EES catalysis最新文献

Hydrogenation reactions are essential to synthesize platform and fine chemicals today and to establish chemical hydrogen storage in the future. However, hydrogen from fossil or biogenic sources contains CO, a potent poison for noble metal hydrogenation catalysts, necessitating costly purification steps. In this work, we demonstrate phosphate modification as an effective strategy to enhance activity and CO tolerance of Pd/Al₂O₃ in benzyltoluene hydrogenation using pure and impure H₂ streams. Under 1.6 vol% CO in H₂, phosphate modified catalysts achieve a 230% increase in productivity over unmodified Pd/Al₂O₃. Characterization reveals that highly dispersed monomeric phosphate species on Al₂O₃ enhance metal–support interaction and induce Pd redispersion, forming smaller, more stable Pd nanoparticles with enhanced resistance against sintering. Notably, the local electronic environment of Pd remains unchanged by phosphate species. We further show that under CO-rich conditions, benzyltoluene is preferentially hydrogenated at Pd edge sites rather than terrace sites, which explains the pronounced activity increase of the smaller Pd nanoparticles. Phosphate-induced acidity provides additional sites for aromatic hydrogenation with spilled-over hydrogen that remain active in the presence of CO.

Zinc–air redox flow batteries have high potential to penetrate the stationary energy storage market, due to the abundancy, and low cost of active species – oxygen and zinc. However, their technological fruition is limited by the development of reversible O₂ electrodes operating at potentials between 0.6 V_RHE to 1.7 V_RHE, under which no catalyst material has been shown to be stable over long durations. Despite heavy research on the topic of reversible O₂ catalysis, little is known about the parameters controlling the stability of the bifunctional catalyst. Several research accounts assess the activity of reversible O₂ catalysts, but only a small portion cover degradation mechanism over such a large potential window. In this perspective, we summarize our current understanding of material challenges for Zn–air batteries, reversible O₂ catalyst integration strategies, and electrochemical behaviour, with a particular focus on catalyst stability. Nickel cobalt oxide (NiCo₂O₄), a promising yet understudied system, is used as an example material for investigations at potentials of both the O₂ reduction (ORR) and evolution (OER) reactions. We also report original data employing ex situ X-ray diffraction, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy, as well as electrochemical measurements to study the activity of NiCo₂O₄. Furthermore, electrochemical accelerated stress tests are coupled with post-mortem transmission electron microscopy, inductively coupled plasma, and X-ray photoelectron spectroscopy to study the dissolution, compositional changes and amorphization of the top surface 5 nm of the catalyst surface. In situ X-ray absorption spectroscopy revealed irreversible oxidation of Co centres in NiCo₂O₄ during OER, which explains the reduction in activity of the ORR after the catalyst was exposed to anodic OER potentials. This methodology provides a broader method to screen reversible O₂ catalyst stability and enables us to summarize future strategies to improve the activity and stability of reversible O₂ catalysts and electrodes.

Ferroelectric materials, such as tetragonal BaTiO₃, have a permanent electric polarization that can be controlled with an external electric field, however, a ferroelectric polarization in cubic SrTiO₃ is forbidden by the higher symmetry of the lattice. Here we demonstrate that hydrogen annealed SrTiO_3−x single crystals can be polarized electrically, and that the polarization controls the activity for photoelectrochemical water oxidation, a pathway to solar hydrogen fuel. Specifically, it is observed that the anodic water oxidation photocurrent increases from 0.99 to 2.22 mA cm⁻² at 1.23 V RHE (60 mW cm⁻², UV illumination) or decreases to 0.50 mA cm⁻² after electric polarization of hydrogen-annealed (111) SrTiO_3−x single crystals in forward or reverse direction. The polarization also modifies the surface photovoltage signal of the material and its flat band potential, based on Mott–Schottky measurements. These observations are attributed to the formation of an electric dipole at the (111) SrTiO_3−x surface, which alters the potential drop across the depletion layer at the solid–liquid junction, and with it the electron transfer barrier. Density functional theory calculations confirm that an electric dipole can result from the movement of oxygen vacancies between the surface or sub-surface layers of SrTiO_3−x. The filling of these surface oxygen vacancies is the probable cause for the observed disappearance of the electric polarization after 24 h storage in air and 48 h in argon. Overall, this work establishes a new surface-based ferroelectric effect in SrTiO_3−x and its use for solar energy conversion during photoelectrochemical water oxidation. Because oxygen vacancy defects are common, similar electric polarization effects are to be expected in other metal oxides.

