely used Au(I)-alkanethiolate complex (Au(I)-SRs, R=-(CH2)12H) with AIE properties as a model system, by carefully manipulating the delicate surface-ligand interactions at the nanoscale interface, together with a careful spectral investigation and an isotopic diagnostic experiment of heavy water (D2O), we demonstrated that the structural water molecules (SWs) trapped in the nanoscale interface or space are the true emission centers of metal nanoclusters (NCs) and the aggregates of Au(I)-SRs complexes, instead of a well-organized metal core dominated by quantum confinement mechanics. Unlike conventional hydrogen-bonded water molecules, due to interfacial adsorption or spatial confinement, the p-orbitals of two O atoms in SWs can form strong electronic interactions through spatial overlap, thus constructing a set of interfacial states, one of which is characterized by π-bonding, thus providing alternative channels (or paths) for the relaxation decay of the excited electrons. Using the one-dimensional free-electron gas model, the energy levels calculated by the Schrödinger equation are in perfect agreement with the experimental observations, further validating the SWs model.

Disentangling heterogeneous thermocatalytic formic acid dehydrogenation from an electrochemical perspective

Heterogeneous thermocatalysis of formic acid dehydrogenation by metals in solution is of great importance for chemical storage and production of hydrogen. Insightful understanding of the complicated formic acid dehydrogenation kinetics at the metal-solution interface is challenging and yet essential for the design of efficient heterogeneous formic acid dehydrogenation systems. In this work, formic acid dehydrogenation kinetics is initially studied from a perspective of electrochemistry by decoupling this reaction on Pd catalyst into two short-circuit half reactions, formic acid oxidation reaction and hydrogen evolution reaction and manipulating the electrical double layer impact from the solution side. The pH-dependences of formic acid dehydrogenation kinetics and the associated cation effect are attributed to the induced change of electric double layer structure and potential by means of electrochemical measurements involving kinetic isotope effect, in situ infrared spectroscopy as well as grand canonical quantum mechanics calculations. This work showcases how kinetic puzzles on some important heterogeneous catalytic reactions can be tackled by electrochemical theories and methodologies.

The nature of crystal facet effect of TiO2-supported Pd/Pt catalysts on selective hydrogenation of cinnamaldehyde: electron transfer process promoted by interfacial oxygen species

Supported noble metal nanocatalysts typically exhibit strong crystal plane dependent catalytic behavior, but their working mechanism is still unclear. Herein, using anatase TiO2 with well-exposed crystal facets of {101}, {100} and {001} as a prototype support, Pd- and Pt-based supported TiO2 nanocatalysts (TiO2-Pd and TiO2-Pt) were prepared by chemical reduction with NaBH4 as reducer, and they showed a distinct metal-dependent crystal facet effect in the selective hydrogenation of cinamaldehyde (CAL). For Pd-based nanocatalysts, most Pd species on the {100} plane of TiO2 are present in the oxidized form with positive charges and unexpectedly show higher reactivity than the Pd species in the zero-valence state on the {101} and {001} planes. On the contrary, Pt species on all three crystal planes of TiO2 show zero-valence state, with relatively low conversion, but much better selectivity for hydrogenation of a CO bond than Pd-based catalysts. Well-designed experiments manipulating the stability and type of surface oxygen species confirmed that the essence of the crystal facet effect of the catalyst support actually creates a unique nanoconfined interface at the molecular level to construct a surface p-band intermediate state (PBIS), which provides a new alternative channel for surface electron transfer and consequently accelerates the reaction kinetics.

P-Band Intermediate States Mediate Electron Transfer at Confined Nanoscale

In this Perspective, mainly based on the model of structural water molecules (SWs) as bright color emitters, we briefly summarize the development and theoretical elaboration of P-band intermediate state (PBIS) theory as well as its application in several typical catalytic redox reactions. In addition, with a simple equation (2∫ψ2σ1' + ∫ψ2σ2 + ∫ψ2π = 1), we clearly define how the interface states correlate with the three basic parameters of heterogeneous catalysis (conversion, selectivity, and stability), and what is the dynamic nature of catalytic active sites. Overall, the proposal of SW-dominated PBIS theory establishes an internal physical connection between the decay kinetics of excited electrons and the catalytic reaction kinetics and provides new insights into the physical origin of photoluminescence emission of low-dimensional quantum nanodots and the physical nature of nanoconfinement and nanoconfined catalysis.

Green carbon science: fundamental aspects

Carbon energy has contributed to the creation of human civilization, and it can be considered that the configuration of the carbon energy system is one of the important laws that govern the operation of everything in the universe. The core of the carbon energy system is the opposition and unity of two aspects: oxidation and reduction. The operation of oxidation and reduction is based on the ternary elemental system composed of the three elements of carbon, hydrogen and oxygen. Its operation produces numerous reactions and reaction products. Ancient Chinese philosophy helps us to understand in depth the essence of green carbon science, to explore its scientific basis, and to identify the related platforms for technology development.

Structural water molecules dominated p band intermediate states as a unified model for the origin on the photoluminescence emission of noble metal nanoclusters: from monolayer protected clusters to cage confined nanoclusters

In the past several decades, noble metal nanoclusters (NMNCs) have been developed as an emerging class of luminescent materials due to their superior photo-stability and biocompatibility, but their luminous quantum yield is relatively low and the physical origin of the bright photoluminescence (PL) of NMNCs remain elusive, which limited their practical application. As the well-defined structure and composition of NMNCs have been determined, in this mini-review, the effect of each component (metal core, ligand shell and interfacial water) on their PL properties and corresponded working mechanism were comprehensively introduced, and a model that structural water molecules dominated p band intermediate state was proposed to give a unified understanding on the PL mechanism of NMNCs and a further perspective to the future developments of NMNCs by revisiting the development of our studies on the PL mechanism of NMNCs in the past decade.