Pt/MoC catalysts have been documented to be highly active for the water–gas shift reaction at low temperatures, but identification of the active metal entity remains challenging primarily because of the co-existence of metal nanoparticles, clusters and single-atoms in the catalysts. Here, Pt dispersion on MoC was finely tuned by the carburization of a Pt/MoO₃ precursor with a CH₄/H₂ mixture at 873–973 K. It was found that the 3 nm Pt particles over MoO₃ redispersed into thin layers (mainly bilayers/trilayers) at 873 K and into loosely arranged monolayers/single-atoms at 973 K during the carburization of MoO₃ to MoC. Tests for the low-temperature water–gas shift reaction found that Pt thin layers showed the most pronounced activity based on the moderate adsorption of CO on Pt and the facile dissociation of water over MoC at their interfacial perimeter. But the activity lowered as Pt further dispersed into monolayers/single-atoms in the Pt/MoC catalysts. In situ IR experiments revealed that the Pt thin layers facilitated the adsorption of CO while the MoC support dissociated H₂O into reactive –OH species that might migrate to the Pt surface and react with CO, expediting the low-temperature WGS reaction.

Highly conductive concentrated brine seawater can be reused as an electrolyte in aluminium–air seawater batteries used in on-board marine applications; however, the severe chloride corrosion in brine seawater often causes Pt-based oxygen reduction reaction (ORR) electrocatalysts at the cathode to degrade rapidly. Fe macrocyclic molecules, such as those in iron phthalocyanine (FePc), are reported to exhibit low affinity to chloride adsorption. On the other hand, the strongly bound O* and OOH* intermediates in the FeN₄ active sites and the localized electron orbitals are well-known to restrict their ORR performance. In this study, by combining a room-temperature plasma-assisted material modification strategy with density functional theory (DFT) calculations and thermodynamic modelling, we successfully substituted boron as an acceptor on the FePc ligand to induce significant electron delocalization in the macrocyclic FePc structure, thereby reducing the ORR energy barrier of FePc. In an alkaline saline environment (0.1 M KOH + 1 M NaCl), B-FePc displays superior catalytic activity (0.932 V vs. RHE) at the half-wave potential with moderate stability, which surpassed the performance of a commercial 20 wt% Pt/Vulcan electrocatalyst and most of the recently reported electrocatalysts. When used as an air cathode catalyst in a brine seawater-based Al–air battery (1 M KOH + 1 M NaCl + seawater), B-FePc as a cathode catalyst exhibited a peak power density of 71.0 mW cm⁻² and an exceptional stability following its discharging for 60 h at 20 mA cm⁻² through a mechanical recharging process.

The development of acid-stable and low-noble-metal electrocatalysts for the oxygen evolution reaction (OER) is challenging but demanding for the large-scale application of proton-exchange membrane water electrolyzers (PEMWE). Herein, taking advantage of the densely packed and stable crystalline structure of β-MnO₂ and the dopant-induced lattice strain, a high-performance OER catalyst with low Ru loading is developed via the thermally-driven and polymer-mediated exsolution and segregation process. While high-resolution microscopic studies clearly illustrate the Schottky mechanism involved in the formation of polycrystalline RuO_x-containing grains anchored to the MnO₂ support, spectroscopic findings unveil a significantly altered electronic structure with reduced Mn and Ru chemical states, as well as populated vacancies. Consequently, the best catalyst Ru–MnO₂-PT achieves remarkable OER activity in acidic medium, requiring an overpotential of only 163 mV to reach a current density of 10 mA cm⁻², in addition to excellent electrolytic stability, enabling a prolonged operation of PEMWE for over 2000 hours. This study sheds new light on controllably regulating the exsolution and segregation process of noble metal-doped transition metal oxides for the fabrication of highly robust OER catalysts.

Sunlight-driven integration of photocatalytic CO₂ reduction with biomass feedstock valorization constitutes a highly efficient strategy for the synergistic production of multi-electron products and high-value fine chemicals, adhering to photo-chemical circular economy and sustainability. To date, no halide perovskite has been utilized for CO₂ reduction coupled with biomass oxidation as the development of more stable, efficient, reusable, and non-toxic halide perovskites continues to be challenging. Herein, we report the room-temperature synthesis of methylammonium tin bromide (MA₂SnBr₆) quantum dots (QDs), a vacancy-ordered hybrid halide perovskite (HHP), without additional capping agents. These novel QDs maintain structural integrity in air, moisture, and polar solvents, addressing a significant issue associated with halide perovskites. Remarkably, the MA₂SnBr₆ QDs remain stable under ambient conditions even after 1 year, as confirmed by PXRD analysis. Interestingly, MA₂SnBr₆ achieved exceptionally high electron consumption rates (R_e) of 5110 μmol g⁻¹ h⁻¹ and 12 383 μmol g⁻¹ h⁻¹ for CO₂ reduction under simulated and natural sunlight, respectively, outperforming previous systems. In situ transient studies demonstrate that the photogenerated electrons of MA₂SnBr₆ diffuse from the conduction band to trap states, reducing CO₂, while synergistically photogenerated holes oxidize biomass-derived alcohols. Additionally, in situ EPR experiments were performed to unravel mechanistic insights. Computational studies identify the Br p-orbitals of MA₂SnBr₆ as the reaction centre for CO₂ reduction. Consequently, this work introduces a lead-free, single-component material that operates without a co-catalyst, sacrificial agent or redox additive, offering a promising path towards achieving photoredox processes in a more sustainable and efficient manner.

Oxide-derived silver (Ag) catalysts have emerged as promising candidates for achieving highly efficient electrochemical CO₂ reduction reaction (eCO₂RR) to CO at industrial current densities. However, the evolution of active site configurations, the atomic-level coordination–activity relationship, and the design of practical solar-driven systems remain insufficiently explored. In this work, we report the facile in situ electrochemical synthesis of Ag₂O-derived Ag (Ag₂O-D-Ag), where the presence of unsaturated (low-coordination) Ag sites is revealed through operando X-ray absorption spectroscopy. The Ag₂O-D-Ag catalyst exhibits a CO faradaic efficiency of 90% at 500 mA cm⁻² and maintains a stability over 100 hours at 200 mA cm⁻² in a 4-cm² membrane electrode assembly (MEA) electrolyzer. In situ Fourier-transform infrared spectroscopy, combined with theoretical calculations, shows that these optimally low-coordinated Ag sites reduce the formation energy barrier of the *COOH intermediate, thereby accelerating CO production. Integration of this catalyst with a photovoltaic module enables a 100-cm² MEA prototype to operate stably for more than 30 hours, achieving a solar-to-CO energy efficiency of 4.87%. This study provides mechanistic insight into active site dynamics and demonstrates a scalable, renewable-energy-driven eCO₂RR system.

Catalytic decomposition and non-oxidative coupling of methane (CDM and NOCM) driven by plasma, especially non-thermal plasma, have been determined as strategic means for sustainable production of CO_x-free hydrogen and value-added chemicals. The ‘one-step’ direct CDM and NOCM bypass the need for intermediate syngas production to hydrogen and chemicals using the Fischer–Tropsch process, thus benefiting from energy savings, but nevertheless, are still plagued by poor yields and stability. Thermal, warm, and non-thermal plasma technologies have gained research momentum due to the efficacy for activation of strong C–H chemical bonds in methane. Herein, the current literature is firstly reviewed to elucidate the mechanistic insights and plasma synergies (with and without catalysts) for CO_x-free H₂ production via methane conversion with a particular focus on CDM and NOCM reactions. Our review ascertains that while plasma-assisted methane activation can resolve the need for high energy activation and dissociation of C–H bonds, the governing reaction pathways and difficulties in tuning product selectivity with plasma alone warrant further research on the role of plasma-catalysis as a promising solution to tune reaction selectivity. Additionally, we explore strategies for catalyst design and the selection of plasma sources to improve synergistic interactions in plasma-catalysis. Selected examples of catalyst use and reactor design in plasma-catalytic setups are presented. Finally, drawing from recent advancements and our research perspective, an advanced plasma integrated system is proposed, especially a concept for a plasma-catalytic reactor featuring a membrane separator, which may serve as an effective unit for hydrogen production and purification.

H₂O₂-related electrochemical reactions, including the two-electron oxygen reduction reaction (2e-ORR), H₂O₂ oxidation reaction (HPOR), and H₂O₂ reduction reaction (HPRR), have received significant attention for the electrosynthesis of H₂O₂ and energy storage. Understanding the complex structure–activity relationships among 2e-ORR/HPOR/HPRR and their connections is crucial for further developing highly efficient catalysts and working systems. Herein, we unveil these intricacies by employing model Co–N–C catalysts with a well-defined active site configuration (Co–N_4-pyrrolic and Co–N_4-pyridinic) in a combined experimental and computational approach. We report the higher 2e-ORR/HPOR but lower HPRR activity of the CoN_4-pyrrolic site than the CoN_4-pyridinic site based on their reaction free energy landscapes remodeled considering the chemisorption steps of O₂ and H₂O₂. The results reveal that the binding free energy of *OOH (ΔG_*OOH) can only be utilized as a reliable descriptor for 2e-ORR/HPOR activity, but not indicative of HPRR activity, regardless of the scaling relationship of the common reaction intermediates (*OOH or *OH). The HPRR activity of CoN₄ sites strongly depends on the H₂O₂ adsorption strength and configuration. These findings provide valuable insights into the design of catalysts for H₂O₂-related electrochemical energy conversion and storage systems.